linux-kernel - Re: [PATCH v7 04/17] X.509: Parse Basic Constraints for CA

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Date:   Thu, 18 Nov 2021 17:59:52 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Eric Snowberg <eric.snowberg@...cle.com>, keyrings@...r.kernel.org,
        linux-integrity@...r.kernel.org, dhowells@...hat.com,
        dwmw2@...radead.org, herbert@...dor.apana.org.au,
        davem@...emloft.net, jarkko@...nel.org, jmorris@...ei.org,
        serge@...lyn.com
Cc:     keescook@...omium.org, torvalds@...ux-foundation.org,
        weiyongjun1@...wei.com, nayna@...ux.ibm.com, ebiggers@...gle.com,
        ardb@...nel.org, nramas@...ux.microsoft.com, lszubowi@...hat.com,
        jason@...c4.com, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        James.Bottomley@...senPartnership.com, pjones@...hat.com,
        konrad.wilk@...cle.com
Subject: Re: [PATCH v7 04/17] X.509: Parse Basic Constraints for CA

Hi Eric,

On Mon, 2021-11-15 at 19:15 -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 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@...cle.com>
> ---
> v7: Initial version
> ---
>  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 6d003096b5bc..f4299b8a4926 100644
> --- a/crypto/asymmetric_keys/x509_cert_parser.c
> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> @@ -571,6 +571,15 @@ int x509_process_extension(void *context, size_t hdrlen,
>  		return 0;
>  	}
>  
> +	if (ctx->last_oid == OID_basicConstraints) {
> +		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 a9b2e600b7cc..61c66be80995 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -28,6 +28,7 @@ struct public_key {
>  	bool key_is_private;
>  	const char *id_type;
>  	const char *pkey_algo;
> +	bool key_is_ca;

David added "key_is_private" intentionally where he did.  Adding the
"key_is_ca" immediately afterwards doesn't change the struct size.

Mimi

>  };
>  
>  extern void public_key_free(struct public_key *key);