[v5] vfs, security: Fix automount superblock LSM init problem, preventing NFS sb sharing

Commit Message

David Howells Nov. 10, 2022, 11:09 a.m. UTC

When NFS superblocks are created by automounting, their LSM parameters
aren't set in the fs_context struct prior to sget_fc() being called,
leading to failure to match existing superblocks.

Fix this by adding a new LSM hook to load fc->security for submount
creation when alloc_fs_context() is creating the fs_context for it.

However, this uncovers a further bug: nfs_get_root() initialises the
superblock security manually by calling security_sb_set_mnt_opts() or
security_sb_clone_mnt_opts() - but then vfs_get_tree() calls
security_sb_set_mnt_opts(), which can lead to SELinux, at least,
complaining.

Fix that by adding a flag to the fs_context that suppresses the
security_sb_set_mnt_opts() call in vfs_get_tree().  This can be set by NFS
when it sets the LSM context on the new superblock.

The first bug leads to messages like the following appearing in dmesg:

	NFS: Cache volume key already in use (nfs,4.2,2,108,106a8c0,1,,,,100000,100000,2ee,3a98,1d4c,3a98,1)

Changes
=======
ver #5)
 - Removed unused variable.
 - Only allocate smack_mnt_opts if we're dealing with a submount.

ver #4)
 - When doing a FOR_SUBMOUNT mount, don't set the root label in SELinux or
   Smack.

ver #3)
 - Made LSM parameter extraction dependent on fc->purpose ==
   FS_CONTEXT_FOR_SUBMOUNT.  Shouldn't happen on FOR_RECONFIGURE.

ver #2)
 - Added Smack support
 - Made LSM parameter extraction dependent on reference != NULL.

Signed-off-by: David Howells <[e-mail]>
Fixes: 9bc61ab18b1d ("vfs: Introduce fs_context, switch vfs_kern_mount() to it.")
Fixes: 779df6a5480f ("NFS: Ensure security label is set for root inode)
Tested-by: Jeff Layton <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Acked-by: Casey Schaufler <[e-mail]>
Acked-by: Christian Brauner (Microsoft) <[e-mail]>
cc: Trond Myklebust <[e-mail]>
cc: Anna Schumaker <[e-mail]>
cc: Alexander Viro <[e-mail]>
cc: Scott Mayhew <[e-mail]>
cc: Jeff Layton <[e-mail]>
cc: Paul Moore <[e-mail]>
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]/ # v1
Link: https://lore.kernel.org/r/[e-mail]/ # v2
Link: https://lore.kernel.org/r/[e-mail]/ # v3
Link: https://lore.kernel.org/r/[e-mail]/ # v4
Link: https://lore.kernel.org/r/[e-mail]/ # v5
---

 fs/fs_context.c               |    4 +++
 fs/nfs/getroot.c              |    1 +
 fs/super.c                    |   10 +++++---
 include/linux/fs_context.h    |    1 +
 include/linux/lsm_hook_defs.h |    1 +
 include/linux/lsm_hooks.h     |    6 ++++-
 include/linux/security.h      |    6 +++++
 security/security.c           |    5 ++++
 security/selinux/hooks.c      |   25 +++++++++++++++++++
 security/smack/smack_lsm.c    |   54 +++++++++++++++++++++++++++++++++++++++++
 10 files changed, 108 insertions(+), 5 deletions(-)

Comments

Paul Moore Nov. 11, 2022, 5:40 p.m. UTC | #1

On Thu, Nov 10, 2022 at 6:09 AM David Howells <[e-mail]> wrote:
>
> When NFS superblocks are created by automounting, their LSM parameters
> aren't set in the fs_context struct prior to sget_fc() being called,
> leading to failure to match existing superblocks.
>
> Fix this by adding a new LSM hook to load fc->security for submount
> creation when alloc_fs_context() is creating the fs_context for it.
>
> However, this uncovers a further bug: nfs_get_root() initialises the
> superblock security manually by calling security_sb_set_mnt_opts() or
> security_sb_clone_mnt_opts() - but then vfs_get_tree() calls
> security_sb_set_mnt_opts(), which can lead to SELinux, at least,
> complaining.
>
> Fix that by adding a flag to the fs_context that suppresses the
> security_sb_set_mnt_opts() call in vfs_get_tree().  This can be set by NFS
> when it sets the LSM context on the new superblock.
>
> The first bug leads to messages like the following appearing in dmesg:
>
>         NFS: Cache volume key already in use (nfs,4.2,2,108,106a8c0,1,,,,100000,100000,2ee,3a98,1d4c,3a98,1)
>
> Changes
> =======
> ver #5)
>  - Removed unused variable.
>  - Only allocate smack_mnt_opts if we're dealing with a submount.
>
> ver #4)
>  - When doing a FOR_SUBMOUNT mount, don't set the root label in SELinux or
>    Smack.
>
> ver #3)
>  - Made LSM parameter extraction dependent on fc->purpose ==
>    FS_CONTEXT_FOR_SUBMOUNT.  Shouldn't happen on FOR_RECONFIGURE.
>
> ver #2)
>  - Added Smack support
>  - Made LSM parameter extraction dependent on reference != NULL.
>
> Signed-off-by: David Howells <[e-mail]>
> Fixes: 9bc61ab18b1d ("vfs: Introduce fs_context, switch vfs_kern_mount() to it.")
> Fixes: 779df6a5480f ("NFS: Ensure security label is set for root inode)
> Tested-by: Jeff Layton <[e-mail]>
> Reviewed-by: Jeff Layton <[e-mail]>
> Acked-by: Casey Schaufler <[e-mail]>
> Acked-by: Christian Brauner (Microsoft) <[e-mail]>
> cc: Trond Myklebust <[e-mail]>
> cc: Anna Schumaker <[e-mail]>
> cc: Alexander Viro <[e-mail]>
> cc: Scott Mayhew <[e-mail]>
> cc: Jeff Layton <[e-mail]>
> cc: Paul Moore <[e-mail]>
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]
> Link: https://lore.kernel.org/r/[e-mail]/ # v1
> Link: https://lore.kernel.org/r/[e-mail]/ # v2
> Link: https://lore.kernel.org/r/[e-mail]/ # v3
> Link: https://lore.kernel.org/r/[e-mail]/ # v4
> Link: https://lore.kernel.org/r/[e-mail]/ # v5
> ---
>
>  fs/fs_context.c               |    4 +++
>  fs/nfs/getroot.c              |    1 +
>  fs/super.c                    |   10 +++++---
>  include/linux/fs_context.h    |    1 +
>  include/linux/lsm_hook_defs.h |    1 +
>  include/linux/lsm_hooks.h     |    6 ++++-
>  include/linux/security.h      |    6 +++++
>  security/security.c           |    5 ++++
>  security/selinux/hooks.c      |   25 +++++++++++++++++++
>  security/smack/smack_lsm.c    |   54 +++++++++++++++++++++++++++++++++++++++++
>  10 files changed, 108 insertions(+), 5 deletions(-)
>
> diff --git a/fs/fs_context.c b/fs/fs_context.c
> index 24ce12f0db32..22248b8a88a8 100644
> --- a/fs/fs_context.c
> +++ b/fs/fs_context.c
> @@ -282,6 +282,10 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
>                 break;
>         }
>
> +       ret = security_fs_context_init(fc, reference);
> +       if (ret < 0)
> +               goto err_fc;
> +
>         /* TODO: Make all filesystems support this unconditionally */
>         init_fs_context = fc->fs_type->init_fs_context;
>         if (!init_fs_context)
> diff --git a/fs/nfs/getroot.c b/fs/nfs/getroot.c
> index 11ff2b2e060f..651bffb0067e 100644
> --- a/fs/nfs/getroot.c
> +++ b/fs/nfs/getroot.c
> @@ -144,6 +144,7 @@ int nfs_get_root(struct super_block *s, struct fs_context *fc)
>         }
>         if (error)
>                 goto error_splat_root;
> +       fc->lsm_set = true;
>         if (server->caps & NFS_CAP_SECURITY_LABEL &&
>                 !(kflags_out & SECURITY_LSM_NATIVE_LABELS))
>                 server->caps &= ~NFS_CAP_SECURITY_LABEL;
> diff --git a/fs/super.c b/fs/super.c
> index 8d39e4f11cfa..f200ae0549ca 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1553,10 +1553,12 @@ int vfs_get_tree(struct fs_context *fc)
>         smp_wmb();
>         sb->s_flags |= SB_BORN;
>
> -       error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
> -       if (unlikely(error)) {
> -               fc_drop_locked(fc);
> -               return error;
> +       if (!(fc->lsm_set)) {
> +               error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
> +               if (unlikely(error)) {
> +                       fc_drop_locked(fc);
> +                       return error;
> +               }
>         }

Thinking about all the different things that an LSM could do, would it
ever be possible that a LSM would want the security_sb_set_mnt_opts()
call to happen here?  I'm wondering if we are better off leaving it up
to the LSM by passing the fs_context in the security_sb_set_mnt_opts()
hook; those that want to effectively skip this call due to a submount
setup already done in security_fs_context_init() can check the
fs_context::purpose value in the security_sb_set_mnt_opts() hook.

Thoughts?

Paul Moore Nov. 11, 2022, 5:43 p.m. UTC | #2

On Fri, Nov 11, 2022 at 12:40 PM Paul Moore <[e-mail]> wrote:
> On Thu, Nov 10, 2022 at 6:09 AM David Howells <[e-mail]> wrote:
> >
> > When NFS superblocks are created by automounting, their LSM parameters
> > aren't set in the fs_context struct prior to sget_fc() being called,
> > leading to failure to match existing superblocks.
> >
> > Fix this by adding a new LSM hook to load fc->security for submount
> > creation when alloc_fs_context() is creating the fs_context for it.
> >
> > However, this uncovers a further bug: nfs_get_root() initialises the
> > superblock security manually by calling security_sb_set_mnt_opts() or
> > security_sb_clone_mnt_opts() - but then vfs_get_tree() calls
> > security_sb_set_mnt_opts(), which can lead to SELinux, at least,
> > complaining.
> >
> > Fix that by adding a flag to the fs_context that suppresses the
> > security_sb_set_mnt_opts() call in vfs_get_tree().  This can be set by NFS
> > when it sets the LSM context on the new superblock.
> >
> > The first bug leads to messages like the following appearing in dmesg:
> >
> >         NFS: Cache volume key already in use (nfs,4.2,2,108,106a8c0,1,,,,100000,100000,2ee,3a98,1d4c,3a98,1)
> >
> > Changes
> > =======
> > ver #5)
> >  - Removed unused variable.
> >  - Only allocate smack_mnt_opts if we're dealing with a submount.
> >
> > ver #4)
> >  - When doing a FOR_SUBMOUNT mount, don't set the root label in SELinux or
> >    Smack.
> >
> > ver #3)
> >  - Made LSM parameter extraction dependent on fc->purpose ==
> >    FS_CONTEXT_FOR_SUBMOUNT.  Shouldn't happen on FOR_RECONFIGURE.
> >
> > ver #2)
> >  - Added Smack support
> >  - Made LSM parameter extraction dependent on reference != NULL.
> >
> > Signed-off-by: David Howells <[e-mail]>
> > Fixes: 9bc61ab18b1d ("vfs: Introduce fs_context, switch vfs_kern_mount() to it.")
> > Fixes: 779df6a5480f ("NFS: Ensure security label is set for root inode)
> > Tested-by: Jeff Layton <[e-mail]>
> > Reviewed-by: Jeff Layton <[e-mail]>
> > Acked-by: Casey Schaufler <[e-mail]>
> > Acked-by: Christian Brauner (Microsoft) <[e-mail]>
> > cc: Trond Myklebust <[e-mail]>
> > cc: Anna Schumaker <[e-mail]>
> > cc: Alexander Viro <[e-mail]>
> > cc: Scott Mayhew <[e-mail]>
> > cc: Jeff Layton <[e-mail]>
> > cc: Paul Moore <[e-mail]>
> > cc: [e-mail]
> > cc: [e-mail]
> > cc: [e-mail]
> > cc: [e-mail]
> > Link: https://lore.kernel.org/r/[e-mail]/ # v1
> > Link: https://lore.kernel.org/r/[e-mail]/ # v2
> > Link: https://lore.kernel.org/r/[e-mail]/ # v3
> > Link: https://lore.kernel.org/r/[e-mail]/ # v4
> > Link: https://lore.kernel.org/r/[e-mail]/ # v5
> > ---
> >
> >  fs/fs_context.c               |    4 +++
> >  fs/nfs/getroot.c              |    1 +
> >  fs/super.c                    |   10 +++++---
> >  include/linux/fs_context.h    |    1 +
> >  include/linux/lsm_hook_defs.h |    1 +
> >  include/linux/lsm_hooks.h     |    6 ++++-
> >  include/linux/security.h      |    6 +++++
> >  security/security.c           |    5 ++++
> >  security/selinux/hooks.c      |   25 +++++++++++++++++++
> >  security/smack/smack_lsm.c    |   54 +++++++++++++++++++++++++++++++++++++++++
> >  10 files changed, 108 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/fs_context.c b/fs/fs_context.c
> > index 24ce12f0db32..22248b8a88a8 100644
> > --- a/fs/fs_context.c
> > +++ b/fs/fs_context.c
> > @@ -282,6 +282,10 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
> >                 break;
> >         }
> >
> > +       ret = security_fs_context_init(fc, reference);
> > +       if (ret < 0)
> > +               goto err_fc;
> > +
> >         /* TODO: Make all filesystems support this unconditionally */
> >         init_fs_context = fc->fs_type->init_fs_context;
> >         if (!init_fs_context)
> > diff --git a/fs/nfs/getroot.c b/fs/nfs/getroot.c
> > index 11ff2b2e060f..651bffb0067e 100644
> > --- a/fs/nfs/getroot.c
> > +++ b/fs/nfs/getroot.c
> > @@ -144,6 +144,7 @@ int nfs_get_root(struct super_block *s, struct fs_context *fc)
> >         }
> >         if (error)
> >                 goto error_splat_root;
> > +       fc->lsm_set = true;
> >         if (server->caps & NFS_CAP_SECURITY_LABEL &&
> >                 !(kflags_out & SECURITY_LSM_NATIVE_LABELS))
> >                 server->caps &= ~NFS_CAP_SECURITY_LABEL;
> > diff --git a/fs/super.c b/fs/super.c
> > index 8d39e4f11cfa..f200ae0549ca 100644
> > --- a/fs/super.c
> > +++ b/fs/super.c
> > @@ -1553,10 +1553,12 @@ int vfs_get_tree(struct fs_context *fc)
> >         smp_wmb();
> >         sb->s_flags |= SB_BORN;
> >
> > -       error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
> > -       if (unlikely(error)) {
> > -               fc_drop_locked(fc);
> > -               return error;
> > +       if (!(fc->lsm_set)) {
> > +               error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
> > +               if (unlikely(error)) {
> > +                       fc_drop_locked(fc);
> > +                       return error;
> > +               }
> >         }
>
> Thinking about all the different things that an LSM could do, would it
> ever be possible that a LSM would want the security_sb_set_mnt_opts()
> call to happen here?  I'm wondering if we are better off leaving it up
> to the LSM by passing the fs_context in the security_sb_set_mnt_opts()
> hook; those that want to effectively skip this call due to a submount
> setup already done in security_fs_context_init() can check the
> fs_context::purpose value in the security_sb_set_mnt_opts() hook.

Actually, we could probably also create a LSM specific flag in
fs_context::security to indicate that the setup has already been done.
That's probably a little safer than relying on fs_context::purpose in
the security_sb_set_mnt_opts() hook.

> Thoughts?

Al Viro Nov. 19, 2022, 8:48 a.m. UTC | #3

On Thu, Nov 10, 2022 at 11:09:27AM +0000, David Howells wrote:
> When NFS superblocks are created by automounting, their LSM parameters
> aren't set in the fs_context struct prior to sget_fc() being called,
> leading to failure to match existing superblocks.
> 
> Fix this by adding a new LSM hook to load fc->security for submount
> creation when alloc_fs_context() is creating the fs_context for it.

FWIW, it feels like security_sb_mnt_opts_compat() would be a saner place
for that.  It would need to get struct dentry *reference passed to it,
but that should be it...

Patch

diff --git a/fs/fs_context.c b/fs/fs_context.c
index 24ce12f0db32..22248b8a88a8 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -282,6 +282,10 @@  static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
 		break;
 	}
 
+	ret = security_fs_context_init(fc, reference);
+	if (ret < 0)
+		goto err_fc;
+
 	/* TODO: Make all filesystems support this unconditionally */
 	init_fs_context = fc->fs_type->init_fs_context;
 	if (!init_fs_context)
diff --git a/fs/nfs/getroot.c b/fs/nfs/getroot.c
index 11ff2b2e060f..651bffb0067e 100644
--- a/fs/nfs/getroot.c
+++ b/fs/nfs/getroot.c
@@ -144,6 +144,7 @@  int nfs_get_root(struct super_block *s, struct fs_context *fc)
 	}
 	if (error)
 		goto error_splat_root;
+	fc->lsm_set = true;
 	if (server->caps & NFS_CAP_SECURITY_LABEL &&
 		!(kflags_out & SECURITY_LSM_NATIVE_LABELS))
 		server->caps &= ~NFS_CAP_SECURITY_LABEL;
diff --git a/fs/super.c b/fs/super.c
index 8d39e4f11cfa..f200ae0549ca 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1553,10 +1553,12 @@  int vfs_get_tree(struct fs_context *fc)
 	smp_wmb();
 	sb->s_flags |= SB_BORN;
 
-	error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
-	if (unlikely(error)) {
-		fc_drop_locked(fc);
-		return error;
+	if (!(fc->lsm_set)) {
+		error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
+		if (unlikely(error)) {
+			fc_drop_locked(fc);
+			return error;
+		}
 	}
 
 	/*
diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index 13fa6f3df8e4..3876dd96bb20 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -110,6 +110,7 @@  struct fs_context {
 	bool			need_free:1;	/* Need to call ops->free() */
 	bool			global:1;	/* Goes into &init_user_ns */
 	bool			oldapi:1;	/* Coming from mount(2) */
+	bool			lsm_set:1;	/* security_sb_set/clone_mnt_opts() already done */
 };
 
 struct fs_context_operations {
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index ec119da1d89b..256b6b0c0e6e 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -54,6 +54,7 @@  LSM_HOOK(int, 0, bprm_creds_from_file, struct linux_binprm *bprm, struct file *f
 LSM_HOOK(int, 0, bprm_check_security, struct linux_binprm *bprm)
 LSM_HOOK(void, LSM_RET_VOID, bprm_committing_creds, struct linux_binprm *bprm)
 LSM_HOOK(void, LSM_RET_VOID, bprm_committed_creds, struct linux_binprm *bprm)
+LSM_HOOK(int, 0, fs_context_init, struct fs_context *fc, struct dentry *reference)
 LSM_HOOK(int, 0, fs_context_dup, struct fs_context *fc,
 	 struct fs_context *src_sc)
 LSM_HOOK(int, -ENOPARAM, fs_context_parse_param, struct fs_context *fc,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 4ec80b96c22e..a4885eb620e7 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -87,8 +87,12 @@ 
  * Security hooks for mount using fs_context.
  *	[See also Documentation/filesystems/mount_api.rst]
  *
+ * @fs_context_init:
+ *	Initialise fc->security.  This is initialised to NULL by the caller.
+ *	@fc indicates the new filesystem context.
+ *	@dentry indicates a reference for submount/remount
  * @fs_context_dup:
- *	Allocate and attach a security structure to sc->security.  This pointer
+ *	Allocate and attach a security structure to fc->security.  This pointer
  *	is initialised to NULL by the caller.
  *	@fc indicates the new filesystem context.
  *	@src_fc indicates the original filesystem context.
diff --git a/include/linux/security.h b/include/linux/security.h
index ca1b7109c0db..6c626ae3bb33 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -293,6 +293,7 @@  int security_bprm_creds_from_file(struct linux_binprm *bprm, struct file *file);
 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_fs_context_init(struct fs_context *fc, struct dentry *reference);
 int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc);
 int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *param);
 int security_sb_alloc(struct super_block *sb);
@@ -625,6 +626,11 @@  static inline void security_bprm_committed_creds(struct linux_binprm *bprm)
 {
 }
 
+static inline int security_fs_context_init(struct fs_context *fc,
+					   struct dentry *reference)
+{
+	return 0;
+}
 static inline int security_fs_context_dup(struct fs_context *fc,
 					  struct fs_context *src_fc)
 {
diff --git a/security/security.c b/security/security.c
index 79d82cb6e469..0732d873740a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -882,6 +882,11 @@  void security_bprm_committed_creds(struct linux_binprm *bprm)
 	call_void_hook(bprm_committed_creds, bprm);
 }
 
+int security_fs_context_init(struct fs_context *fc, struct dentry *reference)
+{
+	return call_int_hook(fs_context_init, 0, fc, reference);
+}
+
 int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
 {
 	return call_int_hook(fs_context_dup, 0, fc, src_fc);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index f553c370397e..426acfc87a0a 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2766,6 +2766,30 @@  static int selinux_umount(struct vfsmount *mnt, int flags)
 				   FILESYSTEM__UNMOUNT, NULL);
 }
 
+static int selinux_fs_context_init(struct fs_context *fc,
+				   struct dentry *reference)
+{
+	const struct superblock_security_struct *sbsec;
+	struct selinux_mnt_opts *opts;
+
+	if (fc->purpose == FS_CONTEXT_FOR_SUBMOUNT) {
+		opts = kzalloc(sizeof(*opts), GFP_KERNEL);
+		if (!opts)
+			return -ENOMEM;
+
+		sbsec = selinux_superblock(reference->d_sb);
+		if (sbsec->flags & FSCONTEXT_MNT)
+			opts->fscontext_sid	= sbsec->sid;
+		if (sbsec->flags & CONTEXT_MNT)
+			opts->context_sid	= sbsec->mntpoint_sid;
+		if (sbsec->flags & DEFCONTEXT_MNT)
+			opts->defcontext_sid	= sbsec->def_sid;
+		fc->security = opts;
+	}
+
+	return 0;
+}
+
 static int selinux_fs_context_dup(struct fs_context *fc,
 				  struct fs_context *src_fc)
 {
@@ -7263,6 +7287,7 @@  static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	/*
 	 * PUT "CLONING" (ACCESSING + ALLOCATING) HOOKS HERE
 	 */
+	LSM_HOOK_INIT(fs_context_init, selinux_fs_context_init),
 	LSM_HOOK_INIT(fs_context_dup, selinux_fs_context_dup),
 	LSM_HOOK_INIT(fs_context_parse_param, selinux_fs_context_parse_param),
 	LSM_HOOK_INIT(sb_eat_lsm_opts, selinux_sb_eat_lsm_opts),
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index b6306d71c908..bef2e10320d4 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -611,6 +611,59 @@  static int smack_add_opt(int token, const char *s, void **mnt_opts)
 	return -EINVAL;
 }
 
+/**
+ * smack_fs_context_init - Initialise security data for a filesystem context
+ * @fc: The filesystem context.
+ * @reference: Reference dentry (automount/reconfigure) or NULL
+ *
+ * Returns 0 on success or -ENOMEM on error.
+ */
+static int smack_fs_context_init(struct fs_context *fc,
+				 struct dentry *reference)
+{
+	struct superblock_smack *sbsp;
+	struct smack_mnt_opts *ctx;
+	struct inode_smack *isp;
+
+	if (fc->purpose == FS_CONTEXT_FOR_SUBMOUNT) {
+		ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+		if (!ctx)
+			return -ENOMEM;
+		fc->security = ctx;
+
+		sbsp = smack_superblock(reference->d_sb);
+		isp = smack_inode(reference->d_sb->s_root->d_inode);
+
+		if (sbsp->smk_default) {
+			ctx->fsdefault = kstrdup(sbsp->smk_default->smk_known, GFP_KERNEL);
+			if (!ctx->fsdefault)
+				return -ENOMEM;
+		}
+
+		if (sbsp->smk_floor) {
+			ctx->fsfloor = kstrdup(sbsp->smk_floor->smk_known, GFP_KERNEL);
+			if (!ctx->fsfloor)
+				return -ENOMEM;
+		}
+
+		if (sbsp->smk_hat) {
+			ctx->fshat = kstrdup(sbsp->smk_hat->smk_known, GFP_KERNEL);
+			if (!ctx->fshat)
+				return -ENOMEM;
+		}
+
+		if (isp->smk_flags & SMK_INODE_TRANSMUTE) {
+			if (sbsp->smk_root) {
+				ctx->fstransmute = kstrdup(sbsp->smk_root->smk_known, GFP_KERNEL);
+				if (!ctx->fstransmute)
+					return -ENOMEM;
+			}
+		}
+	}
+
+	return 0;
+}
+
 /**
  * smack_fs_context_dup - Duplicate the security data on fs_context duplication
  * @fc: The new filesystem context.
@@ -4792,6 +4845,7 @@  static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(ptrace_traceme, smack_ptrace_traceme),
 	LSM_HOOK_INIT(syslog, smack_syslog),
 
+	LSM_HOOK_INIT(fs_context_init, smack_fs_context_init),
 	LSM_HOOK_INIT(fs_context_dup, smack_fs_context_dup),
 	LSM_HOOK_INIT(fs_context_parse_param, smack_fs_context_parse_param),