[NETFILTER]: nf_nat: fix MASQUERADE crash on device down

Check the return value of nfct_nat() in device_cmp(), we might very well
have non NAT conntrack entries as well (Netfilter bugzilla #528).

Signed-off-by: Martin Josefsson <gandalf@wlug.westbo.se>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/ipv4/netfilter/ipt_MASQUERADE.c b/net/ipv4/netfilter/ipt_MASQUERADE.c
index 28b9233956b5..d669685afd04 100644
--- a/net/ipv4/netfilter/ipt_MASQUERADE.c
+++ b/net/ipv4/netfilter/ipt_MASQUERADE.c
@@ -127,10 +127,13 @@ masquerade_target(struct sk_buff **pskb,
 static inline int
 device_cmp(struct ip_conntrack *i, void *ifindex)
 {
+        int ret;
 #ifdef CONFIG_NF_NAT_NEEDED
         struct nf_conn_nat *nat = nfct_nat(i);
+
+        if (!nat)
+                return 0;
 #endif
-        int ret;
 
         read_lock_bh(&masq_lock);
 #ifdef CONFIG_NF_NAT_NEEDED