CVE-2017-9242-ipv6-fix-out-of-bound-writes-in-__ip6_append_data.patch

   1 From 2bb2c56a2089211713a7b1fb379cce741f65ea9e Mon Sep 17 00:00:00 2001
   2 From: Eric Dumazet <edumazet@google.com>
   3 Date: Fri, 19 May 2017 14:17:48 -0700
   4 Subject: [PATCH] ipv6: fix out of bound writes in __ip6_append_data()
   5 MIME-Version: 1.0
   6 Content-Type: text/plain; charset=UTF-8
   7 Content-Transfer-Encoding: 8bit
   8
   9 Andrey Konovalov and idaifish@gmail.com reported crashes caused by
  10 one skb shared_info being overwritten from __ip6_append_data()
  11
  12 Andrey program lead to following state :
  13
  14 copy -4200 datalen 2000 fraglen 2040
  15 maxfraglen 2040 alloclen 2048 transhdrlen 0 offset 0 fraggap 6200
  16
  17 The skb_copy_and_csum_bits(skb_prev, maxfraglen, data + transhdrlen,
  18 fraggap, 0); is overwriting skb->head and skb_shared_info
  19
  20 Since we apparently detect this rare condition too late, move the
  21 code earlier to even avoid allocating skb and risking crashes.
  22
  23 Once again, many thanks to Andrey and syzkaller team.
  24
  25 Signed-off-by: Eric Dumazet <edumazet@google.com>
  26 Reported-by: Andrey Konovalov <andreyknvl@google.com>
  27 Tested-by: Andrey Konovalov <andreyknvl@google.com>
  28 Reported-by: <idaifish@gmail.com>
  29 Signed-off-by: David S. Miller <davem@davemloft.net>
  30
  31 CVE-2017-9242
  32
  33 (cherry-picked from  232cd35d0804cc241eb887bb8d4d9b3b9881c64a)
  34 Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
  35 Acked-by: Colin King <colin.king@canonical.com>
  36 Acked-by: Andy Whitcroft <andy.whitcroft@canonical.com>
  37 Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
  38
  39 Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
  40 ---
  41  net/ipv6/ip6_output.c | 15 ++++++++-------
  42  1 file changed, 8 insertions(+), 7 deletions(-)
  43
  44 diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
  45 index 8f0814d301aa..135ee573eaef 100644
  46 --- a/net/ipv6/ip6_output.c
  47 +++ b/net/ipv6/ip6_output.c
  48 @@ -1463,6 +1463,11 @@ static int __ip6_append_data(struct sock *sk,
  49                          */
  50                         alloclen += sizeof(struct frag_hdr);
  51
  52 +                       copy = datalen - transhdrlen - fraggap;
  53 +                       if (copy < 0) {
  54 +                               err = -EINVAL;
  55 +                               goto error;
  56 +                       }
  57                         if (transhdrlen) {
  58                                 skb = sock_alloc_send_skb(sk,
  59                                                 alloclen + hh_len,
  60 @@ -1512,13 +1517,9 @@ static int __ip6_append_data(struct sock *sk,
  61                                 data += fraggap;
  62                                 pskb_trim_unique(skb_prev, maxfraglen);
  63                         }
  64 -                       copy = datalen - transhdrlen - fraggap;
  65 -
  66 -                       if (copy < 0) {
  67 -                               err = -EINVAL;
  68 -                               kfree_skb(skb);
  69 -                               goto error;
  70 -                       } else if (copy > 0 && getfrag(from, data + transhdrlen, offset, copy, fraggap, skb) < 0) {
  71 +                       if (copy > 0 &&
  72 +                           getfrag(from, data + transhdrlen, offset,
  73 +                                   copy, fraggap, skb) < 0) {
  74                                 err = -EFAULT;
  75                                 kfree_skb(skb);
  76                                 goto error;
  77 --
  78 2.11.0
  79