linux-kernel - Re: [PATCH v2] usb: gadget: udc: remove pointer dereference after free

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Message-ID: <20170213225051.Horde.FuA7hX2Mg68zi7e218F_3so@gator4166.hostgator.com>
Date:   Mon, 13 Feb 2017 22:50:51 -0600
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Michal Nazarewicz <mina86@...a86.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        gregkh@...uxfoundation.org, balbi@...nel.org,
        heikki.krogerus@...ux.intel.com, mail@...oabal.eu,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Senna Tschudin <peter.senna@...il.com>
Subject: Re: [PATCH v2] usb: gadget: udc: remove pointer dereference after
 free

Hi Michal,

Quoting Michal Nazarewicz <mina86@...a86.com>:

> On Sat, Feb 11 2017, Gustavo A. R. Silva wrote:
>> Remove pointer dereference after free and set pointer to NULL after free.
>>
>> Addresses-Coverity-ID: 1091173
>> Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
>
> Acked-by: Michal Nazarewicz <mina86@...a86.com>
>
>> ---
>> Changes in v2:
>>   Move pointer dereference before pci_pool_free()
>>   Set pointer to NULL after free
>>
>>   drivers/usb/gadget/udc/pch_udc.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/gadget/udc/pch_udc.c
>> b/drivers/usb/gadget/udc/pch_udc.c
>> index a97da64..73bb58f 100644
>> --- a/drivers/usb/gadget/udc/pch_udc.c
>> +++ b/drivers/usb/gadget/udc/pch_udc.c
>> @@ -1522,8 +1522,9 @@ static void pch_udc_free_dma_chain(struct
>> pch_udc_dev *dev,
>>   		/* do not free first desc., will be done by free for request */
>>   		td = phys_to_virt(addr);
>>   		addr2 = (dma_addr_t)td->next;
>> -		pci_pool_free(dev->data_requests, td, addr);
>>   		td->next = 0x00;
>
> Or just drop this.  pci_pool_free doesn’t care about contents of td.
> It’s just a void* for it.
>
>> +		pci_pool_free(dev->data_requests, td, addr);
>> +		td = NULL;
>
> This isn’t necessary either.  td will get overwritten on next iteration
> and once we’re done it’s not used again.
>
>>   		addr = addr2;
>>   	}
>>   	req->chain_len = 1;
>

Thanks for your comments, I will send version 3 shortly.
--
Gustavo A. R. Silva