From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout07.his.huawei.com (canpmsgout07.his.huawei.com [113.46.200.222]) (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 6DBAA3DE429 for ; Thu, 20 Aug 2026 08:58:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.222 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787216334; cv=none; b=rrg6HSmxNNnEMCsSBgGEq8Tga1324MwrMIZv7W7qs63fKs4bt9uEgjWomH55ktTQxmkVGr8fgWAJ/Vq2qbVM+GKKTUbixDq3/FcTn9G9I5PcYDLDjiQWoq4LdT3EfJs/ZJCW2IycrEjJh4EOMYahkP4Che+ssjWFX/EJ4vDczmc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787216334; c=relaxed/simple; bh=PSEE1ZHrpIrOGqhtKVFTLlJfsbxfnJmnD7XLbDtuRVM=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=Gaf5KHKRRtvqOWzSIAikxFLzCdIrcyUeWqQ40F+mdKrVAyqssw4+Z0pIPYrwXBVv1dHdvxb1PjzdAe6y4M2bOs/TWx9w3FvP9DilyZ4IHU4+f6hUPkEgFtPwag+SFlO+RT0WTabYU4wFuzMUVCGKhAC/bN4tqbkapsJZLkmwS0o= 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=FukmzVEd; arc=none smtp.client-ip=113.46.200.222 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="FukmzVEd" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=HjlpB81NplEGM8TmYOQ3yWrAodWhSKbszGQgPWMnYx8=; b=FukmzVEdGFs1NiSxH2WplLUQZedeebD5vtAS/y3UrHsLbOPdmvKvJrLDWfiZEI702R8buha4G seytvtgbA8lgvvhbtLFUlDJIkaRQfiY4JDRHtAZ7aSMgWXhCCqUKntZ7q71VDwoH6UdDIA8bX6e gFbsLWn8Eq64VnucH46I+q8= Received: from mail.maildlp.com (unknown [172.19.163.15]) by canpmsgout07.his.huawei.com (SkyGuard) with ESMTPS id 4hQcXH0tB1zLlTg; Thu, 20 Aug 2026 16:47:59 +0800 (CST) Received: from whupemk200012.china.huawei.com (unknown [7.152.185.169]) by mail.maildlp.com (Postfix) with ESMTPS id EDD5140578; Thu, 20 Aug 2026 16:58:40 +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 16:58:39 +0800 Message-ID: <53e86f6f-43b9-4e06-b185-1344f69cd650@huawei.com> Date: Thu, 20 Aug 2026 16:58:38 +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> From: "dongchenchen (A)" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: kwepems100002.china.huawei.com (7.221.188.206) To whupemk200012.china.huawei.com (7.152.185.169) > 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? Best Regards Dong Chenchen > pw-bot: cr