Re: [PATCH bpf-next v3 2/2] selftests/bpf: Add testcase for bpf_task_under_cgroup
From: Yonghong Song
Date: Thu Apr 27 2023 - 01:28:23 EST
On 4/26/23 7:30 PM, Feng zhou wrote:
From: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
test_progs:
Tests new kfunc bpf_task_under_cgroup().
The bpf program saves the pid which call the getpgid syscall within a
given cgroup 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 getpgid syscall, then check if
remote_pid and local_pid are equal.
Signed-off-by: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
---
tools/testing/selftests/bpf/DENYLIST.s390x | 1 +
.../bpf/prog_tests/task_under_cgroup.c | 47 +++++++++++++++++++
.../selftests/bpf/progs/cgrp_kfunc_common.h | 1 +
.../bpf/progs/test_task_under_cgroup.c | 37 +++++++++++++++
4 files changed, 86 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/DENYLIST.s390x b/tools/testing/selftests/bpf/DENYLIST.s390x
index c7463f3ec3c0..5061d9e24c16 100644
--- a/tools/testing/selftests/bpf/DENYLIST.s390x
+++ b/tools/testing/selftests/bpf/DENYLIST.s390x
@@ -26,3 +26,4 @@ user_ringbuf # failed to find kernel BTF type ID of
verif_stats # trace_vprintk__open_and_load unexpected error: -9 (?)
xdp_bonding # failed to auto-attach program 'trace_on_entry': -524 (trampoline)
xdp_metadata # JIT does not support calling kernel function (kfunc)
+test_task_under_cgroup # JIT does not support calling kernel function (kfunc)
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..6d5709a8203d
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Bytedance */
+
+#include <sys/syscall.h>
+#include <test_progs.h>
+#include <cgroup_helpers.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;
+
+ foo = test__join_cgroup(FOO);
+ if (!ASSERT_OK(foo < 0, "cgroup_join_foo"))
+ return;
+
+ skel = test_task_under_cgroup__open();
+ if (!ASSERT_OK_PTR(skel, "test_task_under_cgroup__open"))
+ goto cleanup;
+
+ skel->rodata->local_pid = getpid();
+ skel->rodata->cgid = get_cgroup_id(FOO);
+
+ 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;
+
+ syscall(SYS_getpgid);
+
+ test_task_under_cgroup__detach(skel);
+
+ ASSERT_EQ(skel->bss->remote_pid, skel->rodata->local_pid,
+ "test task_under_cgroup");
+
+cleanup:
+ if (foo >= 0)
+ close(foo);
+
+ test_task_under_cgroup__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
index 22914a70db54..001c416b42bc 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
@@ -26,6 +26,7 @@ struct cgroup *bpf_cgroup_ancestor(struct cgroup *cgrp, int level) __ksym;
struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
void bpf_rcu_read_lock(void) __ksym;
void bpf_rcu_read_unlock(void) __ksym;
+int bpf_task_under_cgroup(struct task_struct *task, struct cgroup *ancestor) __ksym;
return type 'long'?
static inline struct __cgrps_kfunc_map_value *cgrps_kfunc_map_value_lookup(struct cgroup *cgrp)
{
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..8f23a2933fde
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Bytedance */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+#include "bpf_misc.h"
+#include "cgrp_kfunc_common.h"
+
+const volatile int local_pid;
+const volatile long cgid;
+int remote_pid;
+
+SEC("fentry/" SYS_PREFIX "sys_getpgid")
+int sys_getpgid(void *ctx)
+{
+ struct cgroup *cgrp;
+
+ if (local_pid != (bpf_get_current_pid_tgid() >> 32))
+ return 0;
+
+ cgrp = bpf_cgroup_from_id(cgid);
+ if (!cgrp)
+ return 0;
+
+ if (!bpf_task_under_cgroup(bpf_get_current_task_btf(), cgrp))
+ goto out;
The whole point of using bpf_task_under_cgroup() is to test a
non-current task is under a particular cgroup.
Tracing kernel function enqueue_task_fair() is an option, but it
may be inlined with certain compilers as enqueue_task_fair() is
a static function. Also, the 'task' argument in enqueue_task_fair()
is not trusted, could be null ptr and not rcu safe as well.
We could promote 'task' in enqueue_task_fair() by:
- checking NULL ptr, if not
- increase reference count by 1 if current reference count is not 0
(using bpf_task_acquire kfunc)
- if reference count can be increased, it becomes trusted, and
then bpf_task_under_cgroup() can be used.
Could you try this approach or even better if there is another
non-static function also having a task (not the current task)?
+
+ remote_pid = local_pid;
+
+out:
+ bpf_cgroup_release(cgrp);
+ return 0;
+}
+
+char _license[] SEC("license") = "GPL";