[PATCH 2/2] ovl: ignore permissions on underlying lookup

[Miklos Szeredi]

Generally permission checking is not necessary when overlayfs looks up a
dentry on one of the underlying layers, since search permission on base
directory was already checked in ovl_permission().

More specifically using lookup_one_len() causes a problem when the lower
directory lacks search permission for a specific user while the upper
directory does have search permission.  Since lookups are cached, this
causes inconsistency in behavior: success depends on who did the first
lookup.

So instead use lookup_hash() which doesn't do the permission check.

Reported-by: Ignacy GawÄdzki <ignacy.gawedzki@xxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
---
 fs/overlayfs/super.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -379,7 +379,7 @@ static inline struct dentry *ovl_lookup_
 	struct dentry *dentry;
 
 	inode_lock(dir->d_inode);
-	dentry = lookup_one_len(name->name, dir, name->len);
+	dentry = lookup_hash(name, dir, 0);
 	inode_unlock(dir->d_inode);
 
 	if (IS_ERR(dentry)) {