Re: [PATCH] usbip: Fix free of unallocated memory in vhci tx

[shuah <shuah@kernel.org>]

On 10/21/19 9:08 AM, Julia Lawall wrote:
> 
> 
> On Mon, 21 Oct 2019, Suwan Kim wrote:
> 
>> iso_buffer should be set to NULL after use and free in the while loop.
>> In the case of isochronous URB in the while loop, iso_buffer is
>> allocated and after sending it to server, buffer is deallocated. And
>> then, if the next URB in the while loop is not a isochronous pipe,
>> iso_buffer still holds the previously deallocated buffer address and
>> kfree tries to free wrong buffer address.
>>
>> Fixes: ea44d190764b (“usbip: Implement SG support to vhci-hcd and stub driver”)
>> Reported-by: kbuild test robot <lkp@intel.com>
>> Reported-by: Julia Lawall <julia.lawall@lip6.fr>
>> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
>> ---
>>   drivers/usb/usbip/vhci_tx.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/usb/usbip/vhci_tx.c b/drivers/usb/usbip/vhci_tx.c
>> index c3803785f6ef..b290e810d11b 100644
>> --- a/drivers/usb/usbip/vhci_tx.c
>> +++ b/drivers/usb/usbip/vhci_tx.c
>> @@ -73,6 +73,7 @@ static int vhci_send_cmd_submit(struct vhci_device *vdev)
>>   		memset(&pdu_header, 0, sizeof(pdu_header));
>>   		memset(&msg, 0, sizeof(msg));
>>   		memset(&iov, 0, sizeof(iov));
>> +		iso_buffer = NULL;
> 
> Somehow I would have put it after the kfree, since the kfree makes the
> value invalid.  iso_buffer is already initialized to NULL for the first
> iteration.  If you want to put the setting to NULL at the top of the loop,
> maybe the = NULL in the first line should be removed.
> 

It makes sense to clear it after kfree() on line 150.

This kfree() and clearing iso_buffer are necessary only for
PIPE_ISOCHRONOUS case.

Please add a comment above that this is for isoc case.

thanks,
-- Shuah