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

syzbot
2026-04-25T14:43:18Z

Subject: [PATCH] ALSA: caiaq: fix usb_dev refcount leak on probe failure
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

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
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