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Subject[PATCH 3.16 64/72] USB: adutux: fix use-after-free on disconnect
3.16.79-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Johan Hovold <johan@kernel.org>

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@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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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);
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