Re: [PATCH] wusbcore: Fix one more crypto-on-the-stack bug

[Andy Lutomirski]

On Mon, Dec 12, 2016 at 1:44 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Dec 12, 2016 at 12:52:45PM -0800, Andy Lutomirski wrote:
>> The driver put a constant buffer of all zeros on the stack and
>> pointed a scatterlist entry at it.  This doesn't work with virtual
>> stacks.  Make the buffer static to fix it.
>>
>> Cc: stable@xxxxxxxxxxxxxxx # 4.9 only
>> Reported-by: Eric Biggers <ebiggers3@xxxxxxxxx>
>> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
>> ---
>>  drivers/usb/wusbcore/crypto.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/wusbcore/crypto.c b/drivers/usb/wusbcore/crypto.c
>> index 79451f7ef1b7..a7e007a0cd49 100644
>> --- a/drivers/usb/wusbcore/crypto.c
>> +++ b/drivers/usb/wusbcore/crypto.c
>> @@ -216,7 +216,7 @@ static int wusb_ccm_mac(struct crypto_skcipher *tfm_cbc,
>>       struct scatterlist sg[4], sg_dst;
>>       void *dst_buf;
>>       size_t dst_size;
>> -     const u8 bzero[16] = { 0 };
>> +     static const u8 bzero[16] = { 0 };
>
> Hm, can static memory handle DMA?  That's a requirement of the USB
> stack, does this data later end up being sent down to a USB host
> controller?

I think it doesn't, but I'll switch it to use empty_zero_page instead.

--Andy