Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Junwei Hu <hujunwei4@huawei.com>,
        Wenhao Zhang <zhangwenhao8@huawei.com>,
        syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com,
        Zhiqiang Liu <liuzhiqiang26@huawei.com>,
        Martin KaFai Lau <kafai@fb.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.4 077/168] ipv6: Fix dangling pointer when ipv6 fragment
Date:   Wed, 24 Apr 2019 19:08:41 +0200
Message-Id: <20190424170928.504455385@linuxfoundation.org>
In-Reply-To: <20190424170923.452349382@linuxfoundation.org>
References: <20190424170923.452349382@linuxfoundation.org>
User-Agent: quilt/0.66
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Junwei Hu <hujunwei4@huawei.com>

[ Upstream commit ef0efcd3bd3fd0589732b67fb586ffd3c8705806 ]

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 <hujunwei4@huawei.com>
Reported-by: Wenhao Zhang <zhangwenhao8@huawei.com>
Reported-by: syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com
Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/ip6_output.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -575,7 +575,7 @@ int ip6_fragment(struct net *net, struct
 				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;
@@ -586,6 +586,7 @@ int ip6_fragment(struct net *net, struct
 		goto fail;
 	hlen = err;
 	nexthdr = *prevhdr;
+	nexthdr_offset = prevhdr - skb_network_header(skb);
 
 	mtu = ip6_skb_dst_mtu(skb);
 
@@ -620,6 +621,7 @@ int ip6_fragment(struct net *net, struct
 	    (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)) {
 		int first_len = skb_pagelen(skb);