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 3527BC636CC for ; Fri, 3 Feb 2023 10:21:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232279AbjBCKV5 (ORCPT ); Fri, 3 Feb 2023 05:21:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44234 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233345AbjBCKVz (ORCPT ); Fri, 3 Feb 2023 05:21:55 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 542099E9F6 for ; Fri, 3 Feb 2023 02:21:35 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 30F6561EBA for ; Fri, 3 Feb 2023 10:21:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1B54FC433EF; Fri, 3 Feb 2023 10:21:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1675419694; bh=n7iZVRZCPGxn55ZItX8hVgljGjXwUKaTrOHJAspUczE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=zA4OK/ZHlZQtVzD5TriopQL6qI7DbTntUyHsZ0oHQz65mlmRjerh1fmK8D4Ux3tY6 VG35Tc/6pWjjsIvdOn5wqGeA7BetNU2x3MQa5bgKbNtoXN5PaaXEJCF9TiRfj4YIZ5 1EoDUDb24BpOr2D5gRkz2CTT8ps8Ak9IDbrsvT80= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot , Eric Dumazet , Jakub Kicinski , Tudor Ambarus Subject: [PATCH 4.19 79/80] ipv6: ensure sane device mtu in tunnels Date: Fri, 3 Feb 2023 11:13:13 +0100 Message-Id: <20230203101018.635953965@linuxfoundation.org> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230203101015.263854890@linuxfoundation.org> References: <20230203101015.263854890@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Eric Dumazet commit d89d7ff01235f218dad37de84457717f699dee79 upstream. Another syzbot report [1] with no reproducer hints at a bug in ip6_gre tunnel (dev:ip6gretap0) Since ipv6 mcast code makes sure to read dev->mtu once and applies a sanity check on it (see commit b9b312a7a451 "ipv6: mcast: better catch silly mtu values"), a remaining possibility is that a layer is able to set dev->mtu to an underflowed value (high order bit set). This could happen indeed in ip6gre_tnl_link_config_route(), ip6_tnl_link_config() and ipip6_tunnel_bind_dev() Make sure to sanitize mtu value in a local variable before it is written once on dev->mtu, as lockless readers could catch wrong temporary value. [1] skbuff: skb_over_panic: text:ffff80000b7a2f38 len:40 put:40 head:ffff000149dcf200 data:ffff000149dcf2b0 tail:0xd8 end:0xc0 dev:ip6gretap0 ------------[ cut here ]------------ kernel BUG at net/core/skbuff.c:120 Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP Modules linked in: CPU: 1 PID: 10241 Comm: kworker/1:1 Not tainted 6.0.0-rc7-syzkaller-18095-gbbed346d5a96 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/30/2022 Workqueue: mld mld_ifc_work pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : skb_panic+0x4c/0x50 net/core/skbuff.c:116 lr : skb_panic+0x4c/0x50 net/core/skbuff.c:116 sp : ffff800020dd3b60 x29: ffff800020dd3b70 x28: 0000000000000000 x27: ffff00010df2a800 x26: 00000000000000c0 x25: 00000000000000b0 x24: ffff000149dcf200 x23: 00000000000000c0 x22: 00000000000000d8 x21: ffff80000b7a2f38 x20: ffff00014c2f7800 x19: 0000000000000028 x18: 00000000000001a9 x17: 0000000000000000 x16: ffff80000db49158 x15: ffff000113bf1a80 x14: 0000000000000000 x13: 00000000ffffffff x12: ffff000113bf1a80 x11: ff808000081c0d5c x10: 0000000000000000 x9 : 73f125dc5c63ba00 x8 : 73f125dc5c63ba00 x7 : ffff800008161d1c x6 : 0000000000000000 x5 : 0000000000000080 x4 : 0000000000000001 x3 : 0000000000000000 x2 : ffff0001fefddcd0 x1 : 0000000100000000 x0 : 0000000000000089 Call trace: skb_panic+0x4c/0x50 net/core/skbuff.c:116 skb_over_panic net/core/skbuff.c:125 [inline] skb_put+0xd4/0xdc net/core/skbuff.c:2049 ip6_mc_hdr net/ipv6/mcast.c:1714 [inline] mld_newpack+0x14c/0x270 net/ipv6/mcast.c:1765 add_grhead net/ipv6/mcast.c:1851 [inline] add_grec+0xa20/0xae0 net/ipv6/mcast.c:1989 mld_send_cr+0x438/0x5a8 net/ipv6/mcast.c:2115 mld_ifc_work+0x38/0x290 net/ipv6/mcast.c:2653 process_one_work+0x2d8/0x504 kernel/workqueue.c:2289 worker_thread+0x340/0x610 kernel/workqueue.c:2436 kthread+0x12c/0x158 kernel/kthread.c:376 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860 Code: 91011400 aa0803e1 a90027ea 94373093 (d4210000) Fixes: c12b395a4664 ("gre: Support GRE over IPv6") Reported-by: syzbot Signed-off-by: Eric Dumazet Link: https://lore.kernel.org/r/20221024020124.3756833-1-eric.dumazet@gmail.com Signed-off-by: Jakub Kicinski [ta: Backport patch for stable kernels < 5.10.y. Fix conflict in net/ipv6/ip6_tunnel.c, mtu initialized with: mtu = rt->dst.dev->mtu - t_hlen;] Cc: # 4.14.y, 4.19.y, 5.4.y Signed-off-by: Tudor Ambarus Signed-off-by: Greg Kroah-Hartman --- net/ipv6/ip6_gre.c | 12 +++++++----- net/ipv6/ip6_tunnel.c | 10 ++++++---- net/ipv6/sit.c | 8 +++++--- 3 files changed, 18 insertions(+), 12 deletions(-) --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -1154,14 +1154,16 @@ static void ip6gre_tnl_link_config_route dev->needed_headroom = dst_len; if (set_mtu) { - dev->mtu = rt->dst.dev->mtu - t_hlen; + int mtu = rt->dst.dev->mtu - t_hlen; + if (!(t->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT)) - dev->mtu -= 8; + mtu -= 8; if (dev->type == ARPHRD_ETHER) - dev->mtu -= ETH_HLEN; + mtu -= ETH_HLEN; - if (dev->mtu < IPV6_MIN_MTU) - dev->mtu = IPV6_MIN_MTU; + if (mtu < IPV6_MIN_MTU) + mtu = IPV6_MIN_MTU; + WRITE_ONCE(dev->mtu, mtu); } } ip6_rt_put(rt); --- a/net/ipv6/ip6_tunnel.c +++ b/net/ipv6/ip6_tunnel.c @@ -1435,6 +1435,7 @@ static void ip6_tnl_link_config(struct i struct __ip6_tnl_parm *p = &t->parms; struct flowi6 *fl6 = &t->fl.u.ip6; int t_hlen; + int mtu; memcpy(dev->dev_addr, &p->laddr, sizeof(struct in6_addr)); memcpy(dev->broadcast, &p->raddr, sizeof(struct in6_addr)); @@ -1477,12 +1478,13 @@ static void ip6_tnl_link_config(struct i dev->hard_header_len = rt->dst.dev->hard_header_len + t_hlen; - dev->mtu = rt->dst.dev->mtu - t_hlen; + mtu = rt->dst.dev->mtu - t_hlen; if (!(t->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT)) - dev->mtu -= 8; + mtu -= 8; - if (dev->mtu < IPV6_MIN_MTU) - dev->mtu = IPV6_MIN_MTU; + if (mtu < IPV6_MIN_MTU) + mtu = IPV6_MIN_MTU; + WRITE_ONCE(dev->mtu, mtu); } ip6_rt_put(rt); } --- a/net/ipv6/sit.c +++ b/net/ipv6/sit.c @@ -1082,10 +1082,12 @@ static void ipip6_tunnel_bind_dev(struct if (tdev && !netif_is_l3_master(tdev)) { int t_hlen = tunnel->hlen + sizeof(struct iphdr); + int mtu; - dev->mtu = tdev->mtu - t_hlen; - if (dev->mtu < IPV6_MIN_MTU) - dev->mtu = IPV6_MIN_MTU; + mtu = tdev->mtu - t_hlen; + if (mtu < IPV6_MIN_MTU) + mtu = IPV6_MIN_MTU; + WRITE_ONCE(dev->mtu, mtu); } }