Fixes for 4.19

[thirdparty/kernel/stable-queue.git] / releases / 3.6.8 / cifs-do-not-lookup-hashed-negative-dentry-in-cifs_atomic_open.patch

From 3798f47aa276b332c30da499cb4df4577e2f8872 Mon Sep 17 00:00:00 2001
From: Sachin Prabhu <sprabhu@redhat.com>
Date: Mon, 5 Nov 2012 11:39:32 +0000
Subject: cifs: Do not lookup hashed negative dentry in cifs_atomic_open

From: Sachin Prabhu <sprabhu@redhat.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@tiscali.cz>
Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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);