Mask USR1/HUP while waiting for preloading

Preloading may fork and wait for the child to exit. In case waitpid() is
interrupted, the parent exits with a fatal error. This is fine when the
syscall is interrupted by a signal whose disposition is set to terminate
the process, but not otherwise.

In the apache2handler SAPI, the parent is the control process. Restarting
apache2 is done by sending SIGUSR1 or SIGHUP to the control process. Doing that
during the waitpid() syscall would cause the control process to exit instead.

Block the USR1 and HUP signals from being delivered during the syscall when
running the apache2handler SAPI, as these are not supposed to terminate
the process.

FPM is fine as it masks relevant signals during php startup.

Fixes GH-20051
Closes GH-20079

Co-authored-by: mycozyhom <welcomycozyhom@gmail.com>

Author: arnaud-lb

ext/opcache/ZendAccelerator.c

@@ -5090,13 +5090,45 @@ static zend_result accel_finish_startup(void)
 
 		exit(ret == SUCCESS ? 0 : 1);
 	} else { /* parent */
-		int status;
+# ifdef HAVE_SIGPROCMASK
+		/* Interrupting the waitpid() call below with a signal would cause the
+		 * process to exit. This is fine when the signal disposition is set to
+		 * terminate the process, but not otherwise.
+		 * When running the apache2handler, preloading is performed in the
+		 * control process. SIGUSR1 and SIGHUP are used to tell the control
+		 * process to restart children. Exiting when these signals are received
+		 * would unexpectedly shutdown the server instead of restarting it.
+		 * Block the USR1 and HUP signals from being delivered during the
+		 * syscall when running the apache2handler SAPI, as these are not
+		 * supposed to terminate the process. See GH-20051. */
+		bool is_apache2handler = strcmp(sapi_module.name, "apache2handler") == 0;
+		sigset_t set, oldset;
+		if (is_apache2handler) {
+			if (sigemptyset(&set)
+					|| sigaddset(&set, SIGUSR1)
+					|| sigaddset(&set, SIGHUP)) {
+				ZEND_UNREACHABLE();
+			}
+			if (sigprocmask(SIG_BLOCK, &set, &oldset)) {
+				ZEND_UNREACHABLE();
+			}
+		}
+# endif
 
+		int status;
 		if (waitpid(pid, &status, 0) < 0) {
 			zend_shared_alloc_unlock();
 			zend_accel_error_noreturn(ACCEL_LOG_FATAL, "Preloading failed to waitpid(%d)", pid);
 		}
 
+# ifdef HAVE_SIGPROCMASK
+		if (is_apache2handler) {
+			if (sigprocmask(SIG_SETMASK, &oldset, NULL)) {
+				ZEND_UNREACHABLE();
+			}
+		}
+# endif
+
 		if (ZCSG(preload_script)) {
 			preload_load(zend_map_ptr_static_last);
 		}