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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B013C433F5 for ; Fri, 29 Oct 2021 15:39:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 02E16611C1 for ; Fri, 29 Oct 2021 15:39:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229968AbhJ2PmX (ORCPT ); Fri, 29 Oct 2021 11:42:23 -0400 Received: from www62.your-server.de ([213.133.104.62]:57856 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229527AbhJ2PmV (ORCPT ); Fri, 29 Oct 2021 11:42:21 -0400 Received: from sslproxy01.your-server.de ([78.46.139.224]) by www62.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92.3) (envelope-from ) id 1mgTyx-000Er6-T9; Fri, 29 Oct 2021 17:39:51 +0200 Received: from [85.1.206.226] (helo=linux.home) by sslproxy01.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1mgTyx-00055S-Od; Fri, 29 Oct 2021 17:39:51 +0200 Subject: Re: [RFC] should we allow BPF to transmit empty skbs To: Eric Dumazet , Alexei Starovoitov , Networking References: From: Daniel Borkmann Message-ID: Date: Fri, 29 Oct 2021 17:39:51 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.103.3/26337/Fri Oct 29 10:19:12 2021) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 10/29/21 5:22 PM, Eric Dumazet wrote: > Some layers in tx path do not expect skb being empty (skb->len == 0) > > syzbot reported a crash [1] in fq_codel. > > But I expect many drivers would also crash later. > > Sure the immediate fq_codel crash could be 'fixed', but I would rather > add some sanity checks in net/core/filter.c Makes sense, we shouldn't have to add this to fq_codel fast path, but rather a sanity check for bpf_clone_redirect(). I wonder if it's only related to bpf_prog_test_run() infra or if it could also have been generated via stack? Thanks, Daniel > diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c > index bb0cd6d3d2c2749d54e26368fb2558beedea85c9..73688b0ec83c473322669ca6a331bf3f3aefb293 100644 > --- a/net/sched/sch_fq_codel.c > +++ b/net/sched/sch_fq_codel.c > @@ -203,7 +203,14 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch, > codel_set_enqueue_time(skb); > flow = &q->flows[idx]; > flow_queue_add(flow, skb); > - q->backlogs[idx] += qdisc_pkt_len(skb); > + > + /* fq_codel_drop() depends on qdisc_pkt_len(skb) being not zero. */ > + pkt_len = qdisc_pkt_len(skb); > + if (unlikely(!pkt_len)) { > + pkt_len = 1; > + qdisc_skb_cb(skb)->pkt_len = pkt_len; > + } > + q->backlogs[idx] += pkt_len; > qdisc_qstats_backlog_inc(sch, skb); > > if (list_empty(&flow->flowchain)) { > @@ -220,8 +227,6 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch, > prev_backlog = sch->qstats.backlog; > prev_qlen = sch->q.qlen; > > - /* save this packet length as it might be dropped by fq_codel_drop() */ > - pkt_len = qdisc_pkt_len(skb); > /* fq_codel_drop() is quite expensive, as it performs a linear search > * in q->backlogs[] to find a fat flow. > * So instead of dropping a single packet, drop half of its backlog > > > [1] > general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] > CPU: 1 PID: 6542 Comm: syz-executor965 Not tainted 5.15.0-rc7-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > RIP: 0010:dequeue_head net/sched/sch_fq_codel.c:120 [inline] > RIP: 0010:fq_codel_drop net/sched/sch_fq_codel.c:168 [inline] > RIP: 0010:fq_codel_enqueue+0x83e/0x10c0 net/sched/sch_fq_codel.c:230 > Code: f8 e2 25 fa 45 39 ec 0f 83 cb 00 00 00 e8 1a dc 25 fa 48 8b 44 24 10 80 38 00 0f 85 9a 06 00 00 49 8b 07 48 89 c2 48 c1 ea 03 <42> 80 3c 32 00 0f 85 6e 06 00 00 48 8b 10 48 8d 78 28 49 89 17 48 > RSP: 0018:ffffc90001187310 EFLAGS: 00010246 > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: ffffffff87504776 RDI: 0000000000000003 > RBP: ffffc900011874e0 R08: 0000000000000400 R09: 0000000000000001 > R10: ffffffff875046d6 R11: 0000000000000000 R12: 0000000000000400 > R13: 0000000000000000 R14: dffffc0000000000 R15: ffff888071660000 > FS: 0000555556b21300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f9c09885040 CR3: 0000000021c77000 CR4: 00000000003506e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > dev_qdisc_enqueue+0x40/0x300 net/core/dev.c:3771 > __dev_xmit_skb net/core/dev.c:3855 [inline] > __dev_queue_xmit+0x1f0e/0x36e0 net/core/dev.c:4170 > __bpf_tx_skb net/core/filter.c:2114 [inline] > __bpf_redirect_no_mac net/core/filter.c:2139 [inline] > __bpf_redirect+0x5ba/0xd20 net/core/filter.c:2162 > ____bpf_clone_redirect net/core/filter.c:2429 [inline] > bpf_clone_redirect+0x2ae/0x420 net/core/filter.c:2401 > ___bpf_prog_run+0x3592/0x77d0 kernel/bpf/core.c:1548 > __bpf_prog_run512+0x91/0xd0 kernel/bpf/core.c:1776 > bpf_dispatcher_nop_func include/linux/bpf.h:718 [inline] > __bpf_prog_run include/linux/filter.h:624 [inline] > bpf_prog_run include/linux/filter.h:631 [inline] > bpf_test_run+0x37c/0xa20 net/bpf/test_run.c:119 > bpf_prog_test_run_skb+0xa7c/0x1cb0 net/bpf/test_run.c:662 > bpf_prog_test_run kernel/bpf/syscall.c:3307 [inline] > __sys_bpf+0x2137/0x5df0 kernel/bpf/syscall.c:4605 > __do_sys_bpf kernel/bpf/syscall.c:4691 [inline] > __se_sys_bpf kernel/bpf/syscall.c:4689 [inline] > __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:4689 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x44/0xae >