[PATCH v4 3/6] KEYS: X.509: Parse Basic Constraints for CA

[Jarkko Sakkinen]

On Mon, Feb 06, 2023 at 09:59:55PM -0500, 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 public_key.  This will be used
> in a follow on patch that requires knowing if the public key is a CA.
> 
> Link: https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.9
> Signed-off-by: Eric Snowberg <eric.snowberg at oracle.com>
> ---
>  crypto/asymmetric_keys/x509_cert_parser.c | 22 ++++++++++++++++++++++
>  include/crypto/public_key.h               |  2 ++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
> index 7a9b084e2043..77547d4bd94d 100644
> --- a/crypto/asymmetric_keys/x509_cert_parser.c
> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> @@ -586,6 +586,28 @@ int x509_process_extension(void *context, size_t hdrlen,
>  		return 0;
>  	}
>  
> +	if (ctx->last_oid == OID_basicConstraints) {
> +		/*
> +		 * Get hold of the basicConstraints
> +		 * v[1] is the encoding size
> +		 *	(Expect 0x2 or greater, making it 1 or more bytes)
> +		 * v[2] is the encoding type
> +		 *	(Expect an ASN1_BOOL for the CA)
> +		 * v[3] is the contents of the ASN1_BOOL
> +		 *      (Expect 1 if the CA is TRUE)
> +		 * vlen should match the entire extension size
> +		 */
> +		if (v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
> +			return -EBADMSG;
> +		if (vlen < 2)
> +			return -EBADMSG;
> +		if (v[1] != vlen - 2)
> +			return -EBADMSG;
> +		if (vlen >= 4 && v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
> +			ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_CA;
> +		return 0;
> +	}
> +
>  	return 0;
>  }
>  
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index 6d61695e1cde..c401762850f2 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -28,6 +28,8 @@ struct public_key {
>  	bool key_is_private;
>  	const char *id_type;
>  	const char *pkey_algo;
> +	unsigned long key_eflags;	/* key extension flags */
> +#define KEY_EFLAG_CA		0	/* set if the CA basic constraints is set */
>  };
>  
>  extern void public_key_free(struct public_key *key);
> -- 
> 2.27.0
> 

Reviewed-by: Jarkko Sakkinen <jarkko at kernel.org>

BR, Jarkko