x509: move common functions to x509 helper

Move x509_check_for_self_signed as a common helper function
that can be shared by legacy crypto lib and MbedTLS implementation.

Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

1 files changed, 64 insertions, 0 deletions

diff --git a/lib/crypto/x509_helper.c b/lib/crypto/x509_helper.c
new file mode 100644
index 00000000000..87e8ff67ae1
--- /dev/null
+++ b/lib/crypto/x509_helper.c
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * X509 helper functions
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+#include <linux/err.h>
+#include <crypto/public_key.h>
+#include <crypto/x509_parser.h>
+
+/*
+ * Check for self-signedness in an X.509 cert and if found, check the signature
+ * immediately if we can.
+ */
+int x509_check_for_self_signed(struct x509_certificate *cert)
+{
+	int ret = 0;
+
+	if (cert->raw_subject_size != cert->raw_issuer_size ||
+	    memcmp(cert->raw_subject, cert->raw_issuer,
+		   cert->raw_issuer_size))
+		goto not_self_signed;
+
+	if (cert->sig->auth_ids[0] || cert->sig->auth_ids[1]) {
+		/*
+		 * If the AKID is present it may have one or two parts. If
+		 * both are supplied, both must match.
+		 */
+		bool a = asymmetric_key_id_same(cert->skid,
+						cert->sig->auth_ids[1]);
+		bool b = asymmetric_key_id_same(cert->id,
+						cert->sig->auth_ids[0]);
+
+		if (!a && !b)
+			goto not_self_signed;
+
+		ret = -EKEYREJECTED;
+		if (((a && !b) || (b && !a)) &&
+		    cert->sig->auth_ids[0] && cert->sig->auth_ids[1])
+			goto out;
+	}
+
+	ret = -EKEYREJECTED;
+	if (strcmp(cert->pub->pkey_algo, cert->sig->pkey_algo))
+		goto out;
+
+	ret = public_key_verify_signature(cert->pub, cert->sig);
+	if (ret == -ENOPKG) {
+		cert->unsupported_sig = true;
+		goto not_self_signed;
+	}
+	if (ret < 0)
+		goto out;
+
+	pr_devel("Cert Self-signature verified");
+	cert->self_signed = true;
+
+out:
+	return ret;
+
+not_self_signed:
+	return 0;
+}