Re: lockdep: Warning & NULL ptr deref

[Peter Zijlstra <peterz@infradead.org>]

On Tue, 2012-02-28 at 10:24 -0500, Sasha Levin wrote:
> 
> I'll send some patches to prevent the NULL deref itself which happens
> since a chunk of the code in lockdep.c assumed hlock_class() can't
> return NULL.
> 
There's tons of code actually assuming that..

> This won't fix the actual problem though, I'm not sure exactly how a
> held lock wouldn't have a class initialized to it. 

static inline struct lock_class *hlock_class(struct held_lock *hlock)                        
{               
        if (!hlock->class_idx) {                                                             
                /*
                 * Someone passed in garbage, we give up.                                    
                 */                                                                          
                DEBUG_LOCKS_WARN_ON(1);                                                      
                return NULL;
        }
        return lock_classes + hlock->class_idx - 1; 
}

Typically that translates to severe memory corruption.