Re: [PATCH] mm: fix lazy vmap purging (use-after-free error)

[Pekka Enberg <penberg@cs.helsinki.fi>]

On Fri, Feb 20, 2009 at 3:50 PM, Ingo Molnar <mingo@elte.hu> wrote:
>> @@ -537,7 +538,7 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end,
>>
>>       if (nr) {
>>               spin_lock(&vmap_area_lock);
>> -             list_for_each_entry(va, &valist, purge_list)
>> +             list_for_each_entry_safe(va, n_va, &valist, purge_list)
>>                       __free_vmap_area(va);
>>               spin_unlock(&vmap_area_lock);
>
> ah, indeed:
>
>        list_del_rcu(&va->list);
>
> i suspect it could be hit big time in a workload that opens more
> than 512 files, as expand_files() uses a vmalloc()+vfree() pair
> in that case.
>
> Nice catch! .29 must-have. The bug was introduced in
> v2.6.27-5616-gdb64fe0:
>
>  db64fe0: mm: rewrite vmap layer
>
> So 2.6.28 is affected too.
>
> Acked-by: Ingo Molnar <mingo@elte.hu>

Oh, I wish more people would run their code under kmemcheck... ;-)