Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751883AbdFAPyH (ORCPT ); Thu, 1 Jun 2017 11:54:07 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:33979 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752329AbdFAPpT (ORCPT ); Thu, 1 Jun 2017 11:45:19 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Eric Dumazet" , "Andrey Konovalov" , "David S. Miller" , "" Date: Thu, 01 Jun 2017 16:43:16 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 212/212] ipv6: fix out of bound writes in __ip6_append_data() In-Reply-To: X-SA-Exim-Connect-IP: 82.70.136.246 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2012 Lines: 65 3.16.44-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet commit 232cd35d0804cc241eb887bb8d4d9b3b9881c64a upstream. Andrey Konovalov and idaifish@gmail.com reported crashes caused by one skb shared_info being overwritten from __ip6_append_data() Andrey program lead to following state : copy -4200 datalen 2000 fraglen 2040 maxfraglen 2040 alloclen 2048 transhdrlen 0 offset 0 fraggap 6200 The skb_copy_and_csum_bits(skb_prev, maxfraglen, data + transhdrlen, fraggap, 0); is overwriting skb->head and skb_shared_info Since we apparently detect this rare condition too late, move the code earlier to even avoid allocating skb and risking crashes. Once again, many thanks to Andrey and syzkaller team. Signed-off-by: Eric Dumazet Reported-by: Andrey Konovalov Tested-by: Andrey Konovalov Reported-by: Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/ipv6/ip6_output.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -1367,6 +1367,11 @@ alloc_new_skb: */ alloclen += sizeof(struct frag_hdr); + copy = datalen - transhdrlen - fraggap; + if (copy < 0) { + err = -EINVAL; + goto error; + } if (transhdrlen) { skb = sock_alloc_send_skb(sk, alloclen + hh_len, @@ -1419,13 +1424,9 @@ alloc_new_skb: data += fraggap; pskb_trim_unique(skb_prev, maxfraglen); } - copy = datalen - transhdrlen - fraggap; - - if (copy < 0) { - err = -EINVAL; - kfree_skb(skb); - goto error; - } else if (copy > 0 && getfrag(from, data + transhdrlen, offset, copy, fraggap, skb) < 0) { + if (copy > 0 && + getfrag(from, data + transhdrlen, offset, + copy, fraggap, skb) < 0) { err = -EFAULT; kfree_skb(skb); goto error;