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 B06B7C43219 for ; Wed, 2 Nov 2022 00:43:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229906AbiKBAnM (ORCPT ); Tue, 1 Nov 2022 20:43:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56434 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229785AbiKBAnM (ORCPT ); Tue, 1 Nov 2022 20:43:12 -0400 Received: from out2.migadu.com (out2.migadu.com [188.165.223.204]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A31A618E31 for ; Tue, 1 Nov 2022 17:43:10 -0700 (PDT) Message-ID: <1393c4d0-89e0-e5b7-9f40-2c646f2ea2e9@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1667349788; 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=ZUS/E5hQ9xX9JblxzVK1DTwqNYIlIwCx29XNMbYRAj0=; b=iweKww5bQxOBzJPuewI5QeyLcQx6wAyISui0V6UMBED5J9Ggr/07aXkJqIjGvfugZmJx+0 axCfYEzDsJyh5zOACQ0IboDsZKRWA/OYPye9r9rgzvrUdufpfJHoJ2hcI4P8lcmqKDg8V5 wesbfbM0218hQBNpMACQc2KUntiD3v0= Date: Tue, 1 Nov 2022 17:43:04 -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 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: 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: bpf@vger.kernel.org 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. > 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. > >>> 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; >>> + } >>> >>> /* At ingress, the mac header has already been pulled once. >>> * At egress, skb_pospull_rcsum has to be done in case that >>