ALSA: control: Don't embed ctl_dev

Embedding the ctl_dev in the snd_card object may result in UAF when
the delayed kobj release is used; at the delayed kobj release, it
still accesses the struct device itself while the card memory (that
embeds the struct device) may be already gone.

As a workaround, detach the struct device from the card object by
allocating via the new snd_device_alloc() helper.  The rest are just
replacing ctl_dev access to the pointer.

This is based on the fix Curtis posted initially.  In this patch, the
changes are split and use the new helper function instead.

Link: https://lore.kernel.org/r/20230801171928.1460120-1-cujomalainey@chromium.orgReviewed-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Curtis Malainey <cujomalainey@chromium.org>
Tested-by: Curtis Malainey <cujomalainey@chromium.org>
Link: https://lore.kernel.org/r/20230816160252.23396-3-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/core.h

@@ -96,7 +96,7 @@ struct snd_card {
 								private data */
 	struct list_head devices;	/* devices */
 
-	struct device ctl_dev;		/* control device */
+	struct device *ctl_dev;		/* control device */
 	unsigned int last_numid;	/* last used numeric ID */
 	struct rw_semaphore controls_rwsem;	/* controls lock (list and values) */
 	rwlock_t ctl_files_rwlock;	/* ctl_files list lock */

sound/core/control.c

@@ -2389,7 +2389,7 @@ static int snd_ctl_dev_register(struct snd_device *device)
 	int err;
 
 	err = snd_register_device(SNDRV_DEVICE_TYPE_CONTROL, card, -1,
-				  &snd_ctl_f_ops, card, &card->ctl_dev);
+				  &snd_ctl_f_ops, card, card->ctl_dev);
 	if (err < 0)
 		return err;
 	down_read(&card->controls_rwsem);
@@ -2425,7 +2425,7 @@ static int snd_ctl_dev_disconnect(struct snd_device *device)
 	up_read(&snd_ctl_layer_rwsem);
 	up_read(&card->controls_rwsem);
 
-	return snd_unregister_device(&card->ctl_dev);
+	return snd_unregister_device(card->ctl_dev);
 }
 
 /*
@@ -2447,7 +2447,7 @@ static int snd_ctl_dev_free(struct snd_device *device)
 	xa_destroy(&card->ctl_hash);
 #endif
 	up_write(&card->controls_rwsem);
-	put_device(&card->ctl_dev);
+	put_device(card->ctl_dev);
 	return 0;
 }
 
@@ -2469,12 +2469,14 @@ int snd_ctl_create(struct snd_card *card)
 	if (snd_BUG_ON(card->number < 0 || card->number >= SNDRV_CARDS))
 		return -ENXIO;
 
-	snd_device_initialize(&card->ctl_dev, card);
-	dev_set_name(&card->ctl_dev, "controlC%d", card->number);
+	err = snd_device_alloc(&card->ctl_dev, card);
+	if (err < 0)
+		return err;
+	dev_set_name(card->ctl_dev, "controlC%d", card->number);
 
 	err = snd_device_new(card, SNDRV_DEV_CONTROL, card, &ops);
 	if (err < 0)
-		put_device(&card->ctl_dev);
+		put_device(card->ctl_dev);
 	return err;
 }
 

sound/core/control_led.c

@@ -688,7 +688,7 @@ static void snd_ctl_led_sysfs_add(struct snd_card *card)
 			goto cerr;
 		led->cards[card->number] = led_card;
 		snprintf(link_name, sizeof(link_name), "led-%s", led->name);
-		WARN(sysfs_create_link(&card->ctl_dev.kobj, &led_card->dev.kobj, link_name),
+		WARN(sysfs_create_link(&card->ctl_dev->kobj, &led_card->dev.kobj, link_name),
 			"can't create symlink to controlC%i device\n", card->number);
 		WARN(sysfs_create_link(&led_card->dev.kobj, &card->card_dev.kobj, "card"),
 			"can't create symlink to card%i\n", card->number);
@@ -714,7 +714,7 @@ static void snd_ctl_led_sysfs_remove(struct snd_card *card)
 		if (!led_card)
 			continue;
 		snprintf(link_name, sizeof(link_name), "led-%s", led->name);
-		sysfs_remove_link(&card->ctl_dev.kobj, link_name);
+		sysfs_remove_link(&card->ctl_dev->kobj, link_name);
 		sysfs_remove_link(&led_card->dev.kobj, "card");
 		device_unregister(&led_card->dev);
 		led->cards[card->number] = NULL;

sound/usb/media.c

@@ -163,7 +163,7 @@ void snd_media_stop_pipeline(struct snd_usb_substream *subs)
 
 static int snd_media_mixer_init(struct snd_usb_audio *chip)
 {
-	struct device *ctl_dev = &chip->card->ctl_dev;
+	struct device *ctl_dev = chip->card->ctl_dev;
 	struct media_intf_devnode *ctl_intf;
 	struct usb_mixer_interface *mixer;
 	struct media_device *mdev = chip->media_dev;