linux-kernel - Re: [PATCH] selftests/seccomp: Actually sleep for 1/10th second

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Date:   Sun, 27 Jan 2019 02:25:41 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Shuah Khan <shuah@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] selftests/seccomp: Actually sleep for 1/10th second

On Sun, Jan 27, 2019 at 1:44 AM Kees Cook <keescook@...omium.org> wrote:
>
> Clang noticed that some none-zero sleep()s were actually using zero
> anyway. This switches to nanosleep() to gain sub-second granularity.
>
> seccomp_bpf.c:2625:9: warning: implicit conversion from 'double' to
>       'unsigned int' changes value from 0.1 to 0 [-Wliteral-conversion]
>                 sleep(0.1);
>                 ~~~~~ ^~~
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  tools/testing/selftests/seccomp/seccomp_bpf.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> index 067cb4607d6c..a9f278c13f13 100644
> --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> @@ -2569,6 +2569,7 @@ TEST_F(TSYNC, two_siblings_not_under_filter)
>  {
>         long ret, sib;
>         void *status;
> +       struct timespec delay = { .tv_nsec = 100000000 };

"Omitted fields are implicitly initialized the same as for objects
that have static storage duration."
https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html
https://godbolt.org/z/cuGqxM
(So this wont sleep an arbitrary amount of seconds, phew)

>
>         ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
>                 TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!");
> @@ -2622,7 +2623,7 @@ TEST_F(TSYNC, two_siblings_not_under_filter)
>         EXPECT_EQ(SIBLING_EXIT_UNKILLED, (long)status);
>         /* Poll for actual task death. pthread_join doesn't guarantee it. */
>         while (!kill(self->sibling[sib].system_tid, 0))
> -               sleep(0.1);
> +               nanosleep(&delay, NULL);
>         /* Switch to the remaining sibling */
>         sib = !sib;
>
> @@ -2647,7 +2648,7 @@ TEST_F(TSYNC, two_siblings_not_under_filter)
>         EXPECT_EQ(0, (long)status);
>         /* Poll for actual task death. pthread_join doesn't guarantee it. */
>         while (!kill(self->sibling[sib].system_tid, 0))
> -               sleep(0.1);
> +               nanosleep(&delay, NULL);

Interesting bug.  If the sleeps weren't doing anything, are they even
needed? Does adding the tests cause them to continue to pass, or start
to fail?  If they weren't doing anything, and the tests were passing,
maybe it's just better to remove them?

-- 
Thanks,
~Nick Desaulniers