patch "USB: iowarrior: fix use-after-free on disconnect" added to usb-linus

This is a note to let you know that I've just added the patch titled

USB: iowarrior: fix use-after-free on disconnect

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From edc4746f253d907d048de680a621e121517f484b Mon Sep 17 00:00:00 2001
From: Johan Hovold <[email protected]>
Date: Wed, 9 Oct 2019 12:48:41 +0200
Subject: USB: iowarrior: fix use-after-free on disconnect

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().

---
 drivers/usb/misc/iowarrior.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

index f5bed9f29e56..4fe1d3267b3c 100644
@@ -866,8 +866,6 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 	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);

@@ -878,8 +876,7 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 	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 ,

@@ -889,8 +886,10 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 		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);
 	}
 

2.23.0