From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Graf Subject: Re: skb_checksum_help Date: Tue, 25 Jan 2005 00:45:15 +0100 Message-ID: <20050124234515.GA31837@postel.suug.ch> References: <20050124005348.GL23931@postel.suug.ch> <20050123202715.281ac87c.davem@davemloft.net> <20050124121610.GP23931@postel.suug.ch> <41F50B6C.6010107@davidcoulson.net> <20050124151510.GV23931@postel.suug.ch> <20050124225423.GA15405@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Coulson , "David S. Miller" , kaber@trash.net, netdev@oss.sgi.com Return-path: To: Herbert Xu Content-Disposition: inline In-Reply-To: <20050124225423.GA15405@gondor.apana.org.au> Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org * Herbert Xu <20050124225423.GA15405@gondor.apana.org.au> 2005-01-25 09:54 > On Mon, Jan 24, 2005 at 04:15:10PM +0100, Thomas Graf wrote: > > > > After inspecting your iptables rule set I think it is a general UDP DNAT > > problem under some circumstances. Some defragmentation weirdness in > > prerouting might be invovled. It would definitely help to have a dump > > of a complete ip fragments sequence causing this bug but I can't tell > > what exactly is the cause just now so yes it might be a good idea to > > limit the dump to the above subnet and hope the dodgy traffic comes > > from the same subnet again. > > OK, I think I've found the problem. It's a totally innocuous bug > in ip_fragment/ip6_fragment. When we're in the fast path and use > the pre-existing frag_list skb's, we forgot to clear ip_summed. I don't quite understand how this solves the problem. How could ip_summed be non zero after ip_forward? The earliest possible call to ip_fragment is in postrouting. Please correct me if I'm wrong. The bug isn't triggered for every fragment only once in a while so I don't think it's that simple.