Possible null pointer dereference in isp1760.ko

[Anton Volkov]

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@xxxxxxxxx