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

Commit 5e07e672412b ("tcp: Use bhash2 for v4-mapped-v6 non-wildcard
address.") introduced bind() regression for v4-mapped-v6 address.

When we bind() the following two addresses on the same port, the 2nd
bind() should succeed but fails now.

1. [::] w/ IPV6_ONLY
2. ::ffff:127.0.0.1

After the chagne, v4-mapped-v6 uses bhash2 instead of bhash to
detect conflict faster, but I forgot to add a necessary change.

During the 2nd bind(), inet_bind2_bucket_match_addr_any() returns
the tb2 bucket of [::], and inet_bhash2_conflict() finally calls
inet_bind_conflict(), which returns true, meaning conflict.

inet_bhash2_addr_any_conflict
|- inet_bind2_bucket_match_addr_any <-- return [::] bucket
`- inet_bhash2_conflict
`- __inet_bhash2_conflict <-- checks IPV6_ONLY for AF_INET
| but not for v4-mapped-v6 address
`- inet_bind_conflict <-- does not check address

inet_bind_conflict() does not check socket addresses because
__inet_bhash2_conflict() is expected to do so.

However, it checks IPV6_V6ONLY attribute only against AF_INET
socket, and not for v4-mapped-v6 address.

As a result, v4-mapped-v6 address conflicts with v6-only wildcard
address.

To avoid that, let's add the missing test to use bhash2 for
v4-mapped-v6 address.

Fixes: 5e07e672412b ("tcp: Use bhash2 for v4-mapped-v6 non-wildcard address.")
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

···
 				   kuid_t sk_uid, bool relax,
 				   bool reuseport_cb_ok, bool reuseport_ok)
 {
-	if (sk->sk_family == AF_INET && ipv6_only_sock(sk2))
-		return false;
+	if (ipv6_only_sock(sk2)) {
+		if (sk->sk_family == AF_INET)
+			return false;
+
+#if IS_ENABLED(CONFIG_IPV6)
+		if (ipv6_addr_v4mapped(&sk->sk_v6_rcv_saddr))
+			return false;
+#endif
+	}
 
 	return inet_bind_conflict(sk, sk2, sk_uid, relax,
 				  reuseport_cb_ok, reuseport_ok);