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

Hillf Danton
2026-04-26T02:35:48Z

> Date: Sat, 25 Apr 2026 07:43:17 -0700
> For archival purposes, forwarding an incoming command email to
> linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.
>
> ***
>
> Subject: [PATCH] ALSA: caiaq: fix usb_dev refcount leak on probe failure
> Author: kartikey406@gmail.com
>
Deepanshu, can you please correctly fill your Cc list as required to
avoid this forwarded message which is a waste of net bandwidth?

> #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