[PATCH 1/2] fs: Allow bind mounts with locked children on permaenetly empty directories

[Seth Forshee <seth.forshee@canonical.com>]

Forbidding a bind mount due to a locked child on a permanently
empty directory provides no security benefit since the
directory cannot contain any contents which have been overmounted
for security reasons.

Cc: stable@vger.kernel.org # v4.1+
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/namespace.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 4fb1691b4355..930f5557b1d1 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2065,6 +2065,8 @@ static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
 	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
 		if (!is_subdir(child->mnt_mountpoint, dentry))
 			continue;
+		if (is_empty_dir_inode(child->mnt_mountpoint->d_inode))
+			continue;
 
 		if (child->mnt.mnt_flags & MNT_LOCKED)
 			return true;
-- 
1.9.1