Re: [PATCH v2 RESEND] KEYS: asymmetric: enforce SM2 signature use pkey algo

[Tianjia Zhang <tianjia.zhang@linux.alibaba.com>]

Hi Jarkko,

On 6/28/22 7:14 AM, Jarkko Sakkinen wrote:
> On Mon, Jun 27, 2022 at 05:20:27PM +0800, Tianjia Zhang wrote:
>> The signature verification of SM2 needs to add the Za value and
>> recalculate sig->digest, which requires the detection of the pkey_algo
>> in public_key_verify_signature(). As Eric Biggers said, the pkey_algo
>> field in sig is attacker-controlled and should be use pkey->pkey_algo
>> instead of sig->pkey_algo, and secondly, if sig->pkey_algo is NULL, it
>> will also cause signature verification failure.
>>
>> The software_key_determine_akcipher() already forces the algorithms
>> are matched, so the SM3 algorithm is enforced in the SM2 signature,
>> although this has been checked, we still avoid using any algorithm
>> information in the signature as input.
>>
>> Fixes: 215525639631 ("X.509: support OSCCA SM2-with-SM3 certificate verification")
>> Reported-by: Eric Biggers <ebiggers@google.com>
>> Cc: stable@vger.kernel.org # v5.10+
>> Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
>> ---
>>   crypto/asymmetric_keys/public_key.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
>> index 7c9e6be35c30..3f17ee860f89 100644
>> --- a/crypto/asymmetric_keys/public_key.c
>> +++ b/crypto/asymmetric_keys/public_key.c
>> @@ -309,7 +309,8 @@ static int cert_sig_digest_update(const struct public_key_signature *sig,
>>   	if (ret)
>>   		return ret;
>>   
>> -	tfm = crypto_alloc_shash(sig->hash_algo, 0, 0);
>> +	/* SM2 signatures always use the SM3 hash algorithm */
>> +	tfm = crypto_alloc_shash("sm3", 0, 0);
> 
> So, why this should not validate sig->hash_alog *to be* "sm3"?
> 
> I.e. add instead guard before crypto_alloc_hash:
> 
>          if (strncmp(sig->hash_algo, "sm3") != 0) {
>                  /* error */
>          }
>          /* continue */
> 

Thanks, it's reasonable and I'll take your advice.

Best regards,
Tianjia