PKCS#7: Provide a key type for testing PKCS#7

Provide a key type for testing the PKCS#7 parser. It is given a non-detached
PKCS#7 message as payload:

keyctl padd pkcs7_test a @s <stuff.pkcs7

The PKCS#7 wrapper is validated against the trusted certificates available and
then stripped off. If successful, the key can be read, which will give the
data content of the PKCS#7 message.

A suitable message can be created by running make on the attached Makefile.
This will produce a file called stuff.pkcs7 for test loading. The key3.x509
file should be put into the kernel source tree before it is built and
converted to DER form:

openssl x509 -in .../pkcs7/key3.x509 -outform DER -out key3.x509

###############################################################################
#
# Create a pkcs7 message and sign it twice
#
# openssl x509 -text -inform PEM -noout -in key2.x509
#
###############################################################################
stuff.pkcs7: stuff.txt key2.priv key2.x509 key4.priv key4.x509 certs
$(RM) $@
openssl smime -sign \
-signer key2.x509 \
-inkey key2.priv \
-signer key4.x509 \
-inkey key4.priv \
-in stuff.txt \
-certfile certs \
-out $@ -binary -outform DER -nodetach
openssl pkcs7 -inform DER -in stuff.pkcs7 -print_certs -noout
openssl asn1parse -inform DER -in stuff.pkcs7 -i >out

stuff.txt:
echo "The quick red fox jumped over the lazy brown dog" >stuff.txt

certs: key1.x509 key2.x509 key3.x509 key4.x509
cat key{1,3}.x509 >$@

###############################################################################
#
# Generate a signed key
#
# openssl x509 -text -inform PEM -noout -in key2.x509
#
###############################################################################
key2.x509: key2.x509_unsigned key1.priv key1.x509
openssl x509 \
-req -in key2.x509_unsigned \
-out key2.x509 \
-extfile key2.genkey -extensions myexts \
-CA key1.x509 \
-CAkey key1.priv \
-CAcreateserial

key2.priv key2.x509_unsigned: key2.genkey
openssl req -new -nodes -utf8 -sha1 -days 36500 \
-batch -outform PEM \
-config key2.genkey \
-keyout key2.priv \
-out key2.x509_unsigned

key2.genkey:
@echo Generating X.509 key generation config
@echo >$@ "[ req ]"
@echo >>$@ "default_bits = 4096"
@echo >>$@ "distinguished_name = req_distinguished_name"
@echo >>$@ "prompt = no"
@echo >>$@ "string_mask = utf8only"
@echo >>$@ "x509_extensions = myexts"
@echo >>$@
@echo >>$@ "[ req_distinguished_name ]"
@echo >>$@ "O = Magrathea"
@echo >>$@ "CN = PKCS7 key 2"
@echo >>$@ "emailAddress = slartibartfast@magrathea.h2g2"
@echo >>$@
@echo >>$@ "[ myexts ]"
@echo >>$@ "basicConstraints=critical,CA:FALSE"
@echo >>$@ "keyUsage=digitalSignature"
@echo >>$@ "subjectKeyIdentifier=hash"
@echo >>$@ "authorityKeyIdentifier=keyid"

###############################################################################
#
# Generate a couple of signing keys
#
# openssl x509 -text -inform PEM -noout -in key1.x509
#
###############################################################################
key1.x509: key1.x509_unsigned key4.priv key4.x509
openssl x509 \
-req -in key1.x509_unsigned \
-out key1.x509 \
-extfile key1.genkey -extensions myexts \
-CA key4.x509 \
-CAkey key4.priv \
-CAcreateserial

key1.priv key1.x509_unsigned: key1.genkey
openssl req -new -nodes -utf8 -sha1 -days 36500 \
-batch -outform PEM \
-config key1.genkey \
-keyout key1.priv \
-out key1.x509_unsigned

key1.genkey:
@echo Generating X.509 key generation config
@echo >$@ "[ req ]"
@echo >>$@ "default_bits = 4096"
@echo >>$@ "distinguished_name = req_distinguished_name"
@echo >>$@ "prompt = no"
@echo >>$@ "string_mask = utf8only"
@echo >>$@ "x509_extensions = myexts"
@echo >>$@
@echo >>$@ "[ req_distinguished_name ]"
@echo >>$@ "O = Magrathea"
@echo >>$@ "CN = PKCS7 key 1"
@echo >>$@ "emailAddress = slartibartfast@magrathea.h2g2"
@echo >>$@
@echo >>$@ "[ myexts ]"
@echo >>$@ "basicConstraints=critical,CA:TRUE"
@echo >>$@ "keyUsage=digitalSignature,keyCertSign"
@echo >>$@ "subjectKeyIdentifier=hash"
@echo >>$@ "authorityKeyIdentifier=keyid"

###############################################################################
#
# Generate a signed key
#
# openssl x509 -text -inform PEM -noout -in key4.x509
#
###############################################################################
key4.x509: key4.x509_unsigned key3.priv key3.x509
openssl x509 \
-req -in key4.x509_unsigned \
-out key4.x509 \
-extfile key4.genkey -extensions myexts \
-CA key3.x509 \
-CAkey key3.priv \
-CAcreateserial

key4.priv key4.x509_unsigned: key4.genkey
openssl req -new -nodes -utf8 -sha1 -days 36500 \
-batch -outform PEM \
-config key4.genkey \
-keyout key4.priv \
-out key4.x509_unsigned

key4.genkey:
@echo Generating X.509 key generation config
@echo >$@ "[ req ]"
@echo >>$@ "default_bits = 4096"
@echo >>$@ "distinguished_name = req_distinguished_name"
@echo >>$@ "prompt = no"
@echo >>$@ "string_mask = utf8only"
@echo >>$@ "x509_extensions = myexts"
@echo >>$@
@echo >>$@ "[ req_distinguished_name ]"
@echo >>$@ "O = Magrathea"
@echo >>$@ "CN = PKCS7 key 4"
@echo >>$@ "emailAddress = slartibartfast@magrathea.h2g2"
@echo >>$@
@echo >>$@ "[ myexts ]"
@echo >>$@ "basicConstraints=critical,CA:TRUE"
@echo >>$@ "keyUsage=digitalSignature,keyCertSign"
@echo >>$@ "subjectKeyIdentifier=hash"
@echo >>$@ "authorityKeyIdentifier=keyid"

###############################################################################
#
# Generate a couple of signing keys
#
# openssl x509 -text -inform PEM -noout -in key3.x509
#
###############################################################################
key3.priv key3.x509: key3.genkey
openssl req -new -nodes -utf8 -sha1 -days 36500 \
-batch -x509 -outform PEM \
-config key3.genkey \
-keyout key3.priv \
-out key3.x509

key3.genkey:
@echo Generating X.509 key generation config
@echo >$@ "[ req ]"
@echo >>$@ "default_bits = 4096"
@echo >>$@ "distinguished_name = req_distinguished_name"
@echo >>$@ "prompt = no"
@echo >>$@ "string_mask = utf8only"
@echo >>$@ "x509_extensions = myexts"
@echo >>$@
@echo >>$@ "[ req_distinguished_name ]"
@echo >>$@ "O = Magrathea"
@echo >>$@ "CN = PKCS7 key 3"
@echo >>$@ "emailAddress = slartibartfast@magrathea.h2g2"
@echo >>$@
@echo >>$@ "[ myexts ]"
@echo >>$@ "basicConstraints=critical,CA:TRUE"
@echo >>$@ "keyUsage=digitalSignature,keyCertSign"
@echo >>$@ "subjectKeyIdentifier=hash"
@echo >>$@ "authorityKeyIdentifier=keyid"

clean:
$(RM) *~
$(RM) key1.* key2.* key3.* key4.* stuff.* out certs

Signed-off-by: David Howells <[e-mail]>

crypto/asymmetric_keys/Kconfig

···
 	  This option provides support for parsing PKCS#7 format messages for
 	  signature data and provides the ability to verify the signature.
 
+config PKCS7_TEST_KEY
+	tristate "PKCS#7 testing key type"
+	depends on PKCS7_MESSAGE_PARSER
+	select SYSTEM_TRUSTED_KEYRING
+	help
+	  This option provides a type of key that can be loaded up from a
+	  PKCS#7 message - provided the message is signed by a trusted key.  If
+	  it is, the PKCS#7 wrapper is discarded and reading the key returns
+	  just the payload.  If it isn't, adding the key will fail with an
+	  error.
+
+	  This is intended for testing the PKCS#7 parser.
+
 endif # ASYMMETRIC_KEY_TYPE

crypto/asymmetric_keys/Makefile

···
 $(obj)/pkcs7-asn1.o: $(obj)/pkcs7-asn1.c $(obj)/pkcs7-asn1.h
 
 clean-files	+= pkcs7-asn1.c pkcs7-asn1.h
+
+#
+# PKCS#7 parser testing key
+#
+obj-$(CONFIG_PKCS7_TEST_KEY) += pkcs7_test_key.o
+pkcs7_test_key-y := \
+	pkcs7_key_type.o

crypto/asymmetric_keys/pkcs7_key_type.c

···
+/* Testing module to load key from trusted PKCS#7 message
+ *
+ * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([e-mail])
+ *
+ * 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) "PKCS7key: "fmt
+#include <linux/key.h>
+#include <linux/key-type.h>
+#include <crypto/pkcs7.h>
+#include <keys/user-type.h>
+#include <keys/system_keyring.h>
+#include "pkcs7_parser.h"
+
+/*
+ * Instantiate a PKCS#7 wrapped and validated key.
+ */
+int pkcs7_instantiate(struct key *key, struct key_preparsed_payload *prep)
+{
+	struct pkcs7_message *pkcs7;
+	const void *data, *saved_prep_data;
+	size_t datalen, saved_prep_datalen;
+	bool trusted;
+	int ret;
+
+	kenter("");
+
+	saved_prep_data = prep->data;
+	saved_prep_datalen = prep->datalen;
+	pkcs7 = pkcs7_parse_message(saved_prep_data, saved_prep_datalen);
+	if (IS_ERR(pkcs7)) {
+		ret = PTR_ERR(pkcs7);
+		goto error;
+	}
+
+	ret = pkcs7_verify(pkcs7);
+	if (ret < 0)
+		goto error_free;
+
+	ret = pkcs7_validate_trust(pkcs7, system_trusted_keyring, &trusted);
+	if (ret < 0)
+		goto error_free;
+	if (!trusted)
+		pr_warn("PKCS#7 message doesn't chain back to a trusted key\n");
+
+	ret = pkcs7_get_content_data(pkcs7, &data, &datalen, false);
+	if (ret < 0)
+		goto error_free;
+
+	prep->data = data;
+	prep->datalen = datalen;
+	ret = user_instantiate(key, prep);
+	prep->data = saved_prep_data;
+	prep->datalen = saved_prep_datalen;
+
+error_free:
+	pkcs7_free_message(pkcs7);
+error:
+	kleave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * user defined keys take an arbitrary string as the description and an
+ * arbitrary blob of data as the payload
+ */
+struct key_type key_type_pkcs7 = {
+	.name			= "pkcs7_test",
+	.def_lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
+	.instantiate		= pkcs7_instantiate,
+	.match			= user_match,
+	.revoke			= user_revoke,
+	.destroy		= user_destroy,
+	.describe		= user_describe,
+	.read			= user_read,
+};
+
+/*
+ * Module stuff
+ */
+static int __init pkcs7_key_init(void)
+{
+	return register_key_type(&key_type_pkcs7);
+}
+
+static void __exit pkcs7_key_cleanup(void)
+{
+	unregister_key_type(&key_type_pkcs7);
+}
+
+module_init(pkcs7_key_init);
+module_exit(pkcs7_key_cleanup);