Re: [PATCH] usb: atm: ueagle-atm: fix use-after-free in uea_upload_pre_firmware

[Stanislaw Gruszka <stf_xl@wp.pl>]

Hi,

On Sat, Jul 11, 2026 at 10:42:59PM +0800, Yuhong Cheng wrote:
> syzbot reported a slab-use-after-free read in uea_upload_pre_firmware. This is because the usb_device is passed as context to request_firmware_nowait but its reference count is not incremented. Thus, if the USB device is disconnected before the firmware load completes, the callback accesses a freed usb_device.

I think this not true, please see:
https://lore.kernel.org/linux-usb/20260702093707.GA6804@wp.pl/

Regards
Stanislaw

> Fix this by taking a reference with usb_get_dev() before calling request_firmware_nowait() and releasing it with usb_put_dev() in the completion callback or if the request fails to start.
> 
> Reported-by: syzbot+123456@syzkaller.appspotmail.com
> ---
>  drivers/usb/atm/ueagle-atm.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/atm/ueagle-atm.c b/drivers/usb/atm/ueagle-atm.c
> index d610cdcef..eaf2f2d3a 100644
> --- a/drivers/usb/atm/ueagle-atm.c
> +++ b/drivers/usb/atm/ueagle-atm.c
> @@ -663,6 +663,7 @@ static void uea_upload_pre_firmware(const struct firmware *fw_entry,
>  	uea_err(usb, "firmware is corrupted\n");
>  err:
>  	release_firmware(fw_entry);
> +	usb_put_dev(usb);
>  }
>  
>  /*
> @@ -693,13 +694,16 @@ static int uea_load_firmware(struct usb_device *usb, unsigned int ver)
>  		break;
>  	}
>  
> +	usb_get_dev(usb);
>  	ret = request_firmware_nowait(THIS_MODULE, 1, fw_name, &usb->dev,
>  					GFP_KERNEL, usb,
>  					uea_upload_pre_firmware);
> -	if (ret)
> +	if (ret) {
>  		uea_err(usb, "firmware %s is not available\n", fw_name);
> -	else
> +		usb_put_dev(usb);
> +	} else {
>  		uea_info(usb, "loading firmware %s\n", fw_name);
> +	}
>  
>  	return ret;
>  }
> -- 
> 2.46.0.windows.1
>