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Subject[PATCH v9,1/4] X.509: Add CodeSigning extended key usage parsing
Date
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@suse.com>
---
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
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