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

[Gustavo A. R. Silva]

Hi Michal,

Quoting Michal Nazarewicz <min...@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 <gre...@linuxfoundation.org>
Signed-off-by: Gustavo A. R. Silva <garsi...@embeddedor.com>

Acked-by: Michal Nazarewicz <min...@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