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SubjectPossible null pointer dereference in adutux.ko
Date
Hello.

While searching for races in the Linux kernel I've come across
"drivers/usb/misc/adutux.ko" module. Here is a question that I came up
with while analyzing results. Lines are given using the info from Linux
v4.12.

Consider the following case:

Thread 1: Thread 2:
adu_release
->adu_release_internal adu_disconnect
<READ &dev->udev->dev> dev->udev = NULL
(adutux.c: line 298) (adutux.c: line 771)
usb_deregister_dev

Comments in the source code point at the possibility of adu_release()
being called separately from adu_disconnect(). adu_release() and
adu_disconnect() acquire different mutexes, so they are not protected
from one another. If adu_disconnect() changes dev->udev before its value
is read in adu_release_internal() there will be a NULL pointer
dereference on a read attempt. Is this case feasible from your point of
view?

Thank you for your time.

-- Anton Volkov
Linux Verification Center, ISPRAS
web: http://linuxtesting.org
e-mail: avolkov@ispras.ru

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