linux-kernel - [ 14/83] cifs: Do not lookup hashed negative dentry in cifs_atomic

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Message-Id: <20121122004214.037973534@linuxfoundation.org>
Date:	Wed, 21 Nov 2012 16:41:36 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, Vit Zahradka <vit.zahradka@...cali.cz>,
	Sachin Prabhu <sprabhu@...hat.com>
Subject: [ 14/83] cifs: Do not lookup hashed negative dentry in cifs_atomic_open

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

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

From: Sachin Prabhu <sprabhu@...hat.com>

commit 3798f47aa276b332c30da499cb4df4577e2f8872 upstream.

We do not need to lookup a hashed negative directory since we have
already revalidated it before and have found it to be fine.

This also prevents a crash in cifs_lookup() when it attempts to rehash
the already hashed negative lookup dentry.

The patch has been tested using the reproducer at
https://bugzilla.redhat.com/show_bug.cgi?id=867344#c28

Reported-by: Vit Zahradka <vit.zahradka@...cali.cz>
Signed-off-by: Sachin Prabhu <sprabhu@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/cifs/dir.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/fs/cifs/dir.c
+++ b/fs/cifs/dir.c
@@ -392,7 +392,16 @@ cifs_atomic_open(struct inode *inode, st
 	 * in network traffic in the other paths.
 	 */
 	if (!(oflags & O_CREAT)) {
-		struct dentry *res = cifs_lookup(inode, direntry, 0);
+		struct dentry *res;
+
+		/*
+		 * Check for hashed negative dentry. We have already revalidated
+		 * the dentry and it is fine. No need to perform another lookup.
+		 */
+		if (!d_unhashed(direntry))
+			return -ENOENT;
+
+		res = cifs_lookup(inode, direntry, 0);
 		if (IS_ERR(res))
 			return PTR_ERR(res);
 


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