Commit 05ca4476 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: line6: Fix racy initialization of LINE6 MIDI 



The initialization of MIDI devices that are found on some LINE6
drivers are currently done in a racy way; namely, the MIDI buffer
instance is allocated and initialized in each private_init callback
while the communication with the interface is already started via
line6_init_cap_control() call before that point.  This may lead to
Oops in line6_data_received() when a spurious event is received, as
reported by syzkaller.

This patch moves the MIDI initialization to line6_init_cap_control()
as well instead of the too-lately-called private_init for avoiding the
race.  Also this reduces slightly more lines, so it's a win-win
change.

Reported-by: default avatar <syzbot+0d2b3feb0a2887862e06@syzkallerlkml..appspotmail.com>
Link: https://lore.kernel.org/r/000000000000a4be9405c28520de@google.com
Link: https://lore.kernel.org/r/20210517132725.GA50495@hyeyoo
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210518083939.1927-1-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 4c6fe8c5

sound/usb/line6/driver.c

+4 −0
Original line number Diff line number Diff line
@@ -699,6 +699,10 @@ static int line6_init_cap_control(struct usb_line6 *line6) 
		line6->buffer_message = kmalloc(LINE6_MIDI_MESSAGE_MAXLEN, GFP_KERNEL);

		if (!line6->buffer_message)

			return -ENOMEM;



		ret = line6_init_midi(line6);

		if (ret < 0)

			return ret;

	} else {

		ret = line6_hwdep_init(line6);

		if (ret < 0)

sound/usb/line6/pod.c

+0 −5
Original line number Diff line number Diff line
@@ -376,11 +376,6 @@ static int pod_init(struct usb_line6 *line6, 
	if (err < 0)

		return err;



	/* initialize MIDI subsystem: */

	err = line6_init_midi(line6);

	if (err < 0)

		return err;



	/* initialize PCM subsystem: */

	err = line6_init_pcm(line6, &pod_pcm_properties);

	if (err < 0)

sound/usb/line6/variax.c

+0 −6
Original line number Diff line number Diff line
@@ -159,7 +159,6 @@ static int variax_init(struct usb_line6 *line6, 
		       const struct usb_device_id *id)

{

	struct usb_line6_variax *variax = line6_to_variax(line6);

	int err;



	line6->process_message = line6_variax_process_message;

	line6->disconnect = line6_variax_disconnect;
@@ -172,11 +171,6 @@ static int variax_init(struct usb_line6 *line6, 
	if (variax->buffer_activate == NULL)

		return -ENOMEM;



	/* initialize MIDI subsystem: */

	err = line6_init_midi(&variax->line6);

	if (err < 0)

		return err;



	/* initiate startup procedure: */

	schedule_delayed_work(&line6->startup_work,

			      msecs_to_jiffies(VARIAX_STARTUP_DELAY1));