Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932177AbXFBVvb (ORCPT ); Sat, 2 Jun 2007 17:51:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760647AbXFBVvM (ORCPT ); Sat, 2 Jun 2007 17:51:12 -0400 Received: from mail-gw3.sa.ew.hu ([212.108.200.82]:51293 "EHLO mail-gw3.sa.ew.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759736AbXFBVvK (ORCPT ); Sat, 2 Jun 2007 17:51:10 -0400 To: akpm@linux-foundation.org CC: netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] fix race in AF_UNIX Message-Id: From: Miklos Szeredi Date: Sat, 02 Jun 2007 23:50:55 +0200 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2219 Lines: 71 From: Miklos Szeredi A recv() on an AF_UNIX, SOCK_STREAM socket can race with a send()+close() on the peer, causing recv() to return zero, even though the sent data should be received. This happens if the send() and the close() is performed between skb_dequeue() and checking sk->sk_shutdown in unix_stream_recvmsg(): process A skb_dequeue() returns NULL, there's no data in the socket queue process B new data is inserted onto the queue by unix_stream_sendmsg() process B sk->sk_shutdown is set to SHUTDOWN_MASK by unix_release_sock() process A sk->sk_shutdown is checked, unix_release_sock() returns zero I'm surprised nobody noticed this, it's not hard to trigger. Maybe it's just (un)luck with the timing. It's possible to work around this bug in userspace, by retrying the recv() once in case of a zero return value. Signed-off-by: Miklos Szeredi --- Index: linux-2.6.22-rc2/net/unix/af_unix.c =================================================================== --- linux-2.6.22-rc2.orig/net/unix/af_unix.c 2007-06-02 23:45:47.000000000 +0200 +++ linux-2.6.22-rc2/net/unix/af_unix.c 2007-06-02 23:45:49.000000000 +0200 @@ -1711,20 +1711,23 @@ static int unix_stream_recvmsg(struct ki int chunk; struct sk_buff *skb; + unix_state_rlock(sk); skb = skb_dequeue(&sk->sk_receive_queue); if (skb==NULL) { if (copied >= target) - break; + goto unlock; /* * POSIX 1003.1g mandates this order. */ if ((err = sock_error(sk)) != 0) - break; + goto unlock; if (sk->sk_shutdown & RCV_SHUTDOWN) - break; + goto unlock; + + unix_state_runlock(sk); err = -EAGAIN; if (!timeo) break; @@ -1738,7 +1741,11 @@ static int unix_stream_recvmsg(struct ki } mutex_lock(&u->readlock); continue; + unlock: + unix_state_runlock(sk); + break; } + unix_state_runlock(sk); if (check_creds) { /* Never glue messages from different writers */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/