[PULL v2 6/8] fuzz: unblock SIGALRM so the timeout works

[Alexander Bulekov]

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>
---
 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