Revert "tcp: disallow bind() to reuse addr/port"

This reverts commit c191a836.

It causes known regressions for programs that expect to be able to use
SO_REUSEADDR to shutdown a socket, then successfully rebind another
socket to the same ID.

Programs such as haproxy and amavisd expect this to work.

This should fix kernel bugzilla 32832.
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/inet_connection_sock.c

@@ -73,7 +73,7 @@ int inet_csk_bind_conflict(const struct sock *sk,
 		     !sk2->sk_bound_dev_if ||
 		     sk->sk_bound_dev_if == sk2->sk_bound_dev_if)) {
 			if (!reuse || !sk2->sk_reuse ||
-			    ((1 << sk2->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))) {
+			    sk2->sk_state == TCP_LISTEN) {
 				const __be32 sk2_rcv_saddr = sk_rcv_saddr(sk2);
 				if (!sk2_rcv_saddr || !sk_rcv_saddr(sk) ||
 				    sk2_rcv_saddr == sk_rcv_saddr(sk))
@@ -122,8 +122,7 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum)
 					    (tb->num_owners < smallest_size || smallest_size == -1)) {
 						smallest_size = tb->num_owners;
 						smallest_rover = rover;
-						if (atomic_read(&hashinfo->bsockets) > (high - low) + 1 &&
-						    !inet_csk(sk)->icsk_af_ops->bind_conflict(sk, tb)) {
+						if (atomic_read(&hashinfo->bsockets) > (high - low) + 1) {
 							spin_unlock(&head->lock);
 							snum = smallest_rover;
 							goto have_snum;

net/ipv6/inet6_connection_sock.c

@@ -44,7 +44,7 @@ int inet6_csk_bind_conflict(const struct sock *sk,
 		     !sk2->sk_bound_dev_if ||
 		     sk->sk_bound_dev_if == sk2->sk_bound_dev_if) &&
 		    (!sk->sk_reuse || !sk2->sk_reuse ||
-		     ((1 << sk2->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))) &&
+		     sk2->sk_state == TCP_LISTEN) &&
 		     ipv6_rcv_saddr_equal(sk, sk2))
 			break;
 	}