linux-kernel - Re: [PATCH 1/2] usb: gadget: udc: avoid use of freed pointer

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Message-ID: <xa1td1emdqhy.fsf@mina86.com>
Date:   Mon, 13 Feb 2017 17:06:49 +0100
From:   Michal Nazarewicz <mina86@...a86.com>
To:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>, balbi@...nel.org,
        gregkh@...uxfoundation.org, bhelgaas@...gle.com,
        heikki.krogerus@...ux.intel.com
Cc:     linux-geode@...ts.infradead.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] usb: gadget: udc: avoid use of freed pointer

On Mon, Feb 13 2017, Gustavo A. R. Silva wrote:
> Rewrite udc_free_dma_chain() function to avoid use of pointer after free.
>
> Addresses-Coverity-ID: 1091172
> Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>

Acked-by: Michal Nazarewicz <mina86@...a86.com>

> ---
>  drivers/usb/gadget/udc/amd5536udc.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/usb/gadget/udc/amd5536udc.c b/drivers/usb/gadget/udc/amd5536udc.c
> index ea03ca7..ded97a3 100644
> --- a/drivers/usb/gadget/udc/amd5536udc.c
> +++ b/drivers/usb/gadget/udc/amd5536udc.c
> @@ -611,21 +611,23 @@ udc_alloc_request(struct usb_ep *usbep, gfp_t gfp)
>  static int udc_free_dma_chain(struct udc *dev, struct udc_request *req)
>  {
>  	int ret_val = 0;
> -	struct udc_data_dma	*td;
> -	struct udc_data_dma	*td_last = NULL;
> +	struct udc_data_dma *td = req->td_data;
>  	unsigned int i;
>  
> +	dma_addr_t addr_aux = 0x00;

Perhaps call it ‘addr_next’ or ‘next’?

> +	dma_addr_t addr = (dma_addr_t)td->next;
> +	td->next = 0x00;
> +
>  	DBG(dev, "free chain req = %p\n", req);
>  
>  	/* do not free first desc., will be done by free for request */
> -	td_last = req->td_data;
> -	td = phys_to_virt(td_last->next);
> -
>  	for (i = 1; i < req->chain_len; i++) {
> -		pci_pool_free(dev->data_requests, td,
> -			      (dma_addr_t)td_last->next);
> -		td_last = td;
> -		td = phys_to_virt(td_last->next);
> +		td = phys_to_virt(addr);
> +		addr_aux = (dma_addr_t)td->next;
> +		td->next = 0x00;

This is unnecessary.

> +		pci_pool_free(dev->data_requests, td, addr);
> +		td = NULL;

Ditto.

> +		addr = addr_aux;
>  	}
>  
>  	return ret_val;
> -- 
> 2.5.0
>

-- 
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ
«If at first you don’t succeed, give up skydiving»