Calling startMonitoring() and stopMonitoring() multiple times causes segmentation fault (Linux, macOS)

[qtphan734]

In a simple node application, if you execute the folllowing code, you will either get segmentation fault or some memory corruption error on Ubuntu 16.04:

usbDetection.startMonitoring();
usbDetection.stopMonitoring();

usbDetection.startMonitoring();
usbDetection.stopMonitoring();

[MadLittleMods]

Related to #53

[PeterBurner]

I don't think calling them multiple times is the problem. stopMonitoring() seems to be broken on linux.
I can generate a segmentation fault with the following code:

var usbDetect = require('usb-detection');

usbDetect.startMonitoring();

usbDetect.stopMonitoring();

setTimeout(() => console.log('end'), 1000);

If I comment out the line with stopMonitoring() I get a log output but afterwards the process hangs.

Node Version: v12.8.0
OS: Raspbian 10 (buster)

By the way: The code above works just fine on MacOS.

[P0oOOOo0YA]

I can reproduce the problem on my Linux machine with the code posted by @PeterBurner .

    OS: Linux 5.3 Kali GNU/Linux Rolling 2019.4
    Node: 13.5.0

[gre]

I reproduce this situation in [email protected] on Node 12 and Mac.

[frankrobert-ls]

As @gre mentioned this can be reproduced on Mac with Node12. Could we update this issue's title + labels to reflect it better? 🌈

[kfazz]

For 4.10, I was able to fix this with the following patch:

linux_detection_fix_udev_mon_use_after_free.txt

linux_detection_fix_udev_mon_use_after_free patch

Description: linux detection: fix udev mon use after free
 TODO: Put a short summary on the line above and replace this paragraph
 with a longer explanation of this change. Complete the meta-information
 with other relevant fields (see below for details). To make it easier, the
 information below has been extracted from the changelog. Adjust it or drop
 it.
 .
 node-usb-detection (4.10.0-2) UNRELEASED; urgency=medium
 .
   [ Ken Fazzone ]
   * Initial release
Author: Ken Fazzone <[email protected]>

---
The information above should follow the Patch Tagging Guidelines, please
checkout http://dep.debian.net/deps/dep3/ to learn about the format. Here
are templates for supplementary fields that you might want to add:

Origin: <vendor|upstream|other>, <url of original patch>
Bug: <url in upstream bugtracker>
Bug-Debian: https://bugs.debian.org/<bugnumber>
Bug-Ubuntu: https://launchpad.net/bugs/<bugnumber>
Forwarded: <no|not-needed|url proving that it has been forwarded>
Reviewed-By: <name and email of someone who approved the patch>
Last-Update: 2021-01-19

--- node-usb-detection-4.10.0.orig/src/detection_linux.cpp
+++ node-usb-detection-4.10.0/src/detection_linux.cpp
@@ -98,6 +98,7 @@ void Stop() {
 	uv_cond_destroy(&notifyDeviceHandled);
 
 	udev_monitor_unref(mon);
+	mon = NULL;
 	udev_unref(udev);
 }
 
@@ -226,19 +227,21 @@ static void cbWork(uv_work_t *req) {
 		if (!ret) continue;
 		if (ret < 0) break;
 
-		dev = udev_monitor_receive_device(mon);
-		if (dev) {
-			if(udev_device_get_devtype(dev) && strcmp(udev_device_get_devtype(dev), DEVICE_TYPE_DEVICE) == 0) {
-				if(strcmp(udev_device_get_action(dev), DEVICE_ACTION_ADDED) == 0) {
-					WaitForDeviceHandled();
-					DeviceAdded(dev);
-				}
-				else if(strcmp(udev_device_get_action(dev), DEVICE_ACTION_REMOVED) == 0) {
-					WaitForDeviceHandled();
-					DeviceRemoved(dev);
+		if(mon) {
+			dev = udev_monitor_receive_device(mon);
+			if (dev) {
+				if(udev_device_get_devtype(dev) && strcmp(udev_device_get_devtype(dev), DEVICE_TYPE_DEVICE) == 0) {
+					if(strcmp(udev_device_get_action(dev), DEVICE_ACTION_ADDED) == 0) {
+						WaitForDeviceHandled();
+						DeviceAdded(dev);
+					}
+					else if(strcmp(udev_device_get_action(dev), DEVICE_ACTION_REMOVED) == 0) {
+						WaitForDeviceHandled();
+						DeviceRemoved(dev);
+					}
 				}
+				udev_device_unref(dev);
 			}
-			udev_device_unref(dev);
 		}
 	}
 }