[PATCH v9,1/4] X.509: Add CodeSigning extended key usage parsing

["Lee, Chun-Yi" <joeyli.kernel@xxxxxxxxx>]

This patch adds the logic for parsing the CodeSign extended key usage
extension in X.509. The parsing result will be set to the ext_key_usage
flag which is carried by public key. It can be used in the PKCS#7
verification.

Signed-off-by: "Lee, Chun-Yi" <jlee@xxxxxxxx>
---
 crypto/asymmetric_keys/x509_cert_parser.c | 25 +++++++++++++++++++++++
 include/crypto/public_key.h               |  1 +
 include/linux/oid_registry.h              |  5 +++++
 3 files changed, 31 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 2899ed80bb18..1f67e0adef65 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -554,6 +554,8 @@ int x509_process_extension(void *context, size_t hdrlen,
 	struct x509_parse_context *ctx = context;
 	struct asymmetric_key_id *kid;
 	const unsigned char *v = value;
+	int i = 0;
+	enum OID oid;
 
 	pr_debug("Extension: %u\n", ctx->last_oid);
 
@@ -583,6 +585,29 @@ int x509_process_extension(void *context, size_t hdrlen,
 		return 0;
 	}
 
+	if (ctx->last_oid == OID_extKeyUsage) {
+		if (vlen < 2 ||
+		    v[0] != ((ASN1_UNIV << 6) | ASN1_CONS_BIT | ASN1_SEQ) ||
+		    v[1] != vlen - 2)
+			return -EBADMSG;
+		i += 2;
+
+		while (i < vlen) {
+			/* A 10 bytes EKU OID Octet blob =
+			 * ASN1_OID + size byte + 8 bytes OID */
+			if ((i + 10) > vlen || v[i] != ASN1_OID || v[i + 1] != 8)
+				return -EBADMSG;
+
+			oid = look_up_OID(v + i + 2, v[i + 1]);
+			if (oid == OID_codeSigning) {
+				ctx->cert->pub->ext_key_usage |= EKU_codeSigning;
+			}
+			i += 10;
+		}
+		pr_debug("extKeyUsage: %d\n", ctx->cert->pub->ext_key_usage);
+		return 0;
+	}
+
 	return 0;
 }
 
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 68f7aa2a7e55..72c0fcc39d0f 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;
+	unsigned int ext_key_usage : 9;      /* Extended Key Usage (9-bit) */
 };
 
 extern void public_key_free(struct public_key *key);
diff --git a/include/linux/oid_registry.h b/include/linux/oid_registry.h
index 0f4a8903922a..460135c2d918 100644
--- a/include/linux/oid_registry.h
+++ b/include/linux/oid_registry.h
@@ -140,9 +140,14 @@ enum OID {
 	OID_TPMImportableKey,		/* 2.23.133.10.1.4 */
 	OID_TPMSealedData,		/* 2.23.133.10.1.5 */
 
+	/* Extended key purpose OIDs [RFC 5280] */
+	OID_codeSigning,		/* 1.3.6.1.5.5.7.3.3 */
+
 	OID__NR
 };
 
+#define EKU_codeSigning	(1 << 2)
+
 extern enum OID look_up_OID(const void *data, size_t datasize);
 extern int parse_OID(const void *data, size_t datasize, enum OID *oid);
 extern int sprint_oid(const void *, size_t, char *, size_t);
-- 
2.26.2