[ 3.5.y.z extended stable ] Patch "unix: fix a race condition in unix_release()" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    unix: fix a race condition in unix_release()

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 43faf8930399cb27cbc6b0da10cc9be23ec60702 Mon Sep 17 00:00:00 2001
From: Paul Moore <pmoore at redhat.com>
Date: Mon, 25 Mar 2013 03:18:33 +0000
Subject: [PATCH] unix: fix a race condition in unix_release()

commit ded34e0fe8fe8c2d595bfa30626654e4b87621e0 upstream.

As reported by Jan, and others over the past few years, there is a
race condition caused by unix_release setting the sock->sk pointer
to NULL before properly marking the socket as dead/orphaned.  This
can cause a problem with the LSM hook security_unix_may_send() if
there is another socket attempting to write to this partially
released socket in between when sock->sk is set to NULL and it is
marked as dead/orphaned.  This patch fixes this by only setting
sock->sk to NULL after the socket has been marked as dead; I also
take the opportunity to make unix_release_sock() a void function
as it only ever returned 0/success.

Dave, I think this one should go on the -stable pile.

Special thanks to Jan for coming up with a reproducer for this
problem.

Reported-by: Jan Stancek <jan.stancek at gmail.com>
Signed-off-by: Paul Moore <pmoore at redhat.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/unix/af_unix.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 9aa708c..023db69 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -375,7 +375,7 @@ static void unix_sock_destructor(struct sock *sk)
 #endif
 }

-static int unix_release_sock(struct sock *sk, int embrion)
+static void unix_release_sock(struct sock *sk, int embrion)
 {
 	struct unix_sock *u = unix_sk(sk);
 	struct path path;
@@ -444,8 +444,6 @@ static int unix_release_sock(struct sock *sk, int embrion)

 	if (unix_tot_inflight)
 		unix_gc();		/* Garbage collect fds */
-
-	return 0;
 }

 static void init_peercred(struct sock *sk)
@@ -695,9 +693,10 @@ static int unix_release(struct socket *sock)
 	if (!sk)
 		return 0;

+	unix_release_sock(sk, 0);
 	sock->sk = NULL;

-	return unix_release_sock(sk, 0);
+	return 0;
 }

 static int unix_autobind(struct socket *sock)
--
1.8.1.2