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=-17.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, USER_IN_DEF_DKIM_WL autolearn=unavailable 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 D3441C433DF for ; Fri, 9 Oct 2020 18:26:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8EE1622284 for ; Fri, 9 Oct 2020 18:26:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="qD3bQm3Q" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390433AbgJIS0w (ORCPT ); Fri, 9 Oct 2020 14:26:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33930 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390429AbgJIS0w (ORCPT ); Fri, 9 Oct 2020 14:26:52 -0400 Received: from mail-il1-x142.google.com (mail-il1-x142.google.com [IPv6:2607:f8b0:4864:20::142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3D6DFC0613D5 for ; Fri, 9 Oct 2020 11:26:52 -0700 (PDT) Received: by mail-il1-x142.google.com with SMTP id o18so10030775ill.2 for ; Fri, 09 Oct 2020 11:26:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=UKlDCJjsvYo0P5vGdgOWIXrtulmP1H0kYGa0iLKKXug=; b=qD3bQm3QF9uJuQ0BumahUTm2fjD9oRHTyb27jrLD2e7n2gC3/x57epR1+1aw9fDg4I TrVOHp3I8w1rW1f/4CK/txoa01lN+QeHTr90kQaQVetEj+CzzlFr9dva+sXCVNotr3YX Lc0I6rT/BAeHwgq28Jv+WAEpAen0pMQEoyV6XiNLKZU+DKdkSKoXN7NhDRtTQA8K1gb/ ZNOa2mNcidh95mlHApLtF/kO++5k767E5pmx7QcHhOtWvQAPDoyy33+hdNw/du0DFV/y sG2s5531PVaJz0sdnq1B1i0hLputvX9fJcfx63HBlmRKyh1Rc/eGUC3QhpAvbjmuNd0K tLfA== 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=UKlDCJjsvYo0P5vGdgOWIXrtulmP1H0kYGa0iLKKXug=; b=HHggZ1GrjDiKKbR0su6+kREZG5qXVohUQsA3uebINjluYJcgQIuOcpeUvngoiITuNE 5QucuFW9aE3m1yCcApLDrnhRR+ujdk88vEdMYKjG3Xi0Oa4Z0JP2L0rJKpoxS2fEbWv1 rlPqS36IS1q6AO1OSlvuvrYIZgiEjr3mou2wvkNwU/uMUJ4H6zqhSh8fz4voWs414y5H RSQ9iq11Xr5AVETISG8zPK/KVFymF32K+AW7eH84aAP1mZtX6zApLMuDq20TAA+dLj5S DLcZZZrNRmAkjmyNm61MfhdYIPFWasNGgg6WbVd266bgdrcOqRMlvD12paKo3ONUJr9f 2Bcw== X-Gm-Message-State: AOAM533NAtyh/bwfFKrbjcwioQzA4biuhygYLqpQolOpB17NdxQGlpax qGAz4l6GGEcBdTwcxpyqb5Oy74Vq8751ti5M6BXalg== X-Google-Smtp-Source: ABdhPJxRNqtOvFo3Li7SkaWne5Ac+csCZLTieDdE4ei2z4CwY7yiJUDbnzCKUVCadeP6dPlt10kqJRIPTnAifIZ8dKQ= X-Received: by 2002:a92:1503:: with SMTP id v3mr11354132ilk.56.1602268011188; Fri, 09 Oct 2020 11:26:51 -0700 (PDT) MIME-Version: 1.0 References: <160216609656.882446.16642490462568561112.stgit@firesoul> <160216614239.882446.4447190431655011838.stgit@firesoul> <20b1e1dc-7ce7-dc42-54cd-5c4040ccdb30@iogearbox.net> In-Reply-To: <20b1e1dc-7ce7-dc42-54cd-5c4040ccdb30@iogearbox.net> From: =?UTF-8?Q?Maciej_=C5=BBenczykowski?= Date: Fri, 9 Oct 2020 11:26:40 -0700 Message-ID: Subject: Re: [PATCH bpf-next V3 1/6] bpf: Remove MTU check in __bpf_skb_max_len To: Daniel Borkmann Cc: Jesper Dangaard Brouer , bpf , Linux NetDev , Daniel Borkmann , Alexei Starovoitov , Lorenz Bauer , Shaun Crampton , Lorenzo Bianconi , Marek Majkowski , John Fastabend , Jakub Kicinski , Eyal Birger , willemdebruijn.kernel@gmail.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org > > Multiple BPF-helpers that can manipulate/increase the size of the SKB uses > > __bpf_skb_max_len() as the max-length. This function limit size against > > the current net_device MTU (skb->dev->mtu). > > > > When a BPF-prog grow the packet size, then it should not be limited to the > > MTU. The MTU is a transmit limitation, and software receiving this packet > > should be allowed to increase the size. Further more, current MTU check in > > __bpf_skb_max_len uses the MTU from ingress/current net_device, which in > > case of redirects uses the wrong net_device. > > > > Keep a sanity max limit of IP6_MAX_MTU (under CONFIG_IPV6) which is 64KiB > > plus 40 bytes IPv6 header size. If compiled without IPv6 use IP_MAX_MTU. > > > > V3: replace __bpf_skb_max_len() with define and use IPv6 max MTU size. > > > > Signed-off-by: Jesper Dangaard Brouer > > --- > > net/core/filter.c | 16 ++++++++-------- > > 1 file changed, 8 insertions(+), 8 deletions(-) > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index 05df73780dd3..ddc1f9ba89d1 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -3474,11 +3474,11 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff, > > return 0; > > } > > > > -static u32 __bpf_skb_max_len(const struct sk_buff *skb) > > -{ > > - return skb->dev ? skb->dev->mtu + skb->dev->hard_header_len : > > - SKB_MAX_ALLOC; > > -} > > +#ifdef IP6_MAX_MTU /* Depend on CONFIG_IPV6 */ > > +#define BPF_SKB_MAX_LEN IP6_MAX_MTU > > +#else > > +#define BPF_SKB_MAX_LEN IP_MAX_MTU > > +#endif > > Shouldn't that check on skb->protocol? The way I understand it is that a number of devices > including virtual ones use ETH_MAX_MTU as their dev->max_mtu, so the mtu must be in the range > of dev->min_mtu(=ETH_MIN_MTU), dev->max_mtu(=ETH_MAX_MTU). __dev_set_mtu() then sets the user > value to dev->mtu in the core if within this range. That means in your case skb->dev->hard_header_len > for example is left out, meaning if we go for some constant, that would need to be higher. I think in the past skb->protocol was not guaranteed to be correct - could be zero... (with [misconfigured] raw sockets - maybe that's fixed now?)