netdev - Re: [Potential Spoof] [PATCH bpf-next] selftests/bpf: fix nanosleep for real this time

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Date:   Fri, 13 Mar 2020 17:05:10 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Andrii Nakryiko <andriin@...com>
CC:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>, <andrii.nakryiko@...il.com>,
        <kernel-team@...com>
Subject: Re: [Potential Spoof] [PATCH bpf-next] selftests/bpf: fix nanosleep
 for real this time

On Fri, Mar 13, 2020 at 04:35:35PM -0700, Andrii Nakryiko wrote:
> Amazingly, some libc implementations don't call __NR_nanosleep syscall from
> their nanosleep() APIs. Hammer it down with explicit syscall() call and never
> get back to it again. Also simplify code for timespec initialization.
> 
> I verified that nanosleep is called w/ printk and in exactly same Linux image
> that is used in Travis CI. So it should both sleep and call correct syscall.
> 
> Fixes: 4e1fd25d19e8 ("selftests/bpf: Fix usleep() implementation")
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>  tools/testing/selftests/bpf/test_progs.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> index f85a06512541..6956d722a463 100644
> --- a/tools/testing/selftests/bpf/test_progs.c
> +++ b/tools/testing/selftests/bpf/test_progs.c
> @@ -35,16 +35,12 @@ struct prog_test_def {
>   */
>  int usleep(useconds_t usec)
>  {
> -	struct timespec ts;
> -
> -	if (usec > 999999) {
> -		ts.tv_sec = usec / 1000000;
> -		ts.tv_nsec = usec % 1000000;
> -	} else {
> -		ts.tv_sec = 0;
> -		ts.tv_nsec = usec;
> -	}
> -	return nanosleep(&ts, NULL);
> +	struct timespec ts = {
> +		.tv_sec = usec / 1000000,
> +		.tv_nsec = usec % 1000000,
usec is in micro and tv_nsec is in nano?

> +	};
> +
> +	return syscall(__NR_nanosleep, &ts, NULL);
>  }
>