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SubjectRe: [PATCH v1 01/15] perf, tools, stat: Fix buffer overflow while freeing events
On Mon, Jul 24, 2017 at 04:40:01PM -0700, Andi Kleen wrote:

SNIP

>
> The event is allocated with cpus == 1, but freed with cpus == real number
> When the evsel close function walks the file descriptors it exceeds the
> fd xyarray boundaries and reads random memory.
>
> Just make sure to always use the same dummy cpu map following
> the same logic as the open call.
>
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> ---
> tools/perf/builtin-stat.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 48ac53b199fc..97d6b6c42014 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -715,6 +715,8 @@ static int __run_perf_stat(int argc, const char **argv)
> * group leaders.
> */
> read_counters();
> + if (!target__has_cpu(&target))
> + evsel_list->cpus = cpu_map__dummy_new();

you're leaking evsel_list->cpus right here..

I can see there's the issue when we mix system_wide event
(with cpumask defined) and normal event:

- we open such group as per_thread events (not system_wide),
forcing both evsel->fd xyarray to be allocated from dummy
cpus (with ncpus == 1)

- but when we call perf_evlist__close we take ncpus from
int n = evsel->cpus ? evsel->cpus->nr : ncpus;

which is wrong for system_wide event and will
cause the xyarray out of bounds access

I can see the solution either in:
1) keeping the bounds for xyarray in it and use it for iterations
2) or forcing system_wide target if there's single system_wide event
specified (patch below)

but not sure there's any sense in meassuting system_wide
event in non system_wide mode (ad 1).. thoughts?

thanks,
jirka


---
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 866da7aa54bf..9ccb4d671568 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -2540,8 +2540,8 @@ static void setup_system_wide(int forks)
* conditions is met:
*
* - there's no workload specified
- * - there is workload specified but all requested
- * events are system wide events
+ * - there is workload specified and one
+ * of the events is system wide
*/
if (!target__none(&target))
return;
@@ -2552,12 +2552,11 @@ static void setup_system_wide(int forks)
struct perf_evsel *counter;

evlist__for_each_entry(evsel_list, counter) {
- if (!counter->system_wide)
+ if (counter->system_wide) {
+ target.system_wide = true;
return;
+ }
}
-
- if (evsel_list->nr_entries)
- target.system_wide = true;
}
}

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