Re: [PATCH v3] selftests: clone3: Use the capget and capset syscall directly

[Shuah Khan <skhan@linuxfoundation.org>]

On 10/29/24 20:50, zhouyuhang wrote:
> From: zhouyuhang <zhouyuhang@kylinos.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@kylinos.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;
>   }
>