From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752400AbbJTAuu (ORCPT ); Mon, 19 Oct 2015 20:50:50 -0400 Received: from mail.kernel.org ([198.145.29.136]:54823 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751036AbbJTAur (ORCPT ); Mon, 19 Oct 2015 20:50:47 -0400 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Eric Dumazet , Willem de Bruijn , "David S. Miller" , Zefan Li Subject: [PATCH 3.4 38/65] packet: read num_members once in packet_rcv_fanout() Date: Tue, 20 Oct 2015 08:47:48 +0800 Message-Id: <1445302095-4695-38-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1445302030-4607-1-git-send-email-lizf@kernel.org> References: <1445302030-4607-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Dumazet 3.4.110-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit f98f4514d07871da7a113dd9e3e330743fd70ae4 upstream. We need to tell compiler it must not read f->num_members multiple times. Otherwise testing if num is not zero is flaky, and we could attempt an invalid divide by 0 in fanout_demux_cpu() Note bug was present in packet_rcv_fanout_hash() and packet_rcv_fanout_lb() but final 3.1 had a simple location after commit 95ec3eb417115fb ("packet: Add 'cpu' fanout policy.") Fixes: dc99f600698dc ("packet: Add fanout support.") Signed-off-by: Eric Dumazet Cc: Willem de Bruijn Signed-off-by: David S. Miller [lizf: Backported to 3.4: use ACCESS_ONCE() instead of READ_ONCE()] Signed-off-by: Zefan Li --- net/packet/af_packet.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index dbe1715..af067d7 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1210,7 +1210,7 @@ static int packet_rcv_fanout(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev) { struct packet_fanout *f = pt->af_packet_priv; - unsigned int num = f->num_members; + unsigned int num = ACCESS_ONCE(f->num_members); struct packet_sock *po; struct sock *sk; -- 1.9.1