Re: [PATCH v2] keys/encrypted: Fix two crypto-on-the-stack bugs

Andy Lutomirski
2016-12-14T16:23:16Z

On Wed, Dec 14, 2016 at 12:37 AM, David Howells <dhowells@redhat.com> wrote:
> Andy Lutomirski <luto@amacapital.net> wrote:
>
>> > - sg_set_buf(&sg_out[1], pad, sizeof pad);
>> > + sg_set_buf(&sg_out[1], empty_zero_page, 16);
>>
>> My fix here is obviously bogus (I meant to use ZERO_PAGE(0)), but what
>> exactly is the code trying to do? The old code makes no sense. It's
>> setting the *output* buffer to zeroed padding.
>
> Padding goes into the encrypt function and is going to come out of the decrypt
> function. Possibly derived_key_decrypt() should be checking that the padding
> that comes out is actually a bunch of zeros. Maybe we don't actually need to
> get the padding out, but I'm not sure whether the crypto layer will
> malfunction if we don't give it a buffer for the padding.

It was the memset that threw me for a loop.

David, are these encrypted keys ever exported anywhere? If not, could
the code use a mode that doesn't need padding?

--Andy

>
> David

--
Andy Lutomirski
AMA Capital Management, LLC