[PATCH 3.16 64/72] USB: adutux: fix use-after-free on disconnect

[Ben Hutchings]

3.16.79-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@xxxxxxxxxx>

commit 44efc269db7929f6275a1fa927ef082e533ecde0 upstream.

The driver was clearing its struct usb_device pointer, which it used as
an inverted disconnected flag, before deregistering the character device
and without serialising against racing release().

This could lead to a use-after-free if a racing release() callback
observes the cleared pointer and frees the driver data before
disconnect() is finished with it.

This could also lead to NULL-pointer dereferences in a racing open().

Fixes: f08812d5eb8f ("USB: FIx locks and urb->status in adutux (updated)")
Reported-by: syzbot+0243cb250a51eeefb8cc@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: syzbot+0243cb250a51eeefb8cc@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20190925092913.8608-1-johan@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/usb/misc/adutux.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/usb/misc/adutux.c
+++ b/drivers/usb/misc/adutux.c
@@ -799,14 +799,15 @@ static void adu_disconnect(struct usb_in
 
 	dev = usb_get_intfdata(interface);
 
-	mutex_lock(&dev->mtx);	/* not interruptible */
-	dev->udev = NULL;	/* poison */
 	usb_deregister_dev(interface, &adu_class);
-	mutex_unlock(&dev->mtx);
 
 	mutex_lock(&adutux_mutex);
 	usb_set_intfdata(interface, NULL);
 
+	mutex_lock(&dev->mtx);	/* not interruptible */
+	dev->udev = NULL;	/* poison */
+	mutex_unlock(&dev->mtx);
+
 	/* if the device is not opened, then we clean up right now */
 	if (!dev->open_count)
 		adu_delete(dev);