[NETFILTER]: nf_nat: add reference to conntrack from entry of bysource list

I will split 'struct nf_nat_info' out from conntrack. So I cannot use
'offsetof' to get the pointer to conntrack from it.

Signed-off-by: Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netfilter/nf_nat.h

@@ -53,11 +53,14 @@ struct nf_nat_multi_range_compat
 #include <linux/list.h>
 #include <linux/netfilter/nf_conntrack_pptp.h>
 
+struct nf_conn;
+
 /* The structure embedded in the conntrack structure. */
 struct nf_nat_info
 {
 	struct list_head bysource;
 	struct nf_nat_seq seq[IP_CT_DIR_MAX];
+	struct nf_conn *ct;
 };
 
 /* per conntrack: nat application helper private data */
@@ -77,8 +80,6 @@ struct nf_conn_nat
 #endif
 };
 
-struct nf_conn;
-
 /* Set up the info structure to map into this range. */
 extern unsigned int nf_nat_setup_info(struct nf_conn *ct,
 				      const struct nf_nat_range *range,

net/ipv4/netfilter/nf_nat_core.c

@@ -97,6 +97,7 @@ static void nf_nat_cleanup_conntrack(struct nf_conn *conn)
 	nat = nfct_nat(conn);
 	write_lock_bh(&nf_nat_lock);
 	list_del(&nat->info.bysource);
+	nat->info.ct = NULL;
 	write_unlock_bh(&nf_nat_lock);
 }
 
@@ -169,7 +170,7 @@ find_appropriate_src(const struct nf_conntrack_tuple *tuple,
 
 	read_lock_bh(&nf_nat_lock);
 	list_for_each_entry(nat, &bysource[h], info.bysource) {
-		ct = (struct nf_conn *)((char *)nat - offsetof(struct nf_conn, data));
+		ct = nat->info.ct;
 		if (same_src(ct, tuple)) {
 			/* Copy source part from reply tuple. */
 			nf_ct_invert_tuplepr(result,
@@ -337,6 +338,7 @@ nf_nat_setup_info(struct nf_conn *ct,
 
 		srchash = hash_by_src(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
 		write_lock_bh(&nf_nat_lock);
+		info->ct = ct;
 		list_add(&info->bysource, &bysource[srchash]);
 		write_unlock_bh(&nf_nat_lock);
 	}