[PATCH 4.0 55/55] vfs: Ignore unlocked mounts in fs_fully_visible

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@xmission.com>

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>

---
 fs/namespace.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3187,11 +3187,15 @@ bool fs_fully_visible(struct file_system
 		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)