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

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Date:   Mon, 12 Dec 2016 15:57:52 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        Eric Biggers <ebiggers3@...il.com>,
        linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Stephan Mueller <smueller@...onox.de>
Subject: Re: [PATCH] wusbcore: Fix one more crypto-on-the-stack bug

On Mon, Dec 12, 2016 at 1:44 PM, Greg KH <gregkh@...uxfoundation.org> 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@...r.kernel.org # 4.9 only
>> Reported-by: Eric Biggers <ebiggers3@...il.com>
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> ---
>>  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