fuzz: unblock SIGALRM so the timeout works

The timeout mechanism won't work if SIGALRM is blocked. This changes
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>

diff --git a/tests/qtest/fuzz/generic_fuzz.c b/tests/qtest/fuzz/generic_fuzz.c
index de427a37279e97a8bca7e9a27890d585aefc6cb5..dd7e25851cb6dcc55b97f95897c1a65d312b4a10 100644 (file)
--- 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;