From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout09.his.huawei.com (canpmsgout09.his.huawei.com [113.46.200.224]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 00FB640B0ED for ; Thu, 20 Aug 2026 10:04:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.224 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787220297; cv=none; b=UGPABUtWPeuHAx9AjMxKUrGkTNA7TKYw1BqAJii4+ivQMhV07rzFM0ONqq2OuepsxSJ0cdQ1MOxvXhH2ZsNB4XeQ8Y0Z7i4Lp8iA2WzrkkwBHoRPmwUugv+ly94z65ZjZDX1fRn/czTeli2yCCotMucKC5qjs0iU4t9fG9dM1zo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787220297; c=relaxed/simple; bh=TXoqjQcJHjWxjeR2hRkig1J4Fjt9nnj13K7SCM9ShiA=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=gqJyI7btiUoohcxeS/ifs1WWFVGgXvejMxpp6vq2+jxCvbSUYkW2HH0b8c9OxY+2dZVo3VY2mDOqBCl84uQV+TH3Sya/UzpW5bOgckKDqOYKlNOZDF9CGTplvCyELBeTTxsuWw7K2q/B71DbNxWTXkKl5NLXcodz+j7EyCIrjF4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=3F3mWKhl; arc=none smtp.client-ip=113.46.200.224 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="3F3mWKhl" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=MtNLEajdnFZk77rmosl4teGaz+2YGNzPlWlT6lzjbLc=; b=3F3mWKhlNPlEXNHKzkpGXpNDOyaw8rdgx+JrAhhxrNBq5OqaEBShTmGLif6Hdc7yZGO46zqFr vbziZwooOHOkwaN90irMTDF51DCsh7VHeexh8gVGj7fcKEmmDQxcyp95P9Jej290j84K2RHG9Ka 3FVfbWRiwZ9Z/d7dHIDUbTs= Received: from mail.maildlp.com (unknown [172.19.163.200]) by canpmsgout09.his.huawei.com (SkyGuard) with ESMTPS id 4hQf0T5kL1z1cyQ2; Thu, 20 Aug 2026 17:54:01 +0800 (CST) Received: from whupemk200012.china.huawei.com (unknown [7.152.185.169]) by mail.maildlp.com (Postfix) with ESMTPS id 05C214055B; Thu, 20 Aug 2026 18:04:43 +0800 (CST) Received: from [10.174.177.223] (10.174.177.223) by whupemk200012.china.huawei.com (7.152.185.169) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.45; Thu, 20 Aug 2026 18:04:41 +0800 Message-ID: <9a80f88e-c8a6-44fb-a7b2-7cdbaa3bba24@huawei.com> Date: Thu, 20 Aug 2026 18:04:40 +0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] net: iptunnel: fix stale transport header during tunnel decapsulation To: Eric Dumazet CC: , , , , , , , , , , , , , , , References: <20260813033855.3372172-1-dongchenchen2@huawei.com> <53e86f6f-43b9-4e06-b185-1344f69cd650@huawei.com> From: "dongchenchen (A)" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: kwepems500001.china.huawei.com (7.221.188.70) To whupemk200012.china.huawei.com (7.152.185.169) 在 2026/8/20 17:16, Eric Dumazet 写道: > On Thu, Aug 20, 2026 at 10:58 AM dongchenchen (A) > wrote: >> >> >>> On Thu, Aug 13, 2026 at 5:30 AM Dong Chenchen wrote: >>>> >>>> Syzbot reported a crash in qdisc_pkt_len_segs_init() caused by a stale >>>> transport_header offset after tunnel decapsulation. >>>> >>>> BUG: unable to handle page fault for address: ffffed102091a42e >>>> Oops: Oops: 0000 [#1] SMP KASAN NOPTI >>>> CPU: 0 UID: 0 PID: 340 Comm: qdisc_uaf_repro Not tainted 7.2.0-rc4-00061-g248951ddc14d #256 PREEMPT(full) >>>> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 >>>> RIP: 0010:__asan_load2 >>>> >>>> qdisc_pkt_len_segs_init (net/core/dev.c:4145) >>>> __dev_queue_xmit (net/core/dev.c:4787) >>>> br_dev_queue_push_xmit (net/bridge/br_forward.c:53) >>>> br_handle_frame_finish (net/bridge/br_input.c:229) >>>> br_handle_frame (net/bridge/br_input.c:315) >>>> __netif_receive_skb_core.constprop.0 (net/core/dev.c:6099) >>>> __netif_receive_skb_list_core (net/core/dev.c:6287) >>>> netif_receive_skb_list_internal (net/core/dev.c:6445) >>>> napi_complete_done (net/core/dev.c:6813) >>>> gro_cell_poll (net/core/gro_cells.c:74) >>>> __napi_poll (net/core/dev.c:7735) >>>> net_rx_action (net/core/dev.c:7798 net/core/dev.c:7955) >>>> handle_softirqs (kernel/softirq.c:622) >>>> do_softirq (kernel/softirq.c:523 kernel/softirq.c:510 ) >>>> __local_bh_enable_ip (kernel/softirq.c:450) >>>> tun_get_user (drivers/net/tun.c:1986 (discriminator 1)) >>>> tun_chr_write_iter (drivers/net/tun.c:2032) >>>> >>>> The crash requires four conditions to line up: >>>> >>>> 1. The incoming packet is encapsulated and carries GSO metadata. The outer >>>> transport header offset is stored in skb->transport_header while the >>>> packet is still in the outer tunnel context. >>>> 2. The tunnel receiver strips the outer headers. skb->data is advanced to >>>> the inner frame, but skb->transport_header is left pointing to the >>>> now-removed outer L4 header, so it becomes a negative offset relative to >>>> the new data. >>>> 3. The inner frame is not delivered to the local IP stack. Instead, it >>>> is forwarded at L2 by a bridge or HSR, so ip_rcv_core() never runs and >>>> the transport header is not reset to the inner L4 offset. >>>> 4. The forwarding path calls __dev_queue_xmit(), which enters >>>> qdisc_pkt_len_segs_init(). That function computes the GSO header length >>>> from skb_transport_offset(skb). Because the offset is negative, the >>>> unsigned cast overflows and pskb_may_pull(skb, hdr_len + >>>> sizeof(struct tcphdr)) reads past the end of the skb, triggering a >>>> KASAN fault or page fault. >>>> >>>> Fix this by clearing skb->transport_header to the ~0U sentinel at the >>>> tunnel decapsulation boundary, after each tunnel receive function has >>>> finished all processing that needs the outer L4 header and before the skb >>>> is handed to GRO or the stack. The IP/GRO receive paths then set the >>>> transport header correctly when they parse the inner packet. >>>> >>>> Fixes: 7fb4c1967011 ("net: pull headers in qdisc_pkt_len_segs_init()") >>> >>> This Fixes: tag seems pretty random to me. Issue was present long >>> before that commit. >>> Next time, please be precise with the `Fixes:` tag; it's not decoration. >>> >> Thanks for your review. Sorry for the late reply. >> The stale transport header has been present since 1da177e4c3f4 >> ("Linux-2.6.12-rc2"), which is completely latent until >> 7fb4c1967011 ("net: pull headers in qdisc_pkt_len_segs_init()" >> was merged. >> >> From the perspective of the root cause introduced by the issue, >> we can use 1da177e4c3f4 ("Linux-2.6.12-rc2") as fixtag. >> >>> Also, calling skb_unset_transport_header(skb) directly from >>> gro_cells_receive() would make more sense and >>> your patch would be less intrusive. >>> >> >> gtp，sit use netif_rx to receive pkt. so modifying only gro_cells_receive >> cannot solve all the problems. netif_rx is widely >> used and is not only invoked by the tunnel driver, and serval path >> (such as genve encap) will reset transport header before netif_rx. >> Therefore, should we retain unset in the GTP/SIT tunnel? > > Hi Dong, > > 1) Regarding SIT: > > SIT decapsulates IPv6 over IPv4 (IPPROTO_IPV6). There is no outer L4 transport > header (no UDP/TCP), so skb->transport_header is not pointing to an > outer L4 header. > > 2) Regarding GTP: > > GTP is an L3-only point-to-point device (ARPHRD_NONE). It cannot be > enslaved by a bridge > or forwarded at L2; its packets always go through ip_rcv()/ip6_rcv() > where the headers > are properly parsed/reset, > Hi, Eric. Thanks for the review! I missed the rcv path in the commit message. With an ingress qdisc attached to gtp, the stale transport header will been consumed in sch_handle_ingress() and its not covered by gro_cells_receive() either. So maybe gtp is not safe by construction. gtp_encap_rcv gtp_rx //stale transport header __netif_rx __netif_receive_skb_core sch_handle_ingress qdisc_pkt_len_segs_init Best Regards Dong Chenchen > 3) Regarding Geneve: > > When skb->encapsulation is set, inner headers are already parsed and > qdisc_pkt_len_segs_init() > uses skb_inner_transport_offset(skb), not skb_transport_offset(skb). > > When skb->encapsulation is 0, it calls gro_cells_receive(). > > All L2 tunnel drivers that can be bridged/forwarded at L2 (vxlan, > geneve, bareudp, amt, etc.) > use gro_cells_receive(). > > IMO calling skb_unset_transport_header() directly in gro_cells_receive() > is clean and fixes all of them in one place. > > Thanks.