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

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Date:   Mon,  1 Aug 2022 13:46:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Brian Vazquez <brianvv@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Ahern <dsahern@...nel.org>,
        Dmitry Safonov <dima@...sta.com>,
        Leonard Crestez <cdleonard@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH 5.18 34/88] tcp: md5: fix IPv4-mapped support

From: Eric Dumazet <edumazet@...gle.com>

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@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reviewed-by: David Ahern <dsahern@...nel.org>
Reviewed-by: Dmitry Safonov <dima@...sta.com>
Tested-by: Leonard Crestez <cdleonard@...il.com>
Link: https://lore.kernel.org/r/20220726115743.2759832-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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);