selftests/bpf: Allow auto port binding for cgroup connect

Allow auto port binding for cgroup connect test to avoid binding conflict.

Result:
./test_progs -a cgroup_v1v2
59      cgroup_v1v2:OK
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Jiayuan Chen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: mrpre

tools/testing/selftests/bpf/prog_tests/cgroup_v1v2.c

@@ -10,12 +10,18 @@
 static int run_test(int cgroup_fd, int server_fd, bool classid)
 {
 	struct connect4_dropper *skel;
-	int fd, err = 0;
+	int fd, err = 0, port;
 
 	skel = connect4_dropper__open_and_load();
 	if (!ASSERT_OK_PTR(skel, "skel_open"))
 		return -1;
 
+	port = get_socket_local_port(server_fd);
+	if (!ASSERT_GE(port, 0, "get_socket_local_port"))
+		return -1;
+
+	skel->bss->port = ntohs(port);
+
 	skel->links.connect_v4_dropper =
 		bpf_program__attach_cgroup(skel->progs.connect_v4_dropper,
 					   cgroup_fd);
@@ -48,10 +54,9 @@ void test_cgroup_v1v2(void)
 {
 	struct network_helper_opts opts = {};
 	int server_fd, client_fd, cgroup_fd;
-	static const int port = 60120;
 
 	/* Step 1: Check base connectivity works without any BPF. */
-	server_fd = start_server(AF_INET, SOCK_STREAM, NULL, port, 0);
+	server_fd = start_server(AF_INET, SOCK_STREAM, NULL, 0, 0);
 	if (!ASSERT_GE(server_fd, 0, "server_fd"))
 		return;
 	client_fd = connect_to_fd_opts(server_fd, &opts);
@@ -66,7 +71,7 @@ void test_cgroup_v1v2(void)
 	cgroup_fd = test__join_cgroup("/connect_dropper");
 	if (!ASSERT_GE(cgroup_fd, 0, "cgroup_fd"))
 		return;
-	server_fd = start_server(AF_INET, SOCK_STREAM, NULL, port, 0);
+	server_fd = start_server(AF_INET, SOCK_STREAM, NULL, 0, 0);
 	if (!ASSERT_GE(server_fd, 0, "server_fd")) {
 		close(cgroup_fd);
 		return;

tools/testing/selftests/bpf/progs/connect4_dropper.c

@@ -13,12 +13,14 @@
 #define VERDICT_REJECT	0
 #define VERDICT_PROCEED	1
 
+int port;
+
 SEC("cgroup/connect4")
 int connect_v4_dropper(struct bpf_sock_addr *ctx)
 {
 	if (ctx->type != SOCK_STREAM)
 		return VERDICT_PROCEED;
-	if (ctx->user_port == bpf_htons(60120))
+	if (ctx->user_port == bpf_htons(port))
 		return VERDICT_REJECT;
 	return VERDICT_PROCEED;
 }