linux-kernel - Re: [PATCH] usb: gadget: r8a66597-udc: Fix double free in r8a66597

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Message-ID: <20240917145017.dCZwT_uL@linutronix.de>
Date: Tue, 17 Sep 2024 16:50:17 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Mikhail Arkhipov <m.arhipov@...a.ru>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	Felipe Balbi <balbi@...com>, Ben Dooks <ben.dooks@...ethink.co.uk>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	lvc-project@...uxtesting.org
Subject: Re: [PATCH] usb: gadget: r8a66597-udc: Fix double free in
 r8a66597_probe

On 2024-09-17 01:29:37 [+0300], Mikhail Arkhipov wrote:
> The function r8a66597_free_request is called to free r8a66597->ep0_req,
> but the pointer is not set to NULL afterward, which may lead to a double
> free if the function is called again.
> 
> If the probe process fails and the r8a66597_probe function subsequently
> goes through its error handling path. Since r8a66597_free_request is called
> multiple times in different error handling sections, it leads to an attempt
> to free the same memory twice.
> 
> Set r8a66597->ep0_req to NULL after calling r8a66597_free_request
> to prevent any further attempts to free this pointer.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 0f91349b89f3 ("usb: gadget: convert all users to the new udc infrastructure")
> Signed-off-by: Mikhail Arkhipov <m.arhipov@...a.ru>

Looking at how the code looks now and how it looks back then, I simply
haven't seen it. I would suggest to instead assigning NULL simply remove
the second block. The request gets allocated shortly before
usb_add_gadget_udc() is invoked. It does not make sense to have this
conditional check all the way from clean_up2 where it is not allocated.

>  drivers/usb/gadget/udc/r8a66597-udc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/gadget/udc/r8a66597-udc.c b/drivers/usb/gadget/udc/r8a66597-udc.c
> index db4a10a979f9..43b81cae7d17 100644
> --- a/drivers/usb/gadget/udc/r8a66597-udc.c
> +++ b/drivers/usb/gadget/udc/r8a66597-udc.c
> @@ -1952,12 +1952,14 @@ static int r8a66597_probe(struct platform_device *pdev)
>  
>  err_add_udc:
>  	r8a66597_free_request(&r8a66597->ep[0].ep, r8a66597->ep0_req);
> +	r8a66597->ep0_req = NULL;
>  clean_up2:
>  	if (r8a66597->pdata->on_chip)
>  		clk_disable_unprepare(r8a66597->clk);
>  
>  	if (r8a66597->ep0_req)
>  		r8a66597_free_request(&r8a66597->ep[0].ep, r8a66597->ep0_req);
> +		r8a66597->ep0_req = NULL;
>  
>  	return ret;
>  }

Sebastian