[PATCH nf] netfilter: ctnetlink: avoid null pointer dereference

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Dan Carpenter points out that deref occurs after NULL check, we should
re-fetch the pointer and check that instead.

Fixes: 2c205dd3981f7 ("netfilter: add struct nf_nat_hook and use it")
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
---
Not even compile tested, patch is vs. nf-next as nf.git doesn't
contain the problematic change yet.

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 39327a42879f..20a2e37c76d1 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -1446,7 +1446,8 @@ ctnetlink_parse_nat_setup(struct nf_conn *ct,
 		}
 		nfnl_lock(NFNL_SUBSYS_CTNETLINK);
 		rcu_read_lock();
-		if (nat_hook->parse_nat_setup)
+		nat_hook = rcu_dereference(nf_nat_hook);
+		if (nat_hook)
 			return -EAGAIN;
 #endif
 		return -EOPNOTSUPP;
-- 
2.17.1

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