[PATCH RFC 2/9] ALSA: control: Don't embed ctl_dev

[Takashi Iwai <tiwai@suse.de>]

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.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 include/sound/core.h     |  2 +-
 sound/core/control.c     | 14 ++++++++------
 sound/core/control_led.c |  4 ++--
 sound/usb/media.c        |  2 +-
 4 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/include/sound/core.h b/include/sound/core.h
index f986fcc5f18f..f3f6b720a278 100644
--- a/include/sound/core.h
+++ b/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 */
diff --git a/sound/core/control.c b/sound/core/control.c
index 8386b53acdcd..eb975df067fb 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -2315,7 +2315,7 @@ 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);
@@ -2351,7 +2351,7 @@ 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);
 }
 
 /*
@@ -2373,7 +2373,7 @@ 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;
 }
 
@@ -2395,12 +2395,14 @@ 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;
 }
 
diff --git a/sound/core/control_led.c b/sound/core/control_led.c
index ee77547bf8dc..760e46cf25cc 100644
--- a/sound/core/control_led.c
+++ b/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;
diff --git a/sound/usb/media.c b/sound/usb/media.c
index 840f42cb9272..6d11fedb4632 100644
--- a/sound/usb/media.c
+++ b/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;
-- 
2.35.3