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

Gustavo A. R. Silva
2017-02-14T21:54:01Z

Hi Michal,

Quoting Michal Nazarewicz <mina86@mina86.com>:

> 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@linuxfoundation.org>
>> Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
>
> Acked-by: Michal Nazarewicz <mina86@mina86.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
>>
>

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