timeout: ensure a blocked SIGALRM from the parent is unblocked

* src/timeout.c (unblock_signal): A new function to unblock a
specified signal, or warn if not possible.
(set_timeout): Ensure SIGALRM is unblocked before we setup the timer.
* tests/misc/timeout-blocked.pl: A new test for the issue.
* tests/local.mk: Reference the new test.
* NEWS: Mention the fix.
Fixes: http://bugs.gnu.org/13535

1 files changed, 15 insertions, 0 deletions

diff --git a/src/timeout.c b/src/timeout.c
index b163a0ee8..2ffd2b119 100644
--- a/src/timeout.c
+++ b/src/timeout.c
@@ -102,6 +102,16 @@ static struct option const long_options[] =
   {NULL, 0, NULL, 0}
 };
 
+static void
+unblock_signal (int sig)
+{
+  sigset_t unblock_set;
+  sigemptyset (&unblock_set);
+  sigaddset (&unblock_set, sig);
+  if (sigprocmask (SIG_UNBLOCK, &unblock_set, NULL) != 0)
+    error (0, errno, _("warning: sigprocmask"));
+}
+
 /* Start the timeout after which we'll receive a SIGALRM.
    Round DURATION up to the next representable value.
    Treat out-of-range values as if they were maximal,
@@ -110,6 +120,11 @@ static struct option const long_options[] =
 static void
 settimeout (double duration)
 {
+
+  /* We configure timers below so that SIGALRM is sent on expiry.
+     Therefore ensure we don't inherit a mask blocking SIGALRM.  */
+  unblock_signal (SIGALRM);
+
 /* timer_settime() provides potentially nanosecond resolution.
    setitimer() is more portable (to Darwin for example),
    but only provides microsecond resolution and thus is