From nobody Fri Feb 13 17:29:15 2026 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 3E822E7D0A2 for ; Thu, 21 Sep 2023 20:59:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232039AbjIUU76 (ORCPT ); Thu, 21 Sep 2023 16:59:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36010 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230461AbjIUU7Z (ORCPT ); Thu, 21 Sep 2023 16:59:25 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 54617B05A8 for ; Thu, 21 Sep 2023 11:08:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1695319716; 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; bh=R9gyNPaV4zuqNuZuo/vx9UBWKean5gdHBlkkwmtG0SQ=; b=XOT1ZkquHLDF5KYxecldIkAlvz1YAy9XUOfXoxfhBbLGEdCHnCqL6d0ANRy24G6Iz695TE y2EdXZsBVzp4Y5PQLRAB8P6iZyEcBQ1dsT9h2GrpBXxjgS1UomGJgdYDVxT+2ErLeoQuuV b5CT83oWz75Gxo23TbMyR8WycKrz0jU= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-515-0ruNuvMkOS6GtcLt8Ah2FA-1; Thu, 21 Sep 2023 06:41:22 -0400 X-MC-Unique: 0ruNuvMkOS6GtcLt8Ah2FA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BBA57101A529; Thu, 21 Sep 2023 10:41:21 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.42.28.216]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5A0D751E3; Thu, 21 Sep 2023 10:41:20 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells To: netdev@vger.kernel.org cc: dhowells@redhat.com, syzbot+62cbf263225ae13ff153@syzkaller.appspotmail.com, Eric Dumazet , Willem de Bruijn , "David S. Miller" , David Ahern , Paolo Abeni , Jakub Kicinski , bpf@vger.kernel.org, syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org Subject: [PATCH net v3] ipv4, ipv6: Fix handling of transhdrlen in __ip{,6}_append_data() MIME-Version: 1.0 Content-ID: <730407.1695292879.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Thu, 21 Sep 2023 11:41:19 +0100 Message-ID: <730408.1695292879@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" =20 Including the transhdrlen in length is a problem when the packet is partially filled (e.g. something like send(MSG_MORE) happened previously) when appending to an IPv4 or IPv6 packet as we don't want to repeat the transport header or account for it twice. This can happen under some circumstances, such as splicing into an L2TP socket. The symptom observed is a warning in __ip6_append_data(): WARNING: CPU: 1 PID: 5042 at net/ipv6/ip6_output.c:1800 __ip6_append_da= ta.isra.0+0x1be8/0x47f0 net/ipv6/ip6_output.c:1800 that occurs when MSG_SPLICE_PAGES is used to append more data to an already partially occupied skbuff. The warning occurs when 'copy' is larger than the amount of data in the message iterator. This is because the requested length includes the transport header length when it shouldn't. This can be triggered by, for example: sfd =3D socket(AF_INET6, SOCK_DGRAM, IPPROTO_L2TP); bind(sfd, ...); // ::1 connect(sfd, ...); // ::1 port 7 send(sfd, buffer, 4100, MSG_MORE); sendfile(sfd, dfd, NULL, 1024); Fix this by only adding transhdrlen into the length if the write queue is empty in l2tp_ip6_sendmsg(), analogously to how UDP does things. l2tp_ip_sendmsg() looks like it won't suffer from this problem as it builds the UDP packet itself. Fixes: a32e0eec7042 ("l2tp: introduce L2TPv3 IP encapsulation support for I= Pv6") Reported-by: syzbot+62cbf263225ae13ff153@syzkaller.appspotmail.com Link: https://lore.kernel.org/r/0000000000001c12b30605378ce8@google.com/ Suggested-by: Willem de Bruijn Signed-off-by: David Howells cc: Eric Dumazet cc: Willem de Bruijn cc: "David S. Miller" cc: David Ahern cc: Paolo Abeni cc: Jakub Kicinski cc: netdev@vger.kernel.org cc: bpf@vger.kernel.org cc: syzkaller-bugs@googlegroups.com Reviewed-by: Eric Dumazet Reviewed-by: Willem de Bruijn --- net/l2tp/l2tp_ip6.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c index ed8ebb6f5909..11f3d375cec0 100644 --- a/net/l2tp/l2tp_ip6.c +++ b/net/l2tp/l2tp_ip6.c @@ -507,7 +507,6 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msg= hdr *msg, size_t len) */ if (len > INT_MAX - transhdrlen) return -EMSGSIZE; - ulen =3D len + transhdrlen; =20 /* Mirror BSD error message compatibility */ if (msg->msg_flags & MSG_OOB) @@ -628,6 +627,7 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msg= hdr *msg, size_t len) =20 back_from_confirm: lock_sock(sk); + ulen =3D len + skb_queue_empty(&sk->sk_write_queue) ? transhdrlen : 0; err =3D ip6_append_data(sk, ip_generic_getfrag, msg, ulen, transhdrlen, &ipc6, &fl6, (struct rt6_info *)dst,