Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754608AbdDJQFf (ORCPT ); Mon, 10 Apr 2017 12:05:35 -0400 Received: from mx2.suse.de ([195.135.220.15]:37771 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754232AbdDJPeK (ORCPT ); Mon, 10 Apr 2017 11:34:10 -0400 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Florian Westphal , Hannes Frederic Sowa , "David S . Miller" , Jiri Slaby Subject: [PATCH 3.12 033/142] ipv6: avoid write to a possibly cloned skb Date: Mon, 10 Apr 2017 17:31:54 +0200 Message-Id: <4c02875620b969892f5895a5beb409634ba32e19.1491838390.git.jslaby@suse.cz> X-Mailer: git-send-email 2.12.2 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2148 Lines: 68 From: Florian Westphal 3.12-stable review patch. If anyone has any objections, please let me know. =============== [ Upstream commit 79e49503efe53a8c51d8b695bedc8a346c5e4a87 ] ip6_fragment, in case skb has a fraglist, checks if the skb is cloned. If it is, it will move to the 'slow path' and allocates new skbs for each fragment. However, right before entering the slowpath loop, it updates the nexthdr value of the last ipv6 extension header to NEXTHDR_FRAGMENT, to account for the fragment header that will be inserted in the new ipv6-fragment skbs. In case original skb is cloned this munges nexthdr value of another skb. Avoid this by doing the nexthdr update for each of the new fragment skbs separately. This was observed with tcpdump on a bridge device where netfilter ipv6 reassembly is active: tcpdump shows malformed fragment headers as the l4 header (icmpv6, tcp, etc). is decoded as a fragment header. Cc: Hannes Frederic Sowa Reported-by: Andreas Karis Signed-off-by: Florian Westphal Signed-off-by: David S. Miller Signed-off-by: Jiri Slaby --- net/ipv6/ip6_output.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index f5f86850a305..c5db1d52d542 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -716,7 +716,6 @@ slow_path: * Fragment the datagram. */ - *prevhdr = NEXTHDR_FRAGMENT; hroom = LL_RESERVED_SPACE(rt->dst.dev); troom = rt->dst.dev->needed_tailroom; @@ -724,6 +723,8 @@ slow_path: * Keep copying data until we run out. */ while(left > 0) { + u8 *fragnexthdr_offset; + len = left; /* IF: it doesn't fit, use 'mtu' - the data space left */ if (len > mtu) @@ -770,6 +771,10 @@ slow_path: */ skb_copy_from_linear_data(skb, skb_network_header(frag), hlen); + fragnexthdr_offset = skb_network_header(frag); + fragnexthdr_offset += prevhdr - skb_network_header(skb); + *fragnexthdr_offset = NEXTHDR_FRAGMENT; + /* * Build fragment header. */ -- 2.12.2