Re: [PATCH] kref: oops on zero or negative refcount

[Dave Jones <davej@redhat.com>]

On Thu, Feb 20, 2014 at 06:44:59PM +0100, Mateusz Guzik wrote:
 > In use after free situations, it is possible for one thread to write to
 > memory that has just been reallocated to a new user. This could open up
 > potential security issues.
 > 
 > diff --git a/include/linux/kref.h b/include/linux/kref.h
 > index 484604d..c3f8a0a 100644
 > --- a/include/linux/kref.h
 > +++ b/include/linux/kref.h
 > @@ -43,8 +43,10 @@ static inline void kref_get(struct kref *kref)
 >  	/* If refcount was 0 before incrementing then we have a race
 >  	 * condition when this kref is freeing by some other thread right now.
 >  	 * In this case one should use kref_get_unless_zero()
 > +	 *
 > +	 * Terminate the current thread to stop potential security exploits.
 >  	 */
 > -	WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
 > +	BUG_ON(atomic_inc_return(&kref->refcount) < 2);

This isn't "terminating the thread", this is "lock up the box".

	Dave