Re: [RFC/RFT PATCH 02/15] crypto: morus - fix handling chunked inputs

[Ondrej Mosnacek]

Hi Eric,

On Wed, Jan 23, 2019 at 11:52 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> The generic MORUS implementations all fail the improved AEAD tests
> because they produce the wrong result with some data layouts.  Fix them.
>
> Fixes: 396be41f16fd ("crypto: morus - Add generic MORUS AEAD implementations")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.18+
> Cc: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
>  crypto/morus1280.c | 13 +++++++------
>  crypto/morus640.c  | 13 +++++++------
>  2 files changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/crypto/morus1280.c b/crypto/morus1280.c
> index 3889c188f266..b83576b4eb55 100644
> --- a/crypto/morus1280.c
> +++ b/crypto/morus1280.c
> @@ -366,18 +366,19 @@ static void crypto_morus1280_process_crypt(struct morus1280_state *state,
>                                            const struct morus1280_ops *ops)
>  {
>         struct skcipher_walk walk;
> -       u8 *dst;
> -       const u8 *src;
>
>         ops->skcipher_walk_init(&walk, req, false);
>
>         while (walk.nbytes) {
> -               src = walk.src.virt.addr;
> -               dst = walk.dst.virt.addr;
> +               unsigned int nbytes = walk.nbytes;
>
> -               ops->crypt_chunk(state, dst, src, walk.nbytes);
> +               if (nbytes < walk.total)
> +                       nbytes = round_down(nbytes, walk.stride);
>
> -               skcipher_walk_done(&walk, 0);
> +               ops->crypt_chunk(state, walk.dst.virt.addr, walk.src.virt.addr,
> +                                nbytes);
> +
> +               skcipher_walk_done(&walk, walk.nbytes - nbytes);
>         }

Hm... I assume the problem was that skcipher_walk may give you nbytes
that is not rounded to the algorithm's walksize (aka walk.stride) even
in the middle of the stream, right? I must have misread the code in
skcipher.c and assumed that it automatically makes every step of a
round size, with the exception of the very last one, which may include
a final partial block. Thinking about it now it makes sense to me that
this isn't the case, since for stream ciphers it would mean some
unnecessary memcpy'ing in the skcipher_walk code...

Maybe you could explain the problem in one or two sentences in the
commit message(s), since the contract of skcipher_walk doesn't seem to
be documented anywhere and so it is not obvious why the change is
necessary.

Thank you for all your work on this - the improved testmgr tests were
long needed!

>  }
>
> diff --git a/crypto/morus640.c b/crypto/morus640.c
> index da06ec2f6a80..b6a477444f6d 100644
> --- a/crypto/morus640.c
> +++ b/crypto/morus640.c
> @@ -365,18 +365,19 @@ static void crypto_morus640_process_crypt(struct morus640_state *state,
>                                           const struct morus640_ops *ops)
>  {
>         struct skcipher_walk walk;
> -       u8 *dst;
> -       const u8 *src;
>
>         ops->skcipher_walk_init(&walk, req, false);
>
>         while (walk.nbytes) {
> -               src = walk.src.virt.addr;
> -               dst = walk.dst.virt.addr;
> +               unsigned int nbytes = walk.nbytes;
>
> -               ops->crypt_chunk(state, dst, src, walk.nbytes);
> +               if (nbytes < walk.total)
> +                       nbytes = round_down(nbytes, walk.stride);
>
> -               skcipher_walk_done(&walk, 0);
> +               ops->crypt_chunk(state, walk.dst.virt.addr, walk.src.virt.addr,
> +                                nbytes);
> +
> +               skcipher_walk_done(&walk, walk.nbytes - nbytes);
>         }
>  }
>
> --
> 2.20.1.321.g9e740568ce-goog
>

--
Ondrej Mosnacek <omosnace at redhat dot com>
Associate Software Engineer, Security Technologies
Red Hat, Inc.