[NETFILTER]: nf_conntrack: properly use RCU for nf_conntrack_destroyed callback

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/nf_nat_core.c

@@ -617,8 +617,8 @@ static int __init nf_nat_init(void)
 	}
 
 	/* FIXME: Man, this is a hack.  <SIGH> */
-	NF_CT_ASSERT(nf_conntrack_destroyed == NULL);
-	nf_conntrack_destroyed = &nf_nat_cleanup_conntrack;
+	NF_CT_ASSERT(rcu_dereference(nf_conntrack_destroyed) == NULL);
+	rcu_assign_pointer(nf_conntrack_destroyed, nf_nat_cleanup_conntrack);
 
 	/* Initialize fake conntrack so that NAT will skip it */
 	nf_conntrack_untracked.status |= IPS_NAT_DONE_MASK;
@@ -642,7 +642,8 @@ static int clean_nat(struct nf_conn *i, void *data)
 static void __exit nf_nat_cleanup(void)
 {
 	nf_ct_iterate_cleanup(&clean_nat, NULL);
-	nf_conntrack_destroyed = NULL;
+	rcu_assign_pointer(nf_conntrack_destroyed, NULL);
+	synchronize_rcu();
 	vfree(bysource);
 	nf_ct_l3proto_put(l3proto);
 }

net/netfilter/nf_conntrack_core.c

@@ -318,6 +318,7 @@ destroy_conntrack(struct nf_conntrack *nfct)
 	struct nf_conn_help *help = nfct_help(ct);
 	struct nf_conntrack_l3proto *l3proto;
 	struct nf_conntrack_l4proto *l4proto;
+	typeof(nf_conntrack_destroyed) destroyed;
 
 	DEBUGP("destroy_conntrack(%p)\n", ct);
 	NF_CT_ASSERT(atomic_read(&nfct->use) == 0);
@@ -341,10 +342,12 @@ destroy_conntrack(struct nf_conntrack *nfct)
 				       ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.protonum);
 	if (l4proto && l4proto->destroy)
 		l4proto->destroy(ct);
-	rcu_read_unlock();
 
-	if (nf_conntrack_destroyed)
-		nf_conntrack_destroyed(ct);
+	destroyed = rcu_dereference(nf_conntrack_destroyed);
+	if (destroyed)
+		destroyed(ct);
+
+	rcu_read_unlock();
 
 	write_lock_bh(&nf_conntrack_lock);
 	/* Expectations will have been removed in clean_from_lists,