On Wed, Sep 02, 2015 at 12:34:41PM -0400, Vince Weaver wrote: > > OK, this time I found the actual bug. > > event->read_size is declared as a u16 in include/linux/perf_event.h > > but it is very easy to get event->read_size larger than 64k > (in my case, create 10000 events in a group). > > Because we wrap around the u16, the > if (count < event->read_size) return -ENOSPC; > in perf_read_hw() doesn't trigger reliably and so if you do a read > on a large group event the kernel will quite happily copy_to_user() > beyond the bounds of the value set in the read syscall. > > In my case it completely smashed the stack and caused the program to > segfault. > > I'm not sure what the solution is here. Change read_size to be larger? > Ban events whose read size would be larger than 64k? Although that gets > tricky because the related header_size is also only a u16.
I think we should try and just ban events with a read_size > 64k; that's one _large_ group -- there's other issues with that as well I imagine. If we really want to allow something larger, we _could_ fudge something for cases where we do not have PERF_SAMPLE_READ set, but that's not particularly nice either. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
