[bpf-next,v4,2/2] selftests/bpf: Add testcase for bpf_task_under_cgroup

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

test_progs:
Tests new kfunc bpf_task_under_cgroup().

The bpf program saves the new task's pid 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 fork syscall, then check if
remote_pid and local_pid are unequal.

Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
---
 tools/testing/selftests/bpf/DENYLIST.s390x    |  1 +
 .../bpf/prog_tests/task_under_cgroup.c        | 55 +++++++++++++++++++
 .../bpf/progs/test_task_under_cgroup.c        | 51 +++++++++++++++++
 3 files changed, 107 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

在 2023/4/29 00:32, Yonghong Song 写道:
> 
> 
> On 4/28/23 12:17 AM, Feng zhou wrote:
>> From: Feng Zhou <zhoufeng.zf@bytedance.com>
>>
>> test_progs:
>> Tests new kfunc bpf_task_under_cgroup().
>>
>> The bpf program saves the new task's pid 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 fork syscall, then check if
>> remote_pid and local_pid are unequal.
>>
>> Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
> 
> Ack with a few nits below.
> 
> Acked-by: Yonghong Song <yhs@fb.com>
> 
>> ---
>>   tools/testing/selftests/bpf/DENYLIST.s390x    |  1 +
>>   .../bpf/prog_tests/task_under_cgroup.c        | 55 +++++++++++++++++++
>>   .../bpf/progs/test_task_under_cgroup.c        | 51 +++++++++++++++++
>>   3 files changed, 107 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..5e79dff86dec
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
>> @@ -0,0 +1,55 @@
>> +// 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;
>> +    pid_t pid;
>> +
>> +    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->bss->remote_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;
>> +
>> +    pid = fork();
>> +    if (pid == 0)
>> +        exit(0);
>> +    else if (pid == -1)
>> +        printf("Couldn't fork process!\n");
> 
> ASSERT_* is preferred compared to 'printf'. Maybe ASSERT_TRUE(0, 
> "Couldn't fork process")?
> 

Will do.

>> +
>> +    wait(NULL);
>> +
>> +    test_task_under_cgroup__detach(skel);
>> +
>> +    ASSERT_NEQ(skel->bss->remote_pid, skel->rodata->local_pid,
>> +           "test task_under_cgroup");
>> +
>> +cleanup:
>> +    if (foo >= 0)
> 
> "if (foo >= 0)" is not needed. 'foo' is guaranteed ">= 0" as this point.
> 

Yes

>> +        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..5bcb726d6d0a
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
>> @@ -0,0 +1,51 @@
>> +// 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"
>> +
>> +struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
>> +long bpf_task_under_cgroup(struct task_struct *task, struct cgroup 
>> *ancestor) __ksym;
>> +void bpf_cgroup_release(struct cgroup *p) __ksym;
>> +struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym;
>> +void bpf_task_release(struct task_struct *p) __ksym;
>> +
>> +const volatile int local_pid;
>> +const volatile long cgid;
> 
> cgid cannot be a negative number. So let us do
> const volatile __u64 cgid;
> 

Ok

>> +int remote_pid;
>> +
>> +SEC("tp_btf/task_newtask")
>> +int BPF_PROG(handle__task_newtask, struct task_struct *task, u64 
>> clone_flags)
>> +{
>> +    struct cgroup *cgrp = NULL;
>> +    struct task_struct *acquired = NULL;
> 
> "acquired = NULL" is not needed. Just do "struct task_struct *acquired;".
> 

Ok

>> +
>> +    if (local_pid != (bpf_get_current_pid_tgid() >> 32))
>> +        return 0;
>> +
>> +    acquired = bpf_task_acquire(task);
>> +    if (!acquired)
>> +        return 0;
>> +
>> +    if (local_pid == acquired->tgid)
>> +        goto out;
>> +
>> +    cgrp = bpf_cgroup_from_id(cgid);
>> +    if (!cgrp)
>> +        goto out;
>> +
>> +    if (bpf_task_under_cgroup(acquired, cgrp))
>> +        remote_pid = acquired->tgid;
>> +
>> +out:
>> +    if (acquired)
>> +        bpf_task_release(acquired);
>> +    if (cgrp)
>> +        bpf_cgroup_release(cgrp);
>> +    return 0;
>> +}
>> +
>> +char _license[] SEC("license") = "GPL";