vfs: Ignore unlocked mounts in fs_fully_visible

commit ceeb0e5d39fcdf4dca2c997bf225c7fc49200b37 upstream.

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

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index 13b0f7b..f07c769 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3187,11 +3187,15 @@ bool fs_fully_visible(struct file_system_type *type)
                if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
                        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)