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[3/7] KEYS: X.509: Parse Key Usage

Message ID 20220406015337.4000739-4-eric.snowberg@oracle.com (mailing list archive)
State New, archived
Headers show
Series Add CA enforcement keyring restrictions | expand

Commit Message

Eric Snowberg April 6, 2022, 1:53 a.m. UTC
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 is set, store it in the x509_certificate structure.
This will be used in a follow on patch that requires knowing the
certificate key usage type.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 crypto/asymmetric_keys/x509_cert_parser.c | 20 ++++++++++++++++++++
 crypto/asymmetric_keys/x509_parser.h      |  1 +
 2 files changed, 21 insertions(+)

Comments

Mimi Zohar April 8, 2022, 2:39 p.m. UTC | #1
On Tue, 2022-04-05 at 21:53 -0400, 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 is set, store it in the x509_certificate structure.
> This will be used in a follow on patch that requires knowing the
> certificate key usage type.
> 
> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
> ---
>  crypto/asymmetric_keys/x509_cert_parser.c | 20 ++++++++++++++++++++
>  crypto/asymmetric_keys/x509_parser.h      |  1 +
>  2 files changed, 21 insertions(+)
> 
> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
> index 30f7374ea9c0..a89f1e0c8a0f 100644
> --- a/crypto/asymmetric_keys/x509_cert_parser.c
> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> @@ -576,6 +576,26 @@ int x509_process_extension(void *context, size_t hdrlen,
>  		return 0;
>  	}
>  
> +	if (ctx->last_oid == OID_keyUsage) {
> +		/*
> +		 * Get hold of the keyUsage bit string to validate keyCertSign
> +		 * 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)
> +		 * v[3] and possibly v[4] contain the bit string
> +		 * 0x04 is where KeyCertSign lands in this bit string (from
> +		 *      RFC 5280 4.2.1.3)
> +		 */
> +		if (v[0] != ASN1_BTS || vlen < 4)
> +			return -EBADMSG;
> +		if (v[1] == 0x02 && v[2] <= 2 && (v[3] & 0x04))
> +			ctx->cert->is_kcs_set = true;
> +		else if (vlen > 4 && v[1] == 0x03 && (v[3] & 0x04))
> +			ctx->cert->is_kcs_set = true;
> +		return 0;
> +	}
> +
>  	if (ctx->last_oid == OID_authorityKeyIdentifier) {
>  		/* Get hold of the CA key fingerprint */
>  		ctx->raw_akid = v;
> diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
> index dc45df9f6594..d6ac0985d8a5 100644
> --- a/crypto/asymmetric_keys/x509_parser.h
> +++ b/crypto/asymmetric_keys/x509_parser.h
> @@ -39,6 +39,7 @@ struct x509_certificate {
>  	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
>  	bool		blacklisted;
>  	bool		is_root_ca;		/* T if basic constraints CA is set */
> +	bool		is_kcs_set;		/* T if keyCertSign is set */
>  };

Again there is no need to prefix the variable with "is_" or suffix it
with "set".  Simply naming the variable "cert_signing" or
"keycertsign", like "self_signed", will improve code readability.

thanks,

Mimi
diff mbox series

Patch

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 30f7374ea9c0..a89f1e0c8a0f 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -576,6 +576,26 @@  int x509_process_extension(void *context, size_t hdrlen,
 		return 0;
 	}
 
+	if (ctx->last_oid == OID_keyUsage) {
+		/*
+		 * Get hold of the keyUsage bit string to validate keyCertSign
+		 * 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)
+		 * v[3] and possibly v[4] contain the bit string
+		 * 0x04 is where KeyCertSign lands in this bit string (from
+		 *      RFC 5280 4.2.1.3)
+		 */
+		if (v[0] != ASN1_BTS || vlen < 4)
+			return -EBADMSG;
+		if (v[1] == 0x02 && v[2] <= 2 && (v[3] & 0x04))
+			ctx->cert->is_kcs_set = true;
+		else if (vlen > 4 && v[1] == 0x03 && (v[3] & 0x04))
+			ctx->cert->is_kcs_set = true;
+		return 0;
+	}
+
 	if (ctx->last_oid == OID_authorityKeyIdentifier) {
 		/* Get hold of the CA key fingerprint */
 		ctx->raw_akid = v;
diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
index dc45df9f6594..d6ac0985d8a5 100644
--- a/crypto/asymmetric_keys/x509_parser.h
+++ b/crypto/asymmetric_keys/x509_parser.h
@@ -39,6 +39,7 @@  struct x509_certificate {
 	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
 	bool		blacklisted;
 	bool		is_root_ca;		/* T if basic constraints CA is set */
+	bool		is_kcs_set;		/* T if keyCertSign is set */
 };
 
 /*