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

Add a cgroup bpf program test where the bpf program is running
in a pid namespace. The test is successfully:
  #165/3   ns_current_pid_tgid/new_ns_cgrp:OK
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240315184910.2976522-1-yonghong.song@linux.dev

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

@@ -12,6 +12,7 @@
 #include <sys/wait.h>
 #include <sys/mount.h>
 #include <sys/fcntl.h>
+#include "network_helpers.h"
 
 #define STACK_SIZE (1024 * 1024)
 static char child_stack[STACK_SIZE];
@@ -74,6 +75,50 @@ static int test_current_pid_tgid_tp(void *args)
 	return ret;
 }
 
+static int test_current_pid_tgid_cgrp(void *args)
+{
+	struct test_ns_current_pid_tgid__bss *bss;
+	struct test_ns_current_pid_tgid *skel;
+	int server_fd = -1, ret = -1, err;
+	int cgroup_fd = *(int *)args;
+	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.cgroup_bind4, 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, bss))
+		goto cleanup;
+
+	skel->links.cgroup_bind4 = bpf_program__attach_cgroup(
+		skel->progs.cgroup_bind4, cgroup_fd);
+	if (!ASSERT_OK_PTR(skel->links.cgroup_bind4, "bpf_program__attach_cgroup"))
+		goto cleanup;
+
+	server_fd = start_server(AF_INET, SOCK_STREAM, NULL, 0, 0);
+	if (!ASSERT_GE(server_fd, 0, "start_server"))
+		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);
+	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;
@@ -95,6 +140,25 @@ static void test_ns_current_pid_tgid_new_ns(int (*fn)(void *), void *arg)
 		return;
 }
 
+static void test_in_netns(int (*fn)(void *), void *arg)
+{
+	struct nstoken *nstoken = NULL;
+
+	SYS(cleanup, "ip netns add ns_current_pid_tgid");
+	SYS(cleanup, "ip -net ns_current_pid_tgid link set dev lo up");
+
+	nstoken = open_netns("ns_current_pid_tgid");
+	if (!ASSERT_OK_PTR(nstoken, "open_netns"))
+		goto cleanup;
+
+	test_ns_current_pid_tgid_new_ns(fn, arg);
+
+cleanup:
+	if (nstoken)
+		close_netns(nstoken);
+	SYS_NOFAIL("ip netns del ns_current_pid_tgid");
+}
+
 /* TODO: use a different tracepoint */
 void serial_test_ns_current_pid_tgid(void)
 {
@@ -102,4 +166,13 @@ void serial_test_ns_current_pid_tgid(void)
 		test_current_pid_tgid_tp(NULL);
 	if (test__start_subtest("new_ns_tp"))
 		test_ns_current_pid_tgid_new_ns(test_current_pid_tgid_tp, NULL);
+	if (test__start_subtest("new_ns_cgrp")) {
+		int cgroup_fd = -1;
+
+		cgroup_fd = test__join_cgroup("/sock_addr");
+		if (ASSERT_GE(cgroup_fd, 0, "join_cgroup")) {
+			test_in_netns(test_current_pid_tgid_cgrp, &cgroup_fd);
+			close(cgroup_fd);
+		}
+	}
 }

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

@@ -28,4 +28,11 @@ int tp_handler(const void *ctx)
 	return 0;
 }
 
+SEC("?cgroup/bind4")
+int cgroup_bind4(struct bpf_sock_addr *ctx)
+{
+	get_pid_tgid();
+	return 1;
+}
+
 char _license[] SEC("license") = "GPL";