releases/4.19.35/ipv6-fix-dangling-pointer-when-ipv6-fragment.patch

   1 From d70f0c5c48ecf74f6d6a5ef0b786419999d46723 Mon Sep 17 00:00:00 2001
   2 From: Junwei Hu <hujunwei4@huawei.com>
   3 Date: Tue, 2 Apr 2019 19:38:04 +0800
   4 Subject: ipv6: Fix dangling pointer when ipv6 fragment
   5
   6 [ Upstream commit ef0efcd3bd3fd0589732b67fb586ffd3c8705806 ]
   7
   8 At the beginning of ip6_fragment func, the prevhdr pointer is
   9 obtained in the ip6_find_1stfragopt func.
  10 However, all the pointers pointing into skb header may change
  11 when calling skb_checksum_help func with
  12 skb->ip_summed = CHECKSUM_PARTIAL condition.
  13 The prevhdr pointe will be dangling if it is not reloaded after
  14 calling __skb_linearize func in skb_checksum_help func.
  15
  16 Here, I add a variable, nexthdr_offset, to evaluate the offset,
  17 which does not changes even after calling __skb_linearize func.
  18
  19 Fixes: 405c92f7a541 ("ipv6: add defensive check for CHECKSUM_PARTIAL skbs in ip_fragment")
  20 Signed-off-by: Junwei Hu <hujunwei4@huawei.com>
  21 Reported-by: Wenhao Zhang <zhangwenhao8@huawei.com>
  22 Reported-by: syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com
  23 Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
  24 Acked-by: Martin KaFai Lau <kafai@fb.com>
  25 Signed-off-by: David S. Miller <davem@davemloft.net>
  26 Signed-off-by: Sasha Levin <sashal@kernel.org>
  27 ---
  28  net/ipv6/ip6_output.c | 4 +++-
  29  1 file changed, 3 insertions(+), 1 deletion(-)
  30
  31 diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
  32 index 0bb87f3a10c7..eed9231c90ad 100644
  33 --- a/net/ipv6/ip6_output.c
  34 +++ b/net/ipv6/ip6_output.c
  35 @@ -587,7 +587,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
  36                                 inet6_sk(skb->sk) : NULL;
  37         struct ipv6hdr *tmp_hdr;
  38         struct frag_hdr *fh;
  39 -       unsigned int mtu, hlen, left, len;
  40 +       unsigned int mtu, hlen, left, len, nexthdr_offset;
  41         int hroom, troom;
  42         __be32 frag_id;
  43         int ptr, offset = 0, err = 0;
  44 @@ -598,6 +598,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
  45                 goto fail;
  46         hlen = err;
  47         nexthdr = *prevhdr;
  48 +       nexthdr_offset = prevhdr - skb_network_header(skb);
  49
  50         mtu = ip6_skb_dst_mtu(skb);
  51
  52 @@ -632,6 +633,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
  53             (err = skb_checksum_help(skb)))
  54                 goto fail;
  55
  56 +       prevhdr = skb_network_header(skb) + nexthdr_offset;
  57         hroom = LL_RESERVED_SPACE(rt->dst.dev);
  58         if (skb_has_frag_list(skb)) {
  59                 unsigned int first_len = skb_pagelen(skb);
  60 --
  61 2.19.1
  62