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

On Thu, Jan 21, 2021 at 12:23:53PM +0800, joeyli wrote:

Hi Jarkko,

On Thu, Jan 21, 2021 at 01:40:48AM +0200, Jarkko Sakkinen wrote:

quoted

On Wed, Jan 20, 2021 at 05:05:14PM +0800, Lee, Chun-Yi wrote:

quoted

This patch adds the logic for parsing the CodeSign extended key usage
extension in X.509. The parsing result will be set to the eku 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 | 24 ++++++++++++++++++++++++
 include/crypto/public_key.h               |  1 +
 include/linux/oid_registry.h              |  5 +++++
 3 files changed, 30 insertions(+)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 52c9b455fc7d..65721313b265 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c

@@ -497,6 +497,8 @@ 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);
 

@@ -526,6 +528,28 @@ int x509_process_extension(void *context, size_t hdrlen,
 		return 0;
 	}
 
+	if (ctx->last_oid == OID_extKeyUsage) {
+		if (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 (v[i] != ASN1_OID || v[i + 1] != 8 || (i + 10) > vlen)
+				return -EBADMSG;
+
+			oid = look_up_OID(v + i + 2, v[i + 1]);
+			if (oid == OID_codeSigning) {
+				ctx->cert->pub->eku |= EKU_codeSigning;
+			}
+			i += 10;
+		}
+		pr_debug("extKeyUsage: %d\n", ctx->cert->pub->eku);

With eBPF around, does this make any sense?

I think that the dynamic debug log is still easier for checking the EKU
setting.

Why?

Thanks
Joey Lee

/Jarkko