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

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)")
Cc: stable <stable@vger.kernel.org>     # 2.6.24
Reported-by: syzbot+0243cb250a51eeefb8cc@syzkaller.appspotmail.com
Tested-by: syzbot+0243cb250a51eeefb8cc@syzkaller.appspotmail.com
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20190925092913.8608-1-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/misc/adutux.c b/drivers/usb/misc/adutux.c
index f499cab..c88ccd0 100644 (file)
--- a/drivers/usb/misc/adutux.c
+++ b/drivers/usb/misc/adutux.c
@@ -803,14 +803,15 @@ static void adu_disconnect(struct usb_interface *interface)
 
        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);