linux-kernel - Re: [PATCH 2/7] KEYS: X.509: Parse Basic Constraints for CA

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Date:   Fri, 08 Apr 2022 10:39:25 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Eric Snowberg <eric.snowberg@...cle.com>, dhowells@...hat.com,
        dwmw2@...radead.org, jarkko@...nel.org,
        linux-integrity@...r.kernel.org
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com,
        roberto.sassu@...wei.com, nramas@...ux.microsoft.com,
        pvorel@...e.cz, tiwai@...e.de, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH 2/7] KEYS: X.509: Parse Basic Constraints for CA

On Tue, 2022-04-05 at 21:53 -0400, 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 the x509_certificate.  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@...cle.com>
> ---
>  crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
>  crypto/asymmetric_keys/x509_parser.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..30f7374ea9c0 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) {
> +		if (vlen < 2 || v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
> +			return -EBADMSG;
> +		if (v[1] != vlen - 2)
> +			return -EBADMSG;
> +		if (vlen >= 4 && v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
> +			ctx->cert->is_root_ca = true;
> +	}
> +
>  	return 0;
>  }
>  
> diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
> index 97a886cbe01c..dc45df9f6594 100644
> --- a/crypto/asymmetric_keys/x509_parser.h
> +++ b/crypto/asymmetric_keys/x509_parser.h
> @@ -38,6 +38,7 @@ struct x509_certificate {
>  	bool		self_signed;		/* T if self-signed (check unsupported_sig too) */
>  	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
>  	bool		blacklisted;
> +	bool		is_root_ca;		/* T if basic constraints CA is set */

There's no need to prefix variables with "is_".  Similar to the
variable "self_signed" simply name this variable "root_ca".

thanks,

Mimi


>  };
>  
>  /*