Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261704AbTEUIRX (ORCPT ); Wed, 21 May 2003 04:17:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261702AbTEUHza (ORCPT ); Wed, 21 May 2003 03:55:30 -0400 Received: from zeus.kernel.org ([204.152.189.113]:37591 "EHLO zeus.kernel.org") by vger.kernel.org with ESMTP id S261752AbTEUHnN (ORCPT ); Wed, 21 May 2003 03:43:13 -0400 Date: Tue, 20 May 2003 21:43:01 -0700 From: Frank Cusack To: Menno Smits Cc: linux-kernel@vger.kernel.org Subject: Re: Kernel panic with pptpd when mss > mtu Message-ID: <20030520214301.A3632@google.com> References: <20030521091442.1bfb41b6.menno@netbox.biz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5.1i In-Reply-To: <20030521091442.1bfb41b6.menno@netbox.biz>; from menno@netbox.biz on Wed, May 21, 2003 at 09:14:42AM +1000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1555 Lines: 33 On Wed, May 21, 2003 at 09:14:42AM +1000, Menno Smits wrote: > I'm seeing a kernel oops with 2.4.20 which seems to be related to the > PopTop PPTP server. When certain clients connect in (seems to be > Win98) and begin large data transfers the kernel will reliably oops. > The system crashes hard, the oops doesn't make it to the logs. ... > I have been able to deal with the issue by using the workaround > suggested in the the second post. That is, adding netfilter rules with > the TCPMSS target to limit the TCP MSS to PMTU - 40. Apparently the > problem is triggered by the MSS being bigger than the MTU (which is > 750 in this case). Yup. win98 ignores the negotiated MRU from the PPP peer (MTU on the win98 side) and sends PPP packets larger than MTU. As you've discovered. :-) Linux doesn't allocate enough space for the decompressor output, and the mppe module doesn't properly check that enough space exists. (That's because PPP MPPE packets *shrink* after "decompression", and the mppe module assumes at least the same amount of space as the PPP packet is allocated for the decompressor.) Grab the latest ftp://ftp.samba.org/pub/unpacked/ppp which corrects both of the above problems. I'll be posting a patch to lkml to correct the decompressor allocation problem, shortly (a few weeks). /fc - 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/