selftests/bpf: Add a sk_msg prog bpf_get_ns_current_pid_tgid() test

Add a sk_msg bpf program test where the program is running in a pid
namespace. The test is successful:
  #165/4   ns_current_pid_tgid/new_ns_sk_msg:OK
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240315184915.2976718-1-yonghong.song@linux.dev

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

@@ -119,6 +119,66 @@ static int test_current_pid_tgid_cgrp(void *args)
 	return ret;
 }
 
+static int test_current_pid_tgid_sk_msg(void *args)
+{
+	int verdict, map, server_fd = -1, client_fd = -1;
+	struct test_ns_current_pid_tgid__bss *bss;
+	static const char send_msg[] = "message";
+	struct test_ns_current_pid_tgid *skel;
+	int ret = -1, err, key = 0;
+	pid_t tgid, pid;
+
+	skel = test_ns_current_pid_tgid__open();
+	if (!ASSERT_OK_PTR(skel, "test_ns_current_pid_tgid__open"))
+		return ret;
+
+	bpf_program__set_autoload(skel->progs.sk_msg, true);
+
+	err = test_ns_current_pid_tgid__load(skel);
+	if (!ASSERT_OK(err, "test_ns_current_pid_tgid__load"))
+		goto cleanup;
+
+	bss = skel->bss;
+	if (get_pid_tgid(&pid, &tgid, skel->bss))
+		goto cleanup;
+
+	verdict = bpf_program__fd(skel->progs.sk_msg);
+	map = bpf_map__fd(skel->maps.sock_map);
+	err = bpf_prog_attach(verdict, map, BPF_SK_MSG_VERDICT, 0);
+	if (!ASSERT_OK(err, "prog_attach"))
+		goto cleanup;
+
+	server_fd = start_server(AF_INET6, SOCK_STREAM, "::1", 0, 0);
+	if (!ASSERT_GE(server_fd, 0, "start_server"))
+		goto cleanup;
+
+	client_fd = connect_to_fd(server_fd, 0);
+	if (!ASSERT_GE(client_fd, 0, "connect_to_fd"))
+		goto cleanup;
+
+	err = bpf_map_update_elem(map, &key, &client_fd, BPF_ANY);
+	if (!ASSERT_OK(err, "bpf_map_update_elem"))
+		goto cleanup;
+
+	err = send(client_fd, send_msg, sizeof(send_msg), 0);
+	if (!ASSERT_EQ(err, sizeof(send_msg), "send(msg)"))
+		goto cleanup;
+
+	if (!ASSERT_EQ(bss->user_pid, pid, "pid"))
+		goto cleanup;
+	if (!ASSERT_EQ(bss->user_tgid, tgid, "tgid"))
+		goto cleanup;
+	ret = 0;
+
+cleanup:
+	if (server_fd >= 0)
+		close(server_fd);
+	if (client_fd >= 0)
+		close(client_fd);
+	test_ns_current_pid_tgid__destroy(skel);
+	return ret;
+}
+
 static void test_ns_current_pid_tgid_new_ns(int (*fn)(void *), void *arg)
 {
 	int wstatus;
@@ -175,4 +235,6 @@ void serial_test_ns_current_pid_tgid(void)
 			close(cgroup_fd);
 		}
 	}
+	if (test__start_subtest("new_ns_sk_msg"))
+		test_in_netns(test_current_pid_tgid_sk_msg, NULL);
 }

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

@@ -5,6 +5,13 @@
 #include <stdint.h>
 #include <bpf/bpf_helpers.h>
 
+struct {
+	__uint(type, BPF_MAP_TYPE_SOCKMAP);
+	__uint(max_entries, 2);
+	__type(key, __u32);
+	__type(value, __u32);
+} sock_map SEC(".maps");
+
 __u64 user_pid = 0;
 __u64 user_tgid = 0;
 __u64 dev = 0;
@@ -35,4 +42,11 @@ int cgroup_bind4(struct bpf_sock_addr *ctx)
 	return 1;
 }
 
+SEC("?sk_msg")
+int sk_msg(struct sk_msg_md *msg)
+{
+	get_pid_tgid();
+	return SK_PASS;
+}
+
 char _license[] SEC("license") = "GPL";