Possible double free in iowarrior.ko

[Anton Volkov]

Hello.

While searching for races in the Linux kernel I've come across 
"drivers/usb/misc/iowarrior.ko" module. Here are questions 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:
iowarrior_release            iowarrior_disconnect
                               mutex_lock(&dev->mutex)
                               dev->present = 0
                               (iowarrior.c: line 889)
  mutex_lock(&dev->mutex)      mutex_unlock(&dev->mutex)
  dev->opened = 0
  (iowarrior.c: line 666)      if(dev->opened){
  if(dev->present){               //dev->opened == 0
    //dev->present ==0
  } else {                     } else {
    mutex_unlock(&dev->mutex)    iowarrior_delete(dev)
    iowarrior_delete(dev)      }
  }

In this case double free of several pointers inside iowarrior_delete 
becomes possible and no calls to usb_kill_urb() and 
wake_up_interruptible() are present. Is this feasible from your point of 
view? If so, maybe it is a good idea to move mutex_unlock(&dev->mutex) 
in iowarrior_disconnect() further down like in iowarrior_release() in 
both 'if' branches?

Thank you for your time

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