[06/21] VFS: Introduce a superblock configuration context [ver #3]
diff mbox

Message ID 149486154888.23956.10260643844119198576.stgit@warthog.procyon.org.uk
State New
Headers show

Commit Message

David Howells May 15, 2017, 3:19 p.m. UTC
Introduce a superblock configuration context concept to be used during
superblock creation for mount and superblock reconfiguration for remount.
This is allocated at the beginning of the mount procedure and into it is
placed:

 (1) Filesystem type.

 (2) Namespaces.

 (3) Device name.

 (4) Superblock flags (MS_*).

 (5) Security details.

 (6) Filesystem-specific data, as set by the mount options.

It also gives a place in which to hang an error message for later retrieval
(see the mount-by-fd syscall later in this series).

Rather than calling fs_type->mount(), an sb_config struct is created and
fs_type->init_sb_config() is called to set it up.  fs_type->sb_config_size
says how much space should be allocated for the config context.  The
sb_config struct is placed at the beginning and any extra space is for the
filesystem's use.

A set of operations have to be set by ->init_sb_config() to provide
freeing, duplication, option parsing, binary data parsing, validation,
mounting and superblock filling.

It should be noted that, whilst this patch adds a lot of lines of code,
there is quite a bit of duplication with existing code that can be
eliminated should all filesystems be converted over.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 Documentation/filesystems/mounting.txt |  456 ++++++++++++++++++++++++++++++++
 fs/Makefile                            |    3 
 fs/internal.h                          |    2 
 fs/libfs.c                             |    1 
 fs/namespace.c                         |  256 ++++++++++++++++--
 fs/nfs/nfs4super.c                     |    1 
 fs/proc/root.c                         |    1 
 fs/sb_config.c                         |  326 +++++++++++++++++++++++
 fs/super.c                             |   54 +++-
 include/linux/fs.h                     |   14 +
 include/linux/lsm_hooks.h              |   38 +++
 include/linux/mount.h                  |    4 
 include/linux/sb_config.h              |   93 +++++++
 include/linux/security.h               |   29 ++
 security/security.c                    |   25 ++
 security/selinux/hooks.c               |  170 ++++++++++++
 16 files changed, 1442 insertions(+), 31 deletions(-)
 create mode 100644 Documentation/filesystems/mounting.txt
 create mode 100644 fs/sb_config.c
 create mode 100644 include/linux/sb_config.h


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Comments

Miklos Szeredi May 16, 2017, 3:10 p.m. UTC | #1
On Mon, May 15, 2017 at 5:19 PM, David Howells <dhowells@redhat.com> wrote:
> Introduce a superblock configuration context concept to be used during
> superblock creation for mount and superblock reconfiguration for remount.
> This is allocated at the beginning of the mount procedure and into it is
> placed:
>
>  (1) Filesystem type.
>
>  (2) Namespaces.
>
>  (3) Device name.
>
>  (4) Superblock flags (MS_*).
>
>  (5) Security details.
>
>  (6) Filesystem-specific data, as set by the mount options.
>
> It also gives a place in which to hang an error message for later retrieval
> (see the mount-by-fd syscall later in this series).
>
> Rather than calling fs_type->mount(), an sb_config struct is created and
> fs_type->init_sb_config() is called to set it up.  fs_type->sb_config_size
> says how much space should be allocated for the config context.  The
> sb_config struct is placed at the beginning and any extra space is for the
> filesystem's use.
>
> A set of operations have to be set by ->init_sb_config() to provide
> freeing, duplication, option parsing, binary data parsing, validation,
> mounting and superblock filling.
>
> It should be noted that, whilst this patch adds a lot of lines of code,
> there is quite a bit of duplication with existing code that can be
> eliminated should all filesystems be converted over.

<high level musings>

One way to split this large patch up into more managable chunks would be:

 1) common infrastructure
 2) new mount related changes
 3) reconfig (remount) related changes

Would that work?

We currently have the following modes of operation:

  (a) new mount with new super block created
  (b) new mount with existing super block reused
  (c) remount

In addition you there's a "submount" mode that is a subtype of the
"new mount" ones, but AFAICS it doesn't make a difference in how
options are parsed.

Question is, how the actual superblock options are calculated from the
given options. Currently we have

Case (a):

  1) start out with the default options for the superblock
  2) modify options ("foo" turns option on, "nofoo" turns it off)
  3) create sb

Case (b):

  1) find superblock based on some options
  1) ignore other options

Case (c):

  1) start out with the current options for the superblock
  2) modify options ("foo" turns option on, "nofoo" turns it off)
  3) commit changes to sb

The surprising thing here is that we do (a) and (b) via the same route
and (a) and (c) via a different ones.  This doesn't feel right.

What we've largely ignored is the fact that there are several classes
of options that act completely differently:

  i) options that determine the sb instance (such as the blockdev or
the server IP address)
  ii) subpath: this can determine the sb as well as the subtree to use
  iii) options that can be changed while sb in use
  iv) ???

Would it make sense to make the "new mount" case be

  A) find or create sb based on (i) and (ii) options
  B) reconfigure the resulting sb based on (iii) options

This would make legacy new mount be: (A) + if new then (B).  And
legacy remount just (B).

Also I think silently ignoring options is not always the right answer.
The user of the new uapi should at least have the option of knowing if
this is a new filesystem instance or essentially a bind mount without
any sb configuration.  Maybe an O_EXCL type flag would do.

</high level musings>

More comments inline...

>
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
>
>  Documentation/filesystems/mounting.txt |  456 ++++++++++++++++++++++++++++++++
>  fs/Makefile                            |    3
>  fs/internal.h                          |    2
>  fs/libfs.c                             |    1
>  fs/namespace.c                         |  256 ++++++++++++++++--
>  fs/nfs/nfs4super.c                     |    1
>  fs/proc/root.c                         |    1
>  fs/sb_config.c                         |  326 +++++++++++++++++++++++
>  fs/super.c                             |   54 +++-
>  include/linux/fs.h                     |   14 +
>  include/linux/lsm_hooks.h              |   38 +++
>  include/linux/mount.h                  |    4
>  include/linux/sb_config.h              |   93 +++++++
>  include/linux/security.h               |   29 ++
>  security/security.c                    |   25 ++
>  security/selinux/hooks.c               |  170 ++++++++++++
>  16 files changed, 1442 insertions(+), 31 deletions(-)
>  create mode 100644 Documentation/filesystems/mounting.txt
>  create mode 100644 fs/sb_config.c
>  create mode 100644 include/linux/sb_config.h
>
> diff --git a/Documentation/filesystems/mounting.txt b/Documentation/filesystems/mounting.txt
> new file mode 100644
> index 000000000000..03e9086f754d
> --- /dev/null
> +++ b/Documentation/filesystems/mounting.txt
> @@ -0,0 +1,456 @@
> +                             ===================
> +                             FILESYSTEM MOUNTING
> +                             ===================
> +
> +CONTENTS
> +
> + (1) Overview.
> +
> + (2) The superblock configuration context.
> +
> + (3) The superblock config operations.
> +
> + (4) Superblock config security.
> +
> + (5) VFS superblock config operations.
> +
> +
> +========
> +OVERVIEW
> +========
> +
> +The creation of new mounts is now to be done in a multistep process:
> +
> + (1) Create a superblock configuration context.
> +
> + (2) Parse the options and attach them to the context.  Options may be passed
> +     individually from userspace.
> +
> + (3) Validate and pre-process the context.
> +
> + (4) Get or create a superblock and mountable root.
> +
> + (5) Perform the mount.
> +
> + (6) Return an error message attached to the context.
> +
> + (7) Destroy the context.
> +
> +To support this, the file_system_type struct gains two new fields:
> +
> +       unsigned short sb_config_size;
> +
> +which indicates the total amount of space that should be allocated for context
> +data (see the Superblock Configuration Context section), and:
> +
> +       int (*init_sb_config)(struct sb_config *sc, struct super_block *src_sb);
> +
> +which is invoked to set up the filesystem-specific parts of a superblock
> +configuration context, including the additional space.  The src_sb parameter is
> +used to convey the superblock from which the filesystem may draw extra
> +information (such as namespaces), for submount (SB_CONFIG_FOR_SUBMOUNT) or
> +remount (SB_CONFIG_FOR_REMOUNT) purposes or it will be NULL.
> +
> +Note that security initialisation is done *after* the filesystem is called so
> +that the namespaces may be adjusted first.
> +
> +And the super_operations struct gains one:
> +
> +       int (*remount_fs_sc) (struct super_block *, struct sb_config *);

How about reconfig_fs() or just reconfig()?

> +
> +This shadows the ->remount_fs() operation and takes a prepared superblock
> +configuration context instead of the mount flags and data page.  It may modify
> +the ms_flags in the context for the caller to pick up.
> +
> +[NOTE] remount_fs_sc is intended as a replacement for remount_fs.
> +
> +
> +====================================
> +THE SUPERBLOCK CONFIGURATION CONTEXT
> +====================================
> +
> +The creation and reconfiguration of a superblock is governed by a superblock
> +configuration context.  This is represented by the sb_config structure:
> +
> +       struct sb_config {
> +               const struct sb_config_operations *ops;
> +               struct file_system_type *fs;
> +               struct user_namespace   *user_ns;
> +               struct net              *net_ns;
> +               const struct cred       *cred;
> +               char                    *device;
> +               void                    *security;
> +               const char              *error_msg;
> +               unsigned int            ms_flags;
> +               bool                    mounted;
> +               bool                    sloppy;
> +               bool                    silent;
> +               enum mount_type         mount_type : 8;
> +       };
> +
> +When the VFS creates this, it allocates ->sb_config_size bytes (as specified by
> +the file_system_type object) to hold both the sb_config struct and any extra
> +data required by the filesystem.  The sb_config struct is placed at the
> +beginning of this space.  Any extra space beyond that is for use by the
> +filesystem.  The filesystem should wrap the struct in its own, e.g.:
> +
> +       struct nfs_sb_config {
> +               struct sb_config sc;
> +               ...
> +       };
> +
> +placing the sb_config struct first.  container_of() can then be used.  The
> +file_system_type would be initialised thus:
> +
> +       struct file_system_type nfs = {
> +               ...
> +               .sb_config_size = sizeof(struct nfs_sb_config),
> +               .init_sb_config = nfs_init_sb_config,
> +               ...
> +       };
> +
> +The sb_config fields are as follows:
> +
> + (*) const struct sb_config_operations *ops
> +
> +     These are operations that can be done on a superblock configuration
> +     context (see below).  This must be set by the ->init_sb_config()
> +     file_system_type operation.
> +
> + (*) struct file_system_type *fs
> +
> +     A pointer to the file_system_type of the filesystem that is being
> +     constructed or reconfigured.  This retains a ref on the type owner.
> +
> + (*) struct user_namespace *user_ns
> + (*) struct net *net_ns
> +
> +     This is a subset of the namespaces in use by the invoking process.  This
> +     retains a ref on each namespace.  The subscribed namespaces may be
> +     replaced by the filesystem to reflect other sources, such as the parent
> +     mount superblock on an automount.
> +
> + (*) struct cred *cred
> +
> +     The mounter's credentials.  This retains a ref on the credentials.
> +
> + (*) char *device
> +
> +     This is the device to be mounted.  It may be a block device
> +     (e.g. /dev/sda1) or something more exotic, such as the "host:/path" that
> +     NFS desires.
> +
> + (*) void *security
> +
> +     A place for the LSMs to hang their security data for the superblock.  The
> +     relevant security operations are described below.
> +
> + (*) const char *error_msg
> +
> +     A place for the VFS and the filesystem to hang an error message.  This
> +     should be in the form of a static string that doesn't need deallocation
> +     and the pointer to which can just be overwritten.  Under some
> +     circumstances, this can be retrieved by userspace.
> +
> +     Note that the existence of the error string is expected to be guaranteed
> +     by the reference on the file_system_type object held by ->fs or any
> +     filesystem-specific reference held in the filesystem context until the
> +     ->free() operation is called.
> +
> +     Use sb_cfg_error() and sb_cfg_inval() to set this rather than setting it
> +     directly.
> +
> + (*) unsigned int ms_flags
> +
> +     This holds the MS_* flags mount flags.
> +
> + (*) bool mounted
> +
> +     This is set to true once a mount attempt is made.  This causes an error to
> +     be given on subsequent mount attempts with the same context and prevents
> +     multiple mount attempts.
> +
> + (*) bool sloppy
> + (*) bool silent
> +
> +     These are set if the sloppy or silent mount options are given.
> +
> +     [NOTE] sloppy is probably unnecessary when userspace passes over one
> +     option at a time since the error can just be ignored if userspace deems it
> +     to be unimportant.
> +
> +     [NOTE] silent is probably redundant with ms_flags & MS_SILENT.
> +
> + (*) enum mount_type
> +
> +     This indicates the type of mount operation.  The available values are:
> +
> +       SB_CONFIG_FOR_NEW       -- New mount
> +       SB_CONFIG_FOR_SUBMOUNT  -- New automatic submount of extant mount
> +       SB_CONFIG_FOR_REMOUNT   -- Change an existing mount
> +
> +The mount context is created by calling __vfs_new_sb_config(),
> +vfs_new_sb_config(), vfs_sb_reconfig() or vfs_dup_sb_config() and is destroyed
> +with put_sb_config().  Note that the structure is not refcounted.
> +
> +VFS, security and filesystem mount options are set individually with
> +vfs_parse_mount_option() or in bulk with generic_monolithic_mount_data().
> +
> +When mounting, the filesystem is allowed to take data from any of the pointers
> +and attach it to the superblock (or whatever), provided it clears the pointer
> +in the mount context.
> +
> +The filesystem is also allowed to allocate resources and pin them with the
> +mount context.  For instance, NFS might pin the appropriate protocol version
> +module.
> +
> +
> +================================
> +THE SUPERBLOCK CONFIG OPERATIONS
> +================================
> +
> +The superblock configuration context points to a table of operations:
> +
> +       struct sb_config_operations {
> +               void (*free)(struct sb_config *sc);
> +               int (*dup)(struct sb_config *sc, struct sb_config *src_sc);
> +               int (*parse_option)(struct sb_config *sc, char *p);
> +               int (*monolithic_mount_data)(struct sb_config *sc, void *data);
> +               int (*validate)(struct sb_config *sc);
> +               struct dentry *(*mount)(struct sb_config *sc);
> +       };
> +
> +These operations are invoked by the various stages of the mount procedure to
> +manage the superblock configuration context.  They are as follows:
> +
> + (*) void (*free)(struct sb_config *sc);
> +
> +     Called to clean up the filesystem-specific part of the superblock
> +     configuration context when the context is destroyed.  It should be aware
> +     that parts of the context may have been removed and NULL'd out by
> +     ->mount().
> +
> + (*) int (*dup)(struct sb_config *sc, struct sb_config *src_sc);
> +
> +     Called when a superblock configuration context has been duplicated to get
> +     any refs or copy any non-referenced resources held in the
> +     filesystem-specific part of the superblock configuration context.  An
> +     error may be returned to indicate failure to do this.
> +
> +     [!] Note that even if this fails, put_sb_config() will be called
> +        immediately thereafter, so ->dup() *must* make the filesystem-specific
> +        part safe for ->free().
> +
> + (*) int (*parse_option)(struct sb_config *sc, char *p);
> +
> +     Called when an option is to be added to the superblock configuration
> +     context.  p points to the option string, likely in "key[=val]" format.
> +     VFS-specific options will have been weeded out and sc->ms_flags updated in
> +     the context.  Security options will also have been weeded out and
> +     sc->security updated.
> +
> +     If successful, 0 should be returned and a negative error code otherwise.
> +     If an ambiguous error (such as -EINVAL) is returned, sb_cfg_error() or
> +     sb_cfg_inval() should be used to provide a string that provides more
> +     information.
> +
> + (*) int (*monolithic_mount_data)(struct sb_config *sc, void *data);
> +
> +     Called when the mount(2) system call is invoked to pass the entire data
> +     page in one go.  If this is expected to be just a list of "key[=val]"
> +     items separated by commas, then this may be set to NULL.
> +
> +     The return value is as for ->parse_option().
> +
> +     If the filesystem (eg. NFS) needs to examine the data first and then
> +     finds it's the standard key-val list then it may pass it off to:
> +
> +       int generic_monolithic_mount_data(struct sb_config *sc, void *data);
> +
> + (*) int (*validate)(struct sb_config *sc);
> +
> +     Called when all the options have been applied and the mount is about to
> +     take place.  It is should check for inconsistencies from mount options
> +     and it is also allowed to do preliminary resource acquisition.  For
> +     instance, the core NFS module could load the NFS protocol module here.
> +
> +     Note that if sc->mount_type == SB_CONFIG_FOR_REMOUNT, some of the options
> +     necessary for a new mount may not be set.
> +
> +     The return value is as for ->parse_option().
> +
> + (*) struct dentry *(*mount)(struct sb_config *sc);

I'd be much happier with "get_root()" or something.

> +
> +     Called to effect a new mount or new submount using the information stored
> +     in the superblock configuration context (remounts go via a different
> +     vector).  It may detach any resources it desires from the superblock
> +     configuration context and transfer them to the superblock it creates.
> +
> +     On success it should return the dentry that's at the root of the mount.
> +     In future, sc->root_path will then be applied to this.
> +
> +     In the case of an error, it should return a negative error code and invoke
> +     sb_cfg_inval() or sb_cfg_error().
> +
> +
> +=========================================
> +SUPERBLOCK CONFIGURATION CONTEXT SECURITY
> +========================================
> +
> +The superblock configuration context contains a security points that the LSMs can use for
> +building up a security context for the superblock to be mounted.  There are a
> +number of operations used by the new mount code for this purpose:
> +
> + (*) int security_sb_config_alloc(struct sb_config *sc,
> +                                 struct super_block *src_sb);
> +
> +     Called to initialise sc->security (which is preset to NULL) and allocate
> +     any resources needed.  It should return 0 on success and a negative error
> +     code on failure.
> +
> +     src_sb is non-NULL in the case of a remount (SB_CONFIG_FOR_REMOUNT) in
> +     which case it indicates the superblock to be remounted or in the case of a
> +     submount (SB_CONFIG_FOR_SUBMOUNT) in which case it indicates the parent
> +     superblock.
> +
> + (*) int security_sb_config_dup(struct sb_config *sc,
> +                               struct sb_config *src_mc);
> +
> +     Called to initialise sc->security (which is preset to NULL) and allocate
> +     any resources needed.  The original superblock configuration context is pointed to by src_mc
> +     and may be used for reference.  It should return 0 on success and a
> +     negative error code on failure.
> +
> + (*) void security_sb_config_free(struct sb_config *sc);
> +
> +     Called to clean up anything attached to sc->security.  Note that the
> +     contents may have been transferred to a superblock and the pointer NULL'd
> +     out during mount.
> +
> + (*) int security_sb_config_parse_option(struct sb_config *sc, char *opt);
> +
> +     Called for each mount option.  The mount options are in "key[=val]"
> +     form.  An active LSM may reject one with an error, pass one over and
> +     return 0 or consume one and return 1.  If consumed, the option isn't
> +     passed on to the filesystem.
> +
> +     If it returns an error, more information can be returned with
> +     sb_cfg_inval() or sb_cfg_error().
> +
> + (*) int security_sb_get_tree(struct sb_config *sc);
> +
> +     Called during the mount procedure to verify that the specified superblock
> +     is allowed to be mounted and to transfer the security data there.
> +
> +     On success, it should return 0; otherwise it should return an error and
> +     perhaps call sb_cfg_inval() or sb_cfg_error() to indicate the problem.  It
> +     should not return -ENOMEM as this should be taken care of in advance.
> +
> +     [NOTE] Should I add a security_sb_config_validate() operation so that the
> +     LSM has the opportunity to allocate stuff and check the options as a
> +     whole?
> +
> +
> +================================
> +VFS SUPERBLOCK CONFIG OPERATIONS
> +================================
> +
> +There are four operations for creating a superblock configuration context and
> +one for destroying a context:
> +
> + (*) struct sb_config *__vfs_new_sb_config(struct file_system_type *fs_type,
> +                                          struct super_block *src_sb;
> +                                          unsigned int ms_flags);
> +
> +     Create a superblock configuration context given a filesystem type pointer.
> +     This allocates the superblock configuration context, sets the flags,
> +     initialises the security and calls fs_type->init_sb_config() to initialise
> +     the filesystem context.
> +
> +     src_sb can be NULL or it may indicate a superblock that is going to be
> +     remounted (SB_CONFIG_FOR_REMOUNT) or a superblock that is the parent of a
> +     submount (SB_CONFIG_FOR_SUBMOUNT).  This superblock is provided as a
> +     source of namespace information.
> +
> + (*) struct sb_config *vfs_sb_reconfig(struct vfsmount *mnt,
> +                                      unsigned int ms_flags);
> +
> +     Create a superblock configuration context from the same filesystem as an
> +     extant mount and initialise the mount parameters from the superblock
> +     underlying that mount.  This is for use by remount.
> +
> + (*) struct sb_config *vfs_fsopen(const char *fs_name);
> +
> +     Create a superblock configuration context given a filesystem name.  It is
> +     assumed that the mount flags will be passed in as text options or set
> +     directly later.  This is intended to be called from sys_mount() or
> +     sys_fsopen().  This copies current's namespaces to the superblock
> +     configuration context.
> +
> + (*) struct sb_config *vfs_dup_sb_config(struct sb_config *src_sc);
> +
> +     Duplicate a superblock configuration context, copying any options noted
> +     and duplicating or additionally referencing any resources held therein.
> +     This is available for use where a filesystem has to get a mount within a
> +     mount, such as NFS4 does by internally mounting the root of the target
> +     server and then doing a private pathwalk to the target directory.
> +
> + (*) void put_sb_config(struct sb_config *sc);
> +
> +     Destroy a superblock configuration context, releasing any resources it
> +     holds.  This calls the ->free() operation.  This is intended to be called
> +     by anyone who created a superblock configuration context.
> +
> +     [!] superblock configuration contexts are not refcounted, so this causes
> +        unconditional destruction.
> +
> +In all the above operations, apart from the put op, the return is a mount
> +context pointer or a negative error code.  No error string is saved as the
> +error string is only guaranteed as long as the file_system_type is pinned (and
> +thus the module).
> +
> +The next operations can be used to cache an error message in the context for
> +the caller to collect.
> +
> + (*) void sb_cfg_error(struct sb_config *sc, const char *msg);
> +
> +     Set an error message for the caller to pick up.  For lifetime rules, see
> +     the ->error_msg member description.
> +
> + (*) void sb_cfg_inval(struct sb_config *sc, const char *msg);
> +
> +     As sb_cfg_error(), but returns -EINVAL for use with tail calling.
> +
> +In the remaining operations, if an error occurs, a negative error code is
> +returned and, if not obvious, sc->error_msg may have been set to point to a
> +useful string.  This string should not be freed.
> +
> + (*) struct vfsmount *vfs_kern_mount_sc(struct sb_config *sc);
> +
> +     Create a mount given the parameters in the specified superblock
> +     configuration context.  This invokes the ->validate() op and then the
> +     ->mount() op.
> +
> + (*) struct vfsmount *vfs_submount_sc(const struct dentry *mountpoint,
> +                                     struct sb_config *sc);
> +
> +     Create a mount given a superblock configuration context and set
> +     MS_SUBMOUNT on it.  A wrapper around vfs_kern_mount_sc().  This is
> +     intended to be called from filesystems that have automount points (NFS,
> +     AFS, ...).
> +
> + (*) int vfs_parse_mount_option(struct sb_config *sc, char *data);
> +
> +     Supply a single mount option to the superblock configuration context.  The
> +     mount option should likely be in a "key[=val]" string form.  The option is
> +     first checked to see if it corresponds to a standard mount flag (in which
> +     case it is used to mark an MS_xxx flag and consumed) or a security option
> +     (in which case the LSM consumes it) before it is passed on to the
> +     filesystem.
> +
> + (*) int generic_monolithic_mount_data(struct sb_config *sc, void *data);
> +
> +     Parse a sys_mount() data page, assuming the form to be a text list
> +     consisting of key[=val] options separated by commas.  Each item in the
> +     list is passed to vfs_mount_option().  This is the default when the
> +     ->monolithic_mount_data() operation is NULL.
> diff --git a/fs/Makefile b/fs/Makefile
> index 7bbaca9c67b1..8f5142525866 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -11,7 +11,8 @@ obj-y :=      open.o read_write.o file_table.o super.o \
>                 attr.o bad_inode.o file.o filesystems.o namespace.o \
>                 seq_file.o xattr.o libfs.o fs-writeback.o \
>                 pnode.o splice.o sync.o utimes.o \
> -               stack.o fs_struct.o statfs.o fs_pin.o nsfs.o
> +               stack.o fs_struct.o statfs.o fs_pin.o nsfs.o \
> +               sb_config.o
>
>  ifeq ($(CONFIG_BLOCK),y)
>  obj-y +=       buffer.o block_dev.o direct-io.o mpage.o
> diff --git a/fs/internal.h b/fs/internal.h
> index 9676fe11c093..39121a99d930 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -87,7 +87,7 @@ extern struct file *get_empty_filp(void);
>  /*
>   * super.c
>   */
> -extern int do_remount_sb(struct super_block *, int, void *, int);
> +extern int do_remount_sb(struct super_block *, int, void *, int, struct sb_config *);
>  extern bool trylock_super(struct super_block *sb);
>  extern struct dentry *mount_fs(struct file_system_type *,
>                                int, const char *, void *);
> diff --git a/fs/libfs.c b/fs/libfs.c
> index a04395334bb1..8ef519709ee3 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -9,6 +9,7 @@
>  #include <linux/slab.h>
>  #include <linux/cred.h>
>  #include <linux/mount.h>
> +#include <linux/sb_config.h>
>  #include <linux/vfs.h>
>  #include <linux/quotaops.h>
>  #include <linux/mutex.h>
> diff --git a/fs/namespace.c b/fs/namespace.c
> index c076787871e7..91f8a07532cd 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -25,7 +25,9 @@
>  #include <linux/magic.h>
>  #include <linux/bootmem.h>
>  #include <linux/task_work.h>
> +#include <linux/file.h>
>  #include <linux/sched/task.h>
> +#include <linux/sb_config.h>
>
>  #include "pnode.h"
>  #include "internal.h"
> @@ -1593,7 +1595,7 @@ static int do_umount(struct mount *mnt, int flags)
>                         return -EPERM;
>                 down_write(&sb->s_umount);
>                 if (!(sb->s_flags & MS_RDONLY))
> -                       retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
> +                       retval = do_remount_sb(sb, MS_RDONLY, NULL, 0, NULL);
>                 up_write(&sb->s_umount);
>                 return retval;
>         }
> @@ -2276,6 +2278,26 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
>  }
>
>  /*
> + * Parse the monolithic page of mount data given to sys_mount().
> + */
> +static int parse_monolithic_mount_data(struct sb_config *sc, void *data)
> +{
> +       int (*monolithic_mount_data)(struct sb_config *, void *);
> +       int ret;
> +
> +       monolithic_mount_data = sc->ops->monolithic_mount_data;
> +       if (!monolithic_mount_data)
> +               monolithic_mount_data = generic_monolithic_mount_data;
> +
> +       ret = monolithic_mount_data(sc, data);
> +       if (ret < 0)
> +               return ret;
> +       if (sc->ops->validate)
> +               return sc->ops->validate(sc);
> +       return 0;
> +}
> +
> +/*
>   * change filesystem flags. dir should be a physical root of filesystem.
>   * If you've mounted a non-root directory somewhere and want to do remount
>   * on it - tough luck.
> @@ -2283,13 +2305,14 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
>  static int do_remount(struct path *path, int flags, int mnt_flags,
>                       void *data)
>  {
> +       struct sb_config *sc = NULL;
>         int err;
>         struct super_block *sb = path->mnt->mnt_sb;
>         struct mount *mnt = real_mount(path->mnt);
> +       struct file_system_type *type = sb->s_type;
>
>         if (!check_mnt(mnt))
>                 return -EINVAL;
> -
>         if (path->dentry != path->mnt->mnt_root)
>                 return -EINVAL;
>
> @@ -2320,9 +2343,19 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
>                 return -EPERM;
>         }
>
> -       err = security_sb_remount(sb, data);
> -       if (err)
> -               return err;
> +       if (type->init_sb_config) {
> +               sc = vfs_sb_reconfig(path->mnt, flags);
> +               if (IS_ERR(sc))
> +                       return PTR_ERR(sc);
> +
> +               err = parse_monolithic_mount_data(sc, data);
> +               if (err < 0)
> +                       goto err_sc;

If filesystem defines ->monolithic_mount_data() who is responsible for
calling the security hook?


> +       } else {
> +               err = security_sb_remount(sb, data);
> +               if (err)
> +                       return err;
> +       }
>
>         down_write(&sb->s_umount);
>         if (flags & MS_BIND)
> @@ -2330,7 +2363,7 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
>         else if (!capable(CAP_SYS_ADMIN))
>                 err = -EPERM;
>         else
> -               err = do_remount_sb(sb, flags, data, 0);
> +               err = do_remount_sb(sb, flags, data, 0, sc);
>         if (!err) {
>                 lock_mount_hash();
>                 mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
> @@ -2339,6 +2372,9 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
>                 unlock_mount_hash();
>         }
>         up_write(&sb->s_umount);
> +err_sc:
> +       if (sc)
> +               put_sb_config(sc);
>         return err;
>  }
>
> @@ -2492,40 +2528,106 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
>  static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
>
>  /*
> + * Create a new mount using a superblock configuration and request it
> + * be added to the namespace tree.
> + */
> +static int do_new_mount_sc(struct sb_config *sc, struct path *mountpoint,
> +                          unsigned int mnt_flags)
> +{
> +       struct vfsmount *mnt;
> +       int ret;
> +
> +       mnt = vfs_kern_mount_sc(sc);
> +       if (IS_ERR(mnt))
> +               return PTR_ERR(mnt);
> +
> +       if ((sc->fs_type->fs_flags & FS_HAS_SUBTYPE) &&
> +           !mnt->mnt_sb->s_subtype) {
> +               mnt = fs_set_subtype(mnt, sc->fs_type->name);
> +               if (IS_ERR(mnt))
> +                       return PTR_ERR(mnt);
> +       }
> +
> +       ret = -EPERM;
> +       if (mount_too_revealing(mnt, &mnt_flags)) {
> +               sb_cfg_error(sc, "VFS: Mount too revealing");
> +               goto err_mnt;
> +       }
> +
> +       ret = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
> +       if (ret < 0) {
> +               sb_cfg_error(sc, "VFS: Failed to add mount");
> +               goto err_mnt;
> +       }
> +       return ret;
> +
> +err_mnt:
> +       mntput(mnt);
> +       return ret;
> +}
> +
> +/*
>   * create a new mount for userspace and request it to be added into the
>   * namespace's tree
>   */
> -static int do_new_mount(struct path *path, const char *fstype, int flags,
> +static int do_new_mount(struct path *mountpoint, const char *fstype, int flags,
>                         int mnt_flags, const char *name, void *data)
>  {
> -       struct file_system_type *type;
> +       struct sb_config *sc;
>         struct vfsmount *mnt;
>         int err;
>
>         if (!fstype)
>                 return -EINVAL;
>
> -       type = get_fs_type(fstype);
> -       if (!type)
> -               return -ENODEV;
> +       sc = vfs_new_sb_config(fstype);
> +       if (IS_ERR(sc))
> +               return PTR_ERR(sc);
> +       sc->ms_flags = flags;
>
> -       mnt = vfs_kern_mount(type, flags, name, data);
> -       if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
> -           !mnt->mnt_sb->s_subtype)
> -               mnt = fs_set_subtype(mnt, fstype);
> +       err = -ENOMEM;
> +       sc->device = kstrdup(name, GFP_KERNEL);
> +       if (!sc->device)
> +               goto err_sc;
>
> -       put_filesystem(type);
> -       if (IS_ERR(mnt))
> -               return PTR_ERR(mnt);
> +       if (sc->ops) {
> +               err = parse_monolithic_mount_data(sc, data);
> +               if (err < 0)
> +                       goto err_sc;
>
> -       if (mount_too_revealing(mnt, &mnt_flags)) {
> -               mntput(mnt);
> -               return -EPERM;
> +               err = do_new_mount_sc(sc, mountpoint, mnt_flags);
> +               if (err)
> +                       goto err_sc;
> +
> +       } else {
> +               mnt = vfs_kern_mount(sc->fs_type, flags, name, data);
> +               if (!IS_ERR(mnt) && (sc->fs_type->fs_flags & FS_HAS_SUBTYPE) &&
> +                   !mnt->mnt_sb->s_subtype)
> +                       mnt = fs_set_subtype(mnt, fstype);
> +
> +               if (IS_ERR(mnt)) {
> +                       err = PTR_ERR(mnt);
> +                       goto err_sc;
> +               }
> +
> +               err = -EPERM;
> +               if (mount_too_revealing(mnt, &mnt_flags))
> +                       goto err_mnt;
> +
> +               err = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
> +               if (err)
> +                       goto err_mnt;

Largely duplicated do_new_mount_sc().  What's the point?

>         }
>
> -       err = do_add_mount(real_mount(mnt), path, mnt_flags);
> -       if (err)
> -               mntput(mnt);
> +       put_sb_config(sc);
> +       return 0;
> +
> +err_mnt:
> +       mntput(mnt);
> +err_sc:
> +       if (sc->error_msg)
> +               pr_info("Mount failed: %s\n", sc->error_msg);
> +       put_sb_config(sc);
>         return err;
>  }
>
> @@ -3058,6 +3160,95 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
>         return ret;
>  }
>
> +static struct dentry *__do_mount_sc(struct sb_config *sc)
> +{
> +       struct super_block *sb;
> +       struct dentry *root;
> +       int ret;
> +
> +       root = sc->ops->mount(sc);
> +       if (IS_ERR(root))
> +               return root;
> +
> +       sb = root->d_sb;
> +       BUG_ON(!sb);
> +       WARN_ON(!sb->s_bdi);
> +       sb->s_flags |= MS_BORN;
> +
> +       ret = security_sb_config_kern_mount(sc, sb);
> +       if (ret < 0)
> +               goto err_sb;
> +
> +       /*
> +        * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
> +        * but s_maxbytes was an unsigned long long for many releases. Throw
> +        * this warning for a little while to try and catch filesystems that
> +        * violate this rule.
> +        */
> +       WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
> +               "negative value (%lld)\n", sc->fs_type->name, sb->s_maxbytes);
> +
> +       up_write(&sb->s_umount);
> +       return root;
> +
> +err_sb:
> +       dput(root);
> +       deactivate_locked_super(sb);
> +       return ERR_PTR(ret);
> +}
> +
> +struct vfsmount *vfs_kern_mount_sc(struct sb_config *sc)
> +{
> +       struct dentry *root;
> +       struct mount *mnt;
> +       int ret;
> +
> +       if (sc->ops->validate) {
> +               ret = sc->ops->validate(sc);
> +               if (ret < 0)
> +                       return ERR_PTR(ret);
> +       }
> +
> +       mnt = alloc_vfsmnt(sc->device ?: "none");
> +       if (!mnt)
> +               return ERR_PTR(-ENOMEM);
> +
> +       if (sc->ms_flags & MS_KERNMOUNT)
> +               mnt->mnt.mnt_flags = MNT_INTERNAL;
> +
> +       root = __do_mount_sc(sc);
> +       if (IS_ERR(root)) {
> +               mnt_free_id(mnt);
> +               free_vfsmnt(mnt);
> +               return ERR_CAST(root);
> +       }
> +
> +       mnt->mnt.mnt_root       = root;
> +       mnt->mnt.mnt_sb         = root->d_sb;
> +       mnt->mnt_mountpoint     = mnt->mnt.mnt_root;
> +       mnt->mnt_parent         = mnt;
> +       lock_mount_hash();
> +       list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
> +       unlock_mount_hash();
> +       return &mnt->mnt;
> +}
> +EXPORT_SYMBOL_GPL(vfs_kern_mount_sc);
> +
> +struct vfsmount *
> +vfs_submount_sc(const struct dentry *mountpoint, struct sb_config *sc)
> +{
> +       /* Until it is worked out how to pass the user namespace
> +        * through from the parent mount to the submount don't support
> +        * unprivileged mounts with submounts.
> +        */
> +       if (mountpoint->d_sb->s_user_ns != &init_user_ns)
> +               return ERR_PTR(-EPERM);
> +
> +       sc->ms_flags = MS_SUBMOUNT;
> +       return vfs_kern_mount_sc(sc);
> +}
> +EXPORT_SYMBOL_GPL(vfs_submount_sc);
> +
>  /*
>   * Return true if path is reachable from root
>   *
> @@ -3299,6 +3490,23 @@ struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
>  }
>  EXPORT_SYMBOL_GPL(kern_mount_data);
>
> +struct vfsmount *kern_mount_data_sc(struct sb_config *sc)
> +{
> +       struct vfsmount *mnt;
> +
> +       sc->ms_flags = MS_KERNMOUNT;
> +       mnt = vfs_kern_mount_sc(sc);
> +       if (!IS_ERR(mnt)) {
> +               /*
> +                * it is a longterm mount, don't release mnt until
> +                * we unmount before file sys is unregistered
> +               */
> +               real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
> +       }
> +       return mnt;
> +}
> +EXPORT_SYMBOL_GPL(kern_mount_data_sc);
> +
>  void kern_unmount(struct vfsmount *mnt)
>  {
>         /* release long term mount so mount point can be released */
> diff --git a/fs/nfs/nfs4super.c b/fs/nfs/nfs4super.c
> index 6fb7cb6b3f4b..967fa04d5c76 100644
> --- a/fs/nfs/nfs4super.c
> +++ b/fs/nfs/nfs4super.c
> @@ -3,6 +3,7 @@
>   */
>  #include <linux/init.h>
>  #include <linux/module.h>
> +#include <linux/mount.h>
>  #include <linux/nfs4_mount.h>
>  #include <linux/nfs_fs.h>
>  #include "delegation.h"
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index deecb397daa3..3c47399bd095 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -19,6 +19,7 @@
>  #include <linux/bitops.h>
>  #include <linux/user_namespace.h>
>  #include <linux/mount.h>
> +#include <linux/sb_config.h>
>  #include <linux/pid_namespace.h>
>  #include <linux/parser.h>
>  #include <linux/cred.h>
> diff --git a/fs/sb_config.c b/fs/sb_config.c
> new file mode 100644
> index 000000000000..9c45e269b3cc
> --- /dev/null
> +++ b/fs/sb_config.c
> @@ -0,0 +1,326 @@
> +/* Provide a way to create a superblock configuration context within the kernel
> + * that allows a superblock to be set up prior to mounting.
> + *
> + * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@redhat.com)
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public Licence
> + * as published by the Free Software Foundation; either version
> + * 2 of the Licence, or (at your option) any later version.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +#include <linux/sb_config.h>
> +#include <linux/fs.h>
> +#include <linux/mount.h>
> +#include <linux/nsproxy.h>
> +#include <linux/slab.h>
> +#include <linux/magic.h>
> +#include <linux/security.h>
> +#include <linux/parser.h>
> +#include <linux/mnt_namespace.h>
> +#include <linux/pid_namespace.h>
> +#include <linux/user_namespace.h>
> +#include <net/net_namespace.h>
> +#include "mount.h"
> +
> +static const match_table_t common_set_mount_options = {
> +       { MS_DIRSYNC,           "dirsync" },
> +       { MS_I_VERSION,         "iversion" },
> +       { MS_LAZYTIME,          "lazytime" },
> +       { MS_MANDLOCK,          "mand" },
> +       { MS_NOATIME,           "noatime" },
> +       { MS_NODEV,             "nodev" },
> +       { MS_NODIRATIME,        "nodiratime" },
> +       { MS_NOEXEC,            "noexec" },
> +       { MS_NOSUID,            "nosuid" },
> +       { MS_POSIXACL,          "posixacl" },
> +       { MS_RDONLY,            "ro" },
> +       { MS_REC,               "rec" },
> +       { MS_RELATIME,          "relatime" },
> +       { MS_STRICTATIME,       "strictatime" },
> +       { MS_SYNCHRONOUS,       "sync" },
> +       { MS_VERBOSE,           "verbose" },
> +       { },
> +};


Lots of these are not superblock options, and should be moved over to
the forbidden ones.  Look at do_mount() for a hint.

> +
> +static const match_table_t common_clear_mount_options = {
> +       { MS_LAZYTIME,          "nolazytime" },
> +       { MS_MANDLOCK,          "nomand" },
> +       { MS_NODEV,             "dev" },
> +       { MS_NOEXEC,            "exec" },
> +       { MS_NOSUID,            "suid" },
> +       { MS_RDONLY,            "rw" },
> +       { MS_RELATIME,          "norelatime" },
> +       { MS_SILENT,            "silent" },
> +       { MS_STRICTATIME,       "nostrictatime" },
> +       { MS_SYNCHRONOUS,       "async" },
> +       { },
> +};
> +
> +static const match_table_t forbidden_mount_options = {
> +       { MS_BIND,              "bind" },
> +       { MS_MOVE,              "move" },
> +       { MS_PRIVATE,           "private" },
> +       { MS_REMOUNT,           "remount" },
> +       { MS_SHARED,            "shared" },
> +       { MS_SLAVE,             "slave" },
> +       { MS_UNBINDABLE,        "unbindable" },
> +       { },
> +};
> +
> +/*
> + * Check for a common mount option.
> + */
> +static int vfs_parse_ms_mount_option(struct sb_config *sc, char *data)
> +{
> +       substring_t args[MAX_OPT_ARGS];
> +       unsigned int token;
> +
> +       token = match_token(data, common_set_mount_options, args);
> +       if (token) {
> +               sc->ms_flags |= token;
> +               return 1;
> +       }
> +
> +       token = match_token(data, common_clear_mount_options, args);
> +       if (token) {
> +               sc->ms_flags &= ~token;
> +               return 1;
> +       }
> +
> +       token = match_token(data, forbidden_mount_options, args);
> +       if (token)
> +               return sb_cfg_inval(sc, "Mount option, not superblock option");
> +
> +       return 0;
> +}
> +
> +/**
> + * vfs_parse_mount_option - Add a single mount option to a superblock config
> + * @mc: The superblock configuration to modify
> + * @p: The option to apply.
> + *
> + * A single mount option in string form is applied to the superblock
> + * configuration being set up.  Certain standard options (for example "ro") are
> + * translated into flag bits without going to the filesystem.  The active
> + * security module is allowed to observe and poach options.  Any other options
> + * are passed over to the filesystem to parse.
> + *
> + * This may be called multiple times for a context.
> + *
> + * Returns 0 on success and a negative error code on failure.  In the event of
> + * failure, sc->error may have been set to a non-allocated string that gives
> + * more information.
> + */
> +int vfs_parse_mount_option(struct sb_config *sc, char *p)
> +{
> +       int ret;
> +
> +       if (sc->mounted)
> +               return -EBUSY;
> +
> +       ret = vfs_parse_ms_mount_option(sc, p);
> +       if (ret < 0)
> +               return ret;
> +       if (ret == 1)
> +               return 0;
> +
> +       ret = security_sb_config_parse_option(sc, p);
> +       if (ret < 0)
> +               return ret;
> +       if (ret == 1)
> +               return 0;
> +
> +       return sc->ops->parse_option(sc, p);
> +}
> +EXPORT_SYMBOL(vfs_parse_mount_option);
> +
> +/**
> + * generic_monolithic_mount_data - Parse key[=val][,key[=val]]* mount data
> + * @mc: The superblock configuration to fill in.
> + * @data: The data to parse
> + *
> + * Parse a blob of data that's in key[=val][,key[=val]]* form.  This can be
> + * called from the ->monolithic_mount_data() sb_config operation.
> + *
> + * Returns 0 on success or the error returned by the ->parse_option() sb_config
> + * operation on failure.
> + */
> +int generic_monolithic_mount_data(struct sb_config *ctx, void *data)
> +{
> +       char *options = data, *p;
> +       int ret;
> +
> +       if (!options)
> +               return 0;
> +
> +       while ((p = strsep(&options, ",")) != NULL) {
> +               if (*p) {
> +                       ret = vfs_parse_mount_option(ctx, p);
> +                       if (ret < 0)
> +                               return ret;
> +               }
> +       }
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL(generic_monolithic_mount_data);
> +
> +/**
> + * __vfs_new_sb_config - Create a superblock config.
> + * @fs_type: The filesystem type.
> + * @src_sb: A superblock from which this one derives (or NULL)
> + * @ms_flags: Superblock flags and op flags (such as MS_REMOUNT)
> + * @purpose: The purpose that this configuration shall be used for.
> + *
> + * Open a filesystem and create a mount context.  The mount context is
> + * initialised with the supplied flags and, if a submount/automount from
> + * another superblock (@src_sb), may have parameters such as namespaces copied
> + * across from that superblock.
> + */
> +struct sb_config *__vfs_new_sb_config(struct file_system_type *fs_type,
> +                                     struct super_block *src_sb,
> +                                     unsigned int ms_flags,
> +                                     enum sb_config_purpose purpose)
> +{
> +       struct sb_config *sc;
> +       int ret;
> +
> +       BUG_ON(fs_type->init_sb_config &&
> +              fs_type->sb_config_size < sizeof(*sc));
> +
> +       sc = kzalloc(max_t(size_t, fs_type->sb_config_size, sizeof(*sc)),
> +                    GFP_KERNEL);
> +       if (!sc)
> +               return ERR_PTR(-ENOMEM);
> +
> +       sc->purpose     = purpose;
> +       sc->ms_flags    = ms_flags;
> +       sc->fs_type     = get_filesystem(fs_type);
> +       sc->net_ns      = get_net(current->nsproxy->net_ns);
> +       sc->user_ns     = get_user_ns(current_user_ns());
> +       sc->cred        = get_current_cred();
> +
> +       /* TODO: Make all filesystems support this unconditionally */
> +       if (sc->fs_type->init_sb_config) {
> +               ret = sc->fs_type->init_sb_config(sc, src_sb);
> +               if (ret < 0)
> +                       goto err_sc;
> +       }
> +
> +       /* Do the security check last because ->fsopen may change the
> +        * namespace subscriptions.
> +        */
> +       ret = security_sb_config_alloc(sc, src_sb);
> +       if (ret < 0)
> +               goto err_sc;
> +
> +       return sc;
> +
> +err_sc:
> +       put_sb_config(sc);
> +       return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(__vfs_new_sb_config);
> +
> +/**
> + * vfs_new_sb_config - Create a superblock config for a new mount.
> + * @fs_name: The name of the filesystem
> + *
> + * Open a filesystem and create a superblock config context for a new mount
> + * that will hold the mount options, device name, security details, etc..  Note
> + * that the caller should check the ->ops pointer in the returned context to
> + * determine whether the filesystem actually supports the superblock context
> + * itself.
> + */
> +struct sb_config *vfs_new_sb_config(const char *fs_name)
> +{
> +       struct file_system_type *fs_type;
> +       struct sb_config *sc;
> +
> +       fs_type = get_fs_type(fs_name);
> +       if (!fs_type)
> +               return ERR_PTR(-ENODEV);
> +
> +       sc = __vfs_new_sb_config(fs_type, NULL, 0, SB_CONFIG_FOR_NEW);
> +       put_filesystem(fs_type);
> +       return sc;
> +}
> +EXPORT_SYMBOL(vfs_new_sb_config);
> +
> +/**
> + * vfs_sb_reconfig - Create a superblock config for remount/reconfiguration
> + * @mnt: The mountpoint to open
> + * @ms_flags: Superblock flags and op flags (such as MS_REMOUNT)
> + *
> + * Open a mounted filesystem and create a mount context such that a remount can
> + * be effected.
> + */
> +struct sb_config *vfs_sb_reconfig(struct vfsmount *mnt,
> +                                 unsigned int ms_flags)
> +{
> +       return __vfs_new_sb_config(mnt->mnt_sb->s_type, mnt->mnt_sb,
> +                                  ms_flags, SB_CONFIG_FOR_REMOUNT);
> +}
> +
> +/**
> + * vfs_dup_sc_config: Duplicate a superblock configuration context.
> + * @src_sc: The context to copy.
> + */
> +struct sb_config *vfs_dup_sb_config(struct sb_config *src_sc)
> +{
> +       struct sb_config *sc;
> +       int ret;
> +
> +       if (!src_sc->ops->dup)
> +               return ERR_PTR(-ENOTSUPP);
> +
> +       sc = kmemdup(src_sc, src_sc->fs_type->sb_config_size, GFP_KERNEL);
> +       if (!sc)
> +               return ERR_PTR(-ENOMEM);
> +
> +       sc->device      = NULL;
> +       sc->security    = NULL;
> +       sc->error_msg   = NULL;
> +       get_filesystem(sc->fs_type);
> +       get_net(sc->net_ns);
> +       get_user_ns(sc->user_ns);
> +       get_cred(sc->cred);
> +
> +       /* Can't call put until we've called ->dup */
> +       ret = sc->ops->dup(sc, src_sc);
> +       if (ret < 0)
> +               goto err_sc;
> +
> +       ret = security_sb_config_dup(sc, src_sc);
> +       if (ret < 0)
> +               goto err_sc;
> +       return sc;
> +
> +err_sc:
> +       put_sb_config(sc);
> +       return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(vfs_dup_sb_config);
> +
> +/**
> + * put_sb_config - Dispose of a superblock configuration context.
> + * @sc: The context to dispose of.
> + */
> +void put_sb_config(struct sb_config *sc)
> +{
> +       if (sc->ops && sc->ops->free)
> +               sc->ops->free(sc);
> +       security_sb_config_free(sc);
> +       if (sc->net_ns)
> +               put_net(sc->net_ns);
> +       put_user_ns(sc->user_ns);
> +       if (sc->cred)
> +               put_cred(sc->cred);
> +       put_filesystem(sc->fs_type);
> +       kfree(sc->device);
> +       kfree(sc);
> +}
> +EXPORT_SYMBOL(put_sb_config);
> diff --git a/fs/super.c b/fs/super.c
> index adb0c0de428c..4d923a775bd0 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -34,6 +34,7 @@
>  #include <linux/fsnotify.h>
>  #include <linux/lockdep.h>
>  #include <linux/user_namespace.h>
> +#include <linux/sb_config.h>
>  #include "internal.h"
>
>
> @@ -805,10 +806,13 @@ struct super_block *user_get_super(dev_t dev)
>   *     @flags: numeric part of options
>   *     @data:  the rest of options
>   *      @force: whether or not to force the change
> + *     @sc:    the superblock config for filesystems that support it
> + *             (NULL if called from emergency or umount)
>   *
>   *     Alters the mount options of a mounted file system.
>   */
> -int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
> +int do_remount_sb(struct super_block *sb, int flags, void *data, int force,
> +                 struct sb_config *sc)
>  {
>         int retval;
>         int remount_ro;
> @@ -850,8 +854,14 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
>                 }
>         }
>
> -       if (sb->s_op->remount_fs) {
> -               retval = sb->s_op->remount_fs(sb, &flags, data);
> +       if (sb->s_op->remount_fs_sc ||
> +           sb->s_op->remount_fs) {
> +               if (sb->s_op->remount_fs_sc) {
> +                   retval = sb->s_op->remount_fs_sc(sb, sc);
> +                   flags = sc->ms_flags;
> +               } else {
> +                       retval = sb->s_op->remount_fs(sb, &flags, data);
> +               }
>                 if (retval) {
>                         if (!force)
>                                 goto cancel_readonly;
> @@ -898,7 +908,7 @@ static void do_emergency_remount(struct work_struct *work)
>                         /*
>                          * What lock protects sb->s_flags??
>                          */
> -                       do_remount_sb(sb, MS_RDONLY, NULL, 1);
> +                       do_remount_sb(sb, MS_RDONLY, NULL, 1, NULL);
>                 }
>                 up_write(&sb->s_umount);
>                 spin_lock(&sb_lock);
> @@ -1048,6 +1058,40 @@ struct dentry *mount_ns(struct file_system_type *fs_type,
>
>  EXPORT_SYMBOL(mount_ns);
>
> +struct dentry *mount_ns_sc(struct sb_config *sc,
> +                          int (*fill_super)(struct super_block *sb,
> +                                            struct sb_config *sc),
> +                          void *ns)
> +{
> +       struct super_block *sb;
> +
> +       /* Don't allow mounting unless the caller has CAP_SYS_ADMIN
> +        * over the namespace.
> +        */
> +       if (!(sc->ms_flags & MS_KERNMOUNT) &&
> +           !ns_capable(sc->user_ns, CAP_SYS_ADMIN))
> +               return ERR_PTR(-EPERM);
> +
> +       sb = sget_userns(sc->fs_type, ns_test_super, ns_set_super,
> +                        sc->ms_flags, sc->user_ns, ns);
> +       if (IS_ERR(sb))
> +               return ERR_CAST(sb);
> +
> +       if (!sb->s_root) {
> +               int err;
> +               err = fill_super(sb, sc);
> +               if (err) {
> +                       deactivate_locked_super(sb);
> +                       return ERR_PTR(err);
> +               }
> +
> +               sb->s_flags |= MS_ACTIVE;
> +       }
> +
> +       return dget(sb->s_root);
> +}
> +EXPORT_SYMBOL(mount_ns_sc);
> +
>  #ifdef CONFIG_BLOCK
>  static int set_bdev_super(struct super_block *s, void *data)
>  {
> @@ -1196,7 +1240,7 @@ struct dentry *mount_single(struct file_system_type *fs_type,
>                 }
>                 s->s_flags |= MS_ACTIVE;
>         } else {
> -               do_remount_sb(s, flags, data, 0);
> +               do_remount_sb(s, flags, data, 0, NULL);
>         }
>         return dget(s->s_root);
>  }
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index bc0c054894b9..cd6cafcdd2ff 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -54,6 +54,7 @@ struct workqueue_struct;
>  struct iov_iter;
>  struct fscrypt_info;
>  struct fscrypt_operations;
> +struct sb_config;
>
>  extern void __init inode_init(void);
>  extern void __init inode_init_early(void);
> @@ -701,6 +702,11 @@ static inline void inode_unlock(struct inode *inode)
>         up_write(&inode->i_rwsem);
>  }
>
> +static inline int inode_lock_killable(struct inode *inode)
> +{
> +       return down_write_killable(&inode->i_rwsem);
> +}
> +
>  static inline void inode_lock_shared(struct inode *inode)
>  {
>         down_read(&inode->i_rwsem);
> @@ -1787,6 +1793,7 @@ struct super_operations {
>         int (*unfreeze_fs) (struct super_block *);
>         int (*statfs) (struct dentry *, struct kstatfs *);
>         int (*remount_fs) (struct super_block *, int *, char *);
> +       int (*remount_fs_sc) (struct super_block *, struct sb_config *);
>         void (*umount_begin) (struct super_block *);
>
>         int (*show_options)(struct seq_file *, struct dentry *);
> @@ -2021,8 +2028,10 @@ struct file_system_type {
>  #define FS_HAS_SUBTYPE         4
>  #define FS_USERNS_MOUNT                8       /* Can be mounted by userns root */
>  #define FS_RENAME_DOES_D_MOVE  32768   /* FS will handle d_move() during rename() internally. */
> +       unsigned short sb_config_size;  /* Size of superblock config context to allocate */
>         struct dentry *(*mount) (struct file_system_type *, int,
>                        const char *, void *);
> +       int (*init_sb_config)(struct sb_config *, struct super_block *);
>         void (*kill_sb) (struct super_block *);
>         struct module *owner;
>         struct file_system_type * next;
> @@ -2040,6 +2049,10 @@ struct file_system_type {
>
>  #define MODULE_ALIAS_FS(NAME) MODULE_ALIAS("fs-" NAME)
>
> +extern struct dentry *mount_ns_sc(struct sb_config *mc,
> +                                 int (*fill_super)(struct super_block *sb,
> +                                                   struct sb_config *sc),
> +                                 void *ns);
>  extern struct dentry *mount_ns(struct file_system_type *fs_type,
>         int flags, void *data, void *ns, struct user_namespace *user_ns,
>         int (*fill_super)(struct super_block *, void *, int));
> @@ -2106,6 +2119,7 @@ extern int register_filesystem(struct file_system_type *);
>  extern int unregister_filesystem(struct file_system_type *);
>  extern struct vfsmount *kern_mount_data(struct file_system_type *, void *data);
>  #define kern_mount(type) kern_mount_data(type, NULL)
> +extern struct vfsmount *kern_mount_data_sc(struct sb_config *);
>  extern void kern_unmount(struct vfsmount *mnt);
>  extern int may_umount_tree(struct vfsmount *);
>  extern int may_umount(struct vfsmount *);
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 080f34e66017..48bfd49666bc 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -75,6 +75,33 @@
>   *     should enable secure mode.
>   *     @bprm contains the linux_binprm structure.
>   *
> + * Security hooks for mount using fd context.
> + *
> + * @sb_config_alloc:
> + *     Allocate and attach a security structure to sc->security.  This pointer
> + *     is initialised to NULL by the caller.
> + *     @sc indicates the new superblock configuration context.
> + *     @src_sb indicates the source superblock of a submount.
> + * @sb_config_dup:
> + *     Allocate and attach a security structure to sc->security.  This pointer
> + *     is initialised to NULL by the caller.
> + *     @sc indicates the new superblock configuration context.
> + *     @src_sc indicates the original superblock configuration context.
> + * @sb_config_free:
> + *     Clean up a superblock configuration context.
> + *     @sc indicates the superblock configuration context.
> + * @sb_config_parse_option:
> + *     Userspace provided an option to configure a superblock.  The LSM may
> + *     reject it with an error and may use it for itself, in which case it
> + *     should return 1; otherwise it should return 0 to pass it on to the
> + *     filesystem.
> + *     @sc indicates the superblock configuration context.
> + *     @p indicates the option in "key[=val]" form.
> + * @sb_config_kern_mount:
> + *     Equivalent of sb_kern_mount, but with a superblock configuration context.
> + *     @sc indicates the superblock configuration context.
> + *     @src_sb indicates the new superblock.
> + *
>   * Security hooks for filesystem operations.
>   *
>   * @sb_alloc_security:
> @@ -1372,6 +1399,12 @@ union security_list_options {
>         void (*bprm_committing_creds)(struct linux_binprm *bprm);
>         void (*bprm_committed_creds)(struct linux_binprm *bprm);
>
> +       int (*sb_config_alloc)(struct sb_config *sc, struct super_block *src_sb);
> +       int (*sb_config_dup)(struct sb_config *sc, struct sb_config *src_sc);
> +       void (*sb_config_free)(struct sb_config *sc);
> +       int (*sb_config_parse_option)(struct sb_config *sc, char *opt);
> +       int (*sb_config_kern_mount)(struct sb_config *sc, struct super_block *sb);
> +
>         int (*sb_alloc_security)(struct super_block *sb);
>         void (*sb_free_security)(struct super_block *sb);
>         int (*sb_copy_data)(char *orig, char *copy);
> @@ -1683,6 +1716,11 @@ struct security_hook_heads {
>         struct list_head bprm_secureexec;
>         struct list_head bprm_committing_creds;
>         struct list_head bprm_committed_creds;
> +       struct list_head sb_config_alloc;
> +       struct list_head sb_config_dup;
> +       struct list_head sb_config_free;
> +       struct list_head sb_config_parse_option;
> +       struct list_head sb_config_kern_mount;
>         struct list_head sb_alloc_security;
>         struct list_head sb_free_security;
>         struct list_head sb_copy_data;
> diff --git a/include/linux/mount.h b/include/linux/mount.h
> index 8e0352af06b7..a5dca6abc4d5 100644
> --- a/include/linux/mount.h
> +++ b/include/linux/mount.h
> @@ -20,6 +20,7 @@ struct super_block;
>  struct vfsmount;
>  struct dentry;
>  struct mnt_namespace;
> +struct sb_config;
>
>  #define MNT_NOSUID     0x01
>  #define MNT_NODEV      0x02
> @@ -90,9 +91,12 @@ struct file_system_type;
>  extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
>                                       int flags, const char *name,
>                                       void *data);
> +extern struct vfsmount *vfs_kern_mount_sc(struct sb_config *sc);
>  extern struct vfsmount *vfs_submount(const struct dentry *mountpoint,
>                                      struct file_system_type *type,
>                                      const char *name, void *data);
> +extern struct vfsmount *vfs_submount_sc(const struct dentry *mountpoint,
> +                                       struct sb_config *sc);
>
>  extern void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list);
>  extern void mark_mounts_for_expiry(struct list_head *mounts);
> diff --git a/include/linux/sb_config.h b/include/linux/sb_config.h
> new file mode 100644
> index 000000000000..0b21e381d9f0
> --- /dev/null
> +++ b/include/linux/sb_config.h
> @@ -0,0 +1,93 @@
> +/* Superblock configuration and creation handling.
> + *
> + * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@redhat.com)
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public Licence
> + * as published by the Free Software Foundation; either version
> + * 2 of the Licence, or (at your option) any later version.
> + */
> +
> +#ifndef _LINUX_SB_CONFIG_H
> +#define _LINUX_SB_CONFIG_H
> +
> +#include <linux/kernel.h>
> +#include <linux/errno.h>
> +
> +struct cred;
> +struct dentry;
> +struct file_operations;
> +struct file_system_type;
> +struct mnt_namespace;
> +struct net;
> +struct pid_namespace;
> +struct super_block;
> +struct user_namespace;
> +struct vfsmount;
> +
> +enum sb_config_purpose {
> +       SB_CONFIG_FOR_NEW,      /* New superblock for direct mount */
> +       SB_CONFIG_FOR_SUBMOUNT, /* New superblock for automatic submount */
> +       SB_CONFIG_FOR_REMOUNT,  /* Superblock reconfiguration for remount */
> +};
> +
> +/*
> + * Superblock configuration context as allocated and constructed by the
> + * ->init_sb_config() file_system_type operation.  The size of the object
> + * allocated is specified in struct file_system_type::sb_config_size and this
> + * must include sufficient space for the sb_config struct.
> + *
> + * See Documentation/filesystems/mounting.txt
> + */
> +struct sb_config {
> +       const struct sb_config_operations *ops;
> +       struct file_system_type *fs_type;
> +       struct user_namespace   *user_ns;       /* The user namespace for this mount */
> +       struct net              *net_ns;        /* The network namespace for this mount */
> +       const struct cred       *cred;          /* The mounter's credentials */
> +       char                    *device;        /* The device name or mount target */
> +       void                    *security;      /* The LSM context */
> +       const char              *error_msg;     /* Error string to be read by read() */
> +       unsigned int            ms_flags;       /* The superblock flags (MS_*) */
> +       bool                    mounted;        /* Set when mounted */
> +       bool                    sloppy;         /* Unrecognised options are okay */
> +       bool                    silent;
> +       enum sb_config_purpose  purpose : 8;
> +};
> +
> +struct sb_config_operations {
> +       void (*free)(struct sb_config *sc);
> +       int (*dup)(struct sb_config *sc, struct sb_config *src);
> +       int (*parse_option)(struct sb_config *sc, char *p);
> +       int (*monolithic_mount_data)(struct sb_config *sc, void *data);
> +       int (*validate)(struct sb_config *sc);
> +       struct dentry *(*mount)(struct sb_config *sc);
> +};
> +
> +extern const struct file_operations fs_fs_fops;
> +
> +extern struct sb_config *vfs_new_sb_config(const char *fs_name);
> +extern struct sb_config *__vfs_new_sb_config(struct file_system_type *fs_type,
> +                                            struct super_block *src_sb,
> +                                            unsigned int ms_flags,
> +                                            enum sb_config_purpose purpose);
> +extern struct sb_config *vfs_sb_reconfig(struct vfsmount *mnt,
> +                                        unsigned int ms_flags);
> +extern struct sb_config *vfs_dup_sb_config(struct sb_config *src);
> +extern int vfs_parse_mount_option(struct sb_config *sc, char *data);
> +extern int generic_monolithic_mount_data(struct sb_config *sc, void *data);
> +extern void put_sb_config(struct sb_config *sc);
> +
> +static inline void sb_cfg_error(struct sb_config *sc, const char *msg)
> +{
> +       sc->error_msg = msg;
> +}
> +
> +static inline int sb_cfg_inval(struct sb_config *sc, const char *msg)
> +{
> +       sb_cfg_error(sc, msg);
> +       return -EINVAL;
> +}
> +
> +#endif /* _LINUX_SB_CONFIG_H */
> diff --git a/include/linux/security.h b/include/linux/security.h
> index af675b576645..36b3a6779986 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -55,6 +55,7 @@ struct msg_queue;
>  struct xattr;
>  struct xfrm_sec_ctx;
>  struct mm_struct;
> +struct sb_config;
>
>  /* If capable should audit the security request */
>  #define SECURITY_CAP_NOAUDIT 0
> @@ -224,6 +225,11 @@ int security_bprm_check(struct linux_binprm *bprm);
>  void security_bprm_committing_creds(struct linux_binprm *bprm);
>  void security_bprm_committed_creds(struct linux_binprm *bprm);
>  int security_bprm_secureexec(struct linux_binprm *bprm);
> +int security_sb_config_alloc(struct sb_config *sc, struct super_block *sb);
> +int security_sb_config_dup(struct sb_config *sc, struct sb_config *src_sc);
> +void security_sb_config_free(struct sb_config *sc);
> +int security_sb_config_parse_option(struct sb_config *sc, char *opt);
> +int security_sb_config_kern_mount(struct sb_config *sc, struct super_block *sb);
>  int security_sb_alloc(struct super_block *sb);
>  void security_sb_free(struct super_block *sb);
>  int security_sb_copy_data(char *orig, char *copy);
> @@ -520,6 +526,29 @@ static inline int security_bprm_secureexec(struct linux_binprm *bprm)
>         return cap_bprm_secureexec(bprm);
>  }
>
> +static inline int security_sb_config_alloc(struct sb_config *sc,
> +                                          struct super_block *src_sb)
> +{
> +       return 0;
> +}
> +static inline int security_sb_config_dup(struct sb_config *sc,
> +                                        struct sb_config *src_sc)
> +{
> +       return 0;
> +}
> +static inline void security_sb_config_free(struct sb_config *sc)
> +{
> +}
> +static inline int security_sb_config_parse_option(struct sb_config *sc, char *opt)
> +{
> +       return 0;
> +}
> +static inline int security_sb_config_kern_mount(struct sb_config *sc,
> +                                               struct super_block *sb)
> +{
> +       return 0;
> +}
> +
>  static inline int security_sb_alloc(struct super_block *sb)
>  {
>         return 0;
> diff --git a/security/security.c b/security/security.c
> index b9fea3999cf8..3735fad91543 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -316,6 +316,31 @@ int security_bprm_secureexec(struct linux_binprm *bprm)
>         return call_int_hook(bprm_secureexec, 0, bprm);
>  }
>
> +int security_sb_config_alloc(struct sb_config *sc, struct super_block *src_sb)
> +{
> +       return call_int_hook(sb_config_alloc, 0, sc, src_sb);
> +}
> +
> +int security_sb_config_dup(struct sb_config *sc, struct sb_config *src_sc)
> +{
> +       return call_int_hook(sb_config_dup, 0, sc, src_sc);
> +}
> +
> +void security_sb_config_free(struct sb_config *sc)
> +{
> +       call_void_hook(sb_config_free, sc);
> +}
> +
> +int security_sb_config_parse_option(struct sb_config *sc, char *opt)
> +{
> +       return call_int_hook(sb_config_parse_option, 0, sc, opt);
> +}
> +
> +int security_sb_config_kern_mount(struct sb_config *sc, struct super_block *sb)
> +{
> +       return call_int_hook(sb_config_kern_mount, 0, sc, sb);
> +}
> +
>  int security_sb_alloc(struct super_block *sb)
>  {
>         return call_int_hook(sb_alloc_security, 0, sb);
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index e67a526d1f30..286207bced52 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -47,6 +47,7 @@
>  #include <linux/fdtable.h>
>  #include <linux/namei.h>
>  #include <linux/mount.h>
> +#include <linux/sb_config.h>
>  #include <linux/netfilter_ipv4.h>
>  #include <linux/netfilter_ipv6.h>
>  #include <linux/tty.h>
> @@ -2826,6 +2827,169 @@ static int selinux_umount(struct vfsmount *mnt, int flags)
>                                    FILESYSTEM__UNMOUNT, NULL);
>  }
>
> +/* fsopen mount context operations */
> +
> +static int selinux_sb_config_alloc(struct sb_config *sc,
> +                                  struct super_block *src_sb)
> +{
> +       struct security_mnt_opts *opts;
> +
> +       opts = kzalloc(sizeof(*opts), GFP_KERNEL);
> +       if (!opts)
> +               return -ENOMEM;
> +
> +       sc->security = opts;
> +       return 0;
> +}
> +
> +static int selinux_sb_config_dup(struct sb_config *sc,
> +                                struct sb_config *src_sc)
> +{
> +       const struct security_mnt_opts *src = src_sc->security;
> +       struct security_mnt_opts *opts;
> +       int i, n;
> +
> +       opts = kzalloc(sizeof(*opts), GFP_KERNEL);
> +       if (!opts)
> +               return -ENOMEM;
> +       sc->security = opts;
> +
> +       if (!src || !src->num_mnt_opts)
> +               return 0;
> +       n = opts->num_mnt_opts = src->num_mnt_opts;
> +
> +       if (src->mnt_opts) {
> +               opts->mnt_opts = kcalloc(n, sizeof(char *), GFP_KERNEL);
> +               if (!opts->mnt_opts)
> +                       return -ENOMEM;
> +
> +               for (i = 0; i < n; i++) {
> +                       if (src->mnt_opts[i]) {
> +                               opts->mnt_opts[i] = kstrdup(src->mnt_opts[i],
> +                                                           GFP_KERNEL);
> +                               if (!opts->mnt_opts[i])
> +                                       return -ENOMEM;
> +                       }
> +               }
> +       }
> +
> +       if (src->mnt_opts_flags) {
> +               opts->mnt_opts_flags = kmemdup(src->mnt_opts_flags,
> +                                              n * sizeof(int), GFP_KERNEL);
> +               if (!opts->mnt_opts_flags)
> +                       return -ENOMEM;
> +       }
> +
> +       return 0;
> +}
> +
> +static void selinux_sb_config_free(struct sb_config *sc)
> +{
> +       struct security_mnt_opts *opts = sc->security;
> +
> +       security_free_mnt_opts(opts);
> +       sc->security = NULL;
> +}
> +
> +static int selinux_sb_config_parse_option(struct sb_config *sc, char *opt)
> +{
> +       struct security_mnt_opts *opts = sc->security;
> +       substring_t args[MAX_OPT_ARGS];
> +       unsigned int have;
> +       char *c, **oo;
> +       int token, ctx, i, *of;
> +
> +       token = match_token(opt, tokens, args);
> +       if (token == Opt_error)
> +               return 0; /* Doesn't belong to us. */
> +
> +       have = 0;
> +       for (i = 0; i < opts->num_mnt_opts; i++)
> +               have |= 1 << opts->mnt_opts_flags[i];
> +       if (have & (1 << token))
> +               return sb_cfg_inval(sc, "SELinux: Duplicate mount options");
> +
> +       switch (token) {
> +       case Opt_context:
> +               if (have & (1 << Opt_defcontext))
> +                       goto incompatible;
> +               ctx = CONTEXT_MNT;
> +               goto copy_context_string;
> +
> +       case Opt_fscontext:
> +               ctx = FSCONTEXT_MNT;
> +               goto copy_context_string;
> +
> +       case Opt_rootcontext:
> +               ctx = ROOTCONTEXT_MNT;
> +               goto copy_context_string;
> +
> +       case Opt_defcontext:
> +               if (have & (1 << Opt_context))
> +                       goto incompatible;
> +               ctx = DEFCONTEXT_MNT;
> +               goto copy_context_string;
> +
> +       case Opt_labelsupport:
> +               return 1;
> +
> +       default:
> +               return sb_cfg_inval(sc, "SELinux: Unknown mount option");
> +       }
> +
> +copy_context_string:
> +       if (opts->num_mnt_opts > 3)
> +               return sb_cfg_inval(sc, "SELinux: Too many options");
> +
> +       of = krealloc(opts->mnt_opts_flags,
> +                     (opts->num_mnt_opts + 1) * sizeof(int), GFP_KERNEL);
> +       if (!of)
> +               return -ENOMEM;
> +       of[opts->num_mnt_opts] = 0;
> +       opts->mnt_opts_flags = of;
> +
> +       oo = krealloc(opts->mnt_opts,
> +                     (opts->num_mnt_opts + 1) * sizeof(char *), GFP_KERNEL);
> +       if (!oo)
> +               return -ENOMEM;
> +       oo[opts->num_mnt_opts] = NULL;
> +       opts->mnt_opts = oo;
> +
> +       c = match_strdup(&args[0]);
> +       if (!c)
> +               return -ENOMEM;
> +       opts->mnt_opts[opts->num_mnt_opts] = c;
> +       opts->mnt_opts_flags[opts->num_mnt_opts] = ctx;
> +       opts->num_mnt_opts++;
> +       return 1;
> +
> +incompatible:
> +       return sb_cfg_inval(sc, "SELinux: Incompatible mount options");
> +}
> +
> +static int selinux_sb_config_kern_mount(struct sb_config *sc,
> +                                       struct super_block *sb)
> +{
> +       const struct cred *cred = current_cred();
> +       struct common_audit_data ad;
> +       int rc;
> +
> +       rc = selinux_set_mnt_opts(sb, sc->security, 0, NULL);
> +       if (rc)
> +               return rc;
> +
> +       /* Allow all mounts performed by the kernel */
> +       if (sc->ms_flags & MS_KERNMOUNT)
> +               return 0;
> +
> +       ad.type = LSM_AUDIT_DATA_DENTRY;
> +       ad.u.dentry = sb->s_root;
> +       rc = superblock_has_perm(cred, sb, FILESYSTEM__MOUNT, &ad);
> +       if (rc < 0)
> +               sb_cfg_error(sc, "SELinux: Mount of superblock not permitted");
> +       return rc;
> +}
> +
>  /* inode security operations */
>
>  static int selinux_inode_alloc_security(struct inode *inode)
> @@ -6154,6 +6318,12 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
>         LSM_HOOK_INIT(bprm_committed_creds, selinux_bprm_committed_creds),
>         LSM_HOOK_INIT(bprm_secureexec, selinux_bprm_secureexec),
>
> +       LSM_HOOK_INIT(sb_config_alloc, selinux_sb_config_alloc),
> +       LSM_HOOK_INIT(sb_config_dup, selinux_sb_config_dup),
> +       LSM_HOOK_INIT(sb_config_free, selinux_sb_config_free),
> +       LSM_HOOK_INIT(sb_config_parse_option, selinux_sb_config_parse_option),
> +       LSM_HOOK_INIT(sb_config_kern_mount, selinux_sb_config_kern_mount),
> +
>         LSM_HOOK_INIT(sb_alloc_security, selinux_sb_alloc_security),
>         LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
>         LSM_HOOK_INIT(sb_copy_data, selinux_sb_copy_data),
>
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David Howells May 16, 2017, 4:33 p.m. UTC | #2
Miklos Szeredi <mszeredi@redhat.com> wrote:

> One way to split this large patch up into more managable chunks would be:
> 
>  1) common infrastructure
>  2) new mount related changes
>  3) reconfig (remount) related changes
> 
> Would that work?

The problem is that remount seems to generally use the same parsing code as
the new-mount entry point.

Before considering how to split it, can we consider whether to roll patches 20
and 21 into the preceding patches?

>   (a) new mount with new super block created
>   (b) new mount with existing super block reused
>   (c) remount

(b) is internal-only at the moment, used by NFS submounts as triggered by
automounts.  There isn't currently any way to supply mount options to this.

>   2) modify options ("foo" turns option on, "nofoo" turns it off)

Not all options are binary and some options may be mandatory.

> The surprising thing here is that we do (a) and (b) via the same route
> and (a) and (c) via a different ones.  This doesn't feel right.

You need to look at it like this:

	Case	Options	Ref	Call	Modify
		        super	sget	super
	=======	=======	=======	=======	=======
	a	Y	-	Y	-
	b	-	Y	Y	-
	c	Y	[1]	-	Y

[1] We don't have a separate reference sb, only the one we're going to modify,
    but we can preload the sb_config from that.

(a) and (b) have the same action.

>   i) options that determine the sb instance (such as the blockdev or
> the server IP address)
>   ii) subpath: this can determine the sb as well as the subtree to use
>   iii) options that can be changed while sb in use
>   iv) ???

Ah - but some of these options have to be set *inside* sget() or before the
superblock becomes live, even the ones that can be changed in-flight.

> Would it make sense to make the "new mount" case be
> 
>   A) find or create sb based on (i) and (ii) options
>   B) reconfigure the resulting sb based on (iii) options

You would *have* to do the reconfiguration before making the superblock live
to prevent config/use races, and some options in (iii) may be required during
sget(), or even before you get as far as calling sget() (say you need to
access a server).

> This would make legacy new mount be: (A) + if new then (B).  And
> legacy remount just (B).

It's not obvious that this is sufficiently equivalent from your brief
description.

> Also I think silently ignoring options is not always the right answer.

Example?

Do you mean like the NFS 'sloppy' option?  I've noted that that might be best
handled in userspace.

> > +       int (*remount_fs_sc) (struct super_block *, struct sb_config *);
> 
> How about reconfig_fs() or just reconfig()?

Sure.

> > + (*) struct dentry *(*mount)(struct sb_config *sc);
> 
> I'd be much happier with "get_root()" or something.

Changed in patch 21 to ->get_tree() as suggested by Al.  Having looked over
the code, I'm tempted to change it back to ->mount() as being more obvious.

> > +               err = parse_monolithic_mount_data(sc, data);
> > +               if (err < 0)
> > +                       goto err_sc;
> 
> If filesystem defines ->monolithic_mount_data() who is responsible for
> calling the security hook?

Which security hook?  security_sb_remount()?

Note this code has changed in patch 20.  I should update security_sb_remount()
to take an sb_config and call it in all paths.

> Largely duplicated do_new_mount_sc().  What's the point?

Legacy vs new.  Fixed in patch 20.

> Lots of these are not superblock options, and should be moved over to
> the forbidden ones.  Look at do_mount() for a hint.

I still have to support legacy mount option parsing.  Do I actually see these
in legacy mount(2)?  Or are they weeded out by mount(8)?

David
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Miklos Szeredi May 17, 2017, 7:54 a.m. UTC | #3
On Tue, May 16, 2017 at 6:33 PM, David Howells <dhowells@redhat.com> wrote:
> Miklos Szeredi <mszeredi@redhat.com> wrote:
>
>> One way to split this large patch up into more managable chunks would be:
>>
>>  1) common infrastructure
>>  2) new mount related changes
>>  3) reconfig (remount) related changes
>>
>> Would that work?
>
> The problem is that remount seems to generally use the same parsing code as
> the new-mount entry point.

You are talking about fs code?

I was just referring to this single patch, not the others.

>
> Before considering how to split it, can we consider whether to roll patches 20
> and 21 into the preceding patches?
>
>>   (a) new mount with new super block created
>>   (b) new mount with existing super block reused
>>   (c) remount
>
> (b) is internal-only at the moment, used by NFS submounts as triggered by
> automounts.  There isn't currently any way to supply mount options to this.

And all blockdev based fs.

>>   2) modify options ("foo" turns option on, "nofoo" turns it off)
>
> Not all options are binary and some options may be mandatory.

Right, I was simplifying.

>
>> The surprising thing here is that we do (a) and (b) via the same route
>> and (a) and (c) via a different ones.  This doesn't feel right.
>
> You need to look at it like this:
>
>         Case    Options Ref     Call    Modify
>                         super   sget    super
>         ======= ======= ======= ======= =======
>         a       Y       -       Y       -
>         b       -       Y       Y       -
>         c       Y       [1]     -       Y
>
> [1] We don't have a separate reference sb, only the one we're going to modify,
>     but we can preload the sb_config from that.
>
> (a) and (b) have the same action.
>
>>   i) options that determine the sb instance (such as the blockdev or
>> the server IP address)
>>   ii) subpath: this can determine the sb as well as the subtree to use
>>   iii) options that can be changed while sb in use
>>   iv) ???
>
> Ah - but some of these options have to be set *inside* sget() or before the
> superblock becomes live, even the ones that can be changed in-flight.

That would be the "???" category.  Any concrete examples?

>
>> Would it make sense to make the "new mount" case be
>>
>>   A) find or create sb based on (i) and (ii) options
>>   B) reconfigure the resulting sb based on (iii) options
>
> You would *have* to do the reconfiguration before making the superblock live
> to prevent config/use races,

Indeed, the actual attaching into the mount namespace would be the
final step.  I deliberately left it out, because it's largely
orthogonal to the superblock config question.

> and some options in (iii) may be required during
> sget(), or even before you get as far as calling sget() (say you need to
> access a server).
>
>> This would make legacy new mount be: (A) + if new then (B).  And
>> legacy remount just (B).
>
> It's not obvious that this is sufficiently equivalent from your brief
> description.

It's not obvious.  I'm just trying to explore the design space to fix
as much idiocy in the current one as possible.

>
>> Also I think silently ignoring options is not always the right answer.
>
> Example?

mount /dev/sda -oacl /mnt
mount /dev/sda -onoacl /mnt2

>
> Do you mean like the NFS 'sloppy' option?  I've noted that that might be best
> handled in userspace.
>
>> > +       int (*remount_fs_sc) (struct super_block *, struct sb_config *);
>>
>> How about reconfig_fs() or just reconfig()?
>
> Sure.
>
>> > + (*) struct dentry *(*mount)(struct sb_config *sc);
>>
>> I'd be much happier with "get_root()" or something.
>
> Changed in patch 21 to ->get_tree() as suggested by Al.  Having looked over
> the code, I'm tempted to change it back to ->mount() as being more obvious.

Some definitions of mount:

 - to increase in amount or extent
 - to seat oneself (as on a horse) for riding
 - to climb on top of for copulation
 - to launch and carry out (something, such as an assault or a campaign)
 - to attach to a support

No really good match for what this method is doing.  We could call it
->get_tree_to_mount(), but calling it just ->mount() implies that it's
doing the mounting, which it is not.

>
>> > +               err = parse_monolithic_mount_data(sc, data);
>> > +               if (err < 0)
>> > +                       goto err_sc;
>>
>> If filesystem defines ->monolithic_mount_data() who is responsible for
>> calling the security hook?
>
> Which security hook?  security_sb_remount()?
>
> Note this code has changed in patch 20.  I should update security_sb_remount()
> to take an sb_config and call it in all paths.
>
>> Largely duplicated do_new_mount_sc().  What's the point?
>
> Legacy vs new.  Fixed in patch 20.
>
>> Lots of these are not superblock options, and should be moved over to
>> the forbidden ones.  Look at do_mount() for a hint.
>
> I still have to support legacy mount option parsing.  Do I actually see these
> in legacy mount(2)?  Or are they weeded out by mount(8)?

You are thinking on the wrong level.  Of course mount(2) needs to
handle MS_NOSUID et al.  But it's doing it now, and it isn't parsing
"nosuid", just translating MS_NOSUID to MNT_NOSUID.   For the fsopen()
case you won't need to parse "nosuid" because that's a flag for
fsmount().

The only thing fsmount() should take from the sc is the root_dentry.
It should be equivalent to what currently is a bind mount, except it
should be able to fully configure the new mount.

I'm still hoping we can move subpath handling completely to fsmount()
in which case it would just take a struct super_block.  But that would
have to start with lots of filesystem work (not just NFS but CEPH,
CIFS, etc..).

Thanks,
Miklos
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David Howells May 17, 2017, 11:31 a.m. UTC | #4
Miklos Szeredi <mszeredi@redhat.com> wrote:

> > (b) is internal-only at the moment, used by NFS submounts as triggered by
> > automounts.  There isn't currently any way to supply mount options to this.
> 
> And all blockdev based fs.

I see what you're getting at.  In which case there are more cases:

  (a) new mount, new sb struct with no source (eg. procfs, sysfs, tmpfs)
  (b) new mount, new sb struct, params loaded from filesystem data (eg. bdev)
  (c) new mount, new sb struct, params derived from parent (eg. NFS automount)
  (d) new mount, shared extant sb struct
  (e) remount

In the case of (d) where we're attempting to make another mount for an extant
super_block struct and we need to check the consistency of the parameters.

> > Ah - but some of these options have to be set *inside* sget() or before the
> > superblock becomes live, even the ones that can be changed in-flight.
> 
> That would be the "???" category.  Any concrete examples?

NFS is a good example.  You need parameters that indicate the server to talk
to and specify I/O parameters before you even get the superblock as you have
to talk to the server first.  I think this is particularly true of NFSv2/3
where you need to talk to mountd.

This would also be true of AFS.  There you have to access the network to look
up the volume ID before you can call sget() as the volume ID is part of the
index key to the set of super_block structs.

Further, some of these values (I/O parameters in NFS's case, for example) form
part of the super_block struct index key, so you have to set those inside
sget()'s set callback.

> >> Also I think silently ignoring options is not always the right answer.
> >
> > Example?
> 
> mount /dev/sda -oacl /mnt
> mount /dev/sda -onoacl /mnt2

So you'd like to give an error or a warning if ACLs are not supported, either
by the filesystem or the kernel as a whole?

> No really good match for what this method is doing.  We could call it
> ->get_tree_to_mount(), but calling it just ->mount() implies that it's
> doing the mounting, which it is not.

Yes, but my point is that it's part of the mount procedure.  We are, I assume,
intending to try and mount the thing at some point.  I can leave it as
->get_tree() for the moment.

> You are thinking on the wrong level.  Of course mount(2) needs to
> handle MS_NOSUID et al.  But it's doing it now, and it isn't parsing
> "nosuid", just translating MS_NOSUID to MNT_NOSUID.

Ummm...  That's done by the parser in this case, so effectively it is.

> For the fsopen() case you won't need to parse "nosuid" because that's a flag
> for fsmount().

Whilst this is true, that means that the parser has to operate differently in
the mount(2) and fsopen(2) cases - which I was trying to avoid.  I guess I can
set a flag in the sb_config struct to indicate the source and then split out
these options into an only-for-mount(2) list.

> The only thing fsmount() should take from the sc is the root_dentry.
> It should be equivalent to what currently is a bind mount, except it
> should be able to fully configure the new mount.

It needs to take the device name as well.  I wonder if it would be possible to
store the device name on the superblock and then leave a path-in-mount in the
vfsmount struct to fabricate a <source>:/<path> later.  Though this would
change the behaviour if someone did:

	mknod /dev/foo b 8 1
	mknod /dev/bar b 8 1
	mount /dev/foo /mnt/foo
	mount /dev/bar /mnt/bar

as /proc/mounts would now show /dev/foo for /mnt/bar.

Also, I guess the subtype should be wangled in the superblock-getting code
(vfs_get_tree() as of patch 21) rather than in do_new_mount_sc().  If I do
that, then it may be that do_new_mount_sc() only needs the root dentry pointer
and not the sb_config pointer (except for error string passing).

> I'm still hoping we can move subpath handling completely to fsmount()
> in which case it would just take a struct super_block.  But that would
> have to start with lots of filesystem work (not just NFS but CEPH,
> CIFS, etc..).

That would be nice, though NFSv2/3 might be tricky.

David
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Miklos Szeredi May 18, 2017, 8:09 a.m. UTC | #5
On Wed, May 17, 2017 at 1:31 PM, David Howells <dhowells@redhat.com> wrote:
> Miklos Szeredi <mszeredi@redhat.com> wrote:
>
>> > (b) is internal-only at the moment, used by NFS submounts as triggered by
>> > automounts.  There isn't currently any way to supply mount options to this.
>>
>> And all blockdev based fs.
>
> I see what you're getting at.  In which case there are more cases:
>
>   (a) new mount, new sb struct with no source (eg. procfs, sysfs, tmpfs)
>   (b) new mount, new sb struct, params loaded from filesystem data (eg. bdev)
>   (c) new mount, new sb struct, params derived from parent (eg. NFS automount)
>   (d) new mount, shared extant sb struct
>   (e) remount
>
> In the case of (d) where we're attempting to make another mount for an extant
> super_block struct and we need to check the consistency of the parameters.

Yes.  Current behavior seems to just ignore given options (except
MS_RDONLY) in that case, so we need to keep that possibility.

Also I think it would be good to allow selecting when superblock is created:

  - non-exclusive create: if exists return it, if not create it
  - exclusive create: only create if non-existent
  - non-create: only return if exists

>
>> > Ah - but some of these options have to be set *inside* sget() or before the
>> > superblock becomes live, even the ones that can be changed in-flight.
>>
>> That would be the "???" category.  Any concrete examples?
>
> NFS is a good example.  You need parameters that indicate the server to talk
> to and specify I/O parameters before you even get the superblock as you have
> to talk to the server first.  I think this is particularly true of NFSv2/3
> where you need to talk to mountd.
>
> This would also be true of AFS.  There you have to access the network to look
> up the volume ID before you can call sget() as the volume ID is part of the
> index key to the set of super_block structs.
>
> Further, some of these values (I/O parameters in NFS's case, for example) form
> part of the super_block struct index key, so you have to set those inside
> sget()'s set callback.

So what I propose is:

 1) call ->parse_option()

      would get indication what we are trying to do (find and/or
create and/or reconfig)

      this step is optional, the the filesystem type could possibly be
enough for the following steps

 2) call ->get_tree()

      pass sc containing parsed options and flags controlling the
creation of the superblock (create/exclusive)

      this step is optional, not called if we are given an sb to work
with (i.e. only reconfig)

 3) call ->reconfig()

      pass sc containing parsed options

      this step is optional, we might be instructed just to find or
create the sb

>
>> >> Also I think silently ignoring options is not always the right answer.
>> >
>> > Example?
>>
>> mount /dev/sda -oacl /mnt
>> mount /dev/sda -onoacl /mnt2
>
> So you'd like to give an error or a warning if ACLs are not supported, either
> by the filesystem or the kernel as a whole?

What I was getting at is that the second mount will ignore the "noacl"
option.  It's not something we apparently care much about (but will
definitely want to keep as back-compat thing for the mount(2)
interface).  But for the new interface I think we need something less
crazy.  One solution would be the exclusive create, which doesn't have
this problem. Maybe that's enough; not sure if we need anything more
sophisticated.

>> You are thinking on the wrong level.  Of course mount(2) needs to
>> handle MS_NOSUID et al.  But it's doing it now, and it isn't parsing
>> "nosuid", just translating MS_NOSUID to MNT_NOSUID.
>
> Ummm...  That's done by the parser in this case, so effectively it is.

Where exactly?  You are not touching do_mount(), which is where the
MS_*** -> MNT_*** translation is done.


>> For the fsopen() case you won't need to parse "nosuid" because that's a flag
>> for fsmount().
>
> Whilst this is true, that means that the parser has to operate differently in
> the mount(2) and fsopen(2) cases - which I was trying to avoid.

I don't get it.  We never passed MNT_* options as strings to the
kernel.  That was parsed by mount(8) and translated to MS_* flags.
So how would mount(2) and fsopen(2) need to operate differently
regarding parsing MNT_* options, when we want neither to do it?

>> The only thing fsmount() should take from the sc is the root_dentry.
>> It should be equivalent to what currently is a bind mount, except it
>> should be able to fully configure the new mount.
>
> It needs to take the device name as well.  I wonder if it would be possible to
> store the device name on the superblock and then leave a path-in-mount in the

Ah, mnt_devname.  The device name as just a special type of option and
as such should be stored in the superblock.

> vfsmount struct to fabricate a <source>:/<path> later.  Though this would
> change the behaviour if someone did:
>
>         mknod /dev/foo b 8 1
>         mknod /dev/bar b 8 1
>         mount /dev/foo /mnt/foo
>         mount /dev/bar /mnt/bar
>
> as /proc/mounts would now show /dev/foo for /mnt/bar.

I'd very much hope this doesn't introduce regressions, but if it did,
then we'd have to go back to using mnt_devname...

> Also, I guess the subtype should be wangled in the superblock-getting code
> (vfs_get_tree() as of patch 21) rather than in do_new_mount_sc().  If I do
> that, then it may be that do_new_mount_sc() only needs the root dentry pointer
> and not the sb_config pointer (except for error string passing).

Would be nice.

And hopefully error string passing can be made generic and be moved
out of this set.

Thanks,
Miklos
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David Howells May 19, 2017, 2:05 p.m. UTC | #6
Miklos Szeredi <mszeredi@redhat.com> wrote:

> Yes.  Current behavior seems to just ignore given options (except
> MS_RDONLY) in that case, so we need to keep that possibility.

Yeah.  I wonder if we really should be consistency checking some parameters in
some filesystems - or, at least, offering the opportunity.

> Also I think it would be good to allow selecting when superblock is created:
> 
>   - non-exclusive create: if exists return it, if not create it
>   - exclusive create: only create if non-existent
>   - non-create: only return if exists

I quite like that idea.  Use O_CREAT and O_EXCL?  Probably better to define a
new flag space for fsopen() rather than trying to share with open().  I'm not
sure how likely it would be to be used, though.

> So what I propose is:
> 
>  1) call ->parse_option()
> 
>       would get indication what we are trying to do (find and/or
> create and/or reconfig)
> 
>       this step is optional, the the filesystem type could possibly be
> enough for the following steps
> 
>  2) call ->get_tree()
> 
>       pass sc containing parsed options and flags controlling the
> creation of the superblock (create/exclusive)
> 
>       this step is optional, not called if we are given an sb to work
> with (i.e. only reconfig)

No.  We have to call this to get the root dentry.  Whether or not it creates a
superblock - or even if it creates a superblock in someone else's filesystem
(the cpuset fs, for example) - is immaterial.

Further, we aren't given information as to whether the superblock was created
for us or not - though that can be changed.

Even further, I think by the time this returns, the superblock should be
live.  It will be live if we're reusing it, though we can get s_umount to
prevent a race.

>  3) call ->reconfig()
> 
>       pass sc containing parsed options
> 
>       this step is optional, we might be instructed just to find or
> create the sb

Actually, it's arguable that we *shouldn't* be calling this if the superblock
already exists - otherwise we may end up changing the parameters someone else
has set.

For mount(2), for most filesystems, we have to leave the active parameters
unaltered for compatibility.  For fsopen() I'm willing to add a consistency
check - but there probably has to be a flag to waive that as otherwise you
can't mount without determining what the other party's parameters were.

> I don't get it.  We never passed MNT_* options as strings to the
> kernel.

You're right.  I've moved all those flags over to the forbidden list.

> Ah, mnt_devname.  The device name as just a special type of option and
> as such should be stored in the superblock.

I'll leave that for now and deal with it later.  We have to be careful not to
break userspace by changing what's seen in /proc/mounts.

David
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Patch
diff mbox

diff --git a/Documentation/filesystems/mounting.txt b/Documentation/filesystems/mounting.txt
new file mode 100644
index 000000000000..03e9086f754d
--- /dev/null
+++ b/Documentation/filesystems/mounting.txt
@@ -0,0 +1,456 @@ 
+			      ===================
+			      FILESYSTEM MOUNTING
+			      ===================
+
+CONTENTS
+
+ (1) Overview.
+
+ (2) The superblock configuration context.
+
+ (3) The superblock config operations.
+
+ (4) Superblock config security.
+
+ (5) VFS superblock config operations.
+
+
+========
+OVERVIEW
+========
+
+The creation of new mounts is now to be done in a multistep process:
+
+ (1) Create a superblock configuration context.
+
+ (2) Parse the options and attach them to the context.  Options may be passed
+     individually from userspace.
+
+ (3) Validate and pre-process the context.
+
+ (4) Get or create a superblock and mountable root.
+
+ (5) Perform the mount.
+
+ (6) Return an error message attached to the context.
+
+ (7) Destroy the context.
+
+To support this, the file_system_type struct gains two new fields:
+
+	unsigned short sb_config_size;
+
+which indicates the total amount of space that should be allocated for context
+data (see the Superblock Configuration Context section), and:
+
+	int (*init_sb_config)(struct sb_config *sc, struct super_block *src_sb);
+
+which is invoked to set up the filesystem-specific parts of a superblock
+configuration context, including the additional space.  The src_sb parameter is
+used to convey the superblock from which the filesystem may draw extra
+information (such as namespaces), for submount (SB_CONFIG_FOR_SUBMOUNT) or
+remount (SB_CONFIG_FOR_REMOUNT) purposes or it will be NULL.
+
+Note that security initialisation is done *after* the filesystem is called so
+that the namespaces may be adjusted first.
+
+And the super_operations struct gains one:
+
+	int (*remount_fs_sc) (struct super_block *, struct sb_config *);
+
+This shadows the ->remount_fs() operation and takes a prepared superblock
+configuration context instead of the mount flags and data page.  It may modify
+the ms_flags in the context for the caller to pick up.
+
+[NOTE] remount_fs_sc is intended as a replacement for remount_fs.
+
+
+====================================
+THE SUPERBLOCK CONFIGURATION CONTEXT
+====================================
+
+The creation and reconfiguration of a superblock is governed by a superblock
+configuration context.  This is represented by the sb_config structure:
+
+	struct sb_config {
+		const struct sb_config_operations *ops;
+		struct file_system_type *fs;
+		struct user_namespace	*user_ns;
+		struct net		*net_ns;
+		const struct cred	*cred;
+		char			*device;
+		void			*security;
+		const char		*error_msg;
+		unsigned int		ms_flags;
+		bool			mounted;
+		bool			sloppy;
+		bool			silent;
+		enum mount_type		mount_type : 8;
+	};
+
+When the VFS creates this, it allocates ->sb_config_size bytes (as specified by
+the file_system_type object) to hold both the sb_config struct and any extra
+data required by the filesystem.  The sb_config struct is placed at the
+beginning of this space.  Any extra space beyond that is for use by the
+filesystem.  The filesystem should wrap the struct in its own, e.g.:
+
+	struct nfs_sb_config {
+		struct sb_config sc;
+		...
+	};
+
+placing the sb_config struct first.  container_of() can then be used.  The
+file_system_type would be initialised thus:
+
+	struct file_system_type nfs = {
+		...
+		.sb_config_size	= sizeof(struct nfs_sb_config),
+		.init_sb_config	= nfs_init_sb_config,
+		...
+	};
+
+The sb_config fields are as follows:
+
+ (*) const struct sb_config_operations *ops
+
+     These are operations that can be done on a superblock configuration
+     context (see below).  This must be set by the ->init_sb_config()
+     file_system_type operation.
+
+ (*) struct file_system_type *fs
+
+     A pointer to the file_system_type of the filesystem that is being
+     constructed or reconfigured.  This retains a ref on the type owner.
+
+ (*) struct user_namespace *user_ns
+ (*) struct net *net_ns
+
+     This is a subset of the namespaces in use by the invoking process.  This
+     retains a ref on each namespace.  The subscribed namespaces may be
+     replaced by the filesystem to reflect other sources, such as the parent
+     mount superblock on an automount.
+
+ (*) struct cred *cred
+
+     The mounter's credentials.  This retains a ref on the credentials.
+
+ (*) char *device
+
+     This is the device to be mounted.  It may be a block device
+     (e.g. /dev/sda1) or something more exotic, such as the "host:/path" that
+     NFS desires.
+
+ (*) void *security
+
+     A place for the LSMs to hang their security data for the superblock.  The
+     relevant security operations are described below.
+
+ (*) const char *error_msg
+
+     A place for the VFS and the filesystem to hang an error message.  This
+     should be in the form of a static string that doesn't need deallocation
+     and the pointer to which can just be overwritten.  Under some
+     circumstances, this can be retrieved by userspace.
+
+     Note that the existence of the error string is expected to be guaranteed
+     by the reference on the file_system_type object held by ->fs or any
+     filesystem-specific reference held in the filesystem context until the
+     ->free() operation is called.
+
+     Use sb_cfg_error() and sb_cfg_inval() to set this rather than setting it
+     directly.
+
+ (*) unsigned int ms_flags
+
+     This holds the MS_* flags mount flags.
+
+ (*) bool mounted
+
+     This is set to true once a mount attempt is made.  This causes an error to
+     be given on subsequent mount attempts with the same context and prevents
+     multiple mount attempts.
+
+ (*) bool sloppy
+ (*) bool silent
+
+     These are set if the sloppy or silent mount options are given.
+
+     [NOTE] sloppy is probably unnecessary when userspace passes over one
+     option at a time since the error can just be ignored if userspace deems it
+     to be unimportant.
+
+     [NOTE] silent is probably redundant with ms_flags & MS_SILENT.
+
+ (*) enum mount_type
+
+     This indicates the type of mount operation.  The available values are:
+
+	SB_CONFIG_FOR_NEW	-- New mount
+	SB_CONFIG_FOR_SUBMOUNT	-- New automatic submount of extant mount
+	SB_CONFIG_FOR_REMOUNT	-- Change an existing mount
+
+The mount context is created by calling __vfs_new_sb_config(),
+vfs_new_sb_config(), vfs_sb_reconfig() or vfs_dup_sb_config() and is destroyed
+with put_sb_config().  Note that the structure is not refcounted.
+
+VFS, security and filesystem mount options are set individually with
+vfs_parse_mount_option() or in bulk with generic_monolithic_mount_data().
+
+When mounting, the filesystem is allowed to take data from any of the pointers
+and attach it to the superblock (or whatever), provided it clears the pointer
+in the mount context.
+
+The filesystem is also allowed to allocate resources and pin them with the
+mount context.  For instance, NFS might pin the appropriate protocol version
+module.
+
+
+================================
+THE SUPERBLOCK CONFIG OPERATIONS
+================================
+
+The superblock configuration context points to a table of operations:
+
+	struct sb_config_operations {
+		void (*free)(struct sb_config *sc);
+		int (*dup)(struct sb_config *sc, struct sb_config *src_sc);
+		int (*parse_option)(struct sb_config *sc, char *p);
+		int (*monolithic_mount_data)(struct sb_config *sc, void *data);
+		int (*validate)(struct sb_config *sc);
+		struct dentry *(*mount)(struct sb_config *sc);
+	};
+
+These operations are invoked by the various stages of the mount procedure to
+manage the superblock configuration context.  They are as follows:
+
+ (*) void (*free)(struct sb_config *sc);
+
+     Called to clean up the filesystem-specific part of the superblock
+     configuration context when the context is destroyed.  It should be aware
+     that parts of the context may have been removed and NULL'd out by
+     ->mount().
+
+ (*) int (*dup)(struct sb_config *sc, struct sb_config *src_sc);
+
+     Called when a superblock configuration context has been duplicated to get
+     any refs or copy any non-referenced resources held in the
+     filesystem-specific part of the superblock configuration context.  An
+     error may be returned to indicate failure to do this.
+
+     [!] Note that even if this fails, put_sb_config() will be called
+     	 immediately thereafter, so ->dup() *must* make the filesystem-specific
+     	 part safe for ->free().
+
+ (*) int (*parse_option)(struct sb_config *sc, char *p);
+
+     Called when an option is to be added to the superblock configuration
+     context.  p points to the option string, likely in "key[=val]" format.
+     VFS-specific options will have been weeded out and sc->ms_flags updated in
+     the context.  Security options will also have been weeded out and
+     sc->security updated.
+
+     If successful, 0 should be returned and a negative error code otherwise.
+     If an ambiguous error (such as -EINVAL) is returned, sb_cfg_error() or
+     sb_cfg_inval() should be used to provide a string that provides more
+     information.
+
+ (*) int (*monolithic_mount_data)(struct sb_config *sc, void *data);
+
+     Called when the mount(2) system call is invoked to pass the entire data
+     page in one go.  If this is expected to be just a list of "key[=val]"
+     items separated by commas, then this may be set to NULL.
+
+     The return value is as for ->parse_option().
+
+     If the filesystem (eg. NFS) needs to examine the data first and then
+     finds it's the standard key-val list then it may pass it off to:
+
+	int generic_monolithic_mount_data(struct sb_config *sc, void *data);
+
+ (*) int (*validate)(struct sb_config *sc);
+
+     Called when all the options have been applied and the mount is about to
+     take place.  It is should check for inconsistencies from mount options
+     and it is also allowed to do preliminary resource acquisition.  For
+     instance, the core NFS module could load the NFS protocol module here.
+
+     Note that if sc->mount_type == SB_CONFIG_FOR_REMOUNT, some of the options
+     necessary for a new mount may not be set.
+
+     The return value is as for ->parse_option().
+
+ (*) struct dentry *(*mount)(struct sb_config *sc);
+
+     Called to effect a new mount or new submount using the information stored
+     in the superblock configuration context (remounts go via a different
+     vector).  It may detach any resources it desires from the superblock
+     configuration context and transfer them to the superblock it creates.
+
+     On success it should return the dentry that's at the root of the mount.
+     In future, sc->root_path will then be applied to this.
+
+     In the case of an error, it should return a negative error code and invoke
+     sb_cfg_inval() or sb_cfg_error().
+
+
+=========================================
+SUPERBLOCK CONFIGURATION CONTEXT SECURITY
+========================================
+
+The superblock configuration context contains a security points that the LSMs can use for
+building up a security context for the superblock to be mounted.  There are a
+number of operations used by the new mount code for this purpose:
+
+ (*) int security_sb_config_alloc(struct sb_config *sc,
+				  struct super_block *src_sb);
+
+     Called to initialise sc->security (which is preset to NULL) and allocate
+     any resources needed.  It should return 0 on success and a negative error
+     code on failure.
+
+     src_sb is non-NULL in the case of a remount (SB_CONFIG_FOR_REMOUNT) in
+     which case it indicates the superblock to be remounted or in the case of a
+     submount (SB_CONFIG_FOR_SUBMOUNT) in which case it indicates the parent
+     superblock.
+
+ (*) int security_sb_config_dup(struct sb_config *sc,
+				struct sb_config *src_mc);
+
+     Called to initialise sc->security (which is preset to NULL) and allocate
+     any resources needed.  The original superblock configuration context is pointed to by src_mc
+     and may be used for reference.  It should return 0 on success and a
+     negative error code on failure.
+
+ (*) void security_sb_config_free(struct sb_config *sc);
+
+     Called to clean up anything attached to sc->security.  Note that the
+     contents may have been transferred to a superblock and the pointer NULL'd
+     out during mount.
+
+ (*) int security_sb_config_parse_option(struct sb_config *sc, char *opt);
+
+     Called for each mount option.  The mount options are in "key[=val]"
+     form.  An active LSM may reject one with an error, pass one over and
+     return 0 or consume one and return 1.  If consumed, the option isn't
+     passed on to the filesystem.
+
+     If it returns an error, more information can be returned with
+     sb_cfg_inval() or sb_cfg_error().
+
+ (*) int security_sb_get_tree(struct sb_config *sc);
+
+     Called during the mount procedure to verify that the specified superblock
+     is allowed to be mounted and to transfer the security data there.
+
+     On success, it should return 0; otherwise it should return an error and
+     perhaps call sb_cfg_inval() or sb_cfg_error() to indicate the problem.  It
+     should not return -ENOMEM as this should be taken care of in advance.
+
+     [NOTE] Should I add a security_sb_config_validate() operation so that the
+     LSM has the opportunity to allocate stuff and check the options as a
+     whole?
+
+
+================================
+VFS SUPERBLOCK CONFIG OPERATIONS
+================================
+
+There are four operations for creating a superblock configuration context and
+one for destroying a context:
+
+ (*) struct sb_config *__vfs_new_sb_config(struct file_system_type *fs_type,
+					   struct super_block *src_sb;
+					   unsigned int ms_flags);
+
+     Create a superblock configuration context given a filesystem type pointer.
+     This allocates the superblock configuration context, sets the flags,
+     initialises the security and calls fs_type->init_sb_config() to initialise
+     the filesystem context.
+
+     src_sb can be NULL or it may indicate a superblock that is going to be
+     remounted (SB_CONFIG_FOR_REMOUNT) or a superblock that is the parent of a
+     submount (SB_CONFIG_FOR_SUBMOUNT).  This superblock is provided as a
+     source of namespace information.
+
+ (*) struct sb_config *vfs_sb_reconfig(struct vfsmount *mnt,
+				       unsigned int ms_flags);
+
+     Create a superblock configuration context from the same filesystem as an
+     extant mount and initialise the mount parameters from the superblock
+     underlying that mount.  This is for use by remount.
+
+ (*) struct sb_config *vfs_fsopen(const char *fs_name);
+
+     Create a superblock configuration context given a filesystem name.  It is
+     assumed that the mount flags will be passed in as text options or set
+     directly later.  This is intended to be called from sys_mount() or
+     sys_fsopen().  This copies current's namespaces to the superblock
+     configuration context.
+
+ (*) struct sb_config *vfs_dup_sb_config(struct sb_config *src_sc);
+
+     Duplicate a superblock configuration context, copying any options noted
+     and duplicating or additionally referencing any resources held therein.
+     This is available for use where a filesystem has to get a mount within a
+     mount, such as NFS4 does by internally mounting the root of the target
+     server and then doing a private pathwalk to the target directory.
+
+ (*) void put_sb_config(struct sb_config *sc);
+
+     Destroy a superblock configuration context, releasing any resources it
+     holds.  This calls the ->free() operation.  This is intended to be called
+     by anyone who created a superblock configuration context.
+
+     [!] superblock configuration contexts are not refcounted, so this causes
+     	 unconditional destruction.
+
+In all the above operations, apart from the put op, the return is a mount
+context pointer or a negative error code.  No error string is saved as the
+error string is only guaranteed as long as the file_system_type is pinned (and
+thus the module).
+
+The next operations can be used to cache an error message in the context for
+the caller to collect.
+
+ (*) void sb_cfg_error(struct sb_config *sc, const char *msg);
+
+     Set an error message for the caller to pick up.  For lifetime rules, see
+     the ->error_msg member description.
+
+ (*) void sb_cfg_inval(struct sb_config *sc, const char *msg);
+
+     As sb_cfg_error(), but returns -EINVAL for use with tail calling.
+
+In the remaining operations, if an error occurs, a negative error code is
+returned and, if not obvious, sc->error_msg may have been set to point to a
+useful string.  This string should not be freed.
+
+ (*) struct vfsmount *vfs_kern_mount_sc(struct sb_config *sc);
+
+     Create a mount given the parameters in the specified superblock
+     configuration context.  This invokes the ->validate() op and then the
+     ->mount() op.
+
+ (*) struct vfsmount *vfs_submount_sc(const struct dentry *mountpoint,
+				      struct sb_config *sc);
+
+     Create a mount given a superblock configuration context and set
+     MS_SUBMOUNT on it.  A wrapper around vfs_kern_mount_sc().  This is
+     intended to be called from filesystems that have automount points (NFS,
+     AFS, ...).
+
+ (*) int vfs_parse_mount_option(struct sb_config *sc, char *data);
+
+     Supply a single mount option to the superblock configuration context.  The
+     mount option should likely be in a "key[=val]" string form.  The option is
+     first checked to see if it corresponds to a standard mount flag (in which
+     case it is used to mark an MS_xxx flag and consumed) or a security option
+     (in which case the LSM consumes it) before it is passed on to the
+     filesystem.
+
+ (*) int generic_monolithic_mount_data(struct sb_config *sc, void *data);
+
+     Parse a sys_mount() data page, assuming the form to be a text list
+     consisting of key[=val] options separated by commas.  Each item in the
+     list is passed to vfs_mount_option().  This is the default when the
+     ->monolithic_mount_data() operation is NULL.
diff --git a/fs/Makefile b/fs/Makefile
index 7bbaca9c67b1..8f5142525866 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -11,7 +11,8 @@  obj-y :=	open.o read_write.o file_table.o super.o \
 		attr.o bad_inode.o file.o filesystems.o namespace.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
 		pnode.o splice.o sync.o utimes.o \
-		stack.o fs_struct.o statfs.o fs_pin.o nsfs.o
+		stack.o fs_struct.o statfs.o fs_pin.o nsfs.o \
+		sb_config.o
 
 ifeq ($(CONFIG_BLOCK),y)
 obj-y +=	buffer.o block_dev.o direct-io.o mpage.o
diff --git a/fs/internal.h b/fs/internal.h
index 9676fe11c093..39121a99d930 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -87,7 +87,7 @@  extern struct file *get_empty_filp(void);
 /*
  * super.c
  */
-extern int do_remount_sb(struct super_block *, int, void *, int);
+extern int do_remount_sb(struct super_block *, int, void *, int, struct sb_config *);
 extern bool trylock_super(struct super_block *sb);
 extern struct dentry *mount_fs(struct file_system_type *,
 			       int, const char *, void *);
diff --git a/fs/libfs.c b/fs/libfs.c
index a04395334bb1..8ef519709ee3 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -9,6 +9,7 @@ 
 #include <linux/slab.h>
 #include <linux/cred.h>
 #include <linux/mount.h>
+#include <linux/sb_config.h>
 #include <linux/vfs.h>
 #include <linux/quotaops.h>
 #include <linux/mutex.h>
diff --git a/fs/namespace.c b/fs/namespace.c
index c076787871e7..91f8a07532cd 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -25,7 +25,9 @@ 
 #include <linux/magic.h>
 #include <linux/bootmem.h>
 #include <linux/task_work.h>
+#include <linux/file.h>
 #include <linux/sched/task.h>
+#include <linux/sb_config.h>
 
 #include "pnode.h"
 #include "internal.h"
@@ -1593,7 +1595,7 @@  static int do_umount(struct mount *mnt, int flags)
 			return -EPERM;
 		down_write(&sb->s_umount);
 		if (!(sb->s_flags & MS_RDONLY))
-			retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
+			retval = do_remount_sb(sb, MS_RDONLY, NULL, 0, NULL);
 		up_write(&sb->s_umount);
 		return retval;
 	}
@@ -2276,6 +2278,26 @@  static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
 }
 
 /*
+ * Parse the monolithic page of mount data given to sys_mount().
+ */
+static int parse_monolithic_mount_data(struct sb_config *sc, void *data)
+{
+	int (*monolithic_mount_data)(struct sb_config *, void *);
+	int ret;
+
+	monolithic_mount_data = sc->ops->monolithic_mount_data;
+	if (!monolithic_mount_data)
+		monolithic_mount_data = generic_monolithic_mount_data;
+
+	ret = monolithic_mount_data(sc, data);
+	if (ret < 0)
+		return ret;
+	if (sc->ops->validate)
+		return sc->ops->validate(sc);
+	return 0;
+}
+
+/*
  * change filesystem flags. dir should be a physical root of filesystem.
  * If you've mounted a non-root directory somewhere and want to do remount
  * on it - tough luck.
@@ -2283,13 +2305,14 @@  static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
 static int do_remount(struct path *path, int flags, int mnt_flags,
 		      void *data)
 {
+	struct sb_config *sc = NULL;
 	int err;
 	struct super_block *sb = path->mnt->mnt_sb;
 	struct mount *mnt = real_mount(path->mnt);
+	struct file_system_type *type = sb->s_type;
 
 	if (!check_mnt(mnt))
 		return -EINVAL;
-
 	if (path->dentry != path->mnt->mnt_root)
 		return -EINVAL;
 
@@ -2320,9 +2343,19 @@  static int do_remount(struct path *path, int flags, int mnt_flags,
 		return -EPERM;
 	}
 
-	err = security_sb_remount(sb, data);
-	if (err)
-		return err;
+	if (type->init_sb_config) {
+		sc = vfs_sb_reconfig(path->mnt, flags);
+		if (IS_ERR(sc))
+			return PTR_ERR(sc);
+
+		err = parse_monolithic_mount_data(sc, data);
+		if (err < 0)
+			goto err_sc;
+	} else {
+		err = security_sb_remount(sb, data);
+		if (err)
+			return err;
+	}
 
 	down_write(&sb->s_umount);
 	if (flags & MS_BIND)
@@ -2330,7 +2363,7 @@  static int do_remount(struct path *path, int flags, int mnt_flags,
 	else if (!capable(CAP_SYS_ADMIN))
 		err = -EPERM;
 	else
-		err = do_remount_sb(sb, flags, data, 0);
+		err = do_remount_sb(sb, flags, data, 0, sc);
 	if (!err) {
 		lock_mount_hash();
 		mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
@@ -2339,6 +2372,9 @@  static int do_remount(struct path *path, int flags, int mnt_flags,
 		unlock_mount_hash();
 	}
 	up_write(&sb->s_umount);
+err_sc:
+	if (sc)
+		put_sb_config(sc);
 	return err;
 }
 
@@ -2492,40 +2528,106 @@  static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
 static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
 
 /*
+ * Create a new mount using a superblock configuration and request it
+ * be added to the namespace tree.
+ */
+static int do_new_mount_sc(struct sb_config *sc, struct path *mountpoint,
+			   unsigned int mnt_flags)
+{
+	struct vfsmount *mnt;
+	int ret;
+
+	mnt = vfs_kern_mount_sc(sc);
+	if (IS_ERR(mnt))
+		return PTR_ERR(mnt);
+
+	if ((sc->fs_type->fs_flags & FS_HAS_SUBTYPE) &&
+	    !mnt->mnt_sb->s_subtype) {
+		mnt = fs_set_subtype(mnt, sc->fs_type->name);
+		if (IS_ERR(mnt))
+			return PTR_ERR(mnt);
+	}
+
+	ret = -EPERM;
+	if (mount_too_revealing(mnt, &mnt_flags)) {
+		sb_cfg_error(sc, "VFS: Mount too revealing");
+		goto err_mnt;
+	}
+
+	ret = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
+	if (ret < 0) {
+		sb_cfg_error(sc, "VFS: Failed to add mount");
+		goto err_mnt;
+	}
+	return ret;
+
+err_mnt:
+	mntput(mnt);
+	return ret;
+}
+
+/*
  * create a new mount for userspace and request it to be added into the
  * namespace's tree
  */
-static int do_new_mount(struct path *path, const char *fstype, int flags,
+static int do_new_mount(struct path *mountpoint, const char *fstype, int flags,
 			int mnt_flags, const char *name, void *data)
 {
-	struct file_system_type *type;
+	struct sb_config *sc;
 	struct vfsmount *mnt;
 	int err;
 
 	if (!fstype)
 		return -EINVAL;
 
-	type = get_fs_type(fstype);
-	if (!type)
-		return -ENODEV;
+	sc = vfs_new_sb_config(fstype);
+	if (IS_ERR(sc))
+		return PTR_ERR(sc);
+	sc->ms_flags = flags;
 
-	mnt = vfs_kern_mount(type, flags, name, data);
-	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
-	    !mnt->mnt_sb->s_subtype)
-		mnt = fs_set_subtype(mnt, fstype);
+	err = -ENOMEM;
+	sc->device = kstrdup(name, GFP_KERNEL);
+	if (!sc->device)
+		goto err_sc;
 
-	put_filesystem(type);
-	if (IS_ERR(mnt))
-		return PTR_ERR(mnt);
+	if (sc->ops) {
+		err = parse_monolithic_mount_data(sc, data);
+		if (err < 0)
+			goto err_sc;
 
-	if (mount_too_revealing(mnt, &mnt_flags)) {
-		mntput(mnt);
-		return -EPERM;
+		err = do_new_mount_sc(sc, mountpoint, mnt_flags);
+		if (err)
+			goto err_sc;
+
+	} else {
+		mnt = vfs_kern_mount(sc->fs_type, flags, name, data);
+		if (!IS_ERR(mnt) && (sc->fs_type->fs_flags & FS_HAS_SUBTYPE) &&
+		    !mnt->mnt_sb->s_subtype)
+			mnt = fs_set_subtype(mnt, fstype);
+
+		if (IS_ERR(mnt)) {
+			err = PTR_ERR(mnt);
+			goto err_sc;
+		}
+
+		err = -EPERM;
+		if (mount_too_revealing(mnt, &mnt_flags))
+			goto err_mnt;
+
+		err = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
+		if (err)
+			goto err_mnt;
 	}
 
-	err = do_add_mount(real_mount(mnt), path, mnt_flags);
-	if (err)
-		mntput(mnt);
+	put_sb_config(sc);
+	return 0;
+
+err_mnt:
+	mntput(mnt);
+err_sc:
+	if (sc->error_msg)
+		pr_info("Mount failed: %s\n", sc->error_msg);
+	put_sb_config(sc);
 	return err;
 }
 
@@ -3058,6 +3160,95 @@  SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
 	return ret;
 }
 
+static struct dentry *__do_mount_sc(struct sb_config *sc)
+{
+	struct super_block *sb;
+	struct dentry *root;
+	int ret;
+
+	root = sc->ops->mount(sc);
+	if (IS_ERR(root))
+		return root;
+
+	sb = root->d_sb;
+	BUG_ON(!sb);
+	WARN_ON(!sb->s_bdi);
+	sb->s_flags |= MS_BORN;
+
+	ret = security_sb_config_kern_mount(sc, sb);
+	if (ret < 0)
+		goto err_sb;
+
+	/*
+	 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
+	 * but s_maxbytes was an unsigned long long for many releases. Throw
+	 * this warning for a little while to try and catch filesystems that
+	 * violate this rule.
+	 */
+	WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
+		"negative value (%lld)\n", sc->fs_type->name, sb->s_maxbytes);
+
+	up_write(&sb->s_umount);
+	return root;
+
+err_sb:
+	dput(root);
+	deactivate_locked_super(sb);
+	return ERR_PTR(ret);
+}
+
+struct vfsmount *vfs_kern_mount_sc(struct sb_config *sc)
+{
+	struct dentry *root;
+	struct mount *mnt;
+	int ret;
+
+	if (sc->ops->validate) {
+		ret = sc->ops->validate(sc);
+		if (ret < 0)
+			return ERR_PTR(ret);
+	}
+
+	mnt = alloc_vfsmnt(sc->device ?: "none");
+	if (!mnt)
+		return ERR_PTR(-ENOMEM);
+
+	if (sc->ms_flags & MS_KERNMOUNT)
+		mnt->mnt.mnt_flags = MNT_INTERNAL;
+
+	root = __do_mount_sc(sc);
+	if (IS_ERR(root)) {
+		mnt_free_id(mnt);
+		free_vfsmnt(mnt);
+		return ERR_CAST(root);
+	}
+
+	mnt->mnt.mnt_root	= root;
+	mnt->mnt.mnt_sb		= root->d_sb;
+	mnt->mnt_mountpoint	= mnt->mnt.mnt_root;
+	mnt->mnt_parent		= mnt;
+	lock_mount_hash();
+	list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
+	unlock_mount_hash();
+	return &mnt->mnt;
+}
+EXPORT_SYMBOL_GPL(vfs_kern_mount_sc);
+
+struct vfsmount *
+vfs_submount_sc(const struct dentry *mountpoint, struct sb_config *sc)
+{
+	/* Until it is worked out how to pass the user namespace
+	 * through from the parent mount to the submount don't support
+	 * unprivileged mounts with submounts.
+	 */
+	if (mountpoint->d_sb->s_user_ns != &init_user_ns)
+		return ERR_PTR(-EPERM);
+
+	sc->ms_flags = MS_SUBMOUNT;
+	return vfs_kern_mount_sc(sc);
+}
+EXPORT_SYMBOL_GPL(vfs_submount_sc);
+
 /*
  * Return true if path is reachable from root
  *
@@ -3299,6 +3490,23 @@  struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
 }
 EXPORT_SYMBOL_GPL(kern_mount_data);
 
+struct vfsmount *kern_mount_data_sc(struct sb_config *sc)
+{
+	struct vfsmount *mnt;
+
+	sc->ms_flags = MS_KERNMOUNT;
+	mnt = vfs_kern_mount_sc(sc);
+	if (!IS_ERR(mnt)) {
+		/*
+		 * it is a longterm mount, don't release mnt until
+		 * we unmount before file sys is unregistered
+		*/
+		real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
+	}
+	return mnt;
+}
+EXPORT_SYMBOL_GPL(kern_mount_data_sc);
+
 void kern_unmount(struct vfsmount *mnt)
 {
 	/* release long term mount so mount point can be released */
diff --git a/fs/nfs/nfs4super.c b/fs/nfs/nfs4super.c
index 6fb7cb6b3f4b..967fa04d5c76 100644
--- a/fs/nfs/nfs4super.c
+++ b/fs/nfs/nfs4super.c
@@ -3,6 +3,7 @@ 
  */
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/mount.h>
 #include <linux/nfs4_mount.h>
 #include <linux/nfs_fs.h>
 #include "delegation.h"
diff --git a/fs/proc/root.c b/fs/proc/root.c
index deecb397daa3..3c47399bd095 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -19,6 +19,7 @@ 
 #include <linux/bitops.h>
 #include <linux/user_namespace.h>
 #include <linux/mount.h>
+#include <linux/sb_config.h>
 #include <linux/pid_namespace.h>
 #include <linux/parser.h>
 #include <linux/cred.h>
diff --git a/fs/sb_config.c b/fs/sb_config.c
new file mode 100644
index 000000000000..9c45e269b3cc
--- /dev/null
+++ b/fs/sb_config.c
@@ -0,0 +1,326 @@ 
+/* Provide a way to create a superblock configuration context within the kernel
+ * that allows a superblock to be set up prior to mounting.
+ *
+ * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#include <linux/sb_config.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/nsproxy.h>
+#include <linux/slab.h>
+#include <linux/magic.h>
+#include <linux/security.h>
+#include <linux/parser.h>
+#include <linux/mnt_namespace.h>
+#include <linux/pid_namespace.h>
+#include <linux/user_namespace.h>
+#include <net/net_namespace.h>
+#include "mount.h"
+
+static const match_table_t common_set_mount_options = {
+	{ MS_DIRSYNC,		"dirsync" },
+	{ MS_I_VERSION,		"iversion" },
+	{ MS_LAZYTIME,		"lazytime" },
+	{ MS_MANDLOCK,		"mand" },
+	{ MS_NOATIME,		"noatime" },
+	{ MS_NODEV,		"nodev" },
+	{ MS_NODIRATIME,	"nodiratime" },
+	{ MS_NOEXEC,		"noexec" },
+	{ MS_NOSUID,		"nosuid" },
+	{ MS_POSIXACL,		"posixacl" },
+	{ MS_RDONLY,		"ro" },
+	{ MS_REC,		"rec" },
+	{ MS_RELATIME,		"relatime" },
+	{ MS_STRICTATIME,	"strictatime" },
+	{ MS_SYNCHRONOUS,	"sync" },
+	{ MS_VERBOSE,		"verbose" },
+	{ },
+};
+
+static const match_table_t common_clear_mount_options = {
+	{ MS_LAZYTIME,		"nolazytime" },
+	{ MS_MANDLOCK,		"nomand" },
+	{ MS_NODEV,		"dev" },
+	{ MS_NOEXEC,		"exec" },
+	{ MS_NOSUID,		"suid" },
+	{ MS_RDONLY,		"rw" },
+	{ MS_RELATIME,		"norelatime" },
+	{ MS_SILENT,		"silent" },
+	{ MS_STRICTATIME,	"nostrictatime" },
+	{ MS_SYNCHRONOUS,	"async" },
+	{ },
+};
+
+static const match_table_t forbidden_mount_options = {
+	{ MS_BIND,		"bind" },
+	{ MS_MOVE,		"move" },
+	{ MS_PRIVATE,		"private" },
+	{ MS_REMOUNT,		"remount" },
+	{ MS_SHARED,		"shared" },
+	{ MS_SLAVE,		"slave" },
+	{ MS_UNBINDABLE,	"unbindable" },
+	{ },
+};
+
+/*
+ * Check for a common mount option.
+ */
+static int vfs_parse_ms_mount_option(struct sb_config *sc, char *data)
+{
+	substring_t args[MAX_OPT_ARGS];
+	unsigned int token;
+
+	token = match_token(data, common_set_mount_options, args);
+	if (token) {
+		sc->ms_flags |= token;
+		return 1;
+	}
+
+	token = match_token(data, common_clear_mount_options, args);
+	if (token) {
+		sc->ms_flags &= ~token;
+		return 1;
+	}
+
+	token = match_token(data, forbidden_mount_options, args);
+	if (token)
+		return sb_cfg_inval(sc, "Mount option, not superblock option");
+
+	return 0;
+}
+
+/**
+ * vfs_parse_mount_option - Add a single mount option to a superblock config
+ * @mc: The superblock configuration to modify
+ * @p: The option to apply.
+ *
+ * A single mount option in string form is applied to the superblock
+ * configuration being set up.  Certain standard options (for example "ro") are
+ * translated into flag bits without going to the filesystem.  The active
+ * security module is allowed to observe and poach options.  Any other options
+ * are passed over to the filesystem to parse.
+ *
+ * This may be called multiple times for a context.
+ *
+ * Returns 0 on success and a negative error code on failure.  In the event of
+ * failure, sc->error may have been set to a non-allocated string that gives
+ * more information.
+ */
+int vfs_parse_mount_option(struct sb_config *sc, char *p)
+{
+	int ret;
+
+	if (sc->mounted)
+		return -EBUSY;
+
+	ret = vfs_parse_ms_mount_option(sc, p);
+	if (ret < 0)
+		return ret;
+	if (ret == 1)
+		return 0;
+
+	ret = security_sb_config_parse_option(sc, p);
+	if (ret < 0)
+		return ret;
+	if (ret == 1)
+		return 0;
+
+	return sc->ops->parse_option(sc, p);
+}
+EXPORT_SYMBOL(vfs_parse_mount_option);
+
+/**
+ * generic_monolithic_mount_data - Parse key[=val][,key[=val]]* mount data
+ * @mc: The superblock configuration to fill in.
+ * @data: The data to parse
+ *
+ * Parse a blob of data that's in key[=val][,key[=val]]* form.  This can be
+ * called from the ->monolithic_mount_data() sb_config operation.
+ *
+ * Returns 0 on success or the error returned by the ->parse_option() sb_config
+ * operation on failure.
+ */
+int generic_monolithic_mount_data(struct sb_config *ctx, void *data)
+{
+	char *options = data, *p;
+	int ret;
+
+	if (!options)
+		return 0;
+
+	while ((p = strsep(&options, ",")) != NULL) {
+		if (*p) {
+			ret = vfs_parse_mount_option(ctx, p);
+			if (ret < 0)
+				return ret;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(generic_monolithic_mount_data);
+
+/**
+ * __vfs_new_sb_config - Create a superblock config.
+ * @fs_type: The filesystem type.
+ * @src_sb: A superblock from which this one derives (or NULL)
+ * @ms_flags: Superblock flags and op flags (such as MS_REMOUNT)
+ * @purpose: The purpose that this configuration shall be used for.
+ *
+ * Open a filesystem and create a mount context.  The mount context is
+ * initialised with the supplied flags and, if a submount/automount from
+ * another superblock (@src_sb), may have parameters such as namespaces copied
+ * across from that superblock.
+ */
+struct sb_config *__vfs_new_sb_config(struct file_system_type *fs_type,
+				      struct super_block *src_sb,
+				      unsigned int ms_flags,
+				      enum sb_config_purpose purpose)
+{
+	struct sb_config *sc;
+	int ret;
+
+	BUG_ON(fs_type->init_sb_config &&
+	       fs_type->sb_config_size < sizeof(*sc));
+
+	sc = kzalloc(max_t(size_t, fs_type->sb_config_size, sizeof(*sc)),
+		     GFP_KERNEL);
+	if (!sc)
+		return ERR_PTR(-ENOMEM);
+
+	sc->purpose	= purpose;
+	sc->ms_flags	= ms_flags;
+	sc->fs_type	= get_filesystem(fs_type);
+	sc->net_ns	= get_net(current->nsproxy->net_ns);
+	sc->user_ns	= get_user_ns(current_user_ns());
+	sc->cred	= get_current_cred();
+
+	/* TODO: Make all filesystems support this unconditionally */
+	if (sc->fs_type->init_sb_config) {
+		ret = sc->fs_type->init_sb_config(sc, src_sb);
+		if (ret < 0)
+			goto err_sc;
+	}
+
+	/* Do the security check last because ->fsopen may change the
+	 * namespace subscriptions.
+	 */
+	ret = security_sb_config_alloc(sc, src_sb);
+	if (ret < 0)
+		goto err_sc;
+
+	return sc;
+
+err_sc:
+	put_sb_config(sc);
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL(__vfs_new_sb_config);
+
+/**
+ * vfs_new_sb_config - Create a superblock config for a new mount.
+ * @fs_name: The name of the filesystem
+ *
+ * Open a filesystem and create a superblock config context for a new mount
+ * that will hold the mount options, device name, security details, etc..  Note
+ * that the caller should check the ->ops pointer in the returned context to
+ * determine whether the filesystem actually supports the superblock context
+ * itself.
+ */
+struct sb_config *vfs_new_sb_config(const char *fs_name)
+{
+	struct file_system_type *fs_type;
+	struct sb_config *sc;
+
+	fs_type = get_fs_type(fs_name);
+	if (!fs_type)
+		return ERR_PTR(-ENODEV);
+
+	sc = __vfs_new_sb_config(fs_type, NULL, 0, SB_CONFIG_FOR_NEW);
+	put_filesystem(fs_type);
+	return sc;
+}
+EXPORT_SYMBOL(vfs_new_sb_config);
+
+/**
+ * vfs_sb_reconfig - Create a superblock config for remount/reconfiguration
+ * @mnt: The mountpoint to open
+ * @ms_flags: Superblock flags and op flags (such as MS_REMOUNT)
+ *
+ * Open a mounted filesystem and create a mount context such that a remount can
+ * be effected.
+ */
+struct sb_config *vfs_sb_reconfig(struct vfsmount *mnt,
+				  unsigned int ms_flags)
+{
+	return __vfs_new_sb_config(mnt->mnt_sb->s_type, mnt->mnt_sb,
+				   ms_flags, SB_CONFIG_FOR_REMOUNT);
+}
+
+/**
+ * vfs_dup_sc_config: Duplicate a superblock configuration context.
+ * @src_sc: The context to copy.
+ */
+struct sb_config *vfs_dup_sb_config(struct sb_config *src_sc)
+{
+	struct sb_config *sc;
+	int ret;
+
+	if (!src_sc->ops->dup)
+		return ERR_PTR(-ENOTSUPP);
+
+	sc = kmemdup(src_sc, src_sc->fs_type->sb_config_size, GFP_KERNEL);
+	if (!sc)
+		return ERR_PTR(-ENOMEM);
+
+	sc->device	= NULL;
+	sc->security	= NULL;
+	sc->error_msg	= NULL;
+	get_filesystem(sc->fs_type);
+	get_net(sc->net_ns);
+	get_user_ns(sc->user_ns);
+	get_cred(sc->cred);
+
+	/* Can't call put until we've called ->dup */
+	ret = sc->ops->dup(sc, src_sc);
+	if (ret < 0)
+		goto err_sc;
+
+	ret = security_sb_config_dup(sc, src_sc);
+	if (ret < 0)
+		goto err_sc;
+	return sc;
+
+err_sc:
+	put_sb_config(sc);
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL(vfs_dup_sb_config);
+
+/**
+ * put_sb_config - Dispose of a superblock configuration context.
+ * @sc: The context to dispose of.
+ */
+void put_sb_config(struct sb_config *sc)
+{
+	if (sc->ops && sc->ops->free)
+		sc->ops->free(sc);
+	security_sb_config_free(sc);
+	if (sc->net_ns)
+		put_net(sc->net_ns);
+	put_user_ns(sc->user_ns);
+	if (sc->cred)
+		put_cred(sc->cred);
+	put_filesystem(sc->fs_type);
+	kfree(sc->device);
+	kfree(sc);
+}
+EXPORT_SYMBOL(put_sb_config);
diff --git a/fs/super.c b/fs/super.c
index adb0c0de428c..4d923a775bd0 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -34,6 +34,7 @@ 
 #include <linux/fsnotify.h>
 #include <linux/lockdep.h>
 #include <linux/user_namespace.h>
+#include <linux/sb_config.h>
 #include "internal.h"
 
 
@@ -805,10 +806,13 @@  struct super_block *user_get_super(dev_t dev)
  *	@flags:	numeric part of options
  *	@data:	the rest of options
  *      @force: whether or not to force the change
+ *	@sc:	the superblock config for filesystems that support it
+ *		(NULL if called from emergency or umount)
  *
  *	Alters the mount options of a mounted file system.
  */
-int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
+int do_remount_sb(struct super_block *sb, int flags, void *data, int force,
+		  struct sb_config *sc)
 {
 	int retval;
 	int remount_ro;
@@ -850,8 +854,14 @@  int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
 		}
 	}
 
-	if (sb->s_op->remount_fs) {
-		retval = sb->s_op->remount_fs(sb, &flags, data);
+	if (sb->s_op->remount_fs_sc ||
+	    sb->s_op->remount_fs) {
+		if (sb->s_op->remount_fs_sc) {
+		    retval = sb->s_op->remount_fs_sc(sb, sc);
+		    flags = sc->ms_flags;
+		} else {
+			retval = sb->s_op->remount_fs(sb, &flags, data);
+		}
 		if (retval) {
 			if (!force)
 				goto cancel_readonly;
@@ -898,7 +908,7 @@  static void do_emergency_remount(struct work_struct *work)
 			/*
 			 * What lock protects sb->s_flags??
 			 */
-			do_remount_sb(sb, MS_RDONLY, NULL, 1);
+			do_remount_sb(sb, MS_RDONLY, NULL, 1, NULL);
 		}
 		up_write(&sb->s_umount);
 		spin_lock(&sb_lock);
@@ -1048,6 +1058,40 @@  struct dentry *mount_ns(struct file_system_type *fs_type,
 
 EXPORT_SYMBOL(mount_ns);
 
+struct dentry *mount_ns_sc(struct sb_config *sc,
+			   int (*fill_super)(struct super_block *sb,
+					     struct sb_config *sc),
+			   void *ns)
+{
+	struct super_block *sb;
+
+	/* Don't allow mounting unless the caller has CAP_SYS_ADMIN
+	 * over the namespace.
+	 */
+	if (!(sc->ms_flags & MS_KERNMOUNT) &&
+	    !ns_capable(sc->user_ns, CAP_SYS_ADMIN))
+		return ERR_PTR(-EPERM);
+
+	sb = sget_userns(sc->fs_type, ns_test_super, ns_set_super,
+			 sc->ms_flags, sc->user_ns, ns);
+	if (IS_ERR(sb))
+		return ERR_CAST(sb);
+
+	if (!sb->s_root) {
+		int err;
+		err = fill_super(sb, sc);
+		if (err) {
+			deactivate_locked_super(sb);
+			return ERR_PTR(err);
+		}
+
+		sb->s_flags |= MS_ACTIVE;
+	}
+
+	return dget(sb->s_root);
+}
+EXPORT_SYMBOL(mount_ns_sc);
+
 #ifdef CONFIG_BLOCK
 static int set_bdev_super(struct super_block *s, void *data)
 {
@@ -1196,7 +1240,7 @@  struct dentry *mount_single(struct file_system_type *fs_type,
 		}
 		s->s_flags |= MS_ACTIVE;
 	} else {
-		do_remount_sb(s, flags, data, 0);
+		do_remount_sb(s, flags, data, 0, NULL);
 	}
 	return dget(s->s_root);
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index bc0c054894b9..cd6cafcdd2ff 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -54,6 +54,7 @@  struct workqueue_struct;
 struct iov_iter;
 struct fscrypt_info;
 struct fscrypt_operations;
+struct sb_config;
 
 extern void __init inode_init(void);
 extern void __init inode_init_early(void);
@@ -701,6 +702,11 @@  static inline void inode_unlock(struct inode *inode)
 	up_write(&inode->i_rwsem);
 }
 
+static inline int inode_lock_killable(struct inode *inode)
+{
+	return down_write_killable(&inode->i_rwsem);
+}
+
 static inline void inode_lock_shared(struct inode *inode)
 {
 	down_read(&inode->i_rwsem);
@@ -1787,6 +1793,7 @@  struct super_operations {
 	int (*unfreeze_fs) (struct super_block *);
 	int (*statfs) (struct dentry *, struct kstatfs *);
 	int (*remount_fs) (struct super_block *, int *, char *);
+	int (*remount_fs_sc) (struct super_block *, struct sb_config *);
 	void (*umount_begin) (struct super_block *);
 
 	int (*show_options)(struct seq_file *, struct dentry *);
@@ -2021,8 +2028,10 @@  struct file_system_type {
 #define FS_HAS_SUBTYPE		4
 #define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
+	unsigned short sb_config_size;	/* Size of superblock config context to allocate */
 	struct dentry *(*mount) (struct file_system_type *, int,
 		       const char *, void *);
+	int (*init_sb_config)(struct sb_config *, struct super_block *);
 	void (*kill_sb) (struct super_block *);
 	struct module *owner;
 	struct file_system_type * next;
@@ -2040,6 +2049,10 @@  struct file_system_type {
 
 #define MODULE_ALIAS_FS(NAME) MODULE_ALIAS("fs-" NAME)
 
+extern struct dentry *mount_ns_sc(struct sb_config *mc,
+				  int (*fill_super)(struct super_block *sb,
+						    struct sb_config *sc),
+				  void *ns);
 extern struct dentry *mount_ns(struct file_system_type *fs_type,
 	int flags, void *data, void *ns, struct user_namespace *user_ns,
 	int (*fill_super)(struct super_block *, void *, int));
@@ -2106,6 +2119,7 @@  extern int register_filesystem(struct file_system_type *);
 extern int unregister_filesystem(struct file_system_type *);
 extern struct vfsmount *kern_mount_data(struct file_system_type *, void *data);
 #define kern_mount(type) kern_mount_data(type, NULL)
+extern struct vfsmount *kern_mount_data_sc(struct sb_config *);
 extern void kern_unmount(struct vfsmount *mnt);
 extern int may_umount_tree(struct vfsmount *);
 extern int may_umount(struct vfsmount *);
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 080f34e66017..48bfd49666bc 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -75,6 +75,33 @@ 
  *	should enable secure mode.
  *	@bprm contains the linux_binprm structure.
  *
+ * Security hooks for mount using fd context.
+ *
+ * @sb_config_alloc:
+ *	Allocate and attach a security structure to sc->security.  This pointer
+ *	is initialised to NULL by the caller.
+ *	@sc indicates the new superblock configuration context.
+ *	@src_sb indicates the source superblock of a submount.
+ * @sb_config_dup:
+ *	Allocate and attach a security structure to sc->security.  This pointer
+ *	is initialised to NULL by the caller.
+ *	@sc indicates the new superblock configuration context.
+ *	@src_sc indicates the original superblock configuration context.
+ * @sb_config_free:
+ *	Clean up a superblock configuration context.
+ *	@sc indicates the superblock configuration context.
+ * @sb_config_parse_option:
+ *	Userspace provided an option to configure a superblock.  The LSM may
+ *	reject it with an error and may use it for itself, in which case it
+ *	should return 1; otherwise it should return 0 to pass it on to the
+ *	filesystem.
+ *	@sc indicates the superblock configuration context.
+ *	@p indicates the option in "key[=val]" form.
+ * @sb_config_kern_mount:
+ *	Equivalent of sb_kern_mount, but with a superblock configuration context.
+ *	@sc indicates the superblock configuration context.
+ *	@src_sb indicates the new superblock.
+ *
  * Security hooks for filesystem operations.
  *
  * @sb_alloc_security:
@@ -1372,6 +1399,12 @@  union security_list_options {
 	void (*bprm_committing_creds)(struct linux_binprm *bprm);
 	void (*bprm_committed_creds)(struct linux_binprm *bprm);
 
+	int (*sb_config_alloc)(struct sb_config *sc, struct super_block *src_sb);
+	int (*sb_config_dup)(struct sb_config *sc, struct sb_config *src_sc);
+	void (*sb_config_free)(struct sb_config *sc);
+	int (*sb_config_parse_option)(struct sb_config *sc, char *opt);
+	int (*sb_config_kern_mount)(struct sb_config *sc, struct super_block *sb);
+
 	int (*sb_alloc_security)(struct super_block *sb);
 	void (*sb_free_security)(struct super_block *sb);
 	int (*sb_copy_data)(char *orig, char *copy);
@@ -1683,6 +1716,11 @@  struct security_hook_heads {
 	struct list_head bprm_secureexec;
 	struct list_head bprm_committing_creds;
 	struct list_head bprm_committed_creds;
+	struct list_head sb_config_alloc;
+	struct list_head sb_config_dup;
+	struct list_head sb_config_free;
+	struct list_head sb_config_parse_option;
+	struct list_head sb_config_kern_mount;
 	struct list_head sb_alloc_security;
 	struct list_head sb_free_security;
 	struct list_head sb_copy_data;
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 8e0352af06b7..a5dca6abc4d5 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -20,6 +20,7 @@  struct super_block;
 struct vfsmount;
 struct dentry;
 struct mnt_namespace;
+struct sb_config;
 
 #define MNT_NOSUID	0x01
 #define MNT_NODEV	0x02
@@ -90,9 +91,12 @@  struct file_system_type;
 extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
 				      int flags, const char *name,
 				      void *data);
+extern struct vfsmount *vfs_kern_mount_sc(struct sb_config *sc);
 extern struct vfsmount *vfs_submount(const struct dentry *mountpoint,
 				     struct file_system_type *type,
 				     const char *name, void *data);
+extern struct vfsmount *vfs_submount_sc(const struct dentry *mountpoint,
+					struct sb_config *sc);
 
 extern void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list);
 extern void mark_mounts_for_expiry(struct list_head *mounts);
diff --git a/include/linux/sb_config.h b/include/linux/sb_config.h
new file mode 100644
index 000000000000..0b21e381d9f0
--- /dev/null
+++ b/include/linux/sb_config.h
@@ -0,0 +1,93 @@ 
+/* Superblock configuration and creation handling.
+ *
+ * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#ifndef _LINUX_SB_CONFIG_H
+#define _LINUX_SB_CONFIG_H
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+
+struct cred;
+struct dentry;
+struct file_operations;
+struct file_system_type;
+struct mnt_namespace;
+struct net;
+struct pid_namespace;
+struct super_block;
+struct user_namespace;
+struct vfsmount;
+
+enum sb_config_purpose {
+	SB_CONFIG_FOR_NEW,	/* New superblock for direct mount */
+	SB_CONFIG_FOR_SUBMOUNT,	/* New superblock for automatic submount */
+	SB_CONFIG_FOR_REMOUNT,	/* Superblock reconfiguration for remount */
+};
+
+/*
+ * Superblock configuration context as allocated and constructed by the
+ * ->init_sb_config() file_system_type operation.  The size of the object
+ * allocated is specified in struct file_system_type::sb_config_size and this
+ * must include sufficient space for the sb_config struct.
+ *
+ * See Documentation/filesystems/mounting.txt
+ */
+struct sb_config {
+	const struct sb_config_operations *ops;
+	struct file_system_type	*fs_type;
+	struct user_namespace	*user_ns;	/* The user namespace for this mount */
+	struct net		*net_ns;	/* The network namespace for this mount */
+	const struct cred	*cred;		/* The mounter's credentials */
+	char			*device;	/* The device name or mount target */
+	void			*security;	/* The LSM context */
+	const char		*error_msg;	/* Error string to be read by read() */
+	unsigned int		ms_flags;	/* The superblock flags (MS_*) */
+	bool			mounted;	/* Set when mounted */
+	bool			sloppy;		/* Unrecognised options are okay */
+	bool			silent;
+	enum sb_config_purpose 	purpose : 8;
+};
+
+struct sb_config_operations {
+	void (*free)(struct sb_config *sc);
+	int (*dup)(struct sb_config *sc, struct sb_config *src);
+	int (*parse_option)(struct sb_config *sc, char *p);
+	int (*monolithic_mount_data)(struct sb_config *sc, void *data);
+	int (*validate)(struct sb_config *sc);
+	struct dentry *(*mount)(struct sb_config *sc);
+};
+
+extern const struct file_operations fs_fs_fops;
+
+extern struct sb_config *vfs_new_sb_config(const char *fs_name);
+extern struct sb_config *__vfs_new_sb_config(struct file_system_type *fs_type,
+					     struct super_block *src_sb,
+					     unsigned int ms_flags,
+					     enum sb_config_purpose purpose);
+extern struct sb_config *vfs_sb_reconfig(struct vfsmount *mnt,
+					 unsigned int ms_flags);
+extern struct sb_config *vfs_dup_sb_config(struct sb_config *src);
+extern int vfs_parse_mount_option(struct sb_config *sc, char *data);
+extern int generic_monolithic_mount_data(struct sb_config *sc, void *data);
+extern void put_sb_config(struct sb_config *sc);
+
+static inline void sb_cfg_error(struct sb_config *sc, const char *msg)
+{
+	sc->error_msg = msg;
+}
+
+static inline int sb_cfg_inval(struct sb_config *sc, const char *msg)
+{
+	sb_cfg_error(sc, msg);
+	return -EINVAL;
+}
+
+#endif /* _LINUX_SB_CONFIG_H */
diff --git a/include/linux/security.h b/include/linux/security.h
index af675b576645..36b3a6779986 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -55,6 +55,7 @@  struct msg_queue;
 struct xattr;
 struct xfrm_sec_ctx;
 struct mm_struct;
+struct sb_config;
 
 /* If capable should audit the security request */
 #define SECURITY_CAP_NOAUDIT 0
@@ -224,6 +225,11 @@  int security_bprm_check(struct linux_binprm *bprm);
 void security_bprm_committing_creds(struct linux_binprm *bprm);
 void security_bprm_committed_creds(struct linux_binprm *bprm);
 int security_bprm_secureexec(struct linux_binprm *bprm);
+int security_sb_config_alloc(struct sb_config *sc, struct super_block *sb);
+int security_sb_config_dup(struct sb_config *sc, struct sb_config *src_sc);
+void security_sb_config_free(struct sb_config *sc);
+int security_sb_config_parse_option(struct sb_config *sc, char *opt);
+int security_sb_config_kern_mount(struct sb_config *sc, struct super_block *sb);
 int security_sb_alloc(struct super_block *sb);
 void security_sb_free(struct super_block *sb);
 int security_sb_copy_data(char *orig, char *copy);
@@ -520,6 +526,29 @@  static inline int security_bprm_secureexec(struct linux_binprm *bprm)
 	return cap_bprm_secureexec(bprm);
 }
 
+static inline int security_sb_config_alloc(struct sb_config *sc,
+					   struct super_block *src_sb)
+{
+	return 0;
+}
+static inline int security_sb_config_dup(struct sb_config *sc,
+					 struct sb_config *src_sc)
+{
+	return 0;
+}
+static inline void security_sb_config_free(struct sb_config *sc)
+{
+}
+static inline int security_sb_config_parse_option(struct sb_config *sc, char *opt)
+{
+	return 0;
+}
+static inline int security_sb_config_kern_mount(struct sb_config *sc,
+						struct super_block *sb)
+{
+	return 0;
+}
+
 static inline int security_sb_alloc(struct super_block *sb)
 {
 	return 0;
diff --git a/security/security.c b/security/security.c
index b9fea3999cf8..3735fad91543 100644
--- a/security/security.c
+++ b/security/security.c
@@ -316,6 +316,31 @@  int security_bprm_secureexec(struct linux_binprm *bprm)
 	return call_int_hook(bprm_secureexec, 0, bprm);
 }
 
+int security_sb_config_alloc(struct sb_config *sc, struct super_block *src_sb)
+{
+	return call_int_hook(sb_config_alloc, 0, sc, src_sb);
+}
+
+int security_sb_config_dup(struct sb_config *sc, struct sb_config *src_sc)
+{
+	return call_int_hook(sb_config_dup, 0, sc, src_sc);
+}
+
+void security_sb_config_free(struct sb_config *sc)
+{
+	call_void_hook(sb_config_free, sc);
+}
+
+int security_sb_config_parse_option(struct sb_config *sc, char *opt)
+{
+	return call_int_hook(sb_config_parse_option, 0, sc, opt);
+}
+
+int security_sb_config_kern_mount(struct sb_config *sc, struct super_block *sb)
+{
+	return call_int_hook(sb_config_kern_mount, 0, sc, sb);
+}
+
 int security_sb_alloc(struct super_block *sb)
 {
 	return call_int_hook(sb_alloc_security, 0, sb);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e67a526d1f30..286207bced52 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -47,6 +47,7 @@ 
 #include <linux/fdtable.h>
 #include <linux/namei.h>
 #include <linux/mount.h>
+#include <linux/sb_config.h>
 #include <linux/netfilter_ipv4.h>
 #include <linux/netfilter_ipv6.h>
 #include <linux/tty.h>
@@ -2826,6 +2827,169 @@  static int selinux_umount(struct vfsmount *mnt, int flags)
 				   FILESYSTEM__UNMOUNT, NULL);
 }
 
+/* fsopen mount context operations */
+
+static int selinux_sb_config_alloc(struct sb_config *sc,
+				   struct super_block *src_sb)
+{
+	struct security_mnt_opts *opts;
+
+	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
+	if (!opts)
+		return -ENOMEM;
+
+	sc->security = opts;
+	return 0;
+}
+
+static int selinux_sb_config_dup(struct sb_config *sc,
+				 struct sb_config *src_sc)
+{
+	const struct security_mnt_opts *src = src_sc->security;
+	struct security_mnt_opts *opts;
+	int i, n;
+
+	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
+	if (!opts)
+		return -ENOMEM;
+	sc->security = opts;
+
+	if (!src || !src->num_mnt_opts)
+		return 0;
+	n = opts->num_mnt_opts = src->num_mnt_opts;
+
+	if (src->mnt_opts) {
+		opts->mnt_opts = kcalloc(n, sizeof(char *), GFP_KERNEL);
+		if (!opts->mnt_opts)
+			return -ENOMEM;
+
+		for (i = 0; i < n; i++) {
+			if (src->mnt_opts[i]) {
+				opts->mnt_opts[i] = kstrdup(src->mnt_opts[i],
+							    GFP_KERNEL);
+				if (!opts->mnt_opts[i])
+					return -ENOMEM;
+			}
+		}
+	}
+
+	if (src->mnt_opts_flags) {
+		opts->mnt_opts_flags = kmemdup(src->mnt_opts_flags,
+					       n * sizeof(int), GFP_KERNEL);
+		if (!opts->mnt_opts_flags)
+			return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static void selinux_sb_config_free(struct sb_config *sc)
+{
+	struct security_mnt_opts *opts = sc->security;
+
+	security_free_mnt_opts(opts);
+	sc->security = NULL;
+}
+
+static int selinux_sb_config_parse_option(struct sb_config *sc, char *opt)
+{
+	struct security_mnt_opts *opts = sc->security;
+	substring_t args[MAX_OPT_ARGS];
+	unsigned int have;
+	char *c, **oo;
+	int token, ctx, i, *of;
+
+	token = match_token(opt, tokens, args);
+	if (token == Opt_error)
+		return 0; /* Doesn't belong to us. */
+
+	have = 0;
+	for (i = 0; i < opts->num_mnt_opts; i++)
+		have |= 1 << opts->mnt_opts_flags[i];
+	if (have & (1 << token))
+		return sb_cfg_inval(sc, "SELinux: Duplicate mount options");
+
+	switch (token) {
+	case Opt_context:
+		if (have & (1 << Opt_defcontext))
+			goto incompatible;
+		ctx = CONTEXT_MNT;
+		goto copy_context_string;
+
+	case Opt_fscontext:
+		ctx = FSCONTEXT_MNT;
+		goto copy_context_string;
+
+	case Opt_rootcontext:
+		ctx = ROOTCONTEXT_MNT;
+		goto copy_context_string;
+
+	case Opt_defcontext:
+		if (have & (1 << Opt_context))
+			goto incompatible;
+		ctx = DEFCONTEXT_MNT;
+		goto copy_context_string;
+
+	case Opt_labelsupport:
+		return 1;
+
+	default:
+		return sb_cfg_inval(sc, "SELinux: Unknown mount option");
+	}
+
+copy_context_string:
+	if (opts->num_mnt_opts > 3)
+		return sb_cfg_inval(sc, "SELinux: Too many options");
+	
+	of = krealloc(opts->mnt_opts_flags,
+		      (opts->num_mnt_opts + 1) * sizeof(int), GFP_KERNEL);
+	if (!of)
+		return -ENOMEM;
+	of[opts->num_mnt_opts] = 0;
+	opts->mnt_opts_flags = of;
+
+	oo = krealloc(opts->mnt_opts,
+		      (opts->num_mnt_opts + 1) * sizeof(char *), GFP_KERNEL);
+	if (!oo)
+		return -ENOMEM;
+	oo[opts->num_mnt_opts] = NULL;
+	opts->mnt_opts = oo;
+
+	c = match_strdup(&args[0]);
+	if (!c)
+		return -ENOMEM;
+	opts->mnt_opts[opts->num_mnt_opts] = c;
+	opts->mnt_opts_flags[opts->num_mnt_opts] = ctx;
+	opts->num_mnt_opts++;
+	return 1;
+
+incompatible:
+	return sb_cfg_inval(sc, "SELinux: Incompatible mount options");
+}
+
+static int selinux_sb_config_kern_mount(struct sb_config *sc,
+					struct super_block *sb)
+{
+	const struct cred *cred = current_cred();
+	struct common_audit_data ad;
+	int rc;
+
+	rc = selinux_set_mnt_opts(sb, sc->security, 0, NULL);
+	if (rc)
+		return rc;
+
+	/* Allow all mounts performed by the kernel */
+	if (sc->ms_flags & MS_KERNMOUNT)
+		return 0;
+
+	ad.type = LSM_AUDIT_DATA_DENTRY;
+	ad.u.dentry = sb->s_root;
+	rc = superblock_has_perm(cred, sb, FILESYSTEM__MOUNT, &ad);
+	if (rc < 0)
+		sb_cfg_error(sc, "SELinux: Mount of superblock not permitted");
+	return rc;
+}
+
 /* inode security operations */
 
 static int selinux_inode_alloc_security(struct inode *inode)
@@ -6154,6 +6318,12 @@  static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(bprm_committed_creds, selinux_bprm_committed_creds),
 	LSM_HOOK_INIT(bprm_secureexec, selinux_bprm_secureexec),
 
+	LSM_HOOK_INIT(sb_config_alloc, selinux_sb_config_alloc),
+	LSM_HOOK_INIT(sb_config_dup, selinux_sb_config_dup),
+	LSM_HOOK_INIT(sb_config_free, selinux_sb_config_free),
+	LSM_HOOK_INIT(sb_config_parse_option, selinux_sb_config_parse_option),
+	LSM_HOOK_INIT(sb_config_kern_mount, selinux_sb_config_kern_mount),
+
 	LSM_HOOK_INIT(sb_alloc_security, selinux_sb_alloc_security),
 	LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
 	LSM_HOOK_INIT(sb_copy_data, selinux_sb_copy_data),