Add locking to ioctl emulation (#92)

When e. g. using libgusb (GLib libusb wrapper), libusb has its mainloop
running in one thread while the main thread might be submitting urbs
directly using another ioctl. This can cause the wrong URB to be
returned.

Fix this issue by adding locking to ioctl_emulate.

Author: benzea

src/libumockdev-preload.c

@@ -120,9 +120,15 @@ path_exists(const char *path)
 /* multi-thread locking for trap_path users */
 pthread_mutex_t trap_path_lock = PTHREAD_MUTEX_INITIALIZER;
 
+/* multi-thread locking for ioctls */
+pthread_mutex_t ioctl_lock = PTHREAD_MUTEX_INITIALIZER;
+
 #define TRAP_PATH_LOCK pthread_mutex_lock (&trap_path_lock)
 #define TRAP_PATH_UNLOCK pthread_mutex_unlock (&trap_path_lock)
 
+#define IOCTL_LOCK pthread_mutex_lock (&ioctl_lock)
+#define IOCTL_UNLOCK pthread_mutex_unlock (&ioctl_lock)
+
 static size_t trap_path_prefix_len = 0;
 
 static const char *
@@ -645,6 +651,8 @@ ioctl_emulate(int fd, IOCTL_REQUEST_TYPE request, void *arg)
     int orig_errno;
     struct ioctl_fd_info *fdinfo;
 
+    IOCTL_LOCK;
+
     if (fd_map_get(&ioctl_wrapped_fds, fd, (const void **)&fdinfo)) {
 	/* we default to erroring and an appropriate error code before
 	 * tree_execute, as handlers might change errno; if they succeed, we
@@ -668,6 +676,8 @@ ioctl_emulate(int fd, IOCTL_REQUEST_TYPE request, void *arg)
 	ioctl_result = UNHANDLED;
     }
 
+    IOCTL_UNLOCK;
+
     return ioctl_result;
 }