linux-kernel - Re: [PATCH] usb: fix reference leak in usb_new

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Message-ID: <ccc1083b-5ae8-490b-b357-52e162ba0a1f@rowland.harvard.edu>
Date: Tue, 17 Dec 2024 11:14:11 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Ma Ke <make_ruc2021@....com>
Cc: gregkh@...uxfoundation.org, mka@...omium.org,
	christophe.jaillet@...adoo.fr, quic_ugoswami@...cinc.com,
	oneukum@...e.com, stanley_chang@...ltek.com,
	javier.carrasco@...fvision.net, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] usb: fix reference leak in usb_new_device()

On Tue, Dec 17, 2024 at 11:53:52AM +0800, Ma Ke wrote:
> When device_add(&udev->dev) failed, calling put_device() to explicitly
> release udev->dev. Otherwise, it could cause double free problem.

If you're worried that the same object might be freed more than once 
(double free), how can calling put_device() help?  Won't that cause 
udev->dev to be freed a third time?

> Found by code review.

In your code review, did you check to see whether the routine which 
calls usb_new_device() will do the put_device() when an error occurs?

> Cc: stable@...r.kernel.org
> Fixes: 9f8b17e643fe ("USB: make usbdevices export their device nodes instead of using a separate class")
> Signed-off-by: Ma Ke <make_ruc2021@....com>
> ---
>  drivers/usb/core/hub.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 4b93c0bd1d4b..05b778d2ad63 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -2651,6 +2651,7 @@ int usb_new_device(struct usb_device *udev)
>  	err = device_add(&udev->dev);
>  	if (err) {
>  		dev_err(&udev->dev, "can't device_add, error %d\n", err);
> +		put_device(&udev->dev);
>  		goto fail;
>  	}
>  
> @@ -2683,6 +2684,9 @@ int usb_new_device(struct usb_device *udev)
>  	pm_runtime_put_sync_autosuspend(&udev->dev);
>  	return err;
>  
> +out_del_dev:
> +	device_del(&udev->dev);
> +	put_device(&udev->dev);

You added a new statement label but you did not add any jumps to that 
label.  As a result, these two lines will never be executed.

Alan Stern

>  fail:
>  	usb_set_device_state(udev, USB_STATE_NOTATTACHED);
>  	pm_runtime_disable(&udev->dev);
> -- 
> 2.25.1
>