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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8009ACDB474 for ; Fri, 20 Oct 2023 05:33:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376262AbjJTFdA (ORCPT ); Fri, 20 Oct 2023 01:33:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346645AbjJTFc4 (ORCPT ); Fri, 20 Oct 2023 01:32:56 -0400 Received: from mail-ua1-x92c.google.com (mail-ua1-x92c.google.com [IPv6:2607:f8b0:4864:20::92c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 33E70D51 for ; Thu, 19 Oct 2023 22:32:54 -0700 (PDT) Received: by mail-ua1-x92c.google.com with SMTP id a1e0cc1a2514c-7b6d6773d05so173403241.2 for ; Thu, 19 Oct 2023 22:32:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloudflare.com; s=google09082023; t=1697779973; x=1698384773; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=QERO0uRdQXqqSaQdJAhee2LXGn28nhRHE84yn6ioXDc=; b=UCHRbXYL3xC0knyXFuBAsnyrkLGlT5t1Rqg+cpKWHrQednZoHGoTfiInP7UE+NCSFR wXSUe6Jwu7zzaVd3n85LoZnXW8+dqlE1Bhuxl3jPFfvL6x46DSNj9/D3DLF2LqmuCB9D tWbot+5hrUbZVTCTn349B4xeWIal6d8nHMFgT+1sGLA7ZjBc5ojYa5D9rR9B8t5ub5VW NV0+7zd6FNrsiehybQSpW6+JXRZkUN448cicU2ypFjj3plmy96MfLdNhMBjvLdQQpkcG wiKlBsYehe+nSW73EcWYNU+qIicC6wCqfKAZSWXlkk4Az0wwxr7oLzYz2pnDrUz+I0OD VnwQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1697779973; x=1698384773; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=QERO0uRdQXqqSaQdJAhee2LXGn28nhRHE84yn6ioXDc=; b=aqQ+LsCZoMiYLBEGsYOTp+vGHqfqYecB+bporfHrgE8OZSC7976KFkEMSRumIjNJYG t4WpeH9zbLKsJJKk8O5V4KwCJbopmTFd6NeAvBw7GCf5Sym8EVQAxvY3SI1k5sx2NGc2 YohNR+8JdUn1g1qoAgWkz2KZENYCPdBNQLdK0X3F09XzLsWxYMLbowF3zkz76Phz49qY JAnGAxlN2pdmfmMXQYT10qtHMyTsShpjnAG2p8zqS0y16ulTxzAH0r5HEEZEqLNrjstd dE2/56xE1SphCBiXB53fK70i/9FyoGTjalE6pVrfb2hDzFCHx40T20d6S06XnjmOhIpg GctQ== X-Gm-Message-State: AOJu0YxiDwRHEwcEZltAN6po6lp/lGU/+Y8jRwlXGLuWAeMWDF/Mwgy1 Q231svhk+SYt9Ffn86a5yuf2HA== X-Google-Smtp-Source: AGHT+IEuHUJNvQq/HPA6H9apAJz8f05F78aDSMAqahV84NRcnvPy5dpCqHEpkhIlb+0srBHZfqHiYw== X-Received: by 2002:a67:ae05:0:b0:452:5798:64bd with SMTP id x5-20020a67ae05000000b00452579864bdmr920744vse.35.1697779973258; Thu, 19 Oct 2023 22:32:53 -0700 (PDT) Received: from debian.debian ([140.141.197.139]) by smtp.gmail.com with ESMTPSA id vq6-20020a05620a558600b0076e672f535asm359098qkn.57.2023.10.19.22.32.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Oct 2023 22:32:52 -0700 (PDT) Date: Thu, 19 Oct 2023 22:32:51 -0700 From: Yan Zhai To: netdev@vger.kernel.org Cc: "David S. Miller" , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Aya Levin , Tariq Toukan , linux-kernel@vger.kernel.org, kernel-team@cloudflare.com, Florian Westphal , Willem de Bruijn , Alexander H Duyck Subject: [PATCH v3 net-next 3/3] ipv6: avoid atomic fragment on GSO packets Message-ID: <77423bb774612f0e8eaabfd9501d03389ff2cdbd.1697779681.git.yan@cloudflare.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When the ipv6 stack output a GSO packet, if its gso_size is larger than dst MTU, then all segments would be fragmented. However, it is possible for a GSO packet to have a trailing segment with smaller actual size than both gso_size as well as the MTU, which leads to an "atomic fragment". Atomic fragments are considered harmful in RFC-8021. An Existing report from APNIC also shows that atomic fragments are more likely to be dropped even it is equivalent to a no-op [1]. Add an extra check in the GSO slow output path. For each segment from the original over-sized packet, if it fits with the path MTU, then avoid generating an atomic fragment. Link: https://www.potaroo.net/presentations/2022-03-01-ipv6-frag.pdf [1] Fixes: b210de4f8c97 ("net: ipv6: Validate GSO SKB before finish IPv6 processing") Reported-by: David Wragg Signed-off-by: Yan Zhai --- net/ipv6/ip6_output.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index 3270d56b5c37..3d4e8edaa10b 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -162,7 +162,13 @@ ip6_finish_output_gso_slowpath_drop(struct net *net, struct sock *sk, int err; skb_mark_not_on_list(segs); - err = ip6_fragment(net, sk, segs, ip6_finish_output2); + /* Last GSO segment can be smaller than gso_size (and MTU). + * Adding a fragment header would produce an "atomic fragment", + * which is considered harmful (RFC-8021). Avoid that. + */ + err = segs->len > mtu ? + ip6_fragment(net, sk, segs, ip6_finish_output2) : + ip6_finish_output2(net, sk, segs); if (err && ret == 0) ret = err; } -- 2.30.2