Re: [PATCH 2/4] X.509: Parse Basic Constraints for CA

[Stefan Berger <stefanb@xxxxxxxxxxxxx>]

On 3/1/22 12:36, Eric Snowberg wrote:
> Parse the X.509 Basic Constraints.  The basic constraints extension
> identifies whether the subject of the certificate is a CA.
>
> BasicConstraints ::= SEQUENCE {
>          cA                      BOOLEAN DEFAULT FALSE,
>          pathLenConstraint       INTEGER (0..MAX) OPTIONAL }
>
> If the CA is true, store it in a new public_key field call key_is_ca.
> This will be used in a follow on patch that requires knowing if the
> public key is a CA.
>
> Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
> ---
>   crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
>   include/crypto/public_key.h               | 1 +
>   2 files changed, 10 insertions(+)
>
> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
> index 2899ed80bb18..38c907f4ce27 100644
> --- a/crypto/asymmetric_keys/x509_cert_parser.c
> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> @@ -583,6 +583,15 @@ int x509_process_extension(void *context, size_t hdrlen,
>   		return 0;
>   	}
>   
> +	if (ctx->last_oid == OID_basicConstraints) {

Don't you have to check whether you can access v[0] and v[1]?

if (vlen < 3)

    return -EBADMSG;

or should it even be

if (vlen != 3)

     return -EBADMSG;


> +		if (v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
> +			return -EBADMSG;
> +		if (v[1] != vlen - 2)
> +			return -EBADMSG;
> +		if (v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
> +			ctx->cert->pub->key_is_ca = true;
> +	}
> +
>   	return 0;
>   }
>   
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index 6d61695e1cde..0521241764b7 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -26,6 +26,7 @@ struct public_key {
>   	void *params;
>   	u32 paramlen;
>   	bool key_is_private;
> +	bool key_is_ca;
>   	const char *id_type;
>   	const char *pkey_algo;
>   };