From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
	aws-us-west-2-korg-lkml-1.web.codeaurora.org
Received: from vger.kernel.org (vger.kernel.org [23.128.96.18])
	by smtp.lore.kernel.org (Postfix) with ESMTP id A0C53CDB465
	for <linux-kernel@archiver.kernel.org>; Thu, 19 Oct 2023 05:03:03 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S232616AbjJSFDC (ORCPT <rfc822;linux-kernel@archiver.kernel.org>);
        Thu, 19 Oct 2023 01:03:02 -0400
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56534 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S232583AbjJSFDA (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 19 Oct 2023 01:03:00 -0400
Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [IPv6:2a03:a000:7:0:5054:ff:fe1c:15ff])
        by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 43DCD114
        for <linux-kernel@vger.kernel.org>; Wed, 18 Oct 2023 22:02:57 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
        d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type:
        MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To:
        Content-Transfer-Encoding:Content-ID:Content-Description;
        bh=OPsw8MvYsqR+rnUHtpa1MRKpBSHQOzp/OTrHhOj2ZcM=; b=PojmyVZnWvHDhJ/lCJ9rKInP5E
        AcUramE3nuJFUZsHIHZtDNIgM6d6To9b7uuWe/zzNaHs9xXSjkNUpsxxltgtJQzmgEKLsHBWo1Z6Z
        JlyJU4vXvWeazhjwMxjCHchzUkX9qO4wNeAEOxtjQynttS1vx0w5MCuY516DpIOhfO5y51ROlpKcl
        6IHLChR8QK4WUE+w+q/aSURzdzSbkkX6Jkm8ri/jGfXTXxjgzDPM9mkG10GbtT6BuyCR37r7ALMzn
        51q7oNT+/IhAos3qKraKcbF1YR8eV1TWjp/v7bIlIWn+8c215Zf5ZhicLSp7ClE0KYUe9taa+zs/F
        4oqEupkQ==;
Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux))
        id 1qtLBK-002eH5-1B;
        Thu, 19 Oct 2023 05:02:50 +0000
Date:   Thu, 19 Oct 2023 06:02:50 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     gus Gusenleitner Klaus <gus@keba.com>
Cc:     Al Viro <viro@ftp.linux.org.uk>,
        Thomas Gleixner <tglx@linutronix.de>,
        lkml <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        "dsahern@kernel.org" <dsahern@kernel.org>,
        "edumazet@google.com" <edumazet@google.com>,
        "kuba@kernel.org" <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Subject: Re: AW: [PATCH] amd64: Fix csum_partial_copy_generic()
Message-ID: <20231019050250.GV800259@ZenIV>
References: <VI1PR0702MB3840EB26EF2A1A35BFEA53BFD9D5A@VI1PR0702MB3840.eurprd07.prod.outlook.com>
 <20231018154205.GT800259@ZenIV>
 <VI1PR0702MB3840F2D594B9681BF2E0CD81D9D4A@VI1PR0702MB3840.eurprd07.prod.outlook.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <VI1PR0702MB3840F2D594B9681BF2E0CD81D9D4A@VI1PR0702MB3840.eurprd07.prod.outlook.com>
Sender: Al Viro <viro@ftp.linux.org.uk>
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Oct 19, 2023 at 04:44:04AM +0000, gus Gusenleitner Klaus wrote:
> > On Wed, Oct 18, 2023 at 06:18:05AM +0000, gus Gusenleitner Klaus wrote:
> > > The checksum calculation is wrong in case of an source buffer
> > > containing zero bytes only. The expected return value is 0, the
> > > actual return value is 0xfffffff.
> > 
> > Expected where?  The actual checksum is defined modulo 0xffff, so
> > 0 and 0xffffffff represent the same final value.
> > 
> > The only twist is that in some situations we internally use 0 for
> > "not calculated yet".
> > 
> > > This problem occurs when a ICMP echo reply is sent that has set
> > > zero identifier, sequence number and data.
> > 
> > What problem?  Could you please either point to specific RFC or
> > show that packets are rejected by some existing system, or...?
> 
> Here's our situation:
> Our device gets pinged by a third party manufacturer robot controller.
> We have updated the kernel in our device to 5.15 from 4.9, the robot
> controller is kept unchanged. At 4.9, our device's ping reply is accepted
> by the robot controller, at 5.15 it's not.
> 
> Wireshark shows a bad checksum warning:
>  'Checksum: 0x0000 incorrect, should be 0xffff' 
> 

Lovely.  I think I see what's going on, give me a few to think about it...