releases/4.14.93/netfilter-nat-can-t-use-dst_hold-on-noref-dst.patch

   1 From fe31e7b578e65d8e55c55aeb66be6c34c10513fd Mon Sep 17 00:00:00 2001
   2 From: Florian Westphal <fw@strlen.de>
   3 Date: Tue, 11 Dec 2018 07:45:29 +0100
   4 Subject: netfilter: nat: can't use dst_hold on noref dst
   5
   6 [ Upstream commit 542fbda0f08f1cbbc250f9e59f7537649651d0c8 ]
   7
   8 The dst entry might already have a zero refcount, waiting on rcu list
   9 to be free'd.  Using dst_hold() transitions its reference count to 1, and
  10 next dst release will try to free it again -- resulting in a double free:
  11
  12   WARNING: CPU: 1 PID: 0 at include/net/dst.h:239 nf_xfrm_me_harder+0xe7/0x130 [nf_nat]
  13   RIP: 0010:nf_xfrm_me_harder+0xe7/0x130 [nf_nat]
  14   Code: 48 8b 5c 24 60 65 48 33 1c 25 28 00 00 00 75 53 48 83 c4 68 5b 5d 41 5c c3 85 c0 74 0d 8d 48 01 f0 0f b1 0a 74 86 85 c0 75 f3 <0f> 0b e9 7b ff ff ff 29 c6 31 d2 b9 20 00 48 00 4c 89 e7 e8 31 27
  15   Call Trace:
  16   nf_nat_ipv4_out+0x78/0x90 [nf_nat_ipv4]
  17   nf_hook_slow+0x36/0xd0
  18   ip_output+0x9f/0xd0
  19   ip_forward+0x328/0x440
  20   ip_rcv+0x8a/0xb0
  21
  22 Use dst_hold_safe instead and bail out if we cannot take a reference.
  23
  24 Fixes: a4c2fd7f7891 ("net: remove DST_NOCACHE flag")
  25 Reported-by: Martin Zaharinov <micron10@gmail.com>
  26 Signed-off-by: Florian Westphal <fw@strlen.de>
  27 Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
  28 Signed-off-by: Sasha Levin <sashal@kernel.org>
  29 ---
  30  net/netfilter/nf_nat_core.c | 3 ++-
  31  1 file changed, 2 insertions(+), 1 deletion(-)
  32
  33 diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
  34 index af8345fc4fbd..ed0ea64b8d04 100644
  35 --- a/net/netfilter/nf_nat_core.c
  36 +++ b/net/netfilter/nf_nat_core.c
  37 @@ -97,7 +97,8 @@ int nf_xfrm_me_harder(struct net *net, struct sk_buff *skb, unsigned int family)
  38         dst = skb_dst(skb);
  39         if (dst->xfrm)
  40                 dst = ((struct xfrm_dst *)dst)->route;
  41 -       dst_hold(dst);
  42 +       if (!dst_hold_safe(dst))
  43 +               return -EHOSTUNREACH;
  44
  45         dst = xfrm_lookup(net, dst, &fl, skb->sk, 0);
  46         if (IS_ERR(dst))
  47 --
  48 2.19.1
  49