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 D10DCC4332F for ; Thu, 3 Nov 2022 21:10:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231508AbiKCVKb (ORCPT ); Thu, 3 Nov 2022 17:10:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33782 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231391AbiKCVKA (ORCPT ); Thu, 3 Nov 2022 17:10:00 -0400 Received: from out2.migadu.com (out2.migadu.com [188.165.223.204]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AF80613F4A; Thu, 3 Nov 2022 14:08:28 -0700 (PDT) Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1667509674; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hQcKEXuHs/7YZtQkNBeKwRLPigLlS9nAKVIGEHzvGaU=; b=Yxm3Oq/Y7WeBDzWz4L8zz22I/FsSLUnL28y2NM6dbdseg9ViJ6gWVDMHi0aYwH5LcwpTY7 OycpSxUV32zu00hDdWahU3vjG6u9Yj+ZPMmjlaxX/l7GKJicQTJkcVUXCcr8UhQG7VC5aq /cYzQWWrwbLN3iA5Yvs78xVGcouNVhM= Date: Thu, 3 Nov 2022 14:07:44 -0700 MIME-Version: 1.0 Subject: Re: [PATCH v4,bpf-next] bpf: Don't redirect packets with invalid pkt_len To: Zhengchao Shao Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, song@kernel.org, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, bigeasy@linutronix.de, imagedong@tencent.com, petrm@nvidia.com, arnd@arndb.de, dsahern@kernel.org, talalahmad@google.com, keescook@chromium.org, haoluo@google.com, jolsa@kernel.org, weiyongjun1@huawei.com, yuehaibing@huawei.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, hawk@kernel.org References: <20220715115559.139691-1-shaozhengchao@huawei.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: <20220715115559.139691-1-shaozhengchao@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 7/15/22 4:55 AM, Zhengchao Shao wrote: > Syzbot found an issue [1]: fq_codel_drop() try to drop a flow whitout any > skbs, that is, the flow->head is null. > The root cause, as the [2] says, is because that bpf_prog_test_run_skb() > run a bpf prog which redirects empty skbs. > So we should determine whether the length of the packet modified by bpf > prog or others like bpf_prog_test is valid before forwarding it directly. > > LINK: [1] https://syzkaller.appspot.com/bug?id=0b84da80c2917757915afa89f7738a9d16ec96c5 > LINK: [2] https://www.spinics.net/lists/netdev/msg777503.html > > Reported-by: syzbot+7a12909485b94426aceb@syzkaller.appspotmail.com > Signed-off-by: Zhengchao Shao > --- > v3: modify debug print > v2: need move checking to convert___skb_to_skb and add debug info > v1: should not check len in fast path > > include/linux/skbuff.h | 8 ++++++++ > net/bpf/test_run.c | 3 +++ > net/core/dev.c | 1 + > 3 files changed, 12 insertions(+) > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > index f6a27ab19202..82e8368ba6e6 100644 > --- a/include/linux/skbuff.h > +++ b/include/linux/skbuff.h > @@ -2459,6 +2459,14 @@ static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset) > > #endif /* NET_SKBUFF_DATA_USES_OFFSET */ > > +static inline void skb_assert_len(struct sk_buff *skb) > +{ > +#ifdef CONFIG_DEBUG_NET > + if (WARN_ONCE(!skb->len, "%s\n", __func__)) > + DO_ONCE_LITE(skb_dump, KERN_ERR, skb, false); > +#endif /* CONFIG_DEBUG_NET */ > +} > + > /* > * Add data to an sk_buff > */ > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c > index 2ca96acbc50a..dc9dc0bedca0 100644 > --- a/net/bpf/test_run.c > +++ b/net/bpf/test_run.c > @@ -955,6 +955,9 @@ static int convert___skb_to_skb(struct sk_buff *skb, struct __sk_buff *__skb) > { > struct qdisc_skb_cb *cb = (struct qdisc_skb_cb *)skb->cb; > > + if (!skb->len) > + return -EINVAL; From another recent report [0], I don't think this change is fixing the report from syzbot. It probably makes sense to revert this patch. afaict, This '!skb->len' test is done after if (is_l2) __skb_push(skb, hh_len); Hence, skb->len is not zero in convert___skb_to_skb(). The proper place to test skb->len is before __skb_push() to ensure there is some network header after the mac or may as well ensure "data_size_in > ETH_HLEN" at the beginning. The fix in [0] is applied. If it turns out there are other cases caused by the skb generated by test_run that needs extra fixes in bpf_redirect_*, it needs to revisit an earlier !skb->len check mentioned above and the existing test cases outside of test_progs would have to adjust accordingly. [0]: https://lore.kernel.org/bpf/20221027225537.353077-1-sdf@google.com/ > + > if (!__skb) > return 0; > > diff --git a/net/core/dev.c b/net/core/dev.c > index d588fd0a54ce..716df64fcfa5 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -4168,6 +4168,7 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev) > bool again = false; > > skb_reset_mac_header(skb); > + skb_assert_len(skb); > > if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP)) > __skb_tstamp_tx(skb, NULL, NULL, skb->sk, SCM_TSTAMP_SCHED);