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

[Gustavo A. R. Silva]

Hi Michal,

Quoting Michal Nazarewicz <mina86@xxxxxxxxxx>:

> 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@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Gustavo A. R. Silva <garsilva@xxxxxxxxxxxxxx>
>
> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
>
> > ---
> >  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 âaddr_nextâ or ânextâ?
>
> > +	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

Thanks for your comments, I will send version 2 shortly.
--
Gustavo A. R. Silva