KEYS: use swapped SKID for performing partial matching

Earlier KEYS code used pure subject key identifiers (fingerprint)
for searching keys. Latest merged code removed that and broke
compatibility with integrity subsytem signatures and original
format of module signatures.

This patch returns back partial matching on SKID.
Reported-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: David Howells <dhowells@redhat.com>

crypto/asymmetric_keys/x509_cert_parser.c

@@ -437,9 +437,9 @@ int x509_process_extension(void *context, size_t hdrlen,
 
 		ctx->cert->raw_skid_size = vlen;
 		ctx->cert->raw_skid = v;
-		kid = asymmetric_key_generate_id(v, vlen,
-						 ctx->cert->raw_subject,
-						 ctx->cert->raw_subject_size);
+		kid = asymmetric_key_generate_id(ctx->cert->raw_subject,
+						 ctx->cert->raw_subject_size,
+						 v, vlen);
 		if (IS_ERR(kid))
 			return PTR_ERR(kid);
 		ctx->cert->skid = kid;
@@ -493,9 +493,9 @@ int x509_process_extension(void *context, size_t hdrlen,
 			v += (sub + 2);
 		}
 
-		kid = asymmetric_key_generate_id(v, vlen,
-						 ctx->cert->raw_issuer,
-						 ctx->cert->raw_issuer_size);
+		kid = asymmetric_key_generate_id(ctx->cert->raw_issuer,
+						 ctx->cert->raw_issuer_size,
+						 v, vlen);
 		if (IS_ERR(kid))
 			return PTR_ERR(kid);
 		pr_debug("authkeyid %*phN\n", kid->len, kid->data);

crypto/asymmetric_keys/x509_parser.h

@@ -19,9 +19,9 @@ struct x509_certificate {
 	struct public_key_signature sig;	/* Signature parameters */
 	char		*issuer;		/* Name of certificate issuer */
 	char		*subject;		/* Name of certificate subject */
-	struct asymmetric_key_id *id;		/* Issuer + serial number */
-	struct asymmetric_key_id *skid;		/* Subject key identifier */
-	struct asymmetric_key_id *authority;	/* Authority key identifier */
+	struct asymmetric_key_id *id;		/* Serial number + issuer */
+	struct asymmetric_key_id *skid;		/* Subject + subjectKeyId (optional) */
+	struct asymmetric_key_id *authority;	/* Authority key identifier (optional) */
 	struct tm	valid_from;
 	struct tm	valid_to;
 	const void	*tbs;			/* Signed data */