linux-kernel - Re: [PATCH bpf-next v2 2/2] selftests/bpf: Add testcase for bpf_task_under

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Date:   Fri, 21 Apr 2023 11:24:18 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Feng zhou <zhoufeng.zf@...edance.com>
Cc:     martin.lau@...ux.dev, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        mykolal@...com, shuah@...nel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org, yangzhenze@...edance.com,
        wangdongdong.6@...edance.com
Subject: Re: [PATCH bpf-next v2 2/2] selftests/bpf: Add testcase for
 bpf_task_under_cgroup

On Fri, Apr 21, 2023 at 05:04:03PM +0800, Feng zhou wrote:
> From: Feng Zhou <zhoufeng.zf@...edance.com>
> 
> test_progs:
> Tests new kfunc bpf_task_under_cgroup().
> 
> The bpf program saves the pid which call the getuid 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 getuid syscall, then check if
> remote_pid and local_pid are equal.
> 
> Signed-off-by: Feng Zhou <zhoufeng.zf@...edance.com>
> ---
>  .../bpf/prog_tests/task_under_cgroup.c        | 46 +++++++++++++++++++
>  .../selftests/bpf/progs/cgrp_kfunc_common.h   |  1 +
>  .../bpf/progs/test_task_under_cgroup.c        | 40 ++++++++++++++++
>  3 files changed, 87 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..bd3deb469938
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
> @@ -0,0 +1,46 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Bytedance */
> +
> +#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(__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);

Looks wrong. should be if (foo >= 0) ?

> +
> +	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..41b3ea231698 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 cgroup *cgrp, struct task_struct *task) __ksym;
>  
>  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..e2740f9b029d
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
> @@ -0,0 +1,40 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Bytedance */
> +
> +#include <vmlinux.h>
> +#include <asm/unistd.h>
> +#include <bpf/bpf_tracing.h>
> +#include <bpf/bpf_helpers.h>
> +
> +#include "cgrp_kfunc_common.h"
> +
> +const volatile int local_pid;
> +const volatile long cgid;
> +int remote_pid;
> +
> +SEC("tp_btf/sys_enter")

pls narrow down to specific syscall. Like you use in user space part: getuid

Also add this test to denylist.s390. See BPF CI failure.

> +int BPF_PROG(sysenter, struct pt_regs *regs, long id)
> +{
> +	struct cgroup *cgrp;
> +
> +	if (id != __NR_getuid)
> +		return 0;
> +
> +	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(cgrp, bpf_get_current_task_btf()))
> +		goto out;
> +
> +	remote_pid = local_pid;
> +
> +out:
> +	bpf_cgroup_release(cgrp);
> +	return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> -- 
> 2.20.1
>