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 08:35:11 +0000
From:   Iuliana Prodan <iuliana.prodan@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
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 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.

>> +{
>> +       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
>>
>