Message-ID: <1540109262.3023.6.camel@HansenPartnership.com>
Subject: Re: [PATCH 1/2] crypto: fix cfb mode decryption
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Cc: "open list:HARDWARE RANDOM NUMBER GENERATOR CORE"
        <linux-crypto@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        stable <stable@vger.kernel.org>
Date: Sun, 21 Oct 2018 09:07:42 +0100
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References: <20181019230153.28201-1-dbaryshkov@gmail.com>
         <CAKv+Gu8eiFXoC2MWjGUG_AgDNq5rduWQN0CC4Q4BM0pjWW3B-w@mail.gmail.com>
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Sender: linux-crypto-owner@vger.kernel.org

On Sun, 2018-10-21 at 09:05 +0200, Ard Biesheuvel wrote:
> (+ James)

Thanks!

> On 20 October 2018 at 01:01, Dmitry Eremin-Solenikov
> <dbaryshkov@gmail.com> wrote:
> > crypto_cfb_decrypt_segment() incorrectly XOR'ed generated keystream
> > with
> > IV, rather than with data stream, resulting in incorrect
> > decryption.
> > Test vectors will be added in the next patch.
> > 
> > Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
> > Cc: stable@vger.kernel.org
> > ---
> >  crypto/cfb.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/crypto/cfb.c b/crypto/cfb.c
> > index a0d68c09e1b9..fd4e8500e121 100644
> > --- a/crypto/cfb.c
> > +++ b/crypto/cfb.c
> > @@ -144,7 +144,7 @@ static int crypto_cfb_decrypt_segment(struct
> > skcipher_walk *walk,
> > 
> >         do {
> >                 crypto_cfb_encrypt_one(tfm, iv, dst);
> > -               crypto_xor(dst, iv, bsize);
> > +               crypto_xor(dst, src, bsize);

This does look right.  I think the reason the TPM code works is that it
always does encrypt/decrypt in-place, which is a separate piece of the
code which appears to be correct.

James