Re: [PATCH] perf report: Fix a memory corrupton issue when enabling --branch-history

["Jin, Yao" <yao.jin@linux.intel.com>]

On 2/13/2018 5:45 PM, Jiri Olsa wrote:
> On Tue, Feb 13, 2018 at 04:44:28PM +0800, Jin Yao wrote:
>> Following command lines will cause perf crash.
>>
>> perf record -j call -g -a <application>
>> perf report --branch-history
>>
>> *** Error in `perf': double free or corruption (!prev): 0x00000000104aa040 ***
>> ======= Backtrace: =========
>> /lib/x86_64-linux-gnu/libc.so.6(+0x77725)[0x7f6b37254725]
>> /lib/x86_64-linux-gnu/libc.so.6(+0x7ff4a)[0x7f6b3725cf4a]
>> /lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7f6b37260abc]
>> perf[0x51b914]
>> perf(hist_entry_iter__add+0x1e5)[0x51f305]
>> perf[0x43cf01]
>> perf[0x4fa3bf]
>> perf[0x4fa923]
>> perf[0x4fd396]
>> perf[0x4f9614]
>> perf(perf_session__process_events+0x89e)[0x4fc38e]
>> perf(cmd_report+0x15d2)[0x43f202]
>> perf[0x4a059f]
>> perf(main+0x631)[0x427b71]
>> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7f6b371fd830]
>> perf(_start+0x29)[0x427d89]
>>
>> The memory corruption happens at:
>>
>> iter_add_next_cumulative_entry()
>> {
>>          ...
>>          for (i = 0; i < iter->curr; i++) {
>>          ...
>> }
>>
>> Whatever in iter_next_cumulative_entry() or in iter_add_next_cumulative_entry(),
>> they all don't check if iter->curr exceeds the array 'he_cache[]'.
>>
>> If there are too many nodes in callchain, it's possible that iter->curr >
>> iter->max_stack, then memory corruption occurs.
>>
>> This patch will reallocate array 'he_cache[]' in iter_next_cumulative_entry()
>> if necessary (the case of too many nodes in callchain).
> 
> right, the max_stack does not say how many nodes end up in
> callchain_cursor at the end.. good catch, please mention
> that also in the changelog
> 

max_stack looks only to limit the number of calls but not for other 
branches.

> however we know the final count from callchain_cursor itself,
> the attached patch might do the same job, right?
> 

I think the attached patch is ok.

> also could we now get rid of iter->max_stack?
> 

 From my opinion, the option '--max-stack' in perf report looks not very 
necessary. While it's just my personal opinion, need to hear from more 
people. :)

Thanks
Jin Yao

> thanks,
> jirka
> 
> 
> ---
> diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
> index b6140950301e..b50b7b70dcca 100644
> --- a/tools/perf/util/hist.c
> +++ b/tools/perf/util/hist.c
> @@ -879,7 +879,7 @@ iter_prepare_cumulative_entry(struct hist_entry_iter *iter,
>   	 * cumulated only one time to prevent entries more than 100%
>   	 * overhead.
>   	 */
> -	he_cache = malloc(sizeof(*he_cache) * (iter->max_stack + 1));
> +	he_cache = malloc(sizeof(*he_cache) * (callchain_cursor.nr + 1));
>   	if (he_cache == NULL)
>   		return -ENOMEM;
>   
>