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 4EE9CC433FE for ; Thu, 3 Nov 2022 21:32:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230377AbiKCVc3 (ORCPT ); Thu, 3 Nov 2022 17:32:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48366 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229496AbiKCVc3 (ORCPT ); Thu, 3 Nov 2022 17:32:29 -0400 Received: from out2.migadu.com (out2.migadu.com [IPv6:2001:41d0:2:aacc::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 470461EEFE for ; Thu, 3 Nov 2022 14:32:26 -0700 (PDT) Message-ID: <5de93174-6e27-1d0b-6ff1-b63c6141b6a2@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1667511144; 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=6mKNiyWkRizy/VAD3D7QUYSHfadJBHqTPUu/yyZMhqY=; b=n5Yyg0gNwz2N6Ui6CW8gbG/aoMa2CtLj4QIZTVxaLAtHGGXP3AJsPxZuA/SxGPJbmeCo/f LYgtKCRZg2V9ERVzV4Mo7LnZd72nkrImXQrO0ULEX0/tWeiBAkOkxlENgEiA6YIDZJcebL o5+WdkFomyFLkMYq1+mWNgDErIjDMeQ= Date: Thu, 3 Nov 2022 14:32:17 -0700 MIME-Version: 1.0 Subject: Re: [PATCH bpf-next] bpf: make sure skb->len != 0 when redirecting to a tunneling device Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau To: Stanislav Fomichev Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, song@kernel.org, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, haoluo@google.com, jolsa@kernel.org, Eric Dumazet , syzbot+f635e86ec3fa0a37e019@syzkaller.appspotmail.com, bpf@vger.kernel.org, Lorenz Bauer References: <20221027225537.353077-1-sdf@google.com> <2efac61c-a477-d3c1-4270-3c98998e6497@linux.dev> <1393c4d0-89e0-e5b7-9f40-2c646f2ea2e9@linux.dev> In-Reply-To: <1393c4d0-89e0-e5b7-9f40-2c646f2ea2e9@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 11/1/22 5:43 PM, Martin KaFai Lau wrote: > On 11/1/22 4:39 PM, Stanislav Fomichev wrote: >> On Tue, Nov 1, 2022 at 1:28 PM Martin KaFai Lau wrote: >>> >>> On 10/27/22 3:55 PM, Stanislav Fomichev wrote: >>>> syzkaller managed to trigger another case where skb->len == 0 >>>> when we enter __dev_queue_xmit: >>>> >>>> WARNING: CPU: 0 PID: 2470 at include/linux/skbuff.h:2576 skb_assert_len >>>> include/linux/skbuff.h:2576 [inline] >>>> WARNING: CPU: 0 PID: 2470 at include/linux/skbuff.h:2576 >>>> __dev_queue_xmit+0x2069/0x35e0 net/core/dev.c:4295 >>>> >>>> Call Trace: >>>>    dev_queue_xmit+0x17/0x20 net/core/dev.c:4406 >>>>    __bpf_tx_skb net/core/filter.c:2115 [inline] >>>>    __bpf_redirect_no_mac net/core/filter.c:2140 [inline] >>>>    __bpf_redirect+0x5fb/0xda0 net/core/filter.c:2163 >>>>    ____bpf_clone_redirect net/core/filter.c:2447 [inline] >>>>    bpf_clone_redirect+0x247/0x390 net/core/filter.c:2419 >>>>    bpf_prog_48159a89cb4a9a16+0x59/0x5e >>>>    bpf_dispatcher_nop_func include/linux/bpf.h:897 [inline] >>>>    __bpf_prog_run include/linux/filter.h:596 [inline] >>>>    bpf_prog_run include/linux/filter.h:603 [inline] >>>>    bpf_test_run+0x46c/0x890 net/bpf/test_run.c:402 >>>>    bpf_prog_test_run_skb+0xbdc/0x14c0 net/bpf/test_run.c:1170 >>>>    bpf_prog_test_run+0x345/0x3c0 kernel/bpf/syscall.c:3648 >>>>    __sys_bpf+0x43a/0x6c0 kernel/bpf/syscall.c:5005 >>>>    __do_sys_bpf kernel/bpf/syscall.c:5091 [inline] >>>>    __se_sys_bpf kernel/bpf/syscall.c:5089 [inline] >>>>    __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5089 >>>>    do_syscall_64+0x54/0x70 arch/x86/entry/common.c:48 >>>>    entry_SYSCALL_64_after_hwframe+0x61/0xc6 >>>> >>>> The reproducer doesn't really reproduce outside of syzkaller >>>> environment, so I'm taking a guess here. It looks like we >>>> do generate correct ETH_HLEN-sized packet, but we redirect >>>> the packet to the tunneling device. Before we do so, we >>>> __skb_pull l2 header and arrive again at skb->len == 0. >>>> Doesn't seem like we can do anything better than having >>>> an explicit check after __skb_pull? >>> hmm... I recall there was similar report but I didn't follow those earlier fixes >>> and discussion.  Not sure if this has been considered: >>> If this skb can only happen in the bpf_prog_test_run (?), >>> how about ensure that the skb will at least have some header after l2 header in >>> bpf_prog_test_run_skb().  Adding some headers/bytes if the data_size_in does not >>> have it.  This may break some external test cases that somehow has no l3/4? >>> test_progs should be mostly fine considering they are using the pkt_v[46] in >>> network_helpers.h. >> >> For the previous issue we've added "skb->len != 0" check which works >> for the cases that remove l2. Yeah, I replied on the "bpf: Don't redirect packets with invalid pkt_len" thread which is hitting the same syzbot report afaict. I don't think that patch is actually fixing it. >> For the ones that don't, I think you're right, and checking at the >> time of bpf_prog_test_run_skb can probably be enough, lemme try >> (require ETH_HLEN+1 vs ETH_HLEN). >> For some reason I was under the impression that Lorenz changed the >> size from 0 to 14 [0], but he went from 14 to 15, so we won't break at >> least cilium again.. >> CC'd him just in case. >> >> 0: https://github.com/cilium/ebpf/pull/788 > > Thanks for the pointer. > > The cilium's prog is SOCKET_FILTER (not l2).  It is why the new "skb->len != 0" > test broke it. > >> >>> Adding some headers/bytes if the data_size_in does not have it. >>> This may break some external test cases that somehow has no l3/4? >> >> Yeah, idk, this seems like a last resort? I'd prefer to explicitly >> fail and communicate it back to the user than slap some extra byte and >> then fail in some other place unpredictably? > > If fixing in the fast path in filter.c, is __bpf_redirect_no_mac the only place > that needs this check?  bpf_redirect_neigh() looks ok to me since the neigh > should have filled the mac header. I took a closer look. This seems to be the only place needed the check, so applied. If it turns out there are other cases caused by test-run generated skb, we will revisit a fix in test_run.c and the existing tests have to adjust. > >> >>>> Cc: Eric Dumazet >>>> Reported-by: syzbot+f635e86ec3fa0a37e019@syzkaller.appspotmail.com >>>> Signed-off-by: Stanislav Fomichev >>>> --- >>>>    net/core/filter.c | 4 ++++ >>>>    1 file changed, 4 insertions(+) >>>> >>>> diff --git a/net/core/filter.c b/net/core/filter.c >>>> index bb0136e7a8e4..cb3b635e35be 100644 >>>> --- a/net/core/filter.c >>>> +++ b/net/core/filter.c >>>> @@ -2126,6 +2126,10 @@ static int __bpf_redirect_no_mac(struct sk_buff *skb, >>>> struct net_device *dev, >>>> >>>>        if (mlen) { >>>>                __skb_pull(skb, mlen); >>>> +             if (unlikely(!skb->len)) { >>>> +                     kfree_skb(skb); >>>> +                     return -ERANGE; >>>> +             } One question, if the "!skb->len" check is deleted from convert___skb_to_skb(), this "unlikely(!skb->len)" block here has to be moved out of the "if (mlen)"?