linux-kernel - [PATCH 065/102] unix: fix a race condition in unix

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Date:	Mon,  8 Apr 2013 10:50:20 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Paul Moore <pmoore@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 065/102] unix: fix a race condition in unix_release()

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

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

From: Paul Moore <pmoore@...hat.com>

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@...il.com>
Signed-off-by: Paul Moore <pmoore@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Luis Henriques <luis.henriques@...onical.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

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