ALSA: seq: Cancel pending autoload work at unbinding device

2017-09-12T10:41:20+00:00

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 
Tested-by: Andrey Konovalov 
Cc: 
Signed-off-by: Takashi Iwai

ALSA: seq: Allow the modular sequencer registration

2017-06-12T06:43:33+00:00

Many drivers bind the sequencer stuff in off-load by another driver
module, so that it's loaded only on demand.  In the current code, this
mechanism doesn't work when the driver is built-in while the sequencer
is module.  We check with IS_REACHABLE() and enable only when the
sequencer is in the same level of build.

However, this is basically a overshoot.  The binder code
(snd-seq-device) is an individual module from the sequencer core
(snd-seq), and we just have to make the former a built-in while
keeping the latter a module for allowing the scenario like the above.

This patch achieves that by rewriting Kconfig slightly.  Now, a driver
that provides the manual sequencer device binding should select
CONFIG_SND_SEQ_DEVICE in a way as
	select SND_SEQ_DEVICE if SND_SEQUENCER != n

Note that the "!=n" is needed here to avoid the influence of the
sequencer core is module while the driver is built-in.

Also, since rawmidi.o may be linked with snd_seq_device.o when
built-in, we have to shuffle the code to make the linker happy.
(the kernel linker isn't smart enough yet to handle such a case.)
That is, snd_seq_device.c is moved to sound/core from sound/core/seq,
as well as Makefile.

Last but not least, the patch replaces the code using IS_REACHABLE()
with IS_ENABLED(), since now the condition meets always when enabled.

Signed-off-by: Takashi Iwai

linux.git/sound/core/seq_device.c, branch v4.14.229

ALSA: seq: Cancel pending autoload work at unbinding device

ALSA: seq: Allow the modular sequencer registration