vsock/test: Add test for connect() retries

Deliberately fail a connect() attempt; expect error. Then verify that
subsequent attempt (using the same socket) can still succeed, rather than
fail outright.

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20250128-vsock-transport-vs-autobind-v3-6-1cf57065b770@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/vsock/vsock_test.c

@@ -1746,6 +1746,48 @@ static void test_stream_transport_uaf_server(const struct test_opts *opts)
 	control_expectln("DONE");
 }
 
+static void test_stream_connect_retry_client(const struct test_opts *opts)
+{
+	int fd;
+
+	fd = socket(AF_VSOCK, SOCK_STREAM, 0);
+	if (fd < 0) {
+		perror("socket");
+		exit(EXIT_FAILURE);
+	}
+
+	if (!vsock_connect_fd(fd, opts->peer_cid, opts->peer_port)) {
+		fprintf(stderr, "Unexpected connect() #1 success\n");
+		exit(EXIT_FAILURE);
+	}
+
+	control_writeln("LISTEN");
+	control_expectln("LISTENING");
+
+	if (vsock_connect_fd(fd, opts->peer_cid, opts->peer_port)) {
+		perror("connect() #2");
+		exit(EXIT_FAILURE);
+	}
+
+	close(fd);
+}
+
+static void test_stream_connect_retry_server(const struct test_opts *opts)
+{
+	int fd;
+
+	control_expectln("LISTEN");
+
+	fd = vsock_stream_accept(VMADDR_CID_ANY, opts->peer_port, NULL);
+	if (fd < 0) {
+		perror("accept");
+		exit(EXIT_FAILURE);
+	}
+
+	vsock_wait_remote_close(fd);
+	close(fd);
+}
+
 static struct test_case test_cases[] = {
 	{
 		.name = "SOCK_STREAM connection reset",
@@ -1896,6 +1938,11 @@ static struct test_case test_cases[] = {
 		.run_client = test_stream_transport_uaf_client,
 		.run_server = test_stream_transport_uaf_server,
 	},
+	{
+		.name = "SOCK_STREAM retry failed connect()",
+		.run_client = test_stream_connect_retry_client,
+		.run_server = test_stream_connect_retry_server,
+	},
 	{},
 };