[PATCH 5.18 34/88] tcp: md5: fix IPv4-mapped support

[Greg Kroah-Hartman]

From: Eric Dumazet <edumazet@xxxxxxxxxx>

commit e62d2e110356093c034998e093675df83057e511 upstream.

After the blamed commit, IPv4 SYN packets handled
by a dual stack IPv6 socket are dropped, even if
perfectly valid.

$ nstat | grep MD5
TcpExtTCPMD5Failure             5                  0.0

For a dual stack listener, an incoming IPv4 SYN packet
would call tcp_inbound_md5_hash() with @family == AF_INET,
while tp->af_specific is pointing to tcp_sock_ipv6_specific.

Only later when an IPv4-mapped child is created, tp->af_specific
is changed to tcp_sock_ipv6_mapped_specific.

Fixes: 7bbb765b7349 ("net/tcp: Merge TCP-MD5 inbound callbacks")
Reported-by: Brian Vazquez <brianvv@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
Reviewed-by: Dmitry Safonov <dima@xxxxxxxxxx>
Tested-by: Leonard Crestez <cdleonard@xxxxxxxxx>
Link: https://lore.kernel.org/r/20220726115743.2759832-1-edumazet@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/ipv4/tcp.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4481,9 +4481,18 @@ tcp_inbound_md5_hash(const struct sock *
 		return SKB_DROP_REASON_TCP_MD5UNEXPECTED;
 	}
 
-	/* check the signature */
-	genhash = tp->af_specific->calc_md5_hash(newhash, hash_expected,
-						 NULL, skb);
+	/* Check the signature.
+	 * To support dual stack listeners, we need to handle
+	 * IPv4-mapped case.
+	 */
+	if (family == AF_INET)
+		genhash = tcp_v4_md5_hash_skb(newhash,
+					      hash_expected,
+					      NULL, skb);
+	else
+		genhash = tp->af_specific->calc_md5_hash(newhash,
+							 hash_expected,
+							 NULL, skb);
 
 	if (genhash || memcmp(hash_location, newhash, 16) != 0) {
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5FAILURE);