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

Mimi Zohar
2021-11-18T23:00:31Z

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@oracle.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);