From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qv1-f45.google.com (mail-qv1-f45.google.com [209.85.219.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 648ED54B1A7 for ; Wed, 14 Oct 2026 17:53:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.45 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792000383; cv=none; b=p27nynST3z+YkwqsOl3KTHOntwX/7baj1H+i+6RyF0EFtJz01m5brJtfX4CcCYAg2ZbbFchDl+JA91tZOMXjwRE0ypzqgn4uzkDd4HiWftJ0ipQxyK1BkXIpQktwX95sNCJg+fZ2IdZXPYGd4InOzxZ8EHRWcukvpSDFkAGpeNo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792000383; c=relaxed/simple; bh=+xRfdEstPEoB/0nLtXWtVVOiZOJPtIXTR+WV6k2Yt1g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Oom4A+MxKTX/EoP81jrm3s4sQQ0EZdTJ3FqlOmRk0iTbZKteej5I6W2DIYrf+eleSb7fv7XmW0Kys+E9aC3nzYARIewEyObYHaS/AKU8j4OuTy+hFJljMd9HvaYea+XdmNVuDCby/iPMvfRC/6MTQi+nSp8W1ES6r671dhnVNLA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=toxicpanda.com; spf=pass smtp.mailfrom=toxicpanda.com; dkim=pass (2048-bit key) header.d=toxicpanda.com header.i=@toxicpanda.com header.b=IHdhk+8T; arc=none smtp.client-ip=209.85.219.45 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=toxicpanda.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=toxicpanda.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=toxicpanda.com header.i=@toxicpanda.com header.b="IHdhk+8T" Received: by mail-qv1-f45.google.com with SMTP id 6a1803df08f44-91b8306b9f8so49920536d6.3 for ; Wed, 14 Oct 2026 10:53:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=toxicpanda.com; s=google; t=1792000381; x=1792605181; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:date:subject:cc:to:from:from:to:cc:subject :date:message-id:reply-to:content-type; bh=zsq92fxVdxK45zQgeZwO9L+7uNriDQM/IAKXxnDi/WI=; b=IHdhk+8TbZ9+MHOja1L3hCQI5WRVs8ODzT+XBsVN9WxfTbjQjv6YviNSZuKqOunIGh b8550FvIYq2uokyw0bE+b7UM2gbjiwN3Zu9N4Em4VUZVwIBOYsr7+NKj4ja5KJTd/aZW gajfntqizqiRuWOw4AB56z7IlQg6IXBIHUplTjUu4NiGXuxmm4cOIpKmdHS0ZIJBqTYz a0iYz22yw3JmaP2GXxtveI46YtDHYsK/VNZWDLd6Pz9VSj6rH8kCuS+aM8ywi4CeDs0C Z1uqImcdTHDtAr/vLEqE64o0Y74XQlHATveWFoecArb+zLr9KVIezzhleSXxEff7iSf8 nwaQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1792000381; x=1792605181; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:date:subject:cc:to:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=zsq92fxVdxK45zQgeZwO9L+7uNriDQM/IAKXxnDi/WI=; b=ChOJV3SYgVV4adaaT3VU90lqo2vvaqO/wpdhBcIC9mdkTYVhxp7QstWTy/GaNxJmWq 3aVud/XVGdEBOgJyLjNGK8jkF5SPGXI4imSIo9g/VXshANqimPh8Zd71bvQzHPf7LyYE iv9FjZPmljn3mZMARWRByJ3+R7E/l7XDpoce6KlcvP6uooHuuetMEl/ML2ag5+6P7eKb OgqWpP1PjlgZoPHDh77vEeJuLkQQHPHJTqBd7b6XofROb1Xvv2l2yms56Snnqd98PrTE U1FbtuJ6KTJlwf0In8WMm9jIa1uQnwDKr90nG/ZSlTS4Bqei7Uxy/0cab5M4B3pbX3pc Bufg== X-Forwarded-Encrypted: i=1; AKwUvBwlYfhl454ksIIJuplzpInNvuykMIG1TxDX4oXnvXsuf0dQsGOMm1Iaz9jVujw28BM6ksS1WSI=@vger.kernel.org X-Gm-Message-State: AFq9FYKV01jh+P0NQSYsKIv63lrHqtvWZs2NnZnuyiSaySvwls6G54sf LSEh95lm7wSmdQCF1dHwPuWEVD8xTJ8omhLB14QgjwJNCuWRcqtcBCj5sABG0C+LCPo= X-Gm-Gg: AYBFou1RVXdNENXu1W+mo1LgRDoM15wUkmUYktMWbpWC2qt9z7CEeA2eea19FIiThXA FkuAVCcGIqaXYqdK/Dx+i+sAiVvn614dpqula71CqYUpPf3CsCT82Yw1Vfki4YL1acGfAM6OvSc Ci3HsAHfuQzldoqUKTlmuEEQLVEFRIX0CMWuZVVe/TJe9mFzDPl4zoz63+gydFsP6hP6WUxQmQb O5zBj7mMI1exoibdFoYTaQ2q9FKlBHbp5o/XoftA2fQZQXW3C9DweJbT5DliVvlDMd/fLOzpGGH 4nDGWFPYAcFxOupOhFdsYtnA77CaLNjqaQ2JgwT9+moXHVa1EBHvjdI+UpVDVMar4b//zc2DOdB Lk2R0a9ZGDvluCiabNL5sxVkbtH7ajd49d1nGZ8IKW4UaB1d6L148DzyJDABD+ophC9lvYsWZFb j8DX3U11Y79OgwxGTgB5znaMPT3nx1X5nS8SFZrTvRpei4BtpRGJmv6ev3EuVZPPPVWROLFZgEN 81HMW9wCudujU1s X-Received: by 2002:a05:620a:17a0:b0:93e:c12c:f13b with SMTP id af79cd13be357-93ec12d085amr2683326985a.69.1792000381143; Wed, 14 Oct 2026 10:53:01 -0700 (PDT) Received: from toxicpanda.com ([153.61.196.254]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-91b97b387e0sm58301296d6.12.2026.10.14.10.53.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Oct 2026 10:53:00 -0700 (PDT) From: Josef Bacik To: David Laight Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Andrew Lunn , David Ahern , Ido Schimmel , Trond Myklebust , Anna Schumaker , Chuck Lever , Jeff Layton , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Mina Almasry , Kaiyuan Zhang , Willem de Bruijn , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH net v2] net: skbuff: make skb_copy_and_csum_bits() report unreadable frags Date: Wed, 14 Oct 2026 17:27:18 +0000 Message-ID: <179199883858343.2.17884063473154560573@toxicpanda.com> In-Reply-To: References: <20261013-b4-skb-segment-nosg-unreadable-v2-1-6c28d8ffa51e@toxicpanda.com> <20261014135154.05de968e@pumpkin> <179198668564919.2.10323410751655182155@toxicpanda.com> <20261014173042.0a74a25d@pumpkin> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit On Wed, Oct 14, 2026 at 12:52 PM Josef Bacik wrote: > ...ERR_PTR would be fine too? I'm arguing for explicit return values, > not "0 means failure". But I don't care enough to argue, I'm > respinning. Thanks, I respun it with the sum starting from ~0, and it changes what goes on the wire, so I was wrong above about ~0 not changing the folded result. csum_add(~0, 0) stays ~0, and csum_fold(~0) is 0x0000 where csum_fold(0) is 0xffff. No other 32 bit value folds to 0xffff, so there's no non-zero value that can stand in for a zero sum. ICMPv4 folds the raw sum with no pseudo-header, so an echo request with id 0, seq 0 and an all-zero payload gets a reply with a checksum of 0x0000 instead of 0xffff, and the sender drops it. I checked that on loopback: the reply has 0xffff with v2 and 0x0000 with the ~0 seed. So 0 can't mean failure here without changing checksums, and v3 will keep the explicit error return from v2. Thanks, Josef