ALSA: line6: Assure canceling delayed work at disconnection

The current code performs the cancel of a delayed work at the late
stage of disconnection procedure, which may lead to the access to the
already cleared state.

This patch assures to call cancel_delayed_work_sync() at the beginning
of the disconnection procedure for avoiding that race.  The delayed
work object is now assigned in the common line6 object instead of its
derivative, so that we can call cancel_delayed_work_sync().

Along with the change, the startup function is called via the new
callback instead.  This will make it easier to port other LINE6
drivers to use the delayed work for startup in later patches.

Reported-by: syzbot+5255458d5e0a2b10bbb9@syzkaller.appspotmail.com
Fixes: 7f84ff68 ("ALSA: line6: toneport: Fix broken usage of timer for delayed execution")
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/line6/driver.c

@@ -720,6 +720,15 @@ static int line6_init_cap_control(struct usb_line6 *line6)
 	return 0;
 }
 
+static void line6_startup_work(struct work_struct *work)
+{
+	struct usb_line6 *line6 =
+		container_of(work, struct usb_line6, startup_work.work);
+
+	if (line6->startup)
+		line6->startup(line6);
+}
+
 /*
 	Probe USB device.
 */
@@ -755,6 +764,7 @@ int line6_probe(struct usb_interface *interface,
 	line6->properties = properties;
 	line6->usbdev = usbdev;
 	line6->ifcdev = &interface->dev;
+	INIT_DELAYED_WORK(&line6->startup_work, line6_startup_work);
 
 	strcpy(card->id, properties->id);
 	strcpy(card->driver, driver_name);
@@ -825,6 +835,8 @@ void line6_disconnect(struct usb_interface *interface)
 	if (WARN_ON(usbdev != line6->usbdev))
 		return;
 
+	cancel_delayed_work(&line6->startup_work);
+
 	if (line6->urb_listen != NULL)
 		line6_stop_listen(line6);
 

sound/usb/line6/driver.h

@@ -178,11 +178,15 @@ struct usb_line6 {
 			fifo;
 	} messages;
 
+	/* Work for delayed PCM startup */
+	struct delayed_work startup_work;
+
 	/* If MIDI is supported, buffer_message contains the pre-processed data;
 	 * otherwise the data is only in urb_listen (buffer_incoming).
 	 */
 	void (*process_message)(struct usb_line6 *);
 	void (*disconnect)(struct usb_line6 *line6);
+	void (*startup)(struct usb_line6 *line6);
 };
 
 extern char *line6_alloc_sysex_buffer(struct usb_line6 *line6, int code1,

sound/usb/line6/toneport.c

@@ -54,9 +54,6 @@ struct usb_line6_toneport {
 	/* Firmware version (x 100) */
 	u8 firmware_version;
 
-	/* Work for delayed PCM startup */
-	struct delayed_work pcm_work;
-
 	/* Device type */
 	enum line6_device_type type;
 
@@ -241,12 +238,8 @@ static int snd_toneport_source_put(struct snd_kcontrol *kcontrol,
 	return 1;
 }
 
-static void toneport_start_pcm(struct work_struct *work)
+static void toneport_startup(struct usb_line6 *line6)
 {
-	struct usb_line6_toneport *toneport =
-		container_of(work, struct usb_line6_toneport, pcm_work.work);
-	struct usb_line6 *line6 = &toneport->line6;
-
 	line6_pcm_acquire(line6->line6pcm, LINE6_STREAM_MONITOR, true);
 }
 
@@ -394,7 +387,7 @@ static int toneport_setup(struct usb_line6_toneport *toneport)
 	if (toneport_has_led(toneport))
 		toneport_update_led(toneport);
 
-	schedule_delayed_work(&toneport->pcm_work,
+	schedule_delayed_work(&toneport->line6.startup_work,
 			      msecs_to_jiffies(TONEPORT_PCM_DELAY * 1000));
 	return 0;
 }
@@ -407,8 +400,6 @@ static void line6_toneport_disconnect(struct usb_line6 *line6)
 	struct usb_line6_toneport *toneport =
 		(struct usb_line6_toneport *)line6;
 
-	cancel_delayed_work_sync(&toneport->pcm_work);
-
 	if (toneport_has_led(toneport))
 		toneport_remove_leds(toneport);
 }
@@ -424,9 +415,9 @@ static int toneport_init(struct usb_line6 *line6,
 	struct usb_line6_toneport *toneport =  (struct usb_line6_toneport *) line6;
 
 	toneport->type = id->driver_info;
-	INIT_DELAYED_WORK(&toneport->pcm_work, toneport_start_pcm);
 
 	line6->disconnect = line6_toneport_disconnect;
+	line6->startup = toneport_startup;
 
 	/* initialize PCM subsystem: */
 	err = line6_init_pcm(line6, &toneport_pcm_properties);