Re: sound: use-after-free in hrtimer_cancel

[Takashi Iwai]

On Fri, 24 Jun 2016 15:48:53 +0200,
Dmitry Vyukov wrote:
> 
> On Fri, Jun 24, 2016 at 3:33 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> > On Tue, 21 Jun 2016 19:41:28 +0200,
> > Dmitry Vyukov wrote:
> >>
> >> On Mon, Jun 6, 2016 at 6:39 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> >> > On Mon, 06 Jun 2016 18:29:25 +0200,
> >> > Dmitry Vyukov wrote:
> >> >>
> >> >> On Mon, Jun 6, 2016 at 4:11 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> >> >> > On Sat, 04 Jun 2016 20:27:50 +0200,
> >> >> > Dmitry Vyukov wrote:
> >> >> >>
> >> >> >> On Sat, Jun 4, 2016 at 8:00 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> >> >> >> > Hello,
> >> >> >> >
> >> >> >> > The following program triggers use-after-free:
> >> >> >>
> >> >> >> Forget to mention that you need to run it in a tight parallel loop. It
> >> >> >> takes around 5 minutes to reproduce for me.
> >> >> >
> >> >> > Hmm, this again is a bug that is difficult to trigger...  At least, I
> >> >> > couldn't reproduce locally.  How many processes are you running with
> >> >> > stress program?
> >> >>
> >> >> I use a VM with 4 cores and use 20 parallel test processes.
> >> >>
> >> >> > It seems that there is nothing more than opening /dev/audio and does
> >> >> > some mmap in the job.  Is there any other relevant thing there?
> >> >>
> >> >>
> >> >> I think poll with timeout is related. It is poll who sets hrtimer, right?
> >> >
> >> > If it's about snd-dummy driver, hrtimer is created at open, and
> >> > started/stopped at PCM trigger, and removed at close.
> >> >
> >> > Is there any good way to decode which syscalls are executed in the
> >> > test code?
> >>
> >> What do you mean?
> >> Here are the syscalls in the program:
> >>
> >>     r[2] = syscall(SYS_open, "/dev/audio", 0xa40ul, 0, 0, 0);
> >>     // r[2] is in the descriptor passed to SYS_poll
> >>     r[15] = syscall(SYS_poll, 0x2001dde8ul, 0x4ul, 0x8ul, 0, 0, 0);
> >>     r[18] = syscall(SYS_readv, r[2], 0x20dc13c0ul, 0x1ul, 0, 0, 0);
> >>     r[19] = syscall(SYS_read, r[2], 0x20dbefe0ul, 0x20ul, 0, 0, 0);
> >
> > I meant some nice way to decode these magic numbers to be more
> > understandable :)
> 
> Short term, run it under strace. It should show file names, decode
> most of flags and structs.

Alright, thanks.


Takashi