Merge tag 'keys-pkcs7-20140708' into keys-next

Here's a set of changes that implement a PKCS#7 message parser in the kernel.

The PKCS#7 message parsing will then be used to limit kexec to authenticated
kernels only if so configured.

The changes provide the following facilities:

 (1) Parse an ASN.1 PKCS#7 message and pick out useful bits such as the data
     content and the X.509 certificates used to sign it and all the data
     signatures.

 (2) Verify all the data signatures against the set of X.509 certificates
     available in the message.

 (3) Follow the certificate chains and verify that:

     (a) for every self-signed X.509 certificate, check that it validly signed
     	 itself, and:

     (b) for every non-self-signed certificate, if we have a 'parent'
     	 certificate, the former is validly signed by the latter.

 (4) Look for intersections between the certificate chains and the trusted
     keyring, if any intersections are found, verify that the trusted
     certificates signed the intersection point in the chain.

 (5) For testing purposes, a key type can be made available that will take a
     PKCS#7 message, check that the message is trustworthy, and if so, add its
     data content into the key.

Note that (5) has to be altered to take account of the preparsing patches
already committed to this branch.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 323 insertions, 0 deletions

diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
new file mode 100644
index 00000000..51ff36f3
--- /dev/null
+++ b/crypto/asymmetric_keys/pkcs7_verify.c
@@ -0,0 +1,323 @@
+/* Verify the signature on a PKCS#7 message.
+ *
+ * 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) "PKCS7: "fmt
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/asn1.h>
+#include <crypto/hash.h>
+#include "public_key.h"
+#include "pkcs7_parser.h"
+
+/*
+ * Digest the relevant parts of the PKCS#7 data
+ */
+static int pkcs7_digest(struct pkcs7_message *pkcs7,
+			struct pkcs7_signed_info *sinfo)
+{
+	struct crypto_shash *tfm;
+	struct shash_desc *desc;
+	size_t digest_size, desc_size;
+	void *digest;
+	int ret;
+
+	kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo);
+
+	if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
+	    !hash_algo_name[sinfo->sig.pkey_hash_algo])
+		return -ENOPKG;
+
+	/* Allocate the hashing algorithm we're going to need and find out how
+	 * big the hash operational data will be.
+	 */
+	tfm = crypto_alloc_shash(hash_algo_name[sinfo->sig.pkey_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);
+	sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm);
+
+	ret = -ENOMEM;
+	digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
+	if (!digest)
+		goto error_no_desc;
+
+	desc = digest + digest_size;
+	desc->tfm   = tfm;
+	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+
+	/* Digest the message [RFC2315 9.3] */
+	ret = crypto_shash_init(desc);
+	if (ret < 0)
+		goto error;
+	ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest);
+	if (ret < 0)
+		goto error;
+	pr_devel("MsgDigest = [%*ph]\n", 8, digest);
+
+	/* However, if there are authenticated attributes, there must be a
+	 * message digest attribute amongst them which corresponds to the
+	 * digest we just calculated.
+	 */
+	if (sinfo->msgdigest) {
+		u8 tag;
+
+		if (sinfo->msgdigest_len != sinfo->sig.digest_size) {
+			pr_debug("Sig %u: Invalid digest size (%u)\n",
+				 sinfo->index, sinfo->msgdigest_len);
+			ret = -EBADMSG;
+			goto error;
+		}
+
+		if (memcmp(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) {
+			pr_debug("Sig %u: Message digest doesn't match\n",
+				 sinfo->index);
+			ret = -EKEYREJECTED;
+			goto error;
+		}
+
+		/* We then calculate anew, using the authenticated attributes
+		 * as the contents of the digest instead.  Note that we need to
+		 * convert the attributes from a CONT.0 into a SET before we
+		 * hash it.
+		 */
+		memset(digest, 0, sinfo->sig.digest_size);
+
+		ret = crypto_shash_init(desc);
+		if (ret < 0)
+			goto error;
+		tag = ASN1_CONS_BIT | ASN1_SET;
+		ret = crypto_shash_update(desc, &tag, 1);
+		if (ret < 0)
+			goto error;
+		ret = crypto_shash_finup(desc, sinfo->authattrs,
+					 sinfo->authattrs_len, digest);
+		if (ret < 0)
+			goto error;
+		pr_devel("AADigest = [%*ph]\n", 8, digest);
+	}
+
+	sinfo->sig.digest = digest;
+	digest = NULL;
+
+error:
+	kfree(digest);
+error_no_desc:
+	crypto_free_shash(tfm);
+	kleave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
+ * uses the issuer's name and the issuing certificate serial number for
+ * matching purposes.  These must match the certificate issuer's name (not
+ * subject's name) and the certificate serial number [RFC 2315 6.7].
+ */
+static int pkcs7_find_key(struct pkcs7_message *pkcs7,
+			  struct pkcs7_signed_info *sinfo)
+{
+	struct x509_certificate *x509;
+	unsigned certix = 1;
+
+	kenter("%u,%u,%u",
+	       sinfo->index, sinfo->raw_serial_size, sinfo->raw_issuer_size);
+
+	for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
+		/* I'm _assuming_ that the generator of the PKCS#7 message will
+		 * encode the fields from the X.509 cert in the same way in the
+		 * PKCS#7 message - but I can't be 100% sure of that.  It's
+		 * possible this will need element-by-element comparison.
+		 */
+		if (x509->raw_serial_size != sinfo->raw_serial_size ||
+		    memcmp(x509->raw_serial, sinfo->raw_serial,
+			   sinfo->raw_serial_size) != 0)
+			continue;
+		pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
+			 sinfo->index, certix);
+
+		if (x509->raw_issuer_size != sinfo->raw_issuer_size ||
+		    memcmp(x509->raw_issuer, sinfo->raw_issuer,
+			   sinfo->raw_issuer_size) != 0) {
+			pr_warn("Sig %u: X.509 subject and PKCS#7 issuer don't match\n",
+				sinfo->index);
+			continue;
+		}
+
+		if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
+			pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
+				sinfo->index);
+			continue;
+		}
+
+		sinfo->signer = x509;
+		return 0;
+	}
+	pr_warn("Sig %u: Issuing X.509 cert not found (#%*ph)\n",
+		sinfo->index, sinfo->raw_serial_size, sinfo->raw_serial);
+	return -ENOKEY;
+}
+
+/*
+ * Verify the internal certificate chain as best we can.
+ */
+static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
+				  struct pkcs7_signed_info *sinfo)
+{
+	struct x509_certificate *x509 = sinfo->signer, *p;
+	int ret;
+
+	kenter("");
+
+	for (p = pkcs7->certs; p; p = p->next)
+		p->seen = false;
+
+	for (;;) {
+		pr_debug("verify %s: %s\n", x509->subject, x509->fingerprint);
+		x509->seen = true;
+		ret = x509_get_sig_params(x509);
+		if (ret < 0)
+			return ret;
+
+		if (x509->issuer)
+			pr_debug("- issuer %s\n", x509->issuer);
+		if (x509->authority)
+			pr_debug("- authkeyid %s\n", x509->authority);
+
+		if (!x509->authority ||
+		    (x509->subject &&
+		     strcmp(x509->subject, x509->issuer) == 0)) {
+			/* If there's no authority certificate specified, then
+			 * the certificate must be self-signed and is the root
+			 * of the chain.  Likewise if the cert is its own
+			 * authority.
+			 */
+			pr_debug("- no auth?\n");
+			if (x509->raw_subject_size != x509->raw_issuer_size ||
+			    memcmp(x509->raw_subject, x509->raw_issuer,
+				   x509->raw_issuer_size) != 0)
+				return 0;
+
+			ret = x509_check_signature(x509->pub, x509);
+			if (ret < 0)
+				return ret;
+			x509->signer = x509;
+			pr_debug("- self-signed\n");
+			return 0;
+		}
+
+		/* Look through the X.509 certificates in the PKCS#7 message's
+		 * list to see if the next one is there.
+		 */
+		pr_debug("- want %s\n", x509->authority);
+		for (p = pkcs7->certs; p; p = p->next) {
+			pr_debug("- cmp [%u] %s\n", p->index, p->fingerprint);
+			if (p->raw_subject_size == x509->raw_issuer_size &&
+			    strcmp(p->fingerprint, x509->authority) == 0 &&
+			    memcmp(p->raw_subject, x509->raw_issuer,
+				   x509->raw_issuer_size) == 0)
+				goto found_issuer;
+		}
+
+		/* We didn't find the root of this chain */
+		pr_debug("- top\n");
+		return 0;
+
+	found_issuer:
+		pr_debug("- issuer %s\n", p->subject);
+		if (p->seen) {
+			pr_warn("Sig %u: X.509 chain contains loop\n",
+				sinfo->index);
+			return 0;
+		}
+		ret = x509_check_signature(p->pub, x509);
+		if (ret < 0)
+			return ret;
+		x509->signer = p;
+		if (x509 == p) {
+			pr_debug("- self-signed\n");
+			return 0;
+		}
+		x509 = p;
+		might_sleep();
+	}
+}
+
+/*
+ * Verify one signed information block from a PKCS#7 message.
+ */
+static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
+			    struct pkcs7_signed_info *sinfo)
+{
+	int ret;
+
+	kenter(",%u", sinfo->index);
+
+	/* First of all, digest the data in the PKCS#7 message and the
+	 * signed information block
+	 */
+	ret = pkcs7_digest(pkcs7, sinfo);
+	if (ret < 0)
+		return ret;
+
+	/* Find the key for the signature */
+	ret = pkcs7_find_key(pkcs7, sinfo);
+	if (ret < 0)
+		return ret;
+
+	pr_devel("Using X.509[%u] for sig %u\n",
+		 sinfo->signer->index, sinfo->index);
+
+	/* Verify the PKCS#7 binary against the key */
+	ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
+	if (ret < 0)
+		return ret;
+
+	pr_devel("Verified signature %u\n", sinfo->index);
+
+	/* Verify the internal certificate chain */
+	return pkcs7_verify_sig_chain(pkcs7, sinfo);
+}
+
+/**
+ * pkcs7_verify - Verify a PKCS#7 message
+ * @pkcs7: The PKCS#7 message to be verified
+ */
+int pkcs7_verify(struct pkcs7_message *pkcs7)
+{
+	struct pkcs7_signed_info *sinfo;
+	struct x509_certificate *x509;
+	int ret, n;
+
+	kenter("");
+
+	for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
+		ret = x509_get_sig_params(x509);
+		if (ret < 0)
+			return ret;
+		pr_debug("X.509[%u] %s\n", n, x509->authority);
+	}
+
+	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
+		ret = pkcs7_verify_one(pkcs7, sinfo);
+		if (ret < 0) {
+			kleave(" = %d", ret);
+			return ret;
+		}
+	}
+
+	kleave(" = 0");
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pkcs7_verify);