linux-kernel - Re: [PATCH v3] usb: gadget : fix use-after-free in composite_dev

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Message-ID: <2025072118-linguini-carded-fcfb@gregkh>
Date: Mon, 21 Jul 2025 09:46:31 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Tao Xue <xuetao09@...wei.com>
Cc: Thinh.Nguyen@...opsys.com, prashanth.k@....qualcomm.com,
	m.grzeschik@...gutronix.de, Chris.Wulff@...mp.com,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	caiyadong@...wei.com, suzhuangluan@...ilicon.com,
	weiwenwen3@...wei.com
Subject: Re: [PATCH v3] usb: gadget : fix use-after-free in
 composite_dev_cleanup()

On Mon, Jul 21, 2025 at 03:29:46PM +0800, Tao Xue wrote:
> 1. In func configfs_composite_bind() -> composite_os_desc_req_prepare():
> if kmalloc fails, the pointer cdev->os_desc_req will be freed but not
> set to NULL. Then it will return a failure to the upper-level function.
> 2. in func configfs_composite_bind() -> composite_dev_cleanup():
> it will checks whether cdev->os_desc_req is NULL. If it is not NULL, it
> will attempt to use it.This will lead to a use-after-free issue.
> 
> BUG: KASAN: use-after-free in composite_dev_cleanup+0xf4/0x2c0
> Read of size 8 at addr 0000004827837a00 by task init/1
> 
> CPU: 10 PID: 1 Comm: init Tainted: G           O      5.10.97-oh #1
>  kasan_report+0x188/0x1cc
>  __asan_load8+0xb4/0xbc
>  composite_dev_cleanup+0xf4/0x2c0
>  configfs_composite_bind+0x210/0x7ac
>  udc_bind_to_driver+0xb4/0x1ec
>  usb_gadget_probe_driver+0xec/0x21c
>  gadget_dev_desc_UDC_store+0x264/0x27c
> 
> Fixes: 37a3a533429e ("usb: gadget: OS Feature Descriptors support")
> Signed-off-by: Tao Xue <xuetao09@...wei.com>
> ---
> v3: add comment in patch
> v2: update Signed-off and commit message
> v1: initial submission
> 
>  drivers/usb/gadget/composite.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> index 8dbc132a505e..adf0a79b3d3d 100644
> --- a/drivers/usb/gadget/composite.c
> +++ b/drivers/usb/gadget/composite.c
> @@ -2489,6 +2489,11 @@ int composite_os_desc_req_prepare(struct usb_composite_dev *cdev,
>  	if (!cdev->os_desc_req->buf) {
>  		ret = -ENOMEM;
>  		usb_ep_free_request(ep0, cdev->os_desc_req);
> +		/* composite_dev_cleanup() will check whether cdev->os_desc_req
> +		 * is NULL and will use it when it is not NULL, so we need to set
> +		 * NULL here.
> +		 */

Didn't checkpatch complain that this is not the correct way to do a
multi-line comment?

And that's a bit verbose, how about
		/* Set os_desc_req to NULL so that composite_dev_cleanup() will not try to free it again */

And you ignored my patch bot for some reason :(

{sigh}