netfilter: nf_nat: use hash random for bysource hash

Use nf_conntrack_hash_rnd in NAT bysource hash to avoid hash chain attacks.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/nf_nat_core.c

@@ -57,7 +57,7 @@ hash_by_src(const struct net *net, u16 zone,
 	/* Original src, to ensure we map it consistently if poss. */
 	hash = jhash_3words((__force u32)tuple->src.u3.ip,
 			    (__force u32)tuple->src.u.all ^ zone,
-			    tuple->dst.protonum, 0);
+			    tuple->dst.protonum, nf_conntrack_hash_rnd);
 	return ((u64)hash * net->ipv4.nat_htable_size) >> 32;
 }
 

net/netfilter/nf_conntrack_core.c

@@ -67,6 +67,7 @@ DEFINE_PER_CPU(struct nf_conn, nf_conntrack_untracked);
 EXPORT_PER_CPU_SYMBOL(nf_conntrack_untracked);
 
 unsigned int nf_conntrack_hash_rnd __read_mostly;
+EXPORT_SYMBOL_GPL(nf_conntrack_hash_rnd);
 
 static u32 hash_conntrack_raw(const struct nf_conntrack_tuple *tuple, u16 zone)
 {