1 files changed, 32 insertions, 3 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 749b0ef9f405..633963e228bc 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -110,8 +110,38 @@ static u32 tcp_v4_init_ts_off(const struct net *net, const struct sk_buff *skb)
 
 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
 {
+	const struct inet_timewait_sock *tw = inet_twsk(sktw);
 	const struct tcp_timewait_sock *tcptw = tcp_twsk(sktw);
 	struct tcp_sock *tp = tcp_sk(sk);
+	int reuse = sock_net(sk)->ipv4.sysctl_tcp_tw_reuse;
+
+	if (reuse == 2) {
+		/* Still does not detect *everything* that goes through
+		 * lo, since we require a loopback src or dst address
+		 * or direct binding to 'lo' interface.
+		 */
+		bool loopback = false;
+		if (tw->tw_bound_dev_if == LOOPBACK_IFINDEX)
+			loopback = true;
+#if IS_ENABLED(CONFIG_IPV6)
+		if (tw->tw_family == AF_INET6) {
+			if (ipv6_addr_loopback(&tw->tw_v6_daddr) ||
+			    (ipv6_addr_v4mapped(&tw->tw_v6_daddr) &&
+			     (tw->tw_v6_daddr.s6_addr[12] == 127)) ||
+			    ipv6_addr_loopback(&tw->tw_v6_rcv_saddr) ||
+			    (ipv6_addr_v4mapped(&tw->tw_v6_rcv_saddr) &&
+			     (tw->tw_v6_rcv_saddr.s6_addr[12] == 127)))
+				loopback = true;
+		} else
+#endif
+		{
+			if (ipv4_is_loopback(tw->tw_daddr) ||
+			    ipv4_is_loopback(tw->tw_rcv_saddr))
+				loopback = true;
+		}
+		if (!loopback)
+			reuse = 0;
+	}
 
 	/* With PAWS, it is safe from the viewpoint
 	   of data integrity. Even without PAWS it is safe provided sequence
@@ -125,8 +155,7 @@ int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
 	   and use initial timestamp retrieved from peer table.
 	 */
 	if (tcptw->tw_ts_recent_stamp &&
-	    (!twp || (sock_net(sk)->ipv4.sysctl_tcp_tw_reuse &&
-			     get_seconds() - tcptw->tw_ts_recent_stamp > 1))) {
+	    (!twp || (reuse && get_seconds() - tcptw->tw_ts_recent_stamp > 1))) {
 		tp->write_seq = tcptw->tw_snd_nxt + 65535 + 2;
 		if (tp->write_seq == 0)
 			tp->write_seq = 1;
@@ -2529,7 +2558,7 @@ static int __net_init tcp_sk_init(struct net *net)
 	net->ipv4.sysctl_tcp_orphan_retries = 0;
 	net->ipv4.sysctl_tcp_fin_timeout = TCP_FIN_TIMEOUT;
 	net->ipv4.sysctl_tcp_notsent_lowat = UINT_MAX;
-	net->ipv4.sysctl_tcp_tw_reuse = 0;
+	net->ipv4.sysctl_tcp_tw_reuse = 2;
 
 	cnt = tcp_hashinfo.ehash_mask + 1;
 	net->ipv4.tcp_death_row.sysctl_max_tw_buckets = (cnt + 1) / 2;