[PATCH] ALSA: caiaq: fix usb_dev refcount leak on probe failure

[PATCH] ALSA: caiaq: fix usb_dev refcount leak on probe failure

[Deepanshu Kartikey]

create_card() takes a reference on the USB device with usb_get_dev()
and stores the matching usb_put_dev() in card_free(), which is
installed as the snd_card's ->private_free destructor.

However, ->private_free is only assigned near the end of init_card(),
after several failure points (usb_set_interface(), EP type checks,
usb_submit_urb(), the EP1_CMD_GET_DEVICE_INFO exchange, and its
timeout). When any of those fail, init_card() returns an error to
snd_probe(), which calls snd_card_free(card). Because ->private_free
is still NULL, card_free() never runs, the usb_get_dev() reference
is not dropped, and the struct usb_device leaks along with its
descriptor allocations and device_private.

syzbot reproduces this with a malformed UAC3 device whose only valid
altsetting is 0; init_card()'s usb_set_interface(usb_dev, 0, 1) call
fails with -EIO and triggers the leak.

Move the ->private_free assignment into create_card(), immediately
after usb_get_dev(), so that every error path reaching snd_card_free()
balances the reference. card_free()'s callees (snd_usb_caiaq_input_free,
free_urbs, kfree) already tolerate the partially-initialized state
because the chip private area is zero-initialized by snd_card_new().

Reported-by: syzbot+2afd7e71155c7e241560@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2afd7e71155c7e241560
Tested-by: syzbot+2afd7e71155c7e241560@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 sound/usb/caiaq/device.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/caiaq/device.c b/sound/usb/caiaq/device.c
index 8af0c04041ee..ad9f744b496b 100644
--- a/sound/usb/caiaq/device.c
+++ b/sound/usb/caiaq/device.c
@@ -423,6 +423,7 @@ static int create_card(struct usb_device *usb_dev,
 
 	cdev = caiaqdev(card);
 	cdev->chip.dev = usb_get_dev(usb_dev);
+	card->private_free = card_free;
 	cdev->chip.card = card;
 	cdev->chip.usb_id = USB_ID(le16_to_cpu(usb_dev->descriptor.idVendor),
 				  le16_to_cpu(usb_dev->descriptor.idProduct));
@@ -511,7 +512,6 @@ static int init_card(struct snd_usb_caiaqdev *cdev)
 	scnprintf(card->longname, sizeof(card->longname), "%s %s (%s)",
 		       cdev->vendor_name, cdev->product_name, usbpath);
 
-	card->private_free = card_free;
 	err = setup_card(cdev);
 	if (err < 0)
 		return err;
-- 
2.43.0

Re: [PATCH] ALSA: caiaq: fix usb_dev refcount leak on probe failure

[Takashi Iwai]

On Sun, 26 Apr 2026 02:19:34 +0200,
Deepanshu Kartikey wrote:
> 
> create_card() takes a reference on the USB device with usb_get_dev()
> and stores the matching usb_put_dev() in card_free(), which is
> installed as the snd_card's ->private_free destructor.
> 
> However, ->private_free is only assigned near the end of init_card(),
> after several failure points (usb_set_interface(), EP type checks,
> usb_submit_urb(), the EP1_CMD_GET_DEVICE_INFO exchange, and its
> timeout). When any of those fail, init_card() returns an error to
> snd_probe(), which calls snd_card_free(card). Because ->private_free
> is still NULL, card_free() never runs, the usb_get_dev() reference
> is not dropped, and the struct usb_device leaks along with its
> descriptor allocations and device_private.
> 
> syzbot reproduces this with a malformed UAC3 device whose only valid
> altsetting is 0; init_card()'s usb_set_interface(usb_dev, 0, 1) call
> fails with -EIO and triggers the leak.
> 
> Move the ->private_free assignment into create_card(), immediately
> after usb_get_dev(), so that every error path reaching snd_card_free()
> balances the reference. card_free()'s callees (snd_usb_caiaq_input_free,
> free_urbs, kfree) already tolerate the partially-initialized state
> because the chip private area is zero-initialized by snd_card_new().
> 
> Reported-by: syzbot+2afd7e71155c7e241560@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2afd7e71155c7e241560
> Tested-by: syzbot+2afd7e71155c7e241560@syzkaller.appspotmail.com
> Cc: stable@vger.kernel.org
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>

Applied now.  Thanks.


Takashi