From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753271AbaFGBhs (ORCPT ); Fri, 6 Jun 2014 21:37:48 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:36022 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752599AbaFGBXh (ORCPT ); Fri, 6 Jun 2014 21:23:37 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Eric Dumazet" , "Liu Yu" , "Neal Cardwell" , "David S. Miller" , "Stephen Hemminger" Date: Sat, 07 Jun 2014 02:26:28 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 19/92] tcp_cubic: fix the range of delayed_ack In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.60-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Liu Yu [ Upstream commit 0cda345d1b2201dd15591b163e3c92bad5191745 ] commit b9f47a3aaeab (tcp_cubic: limit delayed_ack ratio to prevent divide error) try to prevent divide error, but there is still a little chance that delayed_ack can reach zero. In case the param cnt get negative value, then ratio+cnt would overflow and may happen to be zero. As a result, min(ratio, ACK_RATIO_LIMIT) will calculate to be zero. In some old kernels, such as 2.6.32, there is a bug that would pass negative param, which then ultimately leads to this divide error. commit 5b35e1e6e9c (tcp: fix tcp_trim_head() to adjust segment count with skb MSS) fixed the negative param issue. However, it's safe that we fix the range of delayed_ack as well, to make sure we do not hit a divide by zero. CC: Stephen Hemminger Signed-off-by: Liu Yu Signed-off-by: Eric Dumazet Acked-by: Neal Cardwell Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/ipv4/tcp_cubic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index b78eac2..ed3d6d4 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -406,7 +406,7 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT; ratio += cnt; - ca->delayed_ack = min(ratio, ACK_RATIO_LIMIT); + ca->delayed_ack = clamp(ratio, 1U, ACK_RATIO_LIMIT); } /* Some calls are for duplicates without timetamps */