Re: [PATCH URGENT crypto] crypto: arm64/chacha - correctly walk through blocks

[Jason A. Donenfeld]

Hey Eric,

On Wed, Mar 18, 2020 at 6:24 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> Thanks for fixing this!  We definitely should get this fix to Linus for 5.6.
> But I don't think your description of this bug dating back to 2018 is accurate,
> because this bug only affects the new library interface to ChaCha20 which was
> added in v5.5.  In the "regular" crypto API case, the "walksize" is set to
> '5 * CHACHA_BLOCK_SIZE', and chacha_doneon() is guaranteed to be called with a
> multiple of '5 * CHACHA_BLOCK_SIZE' except at the end.  Thus the code worked
> fine with the regular crypto API.

Ahhh, that seems correct.

> > +             state[12] += round_up(l, CHACHA_BLOCK_SIZE) / CHACHA_BLOCK_SIZE;
>
> Use DIV_ROUND_UP(l, CHACHA_BLOCK_SIZE)?

Duh, oops, thanks. Will send a v2 in a few minutes.

By the way, I took a brief look at the other implementations
accessible from lib/crypto and I didn't see the same issue over there.
But I wouldn't mind an extra pair of eyes, if you want to give it a
quick look too.

Jason