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

From: Lee, Chun-Yi
Date: Thu Aug 25 2022 - 10:23:52 EST


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