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authorEric W. Biederman <ebiederm@xmission.com>2016-05-18 13:50:06 -0500
committerEric W. Biederman <ebiederm@xmission.com>2016-06-23 15:47:23 -0500
commit67690f937c38bbab1d94cb45f6a32e61612834ae (patch)
treeb15e18fb82f42d4001c7d0b4e2d9d3b2113db95c
parenta1935c1738af53249a02290ff7c10e8a6e650a16 (diff)
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: Seth Forshee <seth.forshee@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
-rw-r--r--fs/namespace.c19
-rw-r--r--fs/super.c3
2 files changed, 4 insertions, 18 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index b1da7f8182c4..9786a38d1681 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2185,13 +2185,7 @@ 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;
- }
+ return -EPERM;
}
if ((mnt->mnt.mnt_flags & MNT_LOCK_NOSUID) &&
!(mnt_flags & MNT_NOSUID)) {
@@ -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)
diff --git a/fs/super.c b/fs/super.c
index 78790ada7191..25cdceed2ad3 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -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);

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