On Mon, Aug 06, 2018 at 06:23:35PM -0700, Stephane Eranian wrote:
> Depending on memory allocations, it was possible to get a SEGFAULT in
> free_dup_event() because the event pointer was bogus:
>
> perf[1354]: segfault at ffffffff00000006 ip 00000000004b7fc7
is there any reproducer?
>
> Initially, I thought it was some double free. But it turns out
> it looked more like a buffer overrun. Adding padding before
> the union perf_event field in struct ordered_event avoided the
> problem. But it was not obvious where this could be coming from
> given the accesses to the struct, i.e., no internal array.
>
> Then, it struck me that the following was bogus in __dup_event():
>
> __dup_event(struct ordered_events *oe, union perf_event *event)
> {
> ...
> union perf_event *new_event;
> new_event = memdup(event, event->header.size);
> ...
> }
>
> The problem here is that header.size <= sizeof(*new_event). The code
> was trying to copy only what was necessary, but then, the allocation
hum, and I think we should continue to do so.. we can't allocate ~4000
bytes space for 30 bytes sample
> was also only partial. In other words if the event was not the largest
> possible for the union, it would not be fully backed by memory, likely
> causing troubles.
how? using that event allocated space for another type of event?
>
> This patch fixes the problem by passing the size of the union and not
> that of the actual event.
I think that's just bypassing the real issue, please share more details
on how to reproduce this
thanks,
jirka
>
> Signed-off-by: Stephane Eranian <[email protected]>
>
> ---
> tools/perf/util/ordered-events.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/ordered-events.c
> b/tools/perf/util/ordered-events.c
> index bad9e0296e9a..a90dbe5df019 100644
> --- a/tools/perf/util/ordered-events.c
> +++ b/tools/perf/util/ordered-events.c
> @@ -66,9 +66,9 @@ static union perf_event *__dup_event(struct ordered_events
> *oe,
> union perf_event *new_event = NULL;
>
> if (oe->cur_alloc_size < oe->max_alloc_size) {
> - new_event = memdup(event, event->header.size);
> + new_event = memdup(event, sizeof(*event));
> if (new_event)
> - oe->cur_alloc_size += event->header.size;
> + oe->cur_alloc_size += sizeof(*event);
> }
>
> return new_event;
> --
> 2.18.0.597.ga71716f1ad-goog
>
