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

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  Re: [PATCH 1/2] usb: gadget: udc: avoid use of freed pointer "Gustavo A. R. Silva" <garsilva@embeddedor.com> - 2017-02-14 23:00 +0100
    [PATCH v2 1/2] usb: gadget: udc: avoid use of freed pointer "Gustavo A. R. Silva" <garsilva@embeddedor.com> - 2017-02-14 23:00 +0100
      [PATCH v2 2/2] usb: gadget: udc: remove unnecessary variable and  update function prototype "Gustavo A. R. Silva" <garsilva@embeddedor.com> - 2017-02-14 23:10 +0100

#1580895 — Re: [PATCH 1/2] usb: gadget: udc: avoid use of freed pointer

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

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#1580896 — [PATCH v2 1/2] usb: gadget: udc: avoid use of freed pointer

Rewrite udc_free_dma_chain() function to avoid use of pointer after free.

Addresses-Coverity-ID: 1091172
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
---
Changes in v2:
 Remove 'td->next = 0x00' inside for loop.
 Remove unnecessary pointer nullification after free.
 Rename variable addr_aux to addr_next.

 drivers/usb/gadget/udc/amd5536udc.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/drivers/usb/gadget/udc/amd5536udc.c b/drivers/usb/gadget/udc/amd5536udc.c
index ea03ca7..821d088 100644
--- a/drivers/usb/gadget/udc/amd5536udc.c
+++ b/drivers/usb/gadget/udc/amd5536udc.c
@@ -611,21 +611,20 @@ 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_next = 0x00;
+	dma_addr_t addr = (dma_addr_t)td->next;
+
 	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_next = (dma_addr_t)td->next;
+		pci_pool_free(dev->data_requests, td, addr);
+		addr = addr_next;
 	}
 
 	return ret_val;
-- 
2.5.0

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#1580902 — [PATCH v2 2/2] usb: gadget: udc: remove unnecessary variable and update function prototype

Remove unnecessary variable and update function prototype.

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
---
Changes in v2:
 None.

 drivers/usb/gadget/udc/amd5536udc.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/udc/amd5536udc.c b/drivers/usb/gadget/udc/amd5536udc.c
index 821d088..67dd209 100644
--- a/drivers/usb/gadget/udc/amd5536udc.c
+++ b/drivers/usb/gadget/udc/amd5536udc.c
@@ -608,9 +608,8 @@ udc_alloc_request(struct usb_ep *usbep, gfp_t gfp)
 }
 
 /* frees pci pool descriptors of a DMA chain */
-static int udc_free_dma_chain(struct udc *dev, struct udc_request *req)
+static void udc_free_dma_chain(struct udc *dev, struct udc_request *req)
 {
-	int ret_val = 0;
 	struct udc_data_dma *td = req->td_data;
 	unsigned int i;
 
@@ -626,8 +625,6 @@ static int udc_free_dma_chain(struct udc *dev, struct udc_request *req)
 		pci_pool_free(dev->data_requests, td, addr);
 		addr = addr_next;
 	}
-
-	return ret_val;
 }
 
 /* Frees request packet, called by gadget driver */
-- 
2.5.0

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