Re: [PATCH 2/2] fuzz: unblock SIGALRM so the timeout works

[Darren Kenny]

On Wednesday, 2021-08-04 at 09:56:21 -04, Alexander Bulekov wrote:
> The timeout mechanism wont work if SIGALRM is blocked. This changes

NIT: s/wont/won't/
     s/changes/change/

> unmasks SIGALRM when the timer is installed. This doesn't completely
> solve the problem, as the fuzzer could trigger some device activity that
> re-masks SIGALRM. However, there are currently no inputs on OSS-Fuzz
> that re-mask SIGALRM and timeout. If that turns out to be a real issue,
> we could try to hook sigmask-type calls, or use a separate timer thread.
>
> Based-on: <20210713150037.9297-1-alxndr@bu.edu>
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

> ---
>  tests/qtest/fuzz/generic_fuzz.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/tests/qtest/fuzz/generic_fuzz.c b/tests/qtest/fuzz/generic_fuzz.c
> index de427a3727..dd7e25851c 100644
> --- a/tests/qtest/fuzz/generic_fuzz.c
> +++ b/tests/qtest/fuzz/generic_fuzz.c
> @@ -670,6 +670,7 @@ static void generic_fuzz(QTestState *s, const unsigned 
> char *Data, size_t Size)
>      if (fork() == 0) {
>          struct sigaction sact;
>          struct itimerval timer;
> +        sigset_t set;
>          /*
>           * Sometimes the fuzzer will find inputs that take quite a long time 
> to
>           * process. Often times, these inputs do not result in new coverage.
> @@ -684,6 +685,10 @@ static void generic_fuzz(QTestState *s, const unsigned 
> char *Data, size_t Size)
>              sact.sa_handler = handle_timeout;
>              sigaction(SIGALRM, &sact, NULL);
>  
> +            sigemptyset(&set);
> +            sigaddset(&set, SIGALRM);
> +            pthread_sigmask(SIG_UNBLOCK, &set, NULL);
> +
>              memset(&timer, 0, sizeof(timer));
>              timer.it_value.tv_sec = timeout / USEC_IN_SEC;
>              timer.it_value.tv_usec = timeout % USEC_IN_SEC;
> -- 
> 2.30.2