From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout06.his.huawei.com (canpmsgout06.his.huawei.com [113.46.200.221]) (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 8BD1F23EAA6 for ; Tue, 25 Aug 2026 09:41:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.221 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787650893; cv=none; b=pcKXgef7rKFUnPHfrxq65wNyUBqqldnCQUYW7ySpBy5uXtk6uWCdRlZYYnwKRD4wy/qF7akaq5PxsbjLi16soW9UJcM96hEcqGU4wV/vDu8QPdmynj8u90HuUqrr4I488ud3JaM6G1axaob3rTa5Tofx9Ftjgg4CIvggtVGeTq8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787650893; c=relaxed/simple; bh=UjXta4/qBzNdjtnUmPdRD+qgROJ+TLF0pMSC3UgKxRo=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=cjw5xqU5FtXdYLdfuLwAb99wJLRzQEmfSLxk49gXZ1WwQ6wnUB5a4+ayaOYOKmtDW/+NYapR8uP/pQaA2/f+W5FBtb9fJ6ZD3mMNFglE/iIrETwfKh0ChMY3QZtKUWpKf3Gf3egzvyF9AbgATnJ91l2VWbyTiyMRe/uA3nN+3co= 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=WXkWr5ow; arc=none smtp.client-ip=113.46.200.221 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="WXkWr5ow" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=mk7nOAf+e/FaROUlTpjPV2bCZtnbby00JME7ZoGRdjo=; b=WXkWr5owgrpDitcpgeAa6HQ9gycStvSusa5wwIw+VGkmuNUX66oGX+Ch62Hl2hBd/sc0Q9OR7 PI6ji8SDKIeync3JXAmOONwdSyLumEBM9LPN7vXlNnuWHIAlPCS6L+bPD91AWkSQx/g5vPQgnY+ qREC+A3Ro3WN+HPnZCgUkgI= Received: from mail.maildlp.com (unknown [172.19.162.144]) by canpmsgout06.his.huawei.com (SkyGuard) with ESMTPS id 4hTjF75QZfzRhR0; Tue, 25 Aug 2026 17:30:35 +0800 (CST) Received: from whupemk200012.china.huawei.com (unknown [7.152.185.169]) by mail.maildlp.com (Postfix) with ESMTPS id CE40340538; Tue, 25 Aug 2026 17:41:18 +0800 (CST) Received: from localhost.localdomain (10.50.85.175) 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; Tue, 25 Aug 2026 17:41:17 +0800 From: Dong Chenchen To: , , , , , , , CC: , , , , , Dong Chenchen , Subject: [PATCH net v2] net: iptunnel: fix stale transport header during tunnel decapsulation Date: Tue, 25 Aug 2026 17:50:00 +0800 Message-ID: <20260825095000.1461124-1-dongchenchen2@huawei.com> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: kwepems100001.china.huawei.com (7.221.188.238) To whupemk200012.china.huawei.com (7.152.185.169) 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 issue is completely latent until qdisc read transport header in commit 7fb4c1967011 ("net: pull headers in qdisc_pkt_len_segs_init()"). 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. The issue specifically requires GSO packets (shinfo->gso_size != 0), which are processed/aggregated through gro_cells. Fix this by clearing transport_header to the ~0U sentinel in gro_cell for all tunnnel driver. GTP does not support GRO/GSO, drop the evil GSO packets in GTP directly. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+83181a31faf9455499c5@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/69de2bee.a00a0220.475f0.0041.GAE@google.com/T/ Suggested-by: Eric Dumazet Signed-off-by: Dong Chenchen --- drivers/net/gtp.c | 5 +++++ include/linux/skbuff.h | 5 +++++ net/core/gro_cells.c | 2 ++ 3 files changed, 12 insertions(+) diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c index 9a12cc53da00..fbf617b1acc9 100644 --- a/drivers/net/gtp.c +++ b/drivers/net/gtp.c @@ -312,6 +312,11 @@ static int gtp_inner_proto(struct sk_buff *skb, unsigned int hdrlen, static int gtp_rx(struct pdp_ctx *pctx, struct sk_buff *skb, unsigned int hdrlen, unsigned int role, __u16 inner_proto) { + if (skb_is_gso(skb)) { + netdev_dbg(pctx->dev, "GSO is not support in GTP\n"); + goto err; + } + if (!gtp_check_ms(skb, pctx, hdrlen, role, inner_proto)) { netdev_dbg(pctx->dev, "No PDP ctx for this MS\n"); return 1; diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 22eda1d54a0e..626bbb9bae1a 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -3082,6 +3082,11 @@ static inline bool skb_transport_header_was_set(const struct sk_buff *skb) return skb->transport_header != (typeof(skb->transport_header))~0U; } +static inline void skb_unset_transport_header(struct sk_buff *skb) +{ + skb->transport_header = (typeof(skb->transport_header))~0U; +} + static inline unsigned char *skb_transport_header(const struct sk_buff *skb) { DEBUG_NET_WARN_ON_ONCE(!skb_transport_header_was_set(skb)); diff --git a/net/core/gro_cells.c b/net/core/gro_cells.c index 1b84385c04bd..d8c0a2867120 100644 --- a/net/core/gro_cells.c +++ b/net/core/gro_cells.c @@ -22,6 +22,8 @@ int gro_cells_receive(struct gro_cells *gcells, struct sk_buff *skb) if (unlikely(!(dev->flags & IFF_UP))) goto drop; + skb_unset_transport_header(skb); + if (!gcells->cells || skb_cloned(skb) || netif_elide_gro(dev)) { res = netif_rx(skb); goto unlock; -- 2.25.1