[alsa-devel] usb/midi: use-after-free in snd_rawmidi_dev_seq_free

[Takashi Iwai]

On Mon, 11 Sep 2017 13:17:39 +0200,
Andrey Konovalov wrote:
> 
> On Tue, Sep 5, 2017 at 6:08 PM, Takashi Iwai <tiwai at suse.de> 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 at google.com>

Thanks, I merged the fix now.
FWIW, below is the official patch I merged.


Takashi

-- 8< --
From: Takashi Iwai <tiwai at suse.de>
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 at google.com>
Tested-by: Andrey Konovalov <andreyknvl at google.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 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