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 X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5323C43381 for ; Sun, 31 Mar 2019 09:05:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9A39A2146F for ; Sun, 31 Mar 2019 09:05:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726901AbfCaJFb (ORCPT ); Sun, 31 Mar 2019 05:05:31 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:59738 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726710AbfCaJFa (ORCPT ); Sun, 31 Mar 2019 05:05:30 -0400 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 556E12B0468991598D8D; Sun, 31 Mar 2019 17:05:28 +0800 (CST) Received: from [127.0.0.1] (10.184.191.73) by DGGEMS402-HUB.china.huawei.com (10.3.19.202) with Microsoft SMTP Server id 14.3.408.0; Sun, 31 Mar 2019 17:05:19 +0800 Subject: [PATCH v2 net] ipv6: Fix dangling pointer when ipv6 fragment From: hujunwei To: , , , , CC: , , , References: Message-ID: <9104f44b-2ce0-7be9-2fca-8b6c12abbb86@huawei.com> Date: Sun, 31 Mar 2019 17:04:29 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [10.184.191.73] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 Reported-by: syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com Reviewed-by: Zhiqiang Liu --- V1->V2: - change nexthdr_offset to unsigned int - add Reported-by: syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com  net/ipv6/ip6_output.c | 4 +++-  1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index edbd12067170..e51f3c648b09 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -601,7 +601,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,                  inet6_sk(skb->sk) : NULL;      struct ipv6hdr *tmp_hdr;      struct frag_hdr *fh; -    unsigned int mtu, hlen, left, len; +    unsigned int mtu, hlen, left, len, nexthdr_offset;      int hroom, troom;      __be32 frag_id;      int ptr, offset = 0, err = 0; @@ -612,6 +612,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,          goto fail;      hlen = err;      nexthdr = *prevhdr; +    nexthdr_offset = prevhdr - skb_network_header(skb);        mtu = ip6_skb_dst_mtu(skb);   @@ -646,6 +647,7 @@ 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); -- 2.19.1