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SubjectRe: usb/midi: use-after-free in snd_rawmidi_dev_seq_free
On Mon, 11 Sep 2017 13:17:39 +0200,
Andrey Konovalov wrote:
>
> On Tue, Sep 5, 2017 at 6:08 PM, Takashi Iwai <tiwai@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@google.com>

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


Takashi

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