From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04685C33CAA for ; Thu, 23 Jan 2020 08:21:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC0BE22522 for ; Thu, 23 Jan 2020 08:21:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726204AbgAWIVP (ORCPT ); Thu, 23 Jan 2020 03:21:15 -0500 Received: from Chamillionaire.breakpoint.cc ([193.142.43.52]:43226 "EHLO Chamillionaire.breakpoint.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726083AbgAWIVP (ORCPT ); Thu, 23 Jan 2020 03:21:15 -0500 Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1iuXje-0005Xd-Ny; Thu, 23 Jan 2020 09:21:06 +0100 Date: Thu, 23 Jan 2020 09:21:06 +0100 From: Florian Westphal To: Daniel Borkmann Cc: Florian Westphal , Praveen Chaudhary , pablo@netfilter.org, davem@davemloft.net, kadlec@netfilter.org, netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Zhenggen Xu , Andy Stracner Subject: Re: [PATCH v3] [net]: Fix skb->csum update in inet_proto_csum_replace16(). Message-ID: <20200123082106.GT795@breakpoint.cc> References: <1573080729-3102-1-git-send-email-pchaudhary@linkedin.com> <1573080729-3102-2-git-send-email-pchaudhary@linkedin.com> <16d56ee6-53bc-1124-3700-bc0a78f927d6@iogearbox.net> <20200122114333.GQ795@breakpoint.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: netfilter-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org Daniel Borkmann wrote: > On 1/22/20 12:43 PM, Florian Westphal wrote: > > Daniel Borkmann wrote: > > > > @@ -449,9 +464,6 @@ void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb, > > > > if (skb->ip_summed != CHECKSUM_PARTIAL) { > > > > *sum = csum_fold(csum_partial(diff, sizeof(diff), > > > > ~csum_unfold(*sum))); > > > > - if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr) > > > > - skb->csum = ~csum_partial(diff, sizeof(diff), > > > > - ~skb->csum); > > > > > > What is the technical rationale in removing this here but not in any of the > > > other inet_proto_csum_replace*() functions? You changelog has zero analysis > > > on why here but not elsewhere this change would be needed? > > > > Right, I think it could be dropped everywhere BUT there is a major caveat: > > > > At least for the nf_nat case ipv4 header manipulation (which uses the other > > helpers froum utils.c) will eventually also update iph->checksum field > > to account for the changed ip addresses. > > > > And that update doesn't touch skb->csum. > > > > So in a way the update of skb->csum in the other helpers indirectly account > > for later ip header checksum update. > > > > At least that was my conclusion when reviewing the earlier incarnation > > of the patch. > > Mainly asking because not inet_proto_csum_replace16() but the other ones are > exposed via BPF and they are all in no way fundamentally different to each > other, but my concern is that depending on how the BPF prog updates the csums > things could start to break. :/ I'm reasonably sure removing the skb->csum update from the other helpers will also break ipv4 nat :) So, AFAIU from what you're saying above the patch seems fine as-is and just needs a more verbose commit message explaining why replace16() doesn't update skb->csum while all the other ones do. Is that correct?