Re: usb/midi: use-after-free in snd_rawmidi_dev_seq_free

[Andrey Konovalov]

On Tue, Sep 12, 2017 at 12:46 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> On Mon, 11 Sep 2017 13:17:39 +0200,
> Andrey Konovalov wrote:
>>
>> On Tue, Sep 5, 2017 at 6:08 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
>> > On Tue, 05 Sep 2017 13:12:14 +0200,
>> > Andrey Konovalov wrote:
>> >>
>> >> Hi!
>> >>
>> >> While working on adding USB fuzzing support to syzkaller, I got the
>> >> following crash.
>> >>
>> >> On commit 81a84ad3cb5711cec79f4dd53a4ce026b092c432 (4.13+).
>> >>
>> >> My .config is attached. I don't have a reproducer for this bug.
>> >>
>> >> ==================================================================
>> >> BUG: KASAN: use-after-free in snd_rawmidi_dev_seq_free+0x69/0x70
>> >> sound/core/rawmidi.c:1617
>> >> Write of size 8 at addr ffff88006c611d90 by task kworker/2:1/567
>> >>
>> >> CPU: 2 PID: 567 Comm: kworker/2:1 Not tainted 4.13.0+ #29
>> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> >> Workqueue: events autoload_drivers
>> >> Call Trace:
>> >>  __dump_stack lib/dump_stack.c:16 [inline]
>> >>  dump_stack+0x192/0x22c lib/dump_stack.c:52
>> >>  print_address_description+0x78/0x280 mm/kasan/report.c:252
>> >>  kasan_report_error mm/kasan/report.c:351 [inline]
>> >>  kasan_report+0x230/0x340 mm/kasan/report.c:409
>> >>  __asan_report_store8_noabort+0x1c/0x20 mm/kasan/report.c:435
>> >>  snd_rawmidi_dev_seq_free+0x69/0x70 sound/core/rawmidi.c:1617
>> >>  snd_seq_dev_release+0x4f/0x70 sound/core/seq_device.c:192
>> >>  device_release+0x13f/0x210 drivers/base/core.c:814
>> >>  kobject_cleanup lib/kobject.c:648 [inline]
>> >>  kobject_release lib/kobject.c:677 [inline]
>> >>  kref_put include/linux/kref.h:70 [inline]
>> >>  kobject_put+0x145/0x240 lib/kobject.c:694
>> >>  put_device+0x25/0x30 drivers/base/core.c:1799
>> >>  klist_devices_put+0x36/0x40 drivers/base/bus.c:827
>> >>  klist_next+0x264/0x4a0 lib/klist.c:403
>> >>  next_device drivers/base/bus.c:270 [inline]
>> >>  bus_for_each_dev+0x17e/0x210 drivers/base/bus.c:312
>> >>  autoload_drivers+0x3b/0x50 sound/core/seq_device.c:117
>> >>  process_one_work+0x9fb/0x1570 kernel/workqueue.c:2097
>> >>  worker_thread+0x1e4/0x1350 kernel/workqueue.c:2231
>> >>  kthread+0x324/0x3f0 kernel/kthread.c:231
>> >>  ret_from_fork+0x25/0x30 arch/x86/entry/entry_64.S:425
>> >
>> > So this looks like a pending work triggering the issue when performed
>> > during the card free.  What about the patch below as a quick band-aid
>> > fix?
>> >
>> >
>> > thanks,
>> >
>> > Takashi
>>
>> Hi Takashi,
>>
>> I've been running syzkaller with your patch for a few days and didn't
>> see any more of those reports.
>>
>> Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
>
> Thanks, I merged the fix now.
> FWIW, below is the official patch I merged.

Great, thanks!

>
>
> Takashi
>
> -- 8< --
> From: Takashi Iwai <tiwai@xxxxxxx>
> Subject: [PATCH] ALSA: seq: Cancel pending autoload work at unbinding device
>
> ALSA sequencer core has a mechanism to load the enumerated devices
> automatically, and it's performed in an off-load work.  This seems
> causing some race when a sequencer is removed while the pending
> autoload work is running.  As syzkaller spotted, it may lead to some
> use-after-free:
>   BUG: KASAN: use-after-free in snd_rawmidi_dev_seq_free+0x69/0x70
>   sound/core/rawmidi.c:1617
>   Write of size 8 at addr ffff88006c611d90 by task kworker/2:1/567
>
>   CPU: 2 PID: 567 Comm: kworker/2:1 Not tainted 4.13.0+ #29
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>   Workqueue: events autoload_drivers
>   Call Trace:
>    __dump_stack lib/dump_stack.c:16 [inline]
>    dump_stack+0x192/0x22c lib/dump_stack.c:52
>    print_address_description+0x78/0x280 mm/kasan/report.c:252
>    kasan_report_error mm/kasan/report.c:351 [inline]
>    kasan_report+0x230/0x340 mm/kasan/report.c:409
>    __asan_report_store8_noabort+0x1c/0x20 mm/kasan/report.c:435
>    snd_rawmidi_dev_seq_free+0x69/0x70 sound/core/rawmidi.c:1617
>    snd_seq_dev_release+0x4f/0x70 sound/core/seq_device.c:192
>    device_release+0x13f/0x210 drivers/base/core.c:814
>    kobject_cleanup lib/kobject.c:648 [inline]
>    kobject_release lib/kobject.c:677 [inline]
>    kref_put include/linux/kref.h:70 [inline]
>    kobject_put+0x145/0x240 lib/kobject.c:694
>    put_device+0x25/0x30 drivers/base/core.c:1799
>    klist_devices_put+0x36/0x40 drivers/base/bus.c:827
>    klist_next+0x264/0x4a0 lib/klist.c:403
>    next_device drivers/base/bus.c:270 [inline]
>    bus_for_each_dev+0x17e/0x210 drivers/base/bus.c:312
>    autoload_drivers+0x3b/0x50 sound/core/seq_device.c:117
>    process_one_work+0x9fb/0x1570 kernel/workqueue.c:2097
>    worker_thread+0x1e4/0x1350 kernel/workqueue.c:2231
>    kthread+0x324/0x3f0 kernel/kthread.c:231
>    ret_from_fork+0x25/0x30 arch/x86/entry/entry_64.S:425
>
> The fix is simply to assure canceling the autoload work at removing
> the device.
>
> Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> ---
>  sound/core/seq_device.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/sound/core/seq_device.c b/sound/core/seq_device.c
> index c4acf17e9f5e..e40a2cba5002 100644
> --- a/sound/core/seq_device.c
> +++ b/sound/core/seq_device.c
> @@ -148,8 +148,10 @@ void snd_seq_device_load_drivers(void)
>         flush_work(&autoload_work);
>  }
>  EXPORT_SYMBOL(snd_seq_device_load_drivers);
> +#define cancel_autoload_drivers()      cancel_work_sync(&autoload_work)
>  #else
>  #define queue_autoload_drivers() /* NOP */
> +#define cancel_autoload_drivers() /* NOP */
>  #endif
>
>  /*
> @@ -159,6 +161,7 @@ static int snd_seq_device_dev_free(struct snd_device *device)
>  {
>         struct snd_seq_device *dev = device->device_data;
>
> +       cancel_autoload_drivers();
>         put_device(&dev->dev);
>         return 0;
>  }
> --
> 2.14.1
>