Re: [PATCH v3] KEYS: asymmetric: enforce SM2 signature use pkey algo

[Jarkko Sakkinen]

On Tue, Jun 28, 2022 at 11:37:20AM +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@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v5.10+
> Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
> ---
>  crypto/asymmetric_keys/public_key.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
> index 7c9e6be35c30..2f8352e88860 100644
> --- a/crypto/asymmetric_keys/public_key.c
> +++ b/crypto/asymmetric_keys/public_key.c
> @@ -304,6 +304,10 @@ static int cert_sig_digest_update(const struct public_key_signature *sig,
>  
>  	BUG_ON(!sig->data);
>  
> +	/* SM2 signatures always use the SM3 hash algorithm */
> +	if (!sig->hash_algo || strcmp(sig->hash_algo, "sm3") != 0)
> +		return -EINVAL;
> +
>  	ret = sm2_compute_z_digest(tfm_pkey, SM2_DEFAULT_USERID,
>  					SM2_DEFAULT_USERID_LEN, dgst);
>  	if (ret)
> @@ -414,8 +418,7 @@ int public_key_verify_signature(const struct public_key *pkey,
>  	if (ret)
>  		goto error_free_key;
>  
> -	if (sig->pkey_algo && strcmp(sig->pkey_algo, "sm2") == 0 &&
> -	    sig->data_size) {
> +	if (strcmp(pkey->pkey_algo, "sm2") == 0 && sig->data_size) {
>  		ret = cert_sig_digest_update(sig, tfm);
>  		if (ret)
>  			goto error_free_key;
> -- 
> 2.24.3 (Apple Git-128)
> 

Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

BR, Jarkko