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Message-ID: <703c3b4f-399c-45a5-a1e1-45c628fb94fb@linuxfoundation.org>
Date: Thu, 31 Oct 2024 16:59:04 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: zhouyuhang <zhouyuhang1010@....com>, brauner@...nel.org, shuah@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
zhouyuhang <zhouyuhang@...inos.cn>, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v3] selftests: clone3: Use the capget and capset syscall
directly
On 10/29/24 20:50, zhouyuhang wrote:
> From: zhouyuhang <zhouyuhang@...inos.cn>
>
> The libcap commit aca076443591 ("Make cap_t operations thread safe.")
> added a __u8 mutex at the beginning of the struct _cap_struct, it changes
> the offset of the members in the structure that breaks the assumption
> made in the "struct libcap" definition in clone3_cap_checkpoint_restore.c.
> This will cause the test case to fail with the following output:
>
> # RUN global.clone3_cap_checkpoint_restore ...
> # clone3() syscall supported
> # clone3_cap_checkpoint_restore.c:151:clone3_cap_checkpoint_restore:Child has PID 130508
> cap_set_proc: Operation not permitted
Sounds like EPERM is returned here. What's the error number from
cap_set_proc().
> # clone3_cap_checkpoint_restore.c:160:clone3_cap_checkpoint_restore:Expected set_capability() (-1) == 0 (0)
What's the error number here? Looks like this test simply
uses perror - it is better to use strerror() which includes
the error number.
Is this related EPERM?
> # clone3_cap_checkpoint_restore.c:161:clone3_cap_checkpoint_restore:Could not set CAP_CHECKPOINT_RESTORE
> # clone3_cap_checkpoint_restore: Test terminated by assertion
> # FAIL global.clone3_cap_checkpoint_restore
>
> Changing to using capget and capset syscall directly here can fix this error,
> just like what the commit 663af70aabb7 ("bpf: selftests: Add helpers to directly
> use the capget and capset syscall") does.
Is this still accurate for v3 - Does this patch match the
bpf commit?
What is the output with this patch? Include it in the change log.
>
> Signed-off-by: zhouyuhang <zhouyuhang@...inos.cn>> ---
Please mention the changes from v2 to v3 here so it makes it
easier for reviewers associating the changes to the reviewer.
I had to go look up v1 and v2.
> .../clone3/clone3_cap_checkpoint_restore.c | 58 +++++++++----------
> 1 file changed, 27 insertions(+), 31 deletions(-)
>
> diff --git a/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
> index 3c196fa86c99..8b61702bf721 100644
> --- a/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
> +++ b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
> @@ -27,6 +27,13 @@
> #include "../kselftest_harness.h"
> #include "clone3_selftests.h"
>
> +/*
> + * Prevent not being defined in the header file
> + */
> +#ifndef CAP_CHECKPOINT_RESTORE
> +#define CAP_CHECKPOINT_RESTORE 40
> +#endif
> +
> static void child_exit(int ret)
> {
> fflush(stdout);
> @@ -87,47 +94,36 @@ static int test_clone3_set_tid(struct __test_metadata *_metadata,
> return ret;
> }
>
> -struct libcap {
> - struct __user_cap_header_struct hdr;
> - struct __user_cap_data_struct data[2];
> -};
> -
> static int set_capability(void)
> {
> - cap_value_t cap_values[] = { CAP_SETUID, CAP_SETGID };
> - struct libcap *cap;
> - int ret = -1;
> - cap_t caps;
> -
> - caps = cap_get_proc();
> - if (!caps) {
> - perror("cap_get_proc");
> + struct __user_cap_data_struct data[2];
> + struct __user_cap_header_struct hdr = {
> + .version = _LINUX_CAPABILITY_VERSION_3,
cap_validate_magic() handles _LINUX_CAPABILITY_VERSION_1,
_LINUX_CAPABILITY_VERSION_2, and _LINUX_CAPABILITY_VERSION_3
It would help to add a comment on why it is necessary to
set the version here.
> + };
> + __u32 cap0 = 1 << CAP_SETUID | 1 << CAP_SETGID;
> + __u32 cap1 = 1 << (CAP_CHECKPOINT_RESTORE - 32);
Explain why this is necessary - a comment will help future
maintenance of this code.
> + int ret;
> +
> + ret = capget(&hdr, data);
> + if (ret) {
> + perror("capget");
> return -1;
> }
>
> /* Drop all capabilities */
> - if (cap_clear(caps)) {
> - perror("cap_clear");
> - goto out;
> - }
> -
> - cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_values, CAP_SET);
> - cap_set_flag(caps, CAP_PERMITTED, 2, cap_values, CAP_SET);
> + memset(&data, 0, sizeof(data));
>
> - cap = (struct libcap *) caps;
> + data[0].effective |= cap0;
> + data[0].permitted |= cap0;
>
> - /* 40 -> CAP_CHECKPOINT_RESTORE */
> - cap->data[1].effective |= 1 << (40 - 32);
> - cap->data[1].permitted |= 1 << (40 - 32);
> + data[1].effective |= cap1;
> + data[1].permitted |= cap1;
>
> - if (cap_set_proc(caps)) {
> - perror("cap_set_proc");
> - goto out;
> + ret = capset(&hdr, data);
> + if (ret) {
> + perror("capset");
> + return -1;
> }
> - ret = 0;
> -out:
> - if (cap_free(caps))
> - perror("cap_free");
> return ret;
> }
>
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