[PATCH bpf-next 2/2] selftests/bpf: Add testcase for bpf_task_under_cgroup

[Feng zhou <zhoufeng.zf@bytedance.com>]

From: Feng Zhou <zhoufeng.zf@bytedance.com>

test_progs:
Tests new ebpf helpers bpf_task_under_cgroup.

The bpf program saves the pid which call the getuid syscall within a
given cgroup to a map to the remote_pid, which is convenient for the
user-mode program to verify the test correctness.

The user-mode program creates its own mount namespace, and mounts the
cgroupsv2 hierarchy in there, call the getuid syscall, then check if
remote_pid and local_pid are equal.

Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
---
 .../bpf/prog_tests/task_under_cgroup.c        | 49 +++++++++++++++++++
 .../bpf/progs/test_task_under_cgroup.c        | 31 ++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_task_under_cgroup.c

diff --git a/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c b/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
new file mode 100644
index 000000000000..4dd704b11a95
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Bytedance */
+
+#include <test_progs.h>
+#include "test_task_under_cgroup.skel.h"
+
+#define FOO	"/foo"
+
+void test_task_under_cgroup(void)
+{
+	struct test_task_under_cgroup *skel;
+	int ret, foo = -1, idx = 0;
+
+	skel = test_task_under_cgroup__open();
+	if (!ASSERT_OK_PTR(skel, "test_task_under_cgroup__open"))
+		return;
+
+	skel->rodata->local_pid = getpid();
+
+	ret = test_task_under_cgroup__load(skel);
+	if (!ASSERT_OK(ret, "test_task_under_cgroup__load"))
+		goto cleanup;
+
+	ret = test_task_under_cgroup__attach(skel);
+	if (!ASSERT_OK(ret, "test_task_under_cgroup__attach"))
+		goto cleanup;
+
+	foo = test__join_cgroup(FOO);
+	if (!ASSERT_OK(foo < 0, "cgroup_join_foo"))
+		goto cleanup;
+
+	ret = bpf_map_update_elem(bpf_map__fd(skel->maps.cgroup_map), &idx,
+				  &foo, BPF_ANY);
+	if (!ASSERT_OK(ret < 0, "cgroup_map update"))
+		goto cleanup;
+
+	syscall(__NR_getuid);
+
+	test_task_under_cgroup__detach(skel);
+
+	ASSERT_EQ(skel->bss->remote_pid, skel->rodata->local_pid,
+		  "test task_under_cgroup");
+
+cleanup:
+	if (foo)
+		close(foo);
+
+	test_task_under_cgroup__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c b/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
new file mode 100644
index 000000000000..0f3d53f636de
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Bytedance */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+const volatile int local_pid;
+int remote_pid;
+
+struct {
+	__uint(type, BPF_MAP_TYPE_CGROUP_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u32);
+} cgroup_map SEC(".maps");
+
+SEC("tp/syscalls/sys_enter_getuid")
+int sysenter_getuid(const void *ctx)
+{
+	if (local_pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	if (!bpf_task_under_cgroup(&cgroup_map, bpf_get_current_task_btf(), 0))
+		return 0;
+
+	remote_pid = local_pid;
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.20.1