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Commit 67690f93 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

userns: Remove implicit MNT_NODEV fragility. 



Replace the implict setting of MNT_NODEV on mounts that happen with
just user namespace permissions with an implicit setting of SB_I_NODEV
in s_iflags.  The visibility of the implicit MNT_NODEV has caused
problems in the past.

With this change the fragile case where an implicit MNT_NODEV needs to
be preserved in do_remount is removed.  Using SB_I_NODEV is much less
fragile as s_iflags are set during the original mount and never
changed.

In do_new_mount with the implicit setting of MNT_NODEV gone, the only
code that can affect mnt_flags is fs_fully_visible so simplify the if
statement and reduce the indentation of the code to make that clear.

Acked-by: default avatarSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent a1935c17

fs/namespace.c

+1 −18
Original line number Diff line number Diff line
@@ -2185,14 +2185,8 @@ static int do_remount(struct path *path, int flags, int mnt_flags, 
	}

	if ((mnt->mnt.mnt_flags & MNT_LOCK_NODEV) &&

	    !(mnt_flags & MNT_NODEV)) {

		/* Was the nodev implicitly added in mount? */

		if ((mnt->mnt_ns->user_ns != &init_user_ns) &&

		    !(sb->s_type->fs_flags & FS_USERNS_DEV_MOUNT)) {

			mnt_flags |= MNT_NODEV;

		} else {

		return -EPERM;

	}

	}

	if ((mnt->mnt.mnt_flags & MNT_LOCK_NOSUID) &&

	    !(mnt_flags & MNT_NOSUID)) {

		return -EPERM;
@@ -2385,7 +2379,6 @@ static int do_new_mount(struct path *path, const char *fstype, int flags, 
			int mnt_flags, const char *name, void *data)

{

	struct file_system_type *type;

	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;

	struct vfsmount *mnt;

	int err;
@@ -2396,16 +2389,6 @@ static int do_new_mount(struct path *path, const char *fstype, int flags, 
	if (!type)

		return -ENODEV;



	if (user_ns != &init_user_ns) {

		/* Only in special cases allow devices from mounts

		 * created outside the initial user namespace.

		 */

		if (!(type->fs_flags & FS_USERNS_DEV_MOUNT)) {

			flags |= MS_NODEV;

			mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;

		}

	}



	mnt = vfs_kern_mount(type, flags, name, data);

	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&

	    !mnt->mnt_sb->s_subtype)

fs/super.c

+3 −0
Original line number Diff line number Diff line
@@ -206,6 +206,9 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags, 
	init_waitqueue_head(&s->s_writers.wait_unfrozen);

	s->s_bdi = &noop_backing_dev_info;

	s->s_flags = flags;

	if ((s->s_user_ns != &init_user_ns) &&

	    !(type->fs_flags & FS_USERNS_DEV_MOUNT))

		s->s_iflags |= SB_I_NODEV;

	INIT_HLIST_NODE(&s->s_instances);

	INIT_HLIST_BL_HEAD(&s->s_anon);

	mutex_init(&s->s_sync_lock);