[PATCH 3.16 022/136] USB: usblcd: fix I/O after disconnect

Ben Hutchings
2019-12-17T01:00:36Z

From: Johan Hovold <johan@kernel.org>

commit eb7f5a490c5edfe8126f64bc58b9ba2edef0a425 upstream.

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: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20190926091228.24634-7-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/usb/misc/usblcd.c | 33 +++++++++++++++++++++++++++++++--
1 file changed, 31 insertions(+), 2 deletions(-)

--- a/drivers/usb/misc/usblcd.c
+++ b/drivers/usb/misc/usblcd.c
@@ -17,6 +17,7 @@
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/mutex.h>
+#include <linux/rwsem.h>
#include <linux/uaccess.h>
#include <linux/usb.h>

@@ -56,6 +57,8 @@ 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)

@@ -141,6 +144,13 @@ static ssize_t lcd_read(struct file *fil

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,
@@ -157,6 +167,9 @@ static ssize_t lcd_read(struct file *fil
retval = bytes_read;
}

+out_up_io:
+ up_read(&dev->io_rwsem);
+
return retval;
}

@@ -236,11 +249,18 @@ static ssize_t lcd_write(struct file *fi
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,
@@ -277,6 +297,7 @@ static ssize_t lcd_write(struct file *fi
the USB core will eventually free it entirely */
usb_free_urb(urb);

+ up_read(&dev->io_rwsem);
exit:
return count;
error_unanchor:
@@ -284,7 +305,8 @@ error_unanchor:
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;
}
@@ -327,6 +349,7 @@ static int lcd_probe(struct usb_interfac
}
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));
@@ -437,6 +460,12 @@ static void lcd_disconnect(struct usb_in
/* 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);