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mnt: Refactor the logic for mounting sysfs and proc in a user namespace

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Fresh mounts of proc and sysfs are a very special case that works very
much like a bind mount.  Unfortunately the current structure can not
preserve the MNT_LOCK... mount flags.  Therefore refactor the logic
into a form that can be modified to preserve those lock bits.

Add a new filesystem flag FS_USERNS_VISIBLE that requires some mount
of the filesystem be fully visible in the current mount namespace,
before the filesystem may be mounted.

Move the logic for calling fs_fully_visible from proc and sysfs into
fs/namespace.c where it has greater access to mount namespace state.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2015-05-08 23:22:29 -05:00
parent 7e96c1b0e0
commit 1b852bceb0
4 changed files with 10 additions and 10 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

8
fs/namespace.c
View file

@ -2332,6 +2332,8 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
return err; return err;
} }
static bool fs_fully_visible(struct file_system_type *fs_type);
/* /*
* create a new mount for userspace and request it to be added into the * create a new mount for userspace and request it to be added into the
* namespace's tree * namespace's tree
@ -2363,6 +2365,10 @@ static int do_new_mount(struct path *path, const char *fstype, int flags,
flags |= MS_NODEV; flags |= MS_NODEV;
mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV; mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
} }
if (type->fs_flags & FS_USERNS_VISIBLE) {
if (!fs_fully_visible(type))
return -EPERM;
}
} }
mnt = vfs_kern_mount(type, flags, name, data); mnt = vfs_kern_mount(type, flags, name, data);
@ -3164,7 +3170,7 @@ bool current_chrooted(void)
return chrooted; return chrooted;
} }
bool fs_fully_visible(struct file_system_type *type) static bool fs_fully_visible(struct file_system_type *type)
{ {
struct mnt_namespace *ns = current->nsproxy->mnt_ns; struct mnt_namespace *ns = current->nsproxy->mnt_ns;
struct mount *mnt; struct mount *mnt;

5
fs/proc/root.c
View file

@ -112,9 +112,6 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
ns = task_active_pid_ns(current); ns = task_active_pid_ns(current);
options = data; options = data;
if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
return ERR_PTR(-EPERM);
/* Does the mounter have privilege over the pid namespace? */ /* Does the mounter have privilege over the pid namespace? */
if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
return ERR_PTR(-EPERM); return ERR_PTR(-EPERM);
@ -159,7 +156,7 @@ static struct file_system_type proc_fs_type = {
.name = "proc", .name = "proc",
.mount = proc_mount, .mount = proc_mount,
.kill_sb = proc_kill_sb, .kill_sb = proc_kill_sb,
.fs_flags = FS_USERNS_MOUNT, .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
}; };
void __init proc_root_init(void) void __init proc_root_init(void)

5
fs/sysfs/mount.c
View file

@ -31,9 +31,6 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
bool new_sb; bool new_sb;
if (!(flags & MS_KERNMOUNT)) { if (!(flags & MS_KERNMOUNT)) {
if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
return ERR_PTR(-EPERM);
if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET)) if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
return ERR_PTR(-EPERM); return ERR_PTR(-EPERM);
} }
@ -58,7 +55,7 @@ static struct file_system_type sysfs_fs_type = {
.name = "sysfs", .name = "sysfs",
.mount = sysfs_mount, .mount = sysfs_mount,
.kill_sb = sysfs_kill_sb, .kill_sb = sysfs_kill_sb,
.fs_flags = FS_USERNS_MOUNT, .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
}; };
int __init sysfs_init(void) int __init sysfs_init(void)

2
include/linux/fs.h
View file

@ -1897,6 +1897,7 @@ struct file_system_type {
#define FS_HAS_SUBTYPE 4 #define FS_HAS_SUBTYPE 4
#define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */ #define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
#define FS_USERNS_DEV_MOUNT 16 /* A userns mount does not imply MNT_NODEV */ #define FS_USERNS_DEV_MOUNT 16 /* A userns mount does not imply MNT_NODEV */
#define FS_USERNS_VISIBLE 32 /* FS must already be visible */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */ #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
struct dentry *(*mount) (struct file_system_type *, int, struct dentry *(*mount) (struct file_system_type *, int,
const char *, void *); const char *, void *);
@ -1984,7 +1985,6 @@ extern int vfs_ustat(dev_t, struct kstatfs *);
extern int freeze_super(struct super_block *super); extern int freeze_super(struct super_block *super);
extern int thaw_super(struct super_block *super); extern int thaw_super(struct super_block *super);
extern bool our_mnt(struct vfsmount *mnt); extern bool our_mnt(struct vfsmount *mnt);
extern bool fs_fully_visible(struct file_system_type *);
extern int current_umask(void); extern int current_umask(void);