From 05ca447630334c323c9e2b788b61133ab75d60d3 Mon Sep 17 00:00:00 2001

From: Takashi Iwai <tiwai@suse.de>

Date: Tue, 18 May 2021 10:39:39 +0200

Subject: [PATCH] ALSA: line6: Fix racy initialization of LINE6 MIDI

Git-commit: 05ca447630334c323c9e2b788b61133ab75d60d3

Patch-mainline: v5.13-rc3

References: git-fixes

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: 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: Takashi Iwai <tiwai@suse.de>

---

 sound/usb/line6/driver.c | 4 ++++

 sound/usb/line6/pod.c    | 5 -----

 sound/usb/line6/variax.c | 6 ------

 3 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c

index a030dd65eb28..9602929b7de9 100644

--- a/sound/usb/line6/driver.c

+++ b/sound/usb/line6/driver.c

@@ -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)

diff --git a/sound/usb/line6/pod.c b/sound/usb/line6/pod.c

index cd44cb5f1310..16e644330c4d 100644

--- a/sound/usb/line6/pod.c

+++ b/sound/usb/line6/pod.c

@@ -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)

diff --git a/sound/usb/line6/variax.c b/sound/usb/line6/variax.c

index ed158f04de80..c2245aa93b08 100644

--- a/sound/usb/line6/variax.c

+++ b/sound/usb/line6/variax.c

@@ -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));

-- 

2.26.2