Re: use-after-free in __perf_install_in_context

[Dmitry Vyukov]

On Thu, Dec 17, 2015 at 3:28 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> > >> I'm not sure I can explain your problem with this, but I figure its
>> > >> worth a try.
>> > >
>> > > Did it make a difference?
>> > >
>> > > Also, does the syzkaller thing do cpu-hotplug during its runs?
>> >
>> > See my email on Dec 15.
>>
>> I have 4 emails from you on that day (and one private), they pertain to
>> getting stuck in perf_{install,remove}_from_context(). None of those
>> emails seem to contain an answer to either of the two above questions.
>>
>>   CACT4Y+Za4L4q6FZLXjyGbnSYRwa7RJZYcG_s562q+CrNy9C75w@xxxxxxxxxxxxxx
>>   CACT4Y+YUkYgCuQFW6eBTtdfRqdF7EEtrB3VaYJk+LUXE_-iGRQ@xxxxxxxxxxxxxx
>>   CACT4Y+bvHWuyDZjoFhLAOiK1rfNQcfuSJCY0oS5xA=u8j04bXQ@xxxxxxxxxxxxxx
>>   CACT4Y+an67KnTsVVzYVvrYKW9yg7PbDuC8WyB38PiWRoSt0UCQ@xxxxxxxxxxxxxx
>>
>> and in private:
>>
>>   CACT4Y+Zb1vU192JbCnyS9qY3cpsvfAUJdpBVUsmosueCtQjSXQ@xxxxxxxxxxxxxx
>>
>> Did I miss an email?
>
> Yes, I seem to have missed this one:
>
>   CACT4Y+Y_YdEd-YGdWq-wQV6S+1M2nKA6atYO2DOFa8-wtQ8QWg@xxxxxxxxxxxxxx
>
> found it, thanks!

Yes, that one.
In short, I did not see use-after-frees but perf_event_open fuzzing
started hanging VMs very frequently, so testing is inconclusive.

And, no, nobody touches anything in /sys/devices.
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