vfs: Ignore unlocked mounts in fs_fully_visible

Limit the mounts fs_fully_visible considers to locked mounts.
Unlocked can always be unmounted so considering them adds hassle
but no security benefit.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/fs/namespace.c b/fs/namespace.c
index 63b9806..8c7b8e0 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3205,11 +3205,15 @@ static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
                    ((mnt->mnt.mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
                        continue;
 
-               /* This mount is not fully visible if there are any child mounts
-                * that cover anything except for empty directories.
+               /* This mount is not fully visible if there are any
+                * locked child mounts that cover anything except for
+                * empty directories.
                 */
                list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
                        struct inode *inode = child->mnt_mountpoint->d_inode;
+                       /* Only worry about locked mounts */
+                       if (!(mnt->mnt.mnt_flags & MNT_LOCKED))
+                               continue;
                        if (!S_ISDIR(inode->i_mode))
                                goto next;
                        if (inode->i_nlink > 2)