USB: yurex: fix NULL-derefs on disconnect

The driver was using its struct usb_interface pointer as an inverted
disconnected flag, but was setting it to NULL without making sure all
code paths that used it were done with it.

Before commit ef61eb43 ("USB: yurex: Fix protection fault after
device removal") this included the interrupt-in completion handler, but
there are further accesses in dev_err and dev_dbg statements in
yurex_write() and the driver-data destructor (sic!).

Fix this by unconditionally stopping also the control URB at disconnect
and by using a dedicated disconnected flag.

Note that we need to take a reference to the struct usb_interface to
avoid a use-after-free in the destructor whenever the device was
disconnected while the character device was still open.

Fixes: aadd6472 ("USB: yurex.c: remove dbg() usage")
Fixes: 45714104 ("USB: yurex.c: remove err() usage")
Cc: stable <stable@vger.kernel.org>     # 3.5: ef61eb43Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191009153848.8664-6-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/yurex.c

@@ -60,6 +60,7 @@ struct usb_yurex {
 
 	struct kref		kref;
 	struct mutex		io_mutex;
+	unsigned long		disconnected:1;
 	struct fasync_struct	*async_queue;
 	wait_queue_head_t	waitq;
 
@@ -107,6 +108,7 @@ static void yurex_delete(struct kref *kref)
 				dev->int_buffer, dev->urb->transfer_dma);
 		usb_free_urb(dev->urb);
 	}
+	usb_put_intf(dev->interface);
 	usb_put_dev(dev->udev);
 	kfree(dev);
 }
@@ -205,7 +207,7 @@ static int yurex_probe(struct usb_interface *interface, const struct usb_device_
 	init_waitqueue_head(&dev->waitq);
 
 	dev->udev = usb_get_dev(interface_to_usbdev(interface));
-	dev->interface = interface;
+	dev->interface = usb_get_intf(interface);
 
 	/* set up the endpoint information */
 	iface_desc = interface->cur_altsetting;
@@ -316,8 +318,9 @@ static void yurex_disconnect(struct usb_interface *interface)
 
 	/* prevent more I/O from starting */
 	usb_poison_urb(dev->urb);
+	usb_poison_urb(dev->cntl_urb);
 	mutex_lock(&dev->io_mutex);
-	dev->interface = NULL;
+	dev->disconnected = 1;
 	mutex_unlock(&dev->io_mutex);
 
 	/* wakeup waiters */
@@ -405,7 +408,7 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count,
 	dev = file->private_data;
 
 	mutex_lock(&dev->io_mutex);
-	if (!dev->interface) {		/* already disconnected */
+	if (dev->disconnected) {		/* already disconnected */
 		mutex_unlock(&dev->io_mutex);
 		return -ENODEV;
 	}
@@ -440,7 +443,7 @@ static ssize_t yurex_write(struct file *file, const char __user *user_buffer,
 		goto error;
 
 	mutex_lock(&dev->io_mutex);
-	if (!dev->interface) {		/* already disconnected */
+	if (dev->disconnected) {		/* already disconnected */
 		mutex_unlock(&dev->io_mutex);
 		retval = -ENODEV;
 		goto error;