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

[Takashi Iwai]

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

---
diff --git a/sound/core/seq_device.c b/sound/core/seq_device.c
--- 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;
 }