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

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Message-ID: <20160322132302.GE11906@tucsk>
Date:	Tue, 22 Mar 2016 14:23:02 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-unionfs@...r.kernel.org
Subject: [PATCH 2/2] ovl: ignore permissions on underlying lookup

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 Gawędzki <ignacy.gawedzki@...en-communications.fr>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
---
 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)) {