net/rds: Use proper peer port number even when not connected

The function rds_tcp_get_peer_sport() should return the peer port of a
socket, even when the socket is not currently connected, so that RDS
can reliably determine the MPRDS "lane" corresponding to the port.

rds_tcp_get_peer_sport() calls kernel_getpeername() to get the port
number; however, when paths between endpoints frequently drop and
reconnect, kernel_getpeername() can return -ENOTCONN, causing
rds_tcp_get_peer_sport() to return an error, and ultimately causing
RDS to use the wrong lane for a port when reconnecting to a peer.

This patch modifies rds_tcp_get_peer_sport() to directly call the
socket-specific get-name function (inet_getname() in this case) that
kernel_getpeername() also calls.  The socket-specific function offers
an additional argument which, when set to a value greater than 1,
causes the function to return the socket's peer name even when the
socket is not connected, which in turn allows rds_tcp_get_peer_sport()
to return the correct port number.

Orabug: 35896264

Suggested-by: Gerd Rausch <[email protected]>
Signed-off-by: Greg Jumper <[email protected]>
Reviewed-by: Håkon Bugge <[email protected]>

Author: Greg Jumper

net/rds/tcp_listen.c

@@ -68,7 +68,11 @@ rds_tcp_get_peer_sport(struct socket *sock)
 	} saddr;
 	int sport;
 
-	if (kernel_getpeername(sock, &saddr.addr) >= 0) {
+	/* Call the socket's getname() function (inet_getname() in this case)
+	 * with a final argument greater than 1 to get the peer's port
+	 * regardless of whether the socket is currently connected.
+	 */
+	if (sock->ops->getname(sock, &saddr.addr, 2) >= 0) {
 		switch (saddr.addr.sa_family) {
 		case AF_INET:
 			sport = ntohs(saddr.sin.sin_port);