Fix shutdown race with hotplug_libusb rescan pipe

Fix the possibility that the hotplug_libusb rescan thread remains
read()'ing from the rescan pipe throughout the daemon shutdown process.

This is possible because the |rescan_pipe| is created with some delay
after the hotplug mechanism is initialized:
HPEstablishUSBNotifications() first notifies about the initialization
via writing to |pipefd|, and only then creates |rescan_pipe|. So if
HPStopHotPluggables() is called in between, it'll end up doing nothing,
letting the hotplug thread sit infinitely long on the read() call
meanwhile the main daemon thread is shutting down.

The proposed fix is to create |rescan_pipe| in advance, so that the
shutdown logic is guaranteed to be able to write a byte to it, notifying
the background thread about the shutdown regardless of when it happens.

src/hotplug_libusb.c

@@ -468,6 +468,9 @@ static void HPRescanUsbBus(void)
 		}
 		free(driverTracker);
 
+		close(rescan_pipe[0]);
+		rescan_pipe[0] = -1;
+
 		Log1(PCSC_LOG_INFO, "Hotplug stopped");
 		pthread_exit(&retval);
 	}
@@ -531,12 +534,6 @@ static void * HPEstablishUSBNotifications(int pipefd[2])
 	else
 	{
 		char dummy;
-
-		if (pipe(rescan_pipe) == -1)
-		{
-			Log2(PCSC_LOG_ERROR, "pipe: %s", strerror(errno));
-			return NULL;
-		}
 		while (read(rescan_pipe[0], &dummy, sizeof(dummy)) > 0)
 		{
 			Log1(PCSC_LOG_INFO, "Reload serial configuration");
@@ -546,10 +543,11 @@ static void * HPEstablishUSBNotifications(int pipefd[2])
 #endif
 			Log1(PCSC_LOG_INFO, "End reload serial configuration");
 		}
-		close(rescan_pipe[0]);
-		rescan_pipe[0] = -1;
 	}
 
+	close(rescan_pipe[0]);
+	rescan_pipe[0] = -1;
+
 	return NULL;
 }
 
@@ -567,15 +565,22 @@ LONG HPSearchHotPluggables(const char * hpDirPath)
 
 	if (HPReadBundleValues(hpDirPath) > 0)
 	{
+		/* used for waiting for the initialization completion */
 		int pipefd[2];
 		char c;
-
 		if (pipe(pipefd) == -1)
 		{
 			Log2(PCSC_LOG_ERROR, "pipe: %s", strerror(errno));
 			return -1;
 		}
 
+		/* used for rescan events */
+		if (pipe(rescan_pipe) == -1)
+		{
+			Log2(PCSC_LOG_ERROR, "pipe: %s", strerror(errno));
+			return -1;
+		}
+
 		ThreadCreate(&usbNotifyThread, THREAD_ATTR_DETACHED,
 			(PCSCLITE_THREAD_FUNCTION( )) HPEstablishUSBNotifications, pipefd);
 
@@ -584,7 +589,7 @@ LONG HPSearchHotPluggables(const char * hpDirPath)
 		{
 			Log2(PCSC_LOG_ERROR, "read: %s", strerror(errno));
 			return -1;
-		};
+		}
 
 		/* cleanup pipe fd */
 		close(pipefd[0]);