[PATCH 3.16 69/72] USB: iowarrior: 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 edc4746f253d907d048de680a621e121517f484b upstream.

A recent fix addressing a deadlock on disconnect introduced a new bug
by moving the present flag out of the critical section protected by the
driver-data mutex. This could lead to a racing release() freeing the
driver data before disconnect() is done with it.

Due to insufficient locking a related use-after-free could be triggered
also before the above mentioned commit. Specifically, the driver needs
to hold the driver-data mutex also while checking the opened flag at
disconnect().

Fixes: c468a8aa790e ("usb: iowarrior: fix deadlock on disconnect")
Fixes: 946b960d13c1 ("USB: add driver for iowarrior devices.")
Reported-by: syzbot+0761012cebf7bdb38137@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20191009104846.5925-2-johan@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/usb/misc/iowarrior.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/drivers/usb/misc/iowarrior.c
+++ b/drivers/usb/misc/iowarrior.c
@@ -898,8 +898,6 @@ static void iowarrior_disconnect(struct
 	dev = usb_get_intfdata(interface);
 	mutex_lock(&iowarrior_open_disc_lock);
 	usb_set_intfdata(interface, NULL);
-	/* prevent device read, write and ioctl */
-	dev->present = 0;
 
 	minor = dev->minor;
 	mutex_unlock(&iowarrior_open_disc_lock);
@@ -910,8 +908,7 @@ static void iowarrior_disconnect(struct
 	mutex_lock(&dev->mutex);
 
 	/* prevent device read, write and ioctl */
-
-	mutex_unlock(&dev->mutex);
+	dev->present = 0;
 
 	if (dev->opened) {
 		/* There is a process that holds a filedescriptor to the device ,
@@ -921,8 +918,10 @@ static void iowarrior_disconnect(struct
 		usb_kill_urb(dev->int_in_urb);
 		wake_up_interruptible(&dev->read_wait);
 		wake_up_interruptible(&dev->write_wait);
+		mutex_unlock(&dev->mutex);
 	} else {
 		/* no process is using the device, cleanup now */
+		mutex_unlock(&dev->mutex);
 		iowarrior_delete(dev);
 	}