netfilter: xt_TCPMSS: lookup route from proper net namespace

Otherwise the pmtu will be incorrect.
Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_TCPMSS.c

@@ -43,7 +43,8 @@ optlen(const u_int8_t *opt, unsigned int offset)
 		return opt[offset+1];
 }
 
-static u_int32_t tcpmss_reverse_mtu(const struct sk_buff *skb,
+static u_int32_t tcpmss_reverse_mtu(struct net *net,
+				    const struct sk_buff *skb,
 				    unsigned int family)
 {
 	struct flowi fl;
@@ -64,7 +65,7 @@ static u_int32_t tcpmss_reverse_mtu(const struct sk_buff *skb,
 	rcu_read_lock();
 	ai = nf_get_afinfo(family);
 	if (ai != NULL)
-		ai->route(&init_net, (struct dst_entry **)&rt, &fl, false);
+		ai->route(net, (struct dst_entry **)&rt, &fl, false);
 	rcu_read_unlock();
 
 	if (rt != NULL) {
@@ -107,7 +108,8 @@ tcpmss_mangle_packet(struct sk_buff *skb,
 		return -1;
 
 	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
-		unsigned int in_mtu = tcpmss_reverse_mtu(skb, family);
+		struct net *net = dev_net(par->in ? par->in : par->out);
+		unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
 
 		if (dst_mtu(skb_dst(skb)) <= minlen) {
 			net_err_ratelimited("unknown or invalid path-MTU (%u)\n",