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

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Date:   Wed, 31 Jul 2019 08:32:53 +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>,
        linux-imx <linux-imx@....com>
Subject: Re: [PATCH v2 2/2] crypto: aes - helper function to validate key
 length for AES algorithms

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()

> +{
> +       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
>