linux-kernel - Possible null pointer dereference in isp1760.ko

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Date:   Mon, 7 Aug 2017 18:12:38 +0300
From:   Anton Volkov <avolkov@...ras.ru>
To:     bhumirks@...il.com
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, ldv-project@...uxtesting.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>
Subject: Possible null pointer dereference in isp1760.ko

Hello.

While searching for races in the Linux kernel I've come across 
"drivers/usb/isp1760/isp1760.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:
isp1760_plat_probe
-> isp1760_register
    -> isp1760_udc_register
          request_irq(...,udc)
       -> isp1760_udc_init_eps(udc)    isp1760_udc_irq
            for(i = 0; ...){              for(i = 0; ...) {
              ep = &udc->ep[i]               ep = &udc->ep[i%2]
                                          -> isp1760_ep_rx_ready(ep)
              INIT_LIST_HEAD(ep->queue)         list_empty(&ep->queue)
              (isp1760-udc.c: line 1367)        (isp1760-udc.c: line 303)

As far as I understand ep->queue is NULL before its initialization in 
isp1760_udc_init_eps and list_empty() tries to access the '->next' 
pointer member of the passed parameter.

Is this case possible from your point of view?

Thank you for your time.

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