From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: possible kernel oops from user MSS Date: Wed, 10 Nov 2010 12:41:19 -0800 (PST) Message-ID: <20101110.124119.102563803.davem@davemloft.net> References: Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: schen@mvista.com Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:41121 "EHLO sunset.davemloft.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753603Ab0KJUkz (ORCPT ); Wed, 10 Nov 2010 15:40:55 -0500 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: From: Steve Chen Date: Wed, 10 Nov 2010 07:24:51 -0600 > With commit f5fff5dc8a7a3f395b0525c02ba92c95d42b7390, a user program > can pass in TCP_MAXSEG of 12 (or TCPOLEN_TSTAMP_ALIGNED), and cause > kernel oops with division by 0 > in tcp_select_initial_window. One way to prevent it is to change the > minimum value for TCP_MAXSEG in do_tcp_setsockopt from 8 to some value > over 12. Two questions. > > 1. Is this the right solution? > 2. If it is, what is a good minimum value? Thanks Steve, I'll fix this like so: -------------------- tcp: Increase TCP_MAXSEG socket option minimum. As noted by Steve Chen, since commit f5fff5dc8a7a3f395b0525c02ba92c95d42b7390 ("tcp: advertise MSS requested by user") we can end up with a situation where tcp_select_initial_window() does a divide by a zero (or even negative) mss value. The problem is that sometimes we subtract TCPOLEN_TSTAMP_ALIGNED from the mss. Fix this by increasing the minimum from 8 to 8 plus the value of TCPOLEN_TSTATMP_ALIGNED. Reported-by: Steve Chen Signed-off-by: David S. Miller --- net/ipv4/tcp.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 245603c..6b0eb4d 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -2246,7 +2246,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level, /* Values greater than interface MTU won't take effect. However * at the point when this call is done we typically don't yet * know which interface is going to be used */ - if (val < 8 || val > MAX_TCP_WINDOW) { + if (val < TCPOLEN_TSTAMP_ALIGNED + 8 || val > MAX_TCP_WINDOW) { err = -EINVAL; break; } -- 1.7.3.2