USB: usblcd: fix I/O after disconnect

Make sure to stop all I/O on disconnect by adding a disconnected flag
which is used to prevent new I/O from being started and by stopping all
ongoing I/O before returning.

This also fixes a potential use-after-free on driver unbind in case the
driver data is freed before the completion handler has run.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>	# 7bbe990cSigned-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20190926091228.24634-7-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/usblcd.c

@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/errno.h>
 #include <linux/mutex.h>
+#include <linux/rwsem.h>
 #include <linux/uaccess.h>
 #include <linux/usb.h>
 
@@ -57,6 +58,8 @@ struct usb_lcd {
 							   using up all RAM */
 	struct usb_anchor	submitted;		/* URBs to wait for
 							   before suspend */
+	struct rw_semaphore	io_rwsem;
+	unsigned long		disconnected:1;
 };
 #define to_lcd_dev(d) container_of(d, struct usb_lcd, kref)
 
@@ -142,6 +145,13 @@ static ssize_t lcd_read(struct file *file, char __user * buffer,
 
 	dev = file->private_data;
 
+	down_read(&dev->io_rwsem);
+
+	if (dev->disconnected) {
+		retval = -ENODEV;
+		goto out_up_io;
+	}
+
 	/* do a blocking bulk read to get data from the device */
 	retval = usb_bulk_msg(dev->udev,
 			      usb_rcvbulkpipe(dev->udev,
@@ -158,6 +168,9 @@ static ssize_t lcd_read(struct file *file, char __user * buffer,
 			retval = bytes_read;
 	}
 
+out_up_io:
+	up_read(&dev->io_rwsem);
+
 	return retval;
 }
 
@@ -237,11 +250,18 @@ static ssize_t lcd_write(struct file *file, const char __user * user_buffer,
 	if (r < 0)
 		return -EINTR;
 
+	down_read(&dev->io_rwsem);
+
+	if (dev->disconnected) {
+		retval = -ENODEV;
+		goto err_up_io;
+	}
+
 	/* create a urb, and a buffer for it, and copy the data to the urb */
 	urb = usb_alloc_urb(0, GFP_KERNEL);
 	if (!urb) {
 		retval = -ENOMEM;
-		goto err_no_buf;
+		goto err_up_io;
 	}
 
 	buf = usb_alloc_coherent(dev->udev, count, GFP_KERNEL,
@@ -278,6 +298,7 @@ static ssize_t lcd_write(struct file *file, const char __user * user_buffer,
 	   the USB core will eventually free it entirely */
 	usb_free_urb(urb);
 
+	up_read(&dev->io_rwsem);
 exit:
 	return count;
 error_unanchor:
@@ -285,7 +306,8 @@ static ssize_t lcd_write(struct file *file, const char __user * user_buffer,
 error:
 	usb_free_coherent(dev->udev, count, buf, urb->transfer_dma);
 	usb_free_urb(urb);
-err_no_buf:
+err_up_io:
+	up_read(&dev->io_rwsem);
 	up(&dev->limit_sem);
 	return retval;
 }
@@ -325,6 +347,7 @@ static int lcd_probe(struct usb_interface *interface,
 
 	kref_init(&dev->kref);
 	sema_init(&dev->limit_sem, USB_LCD_CONCURRENT_WRITES);
+	init_rwsem(&dev->io_rwsem);
 	init_usb_anchor(&dev->submitted);
 
 	dev->udev = usb_get_dev(interface_to_usbdev(interface));
@@ -422,6 +445,12 @@ static void lcd_disconnect(struct usb_interface *interface)
 	/* give back our minor */
 	usb_deregister_dev(interface, &lcd_class);
 
+	down_write(&dev->io_rwsem);
+	dev->disconnected = 1;
+	up_write(&dev->io_rwsem);
+
+	usb_kill_anchored_urbs(&dev->submitted);
+
 	/* decrement our usage count */
 	kref_put(&dev->kref, lcd_delete);