tcp: Fix bind() regression for v6-only wildcard and v4(-mapped-v6) non-wildcard addresses.

Jianguo Wu reported another bind() regression introduced by bhash2.

Calling bind() for the following 3 addresses on the same port, the
3rd one should fail but now succeeds.

1. 0.0.0.0 or ::ffff:0.0.0.0
2. [::] w/ IPV6_V6ONLY
3. IPv4 non-wildcard address or v4-mapped-v6 non-wildcard address

The first two bind() create tb2 like this:

bhash2 -> tb2(:: w/ IPV6_V6ONLY) -> tb2(0.0.0.0)

The 3rd bind() will match with the IPv6 only wildcard address bucket
in inet_bind2_bucket_match_addr_any(), however, no conflicting socket
exists in the bucket. So, inet_bhash2_conflict() will returns false,
and thus, inet_bhash2_addr_any_conflict() returns false consequently.

As a result, the 3rd bind() bypasses conflict check, which should be
done against the IPv4 wildcard address bucket.

So, in inet_bhash2_addr_any_conflict(), we must iterate over all buckets.

Note that we cannot add ipv6_only flag for inet_bind2_bucket as it
would confuse the following patetrn.

1. [::] w/ SO_REUSE{ADDR,PORT} and IPV6_V6ONLY
2. [::] w/ SO_REUSE{ADDR,PORT}
3. IPv4 non-wildcard address or v4-mapped-v6 non-wildcard address

The first bind() would create a bucket with ipv6_only flag true,
the second bind() would add the [::] socket into the same bucket,
and the third bind() could succeed based on the wrong assumption
that ipv6_only bucket would not conflict with v4(-mapped-v6) address.

Fixes: 28044fc1d495 ("net: Add a bhash2 table hashed by port and address")
Diagnosed-by: Jianguo Wu <[e-mail]>
Signed-off-by: Kuniyuki Iwashima <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ipv4/inet_connection_sock.c

···
 	struct sock_reuseport *reuseport_cb;
 	struct inet_bind_hashbucket *head2;
 	struct inet_bind2_bucket *tb2;
+	bool conflict = false;
 	bool reuseport_cb_ok;
 
 	rcu_read_lock();
···
 
 	spin_lock(&head2->lock);
 
-	inet_bind_bucket_for_each(tb2, &head2->chain)
-		if (inet_bind2_bucket_match_addr_any(tb2, net, port, l3mdev, sk))
-			break;
+	inet_bind_bucket_for_each(tb2, &head2->chain) {
+		if (!inet_bind2_bucket_match_addr_any(tb2, net, port, l3mdev, sk))
+			continue;
 
-	if (tb2 && inet_bhash2_conflict(sk, tb2, uid, relax, reuseport_cb_ok,
-					reuseport_ok)) {
-		spin_unlock(&head2->lock);
-		return true;
+		if (!inet_bhash2_conflict(sk, tb2, uid, relax, reuseport_cb_ok,	reuseport_ok))
+			continue;
+
+		conflict = true;
+		break;
 	}
 
 	spin_unlock(&head2->lock);
-	return false;
+
+	return conflict;
 }
 
 /*