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=-2.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 B16BDC433B4 for ; Tue, 11 May 2021 17:39:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 82358611BD for ; Tue, 11 May 2021 17:39:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231896AbhEKRkb (ORCPT ); Tue, 11 May 2021 13:40:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231459AbhEKRk3 (ORCPT ); Tue, 11 May 2021 13:40:29 -0400 Received: from mail-qk1-x72e.google.com (mail-qk1-x72e.google.com [IPv6:2607:f8b0:4864:20::72e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4FE0CC061574; Tue, 11 May 2021 10:39:18 -0700 (PDT) Received: by mail-qk1-x72e.google.com with SMTP id l129so19563752qke.8; Tue, 11 May 2021 10:39:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=cBzI0fFJVl7rkeGxSkI1T6aieyqCHfIsXgSNZWy3sII=; b=ZMmEprcMtj68TGu/kofxqBTpQBBblASy5MxIJyZAe1O/39gvjjNl0Uvcz756irQIVR o2TiCjkkMaPqakbvJUAACNYKL/mU7Ycxo68reRSzMvDy1DznH+4F+RM31nUGKN6cLfR3 Q6h4PnFhwMyDMcHLRtZz/M4MRU6XkOWwxFgM8ArOFf9AM23Br86g1Pg3xe0pd+mrfcuz gOifHqO2nHPBFc+6Tm2hUT/Ttv4JxCxTQLqF8ehf1rDOwO6yEEU8Iburin7o7zxtUG5K 6Aj04Vwp1R81o+L5ullSyt4tXo0wppL+7hiYNiwCUI/VEX4IQNXOniEmUViVnO+aRhJo 78fw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=cBzI0fFJVl7rkeGxSkI1T6aieyqCHfIsXgSNZWy3sII=; b=JMyRdrmZZ+m/WHZkzBQ5HW17DS+AnV6xp9F7nqT8UH16iigUpqy+4ibKPySJKN7/QU WI42gT7C440QCGUCfoKXWkEUHbHekPl+wiWKZWjWiFYqhW9QBgrLIxNF/5V3a7mSMG0A NCbp/6rbeWCbyjTKo3bIGNFAjXui4WRwXKVL1foZjbjVVKu6XKcTn0R3WhKl68eA4LoY Qf1x8P079xWTg6XMFMkwFKkGt0GdbxKPfCeqB48oeeXA7qgSdLMBNMDFxR4qY7sApPvW dqRLuV2Ywn0piEqyK710HWl0ndor+P+Mf8KWW6sRcvBPUs1Bu9HVeGpTc5IUGb6VsP0x VmQA== X-Gm-Message-State: AOAM532/FLJJDTLsxasP4v5BjQUJt1+FUXeTntkdoEQOAQxLckhaohXv ZPLHCCvJV0487AaEAU6QkOJXTTFoLyPEXlWr8A8= X-Google-Smtp-Source: ABdhPJzb78m/Bx93OXl1S3XKrRFKVVrRBm8yG+xUh1UMHLfr+s9GXBuPKZBqHAEbxD/rxFj6Q+nS3YIfB1xS7riiesM= X-Received: by 2002:a05:620a:158c:: with SMTP id d12mr26777380qkk.127.1620754757565; Tue, 11 May 2021 10:39:17 -0700 (PDT) MIME-Version: 1.0 References: <1619690903-1138-1-git-send-email-dseok.yi@samsung.com> <8c2ea41a-3fc5-d560-16e5-bf706949d857@iogearbox.net> <02bf01d74211$0ff4aed0$2fde0c70$@samsung.com> <02c801d7421f$65287a90$2f796fb0$@samsung.com> <001801d742db$68ab8060$3a028120$@samsung.com> <436dbc62-451b-9b29-178d-9da28f47ef24@huawei.com> <007001d7431a$96281960$c2784c20$@samsung.com> <00c901d74543$57fa3620$07eea260$@samsung.com> <015101d74602$86442210$92cc6630$@samsung.com> In-Reply-To: <015101d74602$86442210$92cc6630$@samsung.com> From: Willem de Bruijn Date: Tue, 11 May 2021 13:38:41 -0400 Message-ID: Subject: Re: [PATCH bpf] bpf: check for data_len before upgrading mss when 6 to 4 To: Dongseok Yi Cc: Yunsheng Lin , Daniel Borkmann , bpf , Alexei Starovoitov , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , "David S. Miller" , Jakub Kicinski , Network Development , linux-kernel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 10, 2021 at 9:11 PM Dongseok Yi wrote: > > On Mon, May 10, 2021 at 09:46:25AM -0400, Willem de Bruijn wrote: > > On Mon, May 10, 2021 at 9:19 AM Willem de Bruijn > > wrote: > > > > > > > > That generates TCP packets with different MSS within the same stream. > > > > > > > > > > My suggestion remains to just not change MSS at all. But this has to > > > > > be a new flag to avoid changing established behavior. > > > > > > > > I don't understand why the mss size should be kept in GSO step. Will > > > > there be any issue with different mss? > > > > > > This issue has come up before and that has been the feedback from > > > TCP experts at one point. > > > > > > > In general, upgrading mss make sense when 6 to 4. The new flag would be > > > > set by user to not change mss. What happened if user does not set the > > > > flag? I still think we should fix the issue with a general approach. Or > > > > can we remove the skb_increase_gso_size line? > > > > > > Admins that insert such BPF packets should be aware of these issues. > > > And likely be using clamping. This is a known issue. > > > > > > We arrived that the flag approach in bpf_skb_net_shrink. Extending > > > that to bpf_skb_change_proto would be consistent. > > > > As for more generic approach: does downgrading to non-TSO by clearing > > gso_size work for this edge case? > > It can hit __skb_linearize in validate_xmit_skb and frags will be > copied to a linear part. The linear part size can exceed the MTU of > skb->dev unexpectedly. When does skb_needs_linearize return true here (besides lack of scatter-gather support, which would also preclude TSO)? > I will make another patch with the flag approach. >