Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756279Ab2KNGEt (ORCPT ); Wed, 14 Nov 2012 01:04:49 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:55063 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754757Ab2KNFuY (ORCPT ); Wed, 14 Nov 2012 00:50:24 -0500 Message-Id: <20121114053943.904278555@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Wed, 14 Nov 2012 05:40:46 +0000 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Jesper Dangaard Brouer , Petr Matousek , Eric Dumazet , Stephen Hemminger , "David S. Miller" Subject: [ 73/82] net: fix divide by zero in tcp algorithm illinois In-Reply-To: <20121114053933.726869752@decadent.org.uk> X-SA-Exim-Connect-IP: 2001:470:1f08:1539:21c:bfff:fe03:f805 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 Content-Length: 2510 Lines: 74 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jesper Dangaard Brouer [ Upstream commit 8f363b77ee4fbf7c3bbcf5ec2c5ca482d396d664 ] Reading TCP stats when using TCP Illinois congestion control algorithm can cause a divide by zero kernel oops. The division by zero occur in tcp_illinois_info() at: do_div(t, ca->cnt_rtt); where ca->cnt_rtt can become zero (when rtt_reset is called) Steps to Reproduce: 1. Register tcp_illinois: # sysctl -w net.ipv4.tcp_congestion_control=illinois 2. Monitor internal TCP information via command "ss -i" # watch -d ss -i 3. Establish new TCP conn to machine Either it fails at the initial conn, or else it needs to wait for a loss or a reset. This is only related to reading stats. The function avg_delay() also performs the same divide, but is guarded with a (ca->cnt_rtt > 0) at its calling point in update_params(). Thus, simply fix tcp_illinois_info(). Function tcp_illinois_info() / get_info() is called without socket lock. Thus, eliminate any race condition on ca->cnt_rtt by using a local stack variable. Simply reuse info.tcpv_rttcnt, as its already set to ca->cnt_rtt. Function avg_delay() is not affected by this race condition, as its called with the socket lock. Cc: Petr Matousek Signed-off-by: Jesper Dangaard Brouer Acked-by: Eric Dumazet Acked-by: Stephen Hemminger Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/ipv4/tcp_illinois.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c index 813b43a..834857f 100644 --- a/net/ipv4/tcp_illinois.c +++ b/net/ipv4/tcp_illinois.c @@ -313,11 +313,13 @@ static void tcp_illinois_info(struct sock *sk, u32 ext, .tcpv_rttcnt = ca->cnt_rtt, .tcpv_minrtt = ca->base_rtt, }; - u64 t = ca->sum_rtt; - do_div(t, ca->cnt_rtt); - info.tcpv_rtt = t; + if (info.tcpv_rttcnt > 0) { + u64 t = ca->sum_rtt; + do_div(t, info.tcpv_rttcnt); + info.tcpv_rtt = t; + } nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info); } } -- 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/