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

From: David Howells
Date: Wed Dec 14 2016 - 03:38:25 EST

Andy Lutomirski <luto@xxxxxxxxxxxxxx> 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.