ell/key.c

/*
 *
 *  Embedded Linux library
 *
 *  Copyright (C) 2016  Intel Corporation. All rights reserved.
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#define _GNU_SOURCE
#include <unistd.h>
#include <stdint.h>
#include <sys/syscall.h>
#include <linux/keyctl.h>
#include <errno.h>

#include "private.h"
#include "useful.h"
#include "key.h"
#include "string.h"
#include "random.h"
#include "missing.h"

#ifndef KEYCTL_DH_COMPUTE
#define KEYCTL_DH_COMPUTE 23
#endif

#ifndef KEYCTL_PKEY_QUERY
#define KEYCTL_PKEY_QUERY	24
#define KEYCTL_PKEY_ENCRYPT	25
#define KEYCTL_PKEY_DECRYPT	26
#define KEYCTL_PKEY_SIGN	27
#define KEYCTL_PKEY_VERIFY	28

#define KEYCTL_SUPPORTS_ENCRYPT	0x01
#define KEYCTL_SUPPORTS_DECRYPT	0x02
#define KEYCTL_SUPPORTS_SIGN	0x04
#define KEYCTL_SUPPORTS_VERIFY	0x08

struct keyctl_pkey_query {
	uint32_t supported_ops;
	uint32_t key_size;
	uint16_t max_data_size;
	uint16_t max_sig_size;
	uint16_t max_enc_size;
	uint16_t max_dec_size;

	uint32_t __spare[10];
};

struct keyctl_pkey_params {
	int32_t key_id;
	uint32_t in_len;
	union {
		uint32_t out_len;
		uint32_t in2_len;
	};
	uint32_t __spare[7];
};

/* Work around the missing (pre-4.7) or broken (4.14.{70,71,72} and
 * 4.18.{8,9,10}) kernel declaration of struct keyctl_dh_params
 */
struct dh_params {
	int32_t private;
	int32_t prime;
	int32_t base;
};
#else
/* When KEYCTL_PKEY_QUERY is defined by the kernel, the
 * struct keyctl_dh_params declaration is valid.
 */
#define dh_params keyctl_dh_params
#endif

#ifndef KEYCTL_RESTRICT_KEYRING
#define KEYCTL_RESTRICT_KEYRING 29
#endif

static int32_t internal_keyring;

struct l_key {
	int type;
	int32_t serial;
};

struct l_keyring {
	int32_t serial;
};

static const char * const key_type_names[] = {
	[L_KEY_RAW] = "user",
	[L_KEY_RSA] = "asymmetric",
};

static long kernel_add_key(const char *type, const char *description,
				const void *payload, size_t len, int32_t keyring)
{
	long result;

	result = syscall(__NR_add_key, type, description, payload, len,
				keyring);

	return result >= 0 ? result : -errno;
}

static long kernel_read_key(int32_t serial, const void *payload, size_t len)
{
	long result;

	result = syscall(__NR_keyctl, KEYCTL_READ, serial, payload, len);

	return result >= 0 ? result : -errno;
}

static long kernel_update_key(int32_t serial, const void *payload, size_t len)
{
	long result;

	result = syscall(__NR_keyctl, KEYCTL_UPDATE, serial, payload, len);

	return result >= 0 ? result : -errno;
}

static long kernel_invalidate_key(int32_t serial)
{
	long result;

	result = syscall(__NR_keyctl, KEYCTL_INVALIDATE, serial);

	return result >= 0 ? result : -errno;
}

static long kernel_link_key(int32_t key_serial, int32_t ring_serial)
{
	long result;

	result = syscall(__NR_keyctl, KEYCTL_LINK, key_serial, ring_serial);

	return result >= 0 ? result : -errno;
}

static long kernel_unlink_key(int32_t key_serial, int32_t ring_serial)
{
	long result;

	result = syscall(__NR_keyctl, KEYCTL_UNLINK, key_serial, ring_serial);

	return result >= 0 ? result : -errno;
}

static char *format_key_info(const char *encoding, const char *hash)
{
	struct l_string *info;

	if (!encoding && !hash)
		return NULL;

	info = l_string_new(0);

	if (encoding)
		l_string_append_printf(info, "enc=%s ", encoding);

	if (hash)
		l_string_append_printf(info, "hash=%s", hash);

	return l_string_unwrap(info);
}

static long kernel_query_key(int32_t key_serial, const char *encoding,
				const char *hash, size_t *size, bool *public)
{
	long result;
	struct keyctl_pkey_query query;
	char *info = format_key_info(encoding, hash);

	memset(&query, 0, sizeof(query));

	result = syscall(__NR_keyctl, KEYCTL_PKEY_QUERY, key_serial, 0,
				info ?: "", &query);
	if (result == 0) {
		*size = query.key_size;
		*public = ((query.supported_ops & KEYCTL_SUPPORTS_ENCRYPT) &&
			!(query.supported_ops & KEYCTL_SUPPORTS_DECRYPT));
	}
	l_free(info);

	return result >= 0 ? result : -errno;
}

static long kernel_dh_compute(int32_t private, int32_t prime, int32_t base,
			      void *payload, size_t len)
{
	long result;

	struct dh_params params = { .private = private,
				    .prime = prime,
				    .base = base };

	result = syscall(__NR_keyctl, KEYCTL_DH_COMPUTE, &params, payload, len,
			NULL);

	return result >= 0 ? result : -errno;
}

static long kernel_restrict_keyring(int32_t serial, const char *keytype,
					const char *restriction)
{
	long result;

	result = syscall(__NR_keyctl, KEYCTL_RESTRICT_KEYRING, serial, keytype,
				restriction);

	return result >= 0 ? result : -errno;
}

static long kernel_key_eds(int op, int32_t serial, const char *encoding,
				const char *hash, const void *in, void *out,
				size_t len_in, size_t len_out)
{
	long result;
	struct keyctl_pkey_params params = { .key_id = serial,
					     .in_len = len_in,
					     .out_len = len_out };
	char *info = format_key_info(encoding, hash);

	memset(out, 0, len_out);

	result = syscall(__NR_keyctl, op, &params, info ?: "", in, out);
	l_free(info);

	return result >= 0 ? result : -errno;
}

static long kernel_key_verify(int32_t serial,
				const char *encoding, const char *hash,
				const void *data, size_t data_len,
				const void *sig, size_t sig_len)
{
	struct keyctl_pkey_params params = {
		.key_id		= serial,
		.in_len		= data_len,
		.in2_len	= sig_len,
	};
	char *info = format_key_info(encoding, hash);
	long result;

	result = syscall(__NR_keyctl, KEYCTL_PKEY_VERIFY, &params,
				info ?: "", data, sig);
	l_free(info);

	return result >= 0 ? result : -errno;
}

static bool setup_internal_keyring(void)
{
	internal_keyring = kernel_add_key("keyring", "ell-internal", NULL, 0,
						KEY_SPEC_THREAD_KEYRING);

	if (internal_keyring <= 0) {
		internal_keyring = 0;
		return false;
	}

	return true;
}

LIB_EXPORT struct l_key *l_key_new(enum l_key_type type, const void *payload,
					size_t payload_length)
{
	struct l_key *key;
	char *description;
	static unsigned long key_idx;

	if (unlikely(!payload))
		return NULL;

	if (unlikely((size_t)type >= L_ARRAY_SIZE(key_type_names)))
		return NULL;

	if (!internal_keyring && !setup_internal_keyring())
		return NULL;

	key = l_new(struct l_key, 1);
	key->type = type;
	description = l_strdup_printf("ell-key-%lu", key_idx++);
	key->serial = kernel_add_key(key_type_names[type], description, payload,
					payload_length, internal_keyring);
	l_free(description);

	if (key->serial < 0) {
		l_free(key);
		key = NULL;
	}

	/*
	 * TODO: Query asymmetric key algorithm from the kernel and
	 * ensure that it matches the expected l_key_type. This can
	 * currently be found by digging through /proc/keys, but a
	 * keyctl() op makes more sense.
	 */

	return key;
}

LIB_EXPORT void l_key_free(struct l_key *key)
{
	if (unlikely(!key))
		return;

	/*
	 * Use invalidate as, unlike revoke, this doesn't delay the
	 * key garbage collection and causes the quota used by the
	 * key to be released sooner and more predictably.
	 */
	kernel_invalidate_key(key->serial);

	l_free(key);
}

LIB_EXPORT void l_key_free_norevoke(struct l_key *key)
{
	if (unlikely(!key))
		return;

	kernel_unlink_key(key->serial, internal_keyring);

	l_free(key);
}

LIB_EXPORT bool l_key_update(struct l_key *key, const void *payload, size_t len)
{
	long error;

	if (unlikely(!key))
		return false;

	error = kernel_update_key(key->serial, payload, len);

	return error == 0;
}

LIB_EXPORT bool l_key_extract(struct l_key *key, void *payload, size_t *len)
{
	long keylen;

	if (unlikely(!key))
		return false;

	keylen = kernel_read_key(key->serial, payload, *len);

	if (keylen < 0 || (size_t)keylen > *len) {
		explicit_bzero(payload, *len);
		return false;
	}

	*len = keylen;
	return true;
}

LIB_EXPORT ssize_t l_key_get_payload_size(struct l_key *key)
{
	return kernel_read_key(key->serial, NULL, 0);
}

static const char *lookup_cipher(enum l_key_cipher_type cipher)
{
	const char* ret = NULL;

	switch (cipher) {
	case L_KEY_RSA_PKCS1_V1_5:
		ret = "pkcs1";
		break;
	case L_KEY_RSA_RAW:
		ret = "raw";
		break;
	}

	return ret;
}

static const char *lookup_checksum(enum l_checksum_type checksum)
{
	const char* ret = NULL;

	switch (checksum) {
	case L_CHECKSUM_NONE:
		break;
	case L_CHECKSUM_MD4:
		ret = "md4";
		break;
	case L_CHECKSUM_MD5:
		ret = "md5";
		break;
	case L_CHECKSUM_SHA1:
		ret = "sha1";
		break;
	case L_CHECKSUM_SHA224:
		ret = "sha224";
		break;
	case L_CHECKSUM_SHA256:
		ret = "sha256";
		break;
	case L_CHECKSUM_SHA384:
		ret = "sha384";
		break;
	case L_CHECKSUM_SHA512:
		ret = "sha512";
		break;
	}

	return ret;
}

LIB_EXPORT bool l_key_get_info(struct l_key *key, enum l_key_cipher_type cipher,
			enum l_checksum_type checksum, size_t *bits,
			bool *public)
{
	if (unlikely(!key))
		return false;

	return !kernel_query_key(key->serial, lookup_cipher(cipher),
					lookup_checksum(checksum), bits,
					public);
}

LIB_EXPORT struct l_key *l_key_generate_dh_private(const void *prime_buf,
							size_t prime_len)
{
	uint8_t *buf;
	const uint8_t *prime = prime_buf;
	size_t prime_bits;
	unsigned int i;
	size_t private_bytes;
	size_t random_bytes;
	struct l_key *private;

	/* Find the prime's bit length excluding leading 0s */

	for (i = 0; i < prime_len && !prime[i]; i++);

	if (i == prime_len || (i == prime_len - 1 && prime[i] < 5))
		return NULL;

	prime_bits = (prime_len - i) * 8 - __builtin_clz(prime[i]);

	/*
	 * Generate a random DH private value conforming to 1 < x < p - 1.
	 * To do this covering all possible values in this range with the
	 * same probability of generating each value generally requires
	 * looping.  Instead we generate a value in the range
	 * [2 ^ (prime_bits - 2), 2 ^ (prime_bits - 1) - 1] by forcing bit
	 * prime_bits - 2 to 1, i.e. the range in PKCS #3 Section 7.1 for
	 * l equal to prime_bits - 1.  This means we're using between
	 * one half and one quarter of the full [2, p - 2] range, i.e.
	 * between 1 and 2 bits fewer.  Note that since p is odd
	 * p - 1 has the same bit length as p and so our maximum value
	 * 2 ^ (prime_bits - 1) - 1 is still less than p - 1.
	 */
	private_bytes = ((prime_bits - 1) + 7) / 8;
	random_bytes = ((prime_bits - 2) + 7) / 8;
	buf = l_malloc(private_bytes);
	l_getrandom(buf + private_bytes - random_bytes, random_bytes);

	buf[0] &= (1 << ((prime_bits - 2) % 8)) - 1;
	buf[0] |= 1 << ((prime_bits - 2) % 8);

	private = l_key_new(L_KEY_RAW, buf, private_bytes);
	explicit_bzero(buf, private_bytes);
	l_free(buf);
	return private;
}

static bool compute_common(struct l_key *base, struct l_key *private,
				struct l_key *prime, void *payload, size_t *len)
{
	long result_len;
	bool usable_payload = *len != 0;

	result_len = kernel_dh_compute(private->serial, prime->serial,
					base->serial, payload, *len);

	if (result_len > 0) {
		*len = result_len;
		return usable_payload;
	}
	return false;
}

LIB_EXPORT bool l_key_compute_dh_public(struct l_key *generator,
					struct l_key *private,
					struct l_key *prime,
					void *payload, size_t *len)
{
	return compute_common(generator, private, prime, payload, len);
}

LIB_EXPORT bool l_key_compute_dh_secret(struct l_key *other_public,
					struct l_key *private,
					struct l_key *prime,
					void *payload, size_t *len)
{
	return compute_common(other_public, private, prime, payload, len);
}

static int be_bignum_compare(const uint8_t *a, size_t a_len,
				const uint8_t *b, size_t b_len)
{
	unsigned int i;

	if (a_len >= b_len) {
		for (i = 0; i < a_len - b_len; i++)
			if (a[i])
				return 1;

		return memcmp(a + i, b, b_len);
	}

	for (i = 0; i < b_len - a_len; i++)
		if (b[i])
			return -1;

	return memcmp(a, b + i, a_len);
}

/*
 * Validate that @payload is within range for a private and public key for
 * a DH computation in the finite field group defined by modulus @prime_buf,
 * both numbers stored as big-endian integers.  We require a key in the
 * [2, prime - 2] (inclusive) interval.  PKCS #3 does not exclude 1 as a
 * private key but other specs do.
 */
LIB_EXPORT bool l_key_validate_dh_payload(const void *payload, size_t len,
				const void *prime_buf, size_t prime_len)
{
	static const uint8_t one[] = { 1 };
	uint8_t prime_1[prime_len];

	/*
	 * Produce prime - 1 for the payload < prime - 1 check.
	 * prime is odd so just zero the LSB.
	 */
	memcpy(prime_1, prime_buf, prime_len);

	if (prime_len < 1 || !(prime_1[prime_len - 1] & 1))
		return false;

	prime_1[prime_len - 1] &= ~1;

	if (be_bignum_compare(payload, len, one, 1) <= 0)
		return false;

	if (be_bignum_compare(payload, len, prime_1, prime_len) >= 0)
		return false;

	return true;
}

/* Common code for encrypt/decrypt/sign */
static ssize_t eds_common(struct l_key *key,
				enum l_key_cipher_type cipher,
				enum l_checksum_type checksum, const void *in,
				void *out, size_t len_in, size_t len_out,
				int op)
{
	if (unlikely(!key))
		return -EINVAL;

	return kernel_key_eds(op, key->serial, lookup_cipher(cipher),
				lookup_checksum(checksum), in, out, len_in,
				len_out);
}

LIB_EXPORT ssize_t l_key_encrypt(struct l_key *key,
					enum l_key_cipher_type cipher,
					enum l_checksum_type checksum,
					const void *in, void *out,
					size_t len_in, size_t len_out)
{
	ssize_t ret_len;

	ret_len = eds_common(key, cipher, checksum, in, out,
				len_in, len_out,
				KEYCTL_PKEY_ENCRYPT);

	return ret_len;
}

LIB_EXPORT ssize_t l_key_decrypt(struct l_key *key,
					enum l_key_cipher_type cipher,
					enum l_checksum_type checksum,
					const void *in, void *out,
					size_t len_in, size_t len_out)
{
	ssize_t ret_len;

	ret_len = eds_common(key, cipher, checksum, in, out, len_in,
				len_out, KEYCTL_PKEY_DECRYPT);

	if (ret_len < 0)
		goto done;

done:
	return ret_len;
}

LIB_EXPORT ssize_t l_key_sign(struct l_key *key,
				enum l_key_cipher_type cipher,
				enum l_checksum_type checksum, const void *in,
				void *out, size_t len_in, size_t len_out)
{
	ssize_t ret_len;

	ret_len = eds_common(key, cipher, checksum, in, out,
				len_in, len_out,
				KEYCTL_PKEY_SIGN);

	return ret_len;
}

LIB_EXPORT bool l_key_verify(struct l_key *key,
				enum l_key_cipher_type cipher,
				enum l_checksum_type checksum, const void *data,
				const void *sig, size_t len_data,
				size_t len_sig)
{
	long result;

	if (unlikely(!key))
		return false;

	result = kernel_key_verify(key->serial, lookup_cipher(cipher),
					lookup_checksum(checksum),
					data, len_data,
					sig, len_sig);

	return result >= 0;
}

LIB_EXPORT struct l_keyring *l_keyring_new(void)
{
	struct l_keyring *keyring;
	char *description;
	static unsigned long keyring_idx;

	if (!internal_keyring && !setup_internal_keyring())
		return NULL;

	keyring = l_new(struct l_keyring, 1);
	description = l_strdup_printf("ell-keyring-%lu", keyring_idx++);
	keyring->serial = kernel_add_key("keyring", description, NULL, 0,
						internal_keyring);
	l_free(description);

	if (keyring->serial < 0) {
		l_free(keyring);
		return NULL;
	}

	return keyring;
}

LIB_EXPORT bool l_keyring_restrict(struct l_keyring *keyring,
					enum l_keyring_restriction res,
					const struct l_keyring *trusted)
{
	char *restriction = NULL;
	long result;

	switch (res) {
	case L_KEYRING_RESTRICT_ASYM:
	case L_KEYRING_RESTRICT_ASYM_CHAIN:
	{
		char *option = "";

		if (res == L_KEYRING_RESTRICT_ASYM_CHAIN)
			option = ":chain";

		restriction = l_strdup_printf("key_or_keyring:%d%s",
						trusted ? trusted->serial : 0,
						option);

		break;
	}
	default:
		/* Unsupported type */
		return NULL;
	}

	result = kernel_restrict_keyring(keyring->serial, "asymmetric",
						restriction);

	l_free(restriction);

	return result == 0;
}

LIB_EXPORT void l_keyring_free(struct l_keyring *keyring)
{
	if (unlikely(!keyring))
		return;

	kernel_invalidate_key(keyring->serial);

	l_free(keyring);
}

LIB_EXPORT void l_keyring_free_norevoke(struct l_keyring *keyring)
{
	if (unlikely(!keyring))
		return;

	kernel_unlink_key(keyring->serial, internal_keyring);

	l_free(keyring);
}

LIB_EXPORT bool l_keyring_link(struct l_keyring *keyring,
							const struct l_key *key)
{
	long error;

	if (unlikely(!keyring) || unlikely(!key))
		return false;

	error = kernel_link_key(key->serial, keyring->serial);

	return error == 0;
}

LIB_EXPORT bool l_keyring_unlink(struct l_keyring *keyring,
							const struct l_key *key)
{
	long error;

	if (unlikely(!keyring) || unlikely(!key))
		return false;

	error = kernel_unlink_key(key->serial, keyring->serial);

	return error == 0;
}

LIB_EXPORT bool l_keyring_link_nested(struct l_keyring *keyring,
						const struct l_keyring *nested)
{
	long error;

	if (unlikely(!keyring) || unlikely(!nested))
		return false;

	error = kernel_link_key(nested->serial, keyring->serial);

	return error == 0;
}

LIB_EXPORT bool l_keyring_unlink_nested(struct l_keyring *keyring,
						const struct l_keyring *nested)
{
	long error;

	if (unlikely(!keyring) || unlikely(!nested))
		return false;

	error = kernel_unlink_key(nested->serial, keyring->serial);

	return error == 0;
}

LIB_EXPORT bool l_key_is_supported(uint32_t features)
{
	long result;

	if (features & L_KEY_FEATURE_DH) {
		result = syscall(__NR_keyctl, KEYCTL_DH_COMPUTE, NULL, "x", 1,
					NULL);

		if (result == -1 && errno == EOPNOTSUPP)
			return false;
	}

	if (features & L_KEY_FEATURE_RESTRICT) {
		result = syscall(__NR_keyctl, KEYCTL_RESTRICT_KEYRING, 0,
					"asymmetric", "");

		if (result == -1 && errno == EOPNOTSUPP)
			return false;
	}

	if (features & L_KEY_FEATURE_CRYPTO) {
		result = syscall(__NR_keyctl, KEYCTL_PKEY_QUERY, 0, 0, "", 0);

		if (result == -1 && errno == EOPNOTSUPP)
			return false;
	}

	return true;
}