From 542fbda0f08f1cbbc250f9e59f7537649651d0c8 Mon Sep 17 00:00:00 2001
From: Florian Westphal <fw@strlen.de>
Date: Tue, 11 Dec 2018 07:45:29 +0100
Subject: [PATCH] netfilter: nat: can't use dst_hold on noref dst
Patch-mainline: v4.20
Git-commit: 542fbda0f08f1cbbc250f9e59f7537649651d0c8
References: bsc#1178878
The dst entry might already have a zero refcount, waiting on rcu list
to be free'd. Using dst_hold() transitions its reference count to 1, and
next dst release will try to free it again -- resulting in a double free:
WARNING: CPU: 1 PID: 0 at include/net/dst.h:239 nf_xfrm_me_harder+0xe7/0x130 [nf_nat]
RIP: 0010:nf_xfrm_me_harder+0xe7/0x130 [nf_nat]
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
Call Trace:
nf_nat_ipv4_out+0x78/0x90 [nf_nat_ipv4]
nf_hook_slow+0x36/0xd0
ip_output+0x9f/0xd0
ip_forward+0x328/0x440
ip_rcv+0x8a/0xb0
Use dst_hold_safe instead and bail out if we cannot take a reference.
Fixes: a4c2fd7f7891 ("net: remove DST_NOCACHE flag")
Reported-by: Martin Zaharinov <micron10@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Denis Kirjanov <denis.kirjanov@suse.com>
---
net/netfilter/nf_nat_core.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index e2b196054dfc..2268b10a9dcf 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -97,7 +97,8 @@ int nf_xfrm_me_harder(struct net *net, s
dst = skb_dst(skb);
if (dst->xfrm)
dst = ((struct xfrm_dst *)dst)->route;
- dst_hold(dst);
+ if (!dst_hold_safe(dst))
+ return -EHOSTUNREACH;
dst = xfrm_lookup(net, dst, &fl, skb->sk, 0);
if (IS_ERR(dst))
--
2.16.4