X.509: Add a crypto key parser for binary (DER) X.509 certificates

Add a crypto key parser for binary (DER) encoded X.509 certificates.  The
certificate is parsed and, if possible, the signature is verified.

An X.509 key can be added like this:

	# keyctl padd crypto bar @s </tmp/x509.cert
	15768135

and displayed like this:

	# cat /proc/keys
	00f09a47 I--Q---     1 perm 39390000     0     0 asymmetri bar: X509.RSA e9fd6d08 []

Note that this only works with binary certificates.  PEM encoded certificates
are ignored by the parser.

Note also that the X.509 key ID is not congruent with the PGP key ID, but for
the moment, they will match.

If a NULL or "" name is given to add_key(), then the parser will generate a key
description from the CertificateSerialNumber and Name fields of the
TBSCertificate:

	00aefc4e I--Q---     1 perm 39390000     0     0 asymmetri bfbc0cd76d050ea4:/C=GB/L=Cambridge/O=Red Hat/CN=kernel key: X509.RSA 0c688c7b []

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 207 insertions, 0 deletions

diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
new file mode 100644
index 0000000..716917c
--- /dev/null
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -0,0 +1,207 @@
+/* Instantiate a public key crypto key from an X.509 Certificate
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define pr_fmt(fmt) "X.509: "fmt
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/mpi.h>
+#include <linux/asn1_decoder.h>
+#include <keys/asymmetric-subtype.h>
+#include <keys/asymmetric-parser.h>
+#include <crypto/hash.h>
+#include "asymmetric_keys.h"
+#include "public_key.h"
+#include "x509_parser.h"
+
+static const
+struct public_key_algorithm *x509_public_key_algorithms[PKEY_ALGO__LAST] = {
+	[PKEY_ALGO_DSA]		= NULL,
+#if defined(CONFIG_PUBLIC_KEY_ALGO_RSA) || \
+	defined(CONFIG_PUBLIC_KEY_ALGO_RSA_MODULE)
+	[PKEY_ALGO_RSA]		= &RSA_public_key_algorithm,
+#endif
+};
+
+/*
+ * Check the signature on a certificate using the provided public key
+ */
+static int x509_check_signature(const struct public_key *pub,
+				const struct x509_certificate *cert)
+{
+	struct public_key_signature *sig;
+	struct crypto_shash *tfm;
+	struct shash_desc *desc;
+	size_t digest_size, desc_size;
+	int ret;
+
+	pr_devel("==>%s()\n", __func__);
+	
+	/* Allocate the hashing algorithm we're going to need and find out how
+	 * big the hash operational data will be.
+	 */
+	tfm = crypto_alloc_shash(pkey_hash_algo[cert->sig_hash_algo], 0, 0);
+	if (IS_ERR(tfm))
+		return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
+
+	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+	digest_size = crypto_shash_digestsize(tfm);
+
+	/* We allocate the hash operational data storage on the end of our
+	 * context data.
+	 */
+	ret = -ENOMEM;
+	sig = kzalloc(sizeof(*sig) + desc_size + digest_size, GFP_KERNEL);
+	if (!sig)
+		goto error_no_sig;
+
+	sig->pkey_hash_algo	= cert->sig_hash_algo;
+	sig->digest		= (u8 *)sig + sizeof(*sig) + desc_size;
+	sig->digest_size	= digest_size;
+
+	desc = (void *)sig + sizeof(*sig);
+	desc->tfm	= tfm;
+	desc->flags	= CRYPTO_TFM_REQ_MAY_SLEEP;
+
+	ret = crypto_shash_init(desc);
+	if (ret < 0)
+		goto error;
+
+	ret = -ENOMEM;
+	sig->rsa.s = mpi_read_raw_data(cert->sig, cert->sig_size);
+	if (!sig->rsa.s)
+		goto error;
+
+	ret = crypto_shash_finup(desc, cert->tbs, cert->tbs_size, sig->digest);
+	if (ret < 0)
+		goto error_mpi;
+
+	ret = pub->algo->verify_signature(pub, sig);
+
+	pr_debug("Cert Verification: %d\n", ret);
+
+error_mpi:
+	mpi_free(sig->rsa.s);
+error:
+	kfree(sig);
+error_no_sig:
+	crypto_free_shash(tfm);
+
+	pr_devel("<==%s() = %d\n", __func__, ret);
+	return ret;
+}
+
+/*
+ * Attempt to parse a data blob for a key as an X509 certificate.
+ */
+static int x509_key_preparse(struct key_preparsed_payload *prep)
+{
+	struct x509_certificate *cert;
+	time_t now;
+	size_t srlen, sulen;
+	char *desc = NULL;
+	int ret;
+
+	cert = x509_cert_parse(prep->data, prep->datalen);
+	if (IS_ERR(cert))
+		return PTR_ERR(cert);
+
+	pr_devel("Cert Issuer: %s\n", cert->issuer);
+	pr_devel("Cert Subject: %s\n", cert->subject);
+	pr_devel("Cert Key Algo: %s\n", pkey_algo[cert->pkey_algo]);
+	pr_devel("Cert Valid: %lu - %lu\n", cert->valid_from, cert->valid_to);
+	pr_devel("Cert Signature: %s + %s\n",
+		 pkey_algo[cert->sig_pkey_algo],
+		 pkey_hash_algo[cert->sig_hash_algo]);
+
+	if (!cert->fingerprint || !cert->authority) {
+		pr_warn("Cert for '%s' must have SubjKeyId and AuthKeyId extensions\n",
+			cert->subject);
+		ret = -EKEYREJECTED;
+		goto error_free_cert;
+	}
+
+	now = CURRENT_TIME.tv_sec;
+	if (now < cert->valid_from) {
+		pr_warn("Cert %s is not yet valid\n", cert->fingerprint);
+		ret = -EKEYREJECTED;
+		goto error_free_cert;
+	}
+	if (now >= cert->valid_to) {
+		pr_warn("Cert %s has expired\n", cert->fingerprint);
+		ret = -EKEYEXPIRED;
+		goto error_free_cert;
+	}
+
+	cert->pub->algo = x509_public_key_algorithms[cert->pkey_algo];
+	cert->pub->id_type = PKEY_ID_X509;
+
+	/* Check the signature on the key */
+	if (strcmp(cert->fingerprint, cert->authority) == 0) {
+		ret = x509_check_signature(cert->pub, cert);
+		if (ret < 0)
+			goto error_free_cert;
+	}
+
+	/* Propose a description */
+	sulen = strlen(cert->subject);
+	srlen = strlen(cert->fingerprint);
+	ret = -ENOMEM;
+	desc = kmalloc(sulen + 2 + srlen + 1, GFP_KERNEL);
+	if (!desc)
+		goto error_free_cert;
+	memcpy(desc, cert->subject, sulen);
+	desc[sulen] = ':';
+	desc[sulen + 1] = ' ';
+	memcpy(desc + sulen + 2, cert->fingerprint, srlen);
+	desc[sulen + 2 + srlen] = 0;
+
+	/* We're pinning the module by being linked against it */
+	__module_get(public_key_subtype.owner);
+	prep->type_data[0] = &public_key_subtype;
+	prep->type_data[1] = cert->fingerprint;
+	prep->payload = cert->pub;
+	prep->description = desc;
+	prep->quotalen = 100;
+
+	/* We've finished with the certificate */
+	cert->pub = NULL;
+	cert->fingerprint = NULL;
+	desc = NULL;
+	ret = 0;
+
+error_free_cert:
+	x509_free_certificate(cert);
+	return ret;
+}
+
+static struct asymmetric_key_parser x509_key_parser = {
+	.owner	= THIS_MODULE,
+	.name	= "x509",
+	.parse	= x509_key_preparse,
+};
+
+/*
+ * Module stuff
+ */
+static int __init x509_key_init(void)
+{
+	return register_asymmetric_key_parser(&x509_key_parser);
+}
+
+static void __exit x509_key_exit(void)
+{
+	unregister_asymmetric_key_parser(&x509_key_parser);
+}
+
+module_init(x509_key_init);
+module_exit(x509_key_exit);