login proxy: Hanging outgoing SSL connections caused using already-fr…

…eed memory

This mainly happened when login proxy closed the connection due to connect
timeout. The ssl-proxy still had a reference and existed for a longer time.
If SSL handshake still succeeded afterwards, it now called
login_proxy_ssl_handshaked(), which accessed the already-freed proxy and
likely crashed.

Fixed the ssl-client proxy code specifically. Alternatively ssl_proxy_free()
could be calling ssl_proxy_destroy() always, but since ssl-server side of
the code seems to have been working fine, I don't want to accidentally
break it.

src/login-common/login-proxy.c

@@ -515,8 +515,10 @@ static void login_proxy_free_final(struct login_proxy *proxy)
 		o_stream_destroy(&proxy->client_output);
 	if (proxy->client_fd != -1)
 		net_disconnect(proxy->client_fd);
-	if (proxy->ssl_server_proxy != NULL)
+	if (proxy->ssl_server_proxy != NULL) {
+		ssl_proxy_destroy(proxy->ssl_server_proxy);
 		ssl_proxy_free(&proxy->ssl_server_proxy);
+	}
 	i_free(proxy->host);
 	i_free(proxy);
 }