On Thu, Mar 02, 2023 at 11:46:50AM -0500, Eric Snowberg wrote:
> Parse the X.509 Key Usage. The key usage extension defines the purpose of
> the key contained in the certificate.
>
> id-ce-keyUsage OBJECT IDENTIFIER ::= { id-ce 15 }
>
> KeyUsage ::= BIT STRING {
> digitalSignature (0),
> contentCommitment (1),
> keyEncipherment (2),
> dataEncipherment (3),
> keyAgreement (4),
> keyCertSign (5),
> cRLSign (6),
> encipherOnly (7),
> decipherOnly (8) }
>
> If the keyCertSign or digitalSignature is set, store it in the
> public_key structure. Having the purpose of the key being stored
> during parsing, allows enforcement on the usage field in the future.
> This will be used in a follow on patch that requires knowing the
> certificate key usage type.
>
> Link: https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.3
> Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
> Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> ---
> crypto/asymmetric_keys/x509_cert_parser.c | 28 +++++++++++++++++++++++
> include/crypto/public_key.h | 2 ++
> 2 files changed, 30 insertions(+)
>
> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
> index 77547d4bd94d..0a7049b470c1 100644
> --- a/crypto/asymmetric_keys/x509_cert_parser.c
> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> @@ -579,6 +579,34 @@ int x509_process_extension(void *context, size_t hdrlen,
> return 0;
> }
>
> + if (ctx->last_oid == OID_keyUsage) {
> + /*
> + * Get hold of the keyUsage bit string
> + * v[1] is the encoding size
> + * (Expect either 0x02 or 0x03, making it 1 or 2 bytes)
> + * v[2] is the number of unused bits in the bit string
> + * (If >= 3 keyCertSign is missing when v[1] = 0x02)
> + * v[3] and possibly v[4] contain the bit string
> + *
> + * From RFC 5280 4.2.1.3:
> + * 0x04 is where keyCertSign lands in this bit string
> + * 0x80 is where digitalSignature lands in this bit string
> + */
> + if (v[0] != ASN1_BTS)
> + return -EBADMSG;
> + if (vlen < 4)
> + return -EBADMSG;
> + if (v[2] >= 8)
> + return -EBADMSG;
> + if (v[3] & 0x80)
> + ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_DIGITALSIG;
> + if (v[1] == 0x02 && v[2] <= 2 && (v[3] & 0x04))
> + ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_KEYCERTSIGN;
> + else if (vlen > 4 && v[1] == 0x03 && (v[3] & 0x04))
> + ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_KEYCERTSIGN;
> + return 0;
> + }
> +
> if (ctx->last_oid == OID_authorityKeyIdentifier) {
> /* Get hold of the CA key fingerprint */
> ctx->raw_akid = v;
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index c401762850f2..03c3fb990d59 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -30,6 +30,8 @@ struct public_key {
> const char *pkey_algo;
> unsigned long key_eflags; /* key extension flags */
> #define KEY_EFLAG_CA 0 /* set if the CA basic constraints is set */
> +#define KEY_EFLAG_DIGITALSIG 1 /* set if the digitalSignature usage is set */
> +#define KEY_EFLAG_KEYCERTSIGN 2 /* set if the keyCertSign usage is set */
> };
>
> extern void public_key_free(struct public_key *key);
> --
> 2.27.0
>
Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
BR, Jarkko
