Re: trace: use-after-free in hist_unreg_all

[Tom Zanussi]

Hi Steve,

On 06/28/2016 09:43 AM, Steven Rostedt wrote:
> On Tue, 28 Jun 2016 14:58:50 +0200
> Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> 
>> Hello,
>>
>> While running tools/testing/selftests test suite with KASAN I hit the
>> following use-after-free report:
>>
>>
>>
>> ==================================================================
>> BUG: KASAN: use-after-free in hist_unreg_all+0x1a1/0x1d0 at addr
>> ffff880031632cc0
>> Read of size 8 by task ftracetest/7413
>> =============================================================================
>> BUG kmalloc-128 (Not tainted): kasan: bad access detected
>> -----------------------------------------------------------------------------
> 
> Thanks for the report. Can you check if this patch fixes the issue?
> 
> -- Steve
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 0c05b8a99806..948adb4b6761 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1699,9 +1699,9 @@ hist_enable_get_trigger_ops(char *cmd, char *param)
>  
>  static void hist_enable_unreg_all(struct trace_event_file *file)

This does fix the problem, if put on hist_unreg_all() instead of this ;-)

Actually, with that gone, I see another problem with the multihist test,
which I'm digging into now.

Actually, I should really run through my whole testsuite with KASAN
turned on...

Thanks for the initial patch, in any case.

Tom

>  {
> -	struct event_trigger_data *test;
> +	struct event_trigger_data *test, *n;
>  
> -	list_for_each_entry_rcu(test, &file->triggers, list) {
> +	list_for_each_entry_safe(test, n, &file->triggers, list) {
>  		if (test->cmd_ops->trigger_type == ETT_HIST_ENABLE) {
>  			list_del_rcu(&test->list);
>  			update_cond_flag(file);
>