From patchwork Sat Mar 30 07:29:32 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: hujunwei X-Patchwork-Id: 1070625 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=huawei.com Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 44WVcp3xrfz9sRx for ; Sat, 30 Mar 2019 18:30:18 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730174AbfC3HaM (ORCPT ); Sat, 30 Mar 2019 03:30:12 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:5764 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726325AbfC3HaM (ORCPT ); Sat, 30 Mar 2019 03:30:12 -0400 Received: from DGGEMS405-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 4692232C626D7813BA63; Sat, 30 Mar 2019 15:30:10 +0800 (CST) Received: from [127.0.0.1] (10.184.191.73) by DGGEMS405-HUB.china.huawei.com (10.3.19.205) with Microsoft SMTP Server id 14.3.408.0; Sat, 30 Mar 2019 15:29:55 +0800 To: , , , , From: hujunwei Subject: [PATCH net] ipv6: Fix dangling pointer when ipv6 fragment CC: , , Message-ID: Date: Sat, 30 Mar 2019 15:29:32 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 Content-Language: en-US X-Originating-IP: [10.184.191.73] X-CFilter-Loop: Reflected Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Junwei Hu At the beginning of ip6_fragment func, the prevhdr pointer is obtained in the ip6_find_1stfragopt func. However, all the pointers pointing into skb header may change when calling skb_checksum_help func with skb->ip_summed = CHECKSUM_PARTIAL condition. The prevhdr pointe will be dangling if it is not reloaded after calling __skb_linearize func in skb_checksum_help func. Here, I add a variable, nexthdr_offset, to evaluate the offset, which does not changes even after calling __skb_linearize func. Fixes: 405c92f7a541 ("ipv6: add defensive check for CHECKSUM_PARTIAL skbs in ip_fragment") Signed-off-by: Junwei Hu Reported-by: Wenhao Zhang Reviewed-by: Zhiqiang Liu Reported-by: syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com ---  net/ipv6/ip6_output.c | 4 ++++  1 file changed, 4 insertions(+) diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index edbd12067170..6db3c60b3b66 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -606,12 +606,14 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,      __be32 frag_id;      int ptr, offset = 0, err = 0;      u8 *prevhdr, nexthdr = 0; +    u8 nexthdr_offset;        err = ip6_find_1stfragopt(skb, &prevhdr);      if (err < 0)          goto fail;      hlen = err;      nexthdr = *prevhdr; +    nexthdr_offset = prevhdr - skb_network_header(skb);        mtu = ip6_skb_dst_mtu(skb);   @@ -646,6 +648,8 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,          (err = skb_checksum_help(skb)))          goto fail;   +    prevhdr = skb_network_header(skb) + nexthdr_offset; +      hroom = LL_RESERVED_SPACE(rt->dst.dev);      if (skb_has_frag_list(skb)) {          unsigned int first_len = skb_pagelen(skb);