| Message ID | 20170509231938.6467-1-avagin@openvz.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Andrei Vagin <avagin@openvz.org> writes: > The introduced ioctl returns a file descriptor that refers to a owning > user namespace for a superblock which is associated with a target file > descriptor. > > EPERM is returned if the current process doesn't have CAP_SYS_ADMIN in > the returned user namespace. > > This information is required to dump and restore mount namespaces. We > need to know to which user namespace a superblock is belonged to. > > We already have the SIOCGSKNS ioctl for sockets to get a network > namespace, so it looks reasonable to use the same interface for > superblocks too. > > This functionality can be useful for users in order to understand > a running system. This will probably work. And the capability check eases any concerns I might have that this would be a trivial information leak. That said can we hold off just a little bit. If open_fs work actually turns into a real interface that would seem to be the perfect place to stick this functionality. Eric > > Cc: Alexander Viro <viro@zeniv.linux.org.uk> > Cc: Eric W. Biederman <ebiederm@xmission.com> > Signed-off-by: Andrei Vagin <avagin@openvz.org> > --- > fs/ioctl.c | 23 +++++++++++++++++++++++ > include/uapi/linux/fs.h | 2 ++ > 2 files changed, 25 insertions(+) > > diff --git a/fs/ioctl.c b/fs/ioctl.c > index 569db68..22bbf37 100644 > --- a/fs/ioctl.c > +++ b/fs/ioctl.c > @@ -16,6 +16,8 @@ > #include <linux/buffer_head.h> > #include <linux/falloc.h> > #include <linux/sched/signal.h> > +#include <linux/proc_fs.h> > +#include <linux/user_namespace.h> > > #include "internal.h" > > @@ -614,6 +616,25 @@ static int ioctl_file_dedupe_range(struct file *file, void __user *arg) > return ret; > } > > +static struct ns_common *get_sb_userns(struct ns_common *ns_common) > +{ > + struct user_namespace *ns; > + > + ns = container_of(ns_common, struct user_namespace, ns); > + > + return &get_user_ns(ns)->ns; > +} > + > +static int ioctl_fs_sb_userns(struct file *filp) > +{ > + struct super_block *sb = file_inode(filp)->i_sb; > + > + if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) > + return -EPERM; > + > + return open_related_ns(&sb->s_user_ns->ns, get_sb_userns); > +} > + > /* > * When you add any new common ioctls to the switches above and below > * please update compat_sys_ioctl() too. > @@ -677,6 +698,8 @@ int do_vfs_ioctl(struct file *filp, unsigned int fd, unsigned int cmd, > > case FIDEDUPERANGE: > return ioctl_file_dedupe_range(filp, argp); > + case FS_IOC_SB_USERNS: > + return ioctl_fs_sb_userns(filp); > > default: > if (S_ISREG(inode->i_mode)) > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h > index 33423aa..26ef2d5 100644 > --- a/include/uapi/linux/fs.h > +++ b/include/uapi/linux/fs.h > @@ -246,6 +246,8 @@ struct fsxattr { > #define FICLONE _IOW(0x94, 9, int) > #define FICLONERANGE _IOW(0x94, 13, struct file_clone_range) > #define FIDEDUPERANGE _IOWR(0x94, 54, struct file_dedupe_range) > +/* Get a file descriptor to an owning userns for a superblock */ > +#define FS_IOC_SB_USERNS _IOR('X', 55, int) > > #define FS_IOC_GETFLAGS _IOR('f', 1, long) > #define FS_IOC_SETFLAGS _IOW('f', 2, long)
On Tue, May 09, 2017 at 07:34:00PM -0500, Eric W. Biederman wrote: > Andrei Vagin <avagin@openvz.org> writes: > > > The introduced ioctl returns a file descriptor that refers to a owning > > user namespace for a superblock which is associated with a target file > > descriptor. > > > > EPERM is returned if the current process doesn't have CAP_SYS_ADMIN in > > the returned user namespace. > > > > This information is required to dump and restore mount namespaces. We > > need to know to which user namespace a superblock is belonged to. > > > > We already have the SIOCGSKNS ioctl for sockets to get a network > > namespace, so it looks reasonable to use the same interface for > > superblocks too. > > > > This functionality can be useful for users in order to understand > > a running system. > > This will probably work. And the capability check eases any concerns > I might have that this would be a trivial information leak. > > That said can we hold off just a little bit. If open_fs work actually > turns into a real interface that would seem to be the perfect place > to stick this functionality. Sure, we can. Do you know any place where to read more information about open_fs? I think I have heared a few times about this idea, but it would be good to get more details. Thanks, Andrei > > Eric > > > > > Cc: Alexander Viro <viro@zeniv.linux.org.uk> > > Cc: Eric W. Biederman <ebiederm@xmission.com> > > Signed-off-by: Andrei Vagin <avagin@openvz.org> > > --- > > fs/ioctl.c | 23 +++++++++++++++++++++++ > > include/uapi/linux/fs.h | 2 ++ > > 2 files changed, 25 insertions(+) > > > > diff --git a/fs/ioctl.c b/fs/ioctl.c > > index 569db68..22bbf37 100644 > > --- a/fs/ioctl.c > > +++ b/fs/ioctl.c > > @@ -16,6 +16,8 @@ > > #include <linux/buffer_head.h> > > #include <linux/falloc.h> > > #include <linux/sched/signal.h> > > +#include <linux/proc_fs.h> > > +#include <linux/user_namespace.h> > > > > #include "internal.h" > > > > @@ -614,6 +616,25 @@ static int ioctl_file_dedupe_range(struct file *file, void __user *arg) > > return ret; > > } > > > > +static struct ns_common *get_sb_userns(struct ns_common *ns_common) > > +{ > > + struct user_namespace *ns; > > + > > + ns = container_of(ns_common, struct user_namespace, ns); > > + > > + return &get_user_ns(ns)->ns; > > +} > > + > > +static int ioctl_fs_sb_userns(struct file *filp) > > +{ > > + struct super_block *sb = file_inode(filp)->i_sb; > > + > > + if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) > > + return -EPERM; > > + > > + return open_related_ns(&sb->s_user_ns->ns, get_sb_userns); > > +} > > + > > /* > > * When you add any new common ioctls to the switches above and below > > * please update compat_sys_ioctl() too. > > @@ -677,6 +698,8 @@ int do_vfs_ioctl(struct file *filp, unsigned int fd, unsigned int cmd, > > > > case FIDEDUPERANGE: > > return ioctl_file_dedupe_range(filp, argp); > > + case FS_IOC_SB_USERNS: > > + return ioctl_fs_sb_userns(filp); > > > > default: > > if (S_ISREG(inode->i_mode)) > > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h > > index 33423aa..26ef2d5 100644 > > --- a/include/uapi/linux/fs.h > > +++ b/include/uapi/linux/fs.h > > @@ -246,6 +246,8 @@ struct fsxattr { > > #define FICLONE _IOW(0x94, 9, int) > > #define FICLONERANGE _IOW(0x94, 13, struct file_clone_range) > > #define FIDEDUPERANGE _IOWR(0x94, 54, struct file_dedupe_range) > > +/* Get a file descriptor to an owning userns for a superblock */ > > +#define FS_IOC_SB_USERNS _IOR('X', 55, int) > > > > #define FS_IOC_GETFLAGS _IOR('f', 1, long) > > #define FS_IOC_SETFLAGS _IOW('f', 2, long)
Andrei Vagin <avagin@virtuozzo.com> writes: > On Tue, May 09, 2017 at 07:34:00PM -0500, Eric W. Biederman wrote: >> Andrei Vagin <avagin@openvz.org> writes: >> >> > The introduced ioctl returns a file descriptor that refers to a owning >> > user namespace for a superblock which is associated with a target file >> > descriptor. >> > >> > EPERM is returned if the current process doesn't have CAP_SYS_ADMIN in >> > the returned user namespace. >> > >> > This information is required to dump and restore mount namespaces. We >> > need to know to which user namespace a superblock is belonged to. >> > >> > We already have the SIOCGSKNS ioctl for sockets to get a network >> > namespace, so it looks reasonable to use the same interface for >> > superblocks too. >> > >> > This functionality can be useful for users in order to understand >> > a running system. >> >> This will probably work. And the capability check eases any concerns >> I might have that this would be a trivial information leak. >> >> That said can we hold off just a little bit. If open_fs work actually >> turns into a real interface that would seem to be the perfect place >> to stick this functionality. > > Sure, we can. Do you know any place where to read more information about > open_fs? I think I have heared a few times about this idea, but it would be > good to get more details. Look for David Howells <dhowells@redhat.com> recent patches on lkml he has implemented an initial rfc for it. Eric
diff --git a/fs/ioctl.c b/fs/ioctl.c index 569db68..22bbf37 100644 --- a/fs/ioctl.c +++ b/fs/ioctl.c @@ -16,6 +16,8 @@ #include <linux/buffer_head.h> #include <linux/falloc.h> #include <linux/sched/signal.h> +#include <linux/proc_fs.h> +#include <linux/user_namespace.h> #include "internal.h" @@ -614,6 +616,25 @@ static int ioctl_file_dedupe_range(struct file *file, void __user *arg) return ret; } +static struct ns_common *get_sb_userns(struct ns_common *ns_common) +{ + struct user_namespace *ns; + + ns = container_of(ns_common, struct user_namespace, ns); + + return &get_user_ns(ns)->ns; +} + +static int ioctl_fs_sb_userns(struct file *filp) +{ + struct super_block *sb = file_inode(filp)->i_sb; + + if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) + return -EPERM; + + return open_related_ns(&sb->s_user_ns->ns, get_sb_userns); +} + /* * When you add any new common ioctls to the switches above and below * please update compat_sys_ioctl() too. @@ -677,6 +698,8 @@ int do_vfs_ioctl(struct file *filp, unsigned int fd, unsigned int cmd, case FIDEDUPERANGE: return ioctl_file_dedupe_range(filp, argp); + case FS_IOC_SB_USERNS: + return ioctl_fs_sb_userns(filp); default: if (S_ISREG(inode->i_mode)) diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 33423aa..26ef2d5 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -246,6 +246,8 @@ struct fsxattr { #define FICLONE _IOW(0x94, 9, int) #define FICLONERANGE _IOW(0x94, 13, struct file_clone_range) #define FIDEDUPERANGE _IOWR(0x94, 54, struct file_dedupe_range) +/* Get a file descriptor to an owning userns for a superblock */ +#define FS_IOC_SB_USERNS _IOR('X', 55, int) #define FS_IOC_GETFLAGS _IOR('f', 1, long) #define FS_IOC_SETFLAGS _IOW('f', 2, long)
The introduced ioctl returns a file descriptor that refers to a owning user namespace for a superblock which is associated with a target file descriptor. EPERM is returned if the current process doesn't have CAP_SYS_ADMIN in the returned user namespace. This information is required to dump and restore mount namespaces. We need to know to which user namespace a superblock is belonged to. We already have the SIOCGSKNS ioctl for sockets to get a network namespace, so it looks reasonable to use the same interface for superblocks too. This functionality can be useful for users in order to understand a running system. Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Andrei Vagin <avagin@openvz.org> --- fs/ioctl.c | 23 +++++++++++++++++++++++ include/uapi/linux/fs.h | 2 ++ 2 files changed, 25 insertions(+)