linux-kernel - Re: [PATCH v2 2/2] crypto: aes - helper function to validate key length for AES algorithms

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Message-ID: <CAKv+Gu8KcL_Q_C+euZ9DOT7VEX68CJZJLrT8hxeCiiiEkxQ=jQ@mail.gmail.com>
Date:   Wed, 31 Jul 2019 11:50:11 +0300
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Iuliana Prodan <iuliana.prodan@....com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH v2 2/2] crypto: aes - helper function to validate key
 length for AES algorithms

On Wed, 31 Jul 2019 at 11:35, Iuliana Prodan <iuliana.prodan@....com> wrote:
>
> On 7/31/2019 8:33 AM, Ard Biesheuvel wrote:
> > On Tue, 30 Jul 2019 at 13:33, Iuliana Prodan <iuliana.prodan@....com> wrote:
> >>
> >> Add inline helper function to check key length for AES algorithms.
> >> The key can be 128, 192 or 256 bits size.
> >> This function is used in the generic aes implementation.
> >>
> >> Signed-off-by: Iuliana Prodan <iuliana.prodan@....com>
> >> ---
> >>   include/crypto/aes.h | 17 +++++++++++++++++
> >>   lib/crypto/aes.c     |  8 ++++----
> >>   2 files changed, 21 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/include/crypto/aes.h b/include/crypto/aes.h
> >> index 8e0f4cf..8ee07a8 100644
> >> --- a/include/crypto/aes.h
> >> +++ b/include/crypto/aes.h
> >> @@ -31,6 +31,23 @@ struct crypto_aes_ctx {
> >>   extern const u32 crypto_ft_tab[4][256] ____cacheline_aligned;
> >>   extern const u32 crypto_it_tab[4][256] ____cacheline_aligned;
> >>
> >> +/*
> >> + * validate key length for AES algorithms
> >> + */
> >> +static inline int crypto_aes_check_keylen(unsigned int keylen)
> >
> > Please rename this to aes_check_keylen()
> >
> I just renamed it to crypto_, the first version was check_aes_keylen
> - see https://patchwork.kernel.org/patch/11058869/.
> I think is better to keep the helper functions with crypto_, as most of
> these type of functions, in crypto, have this prefix.
>

The AES library consists of

aes_encrypt
aes_decrypt
aes_expandkey

and has no dependencies on the crypto API, which is why I omitted the
crypto_ prefix from the identifiers. Please do the same for this
function.
.


> >> +{
> >> +       switch (keylen) {
> >> +       case AES_KEYSIZE_128:
> >> +       case AES_KEYSIZE_192:
> >> +       case AES_KEYSIZE_256:
> >> +               break;
> >> +       default:
> >> +               return -EINVAL;
> >> +       }
> >> +
> >> +       return 0;
> >> +}
> >> +
> >>   int crypto_aes_set_key(struct crypto_tfm *tfm, const u8 *in_key,
> >>                  unsigned int key_len);
> >>
> >> diff --git a/lib/crypto/aes.c b/lib/crypto/aes.c
> >> index 4e100af..3407b01 100644
> >> --- a/lib/crypto/aes.c
> >> +++ b/lib/crypto/aes.c
> >> @@ -187,11 +187,11 @@ int aes_expandkey(struct crypto_aes_ctx *ctx, const u8 *in_key,
> >>   {
> >>          u32 kwords = key_len / sizeof(u32);
> >>          u32 rc, i, j;
> >> +       int err;
> >>
> >> -       if (key_len != AES_KEYSIZE_128 &&
> >> -           key_len != AES_KEYSIZE_192 &&
> >> -           key_len != AES_KEYSIZE_256)
> >> -               return -EINVAL;
> >> +       err = crypto_aes_check_keylen(key_len);
> >> +       if (err)
> >> +               return err;
> >>
> >>          ctx->key_length = key_len;
> >>
> >> --
> >> 2.1.0
> >>
> >
>