ell/dhcp-util.c

/*
 *
 *  Embedded Linux library
 *
 *  Copyright (C) 2020  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
 *
 */
#include <stdint.h>
#include <linux/types.h>
#include <errno.h>
#include <stdbool.h>
#include <stddef.h>
#include <string.h>
#include <arpa/inet.h>

#include "dhcp-private.h"
#include "private.h"
#include "useful.h"

#define BITS_PER_LONG (sizeof(unsigned long) * 8)

static void dhcp_init_header(struct dhcp_message *message, uint8_t type)
{
	switch (type) {
	case DHCP_MESSAGE_TYPE_OFFER:
	case DHCP_MESSAGE_TYPE_NAK:
	case DHCP_MESSAGE_TYPE_ACK:
		message->op = DHCP_OP_CODE_BOOTREPLY;
		break;
	default:
		message->op = DHCP_OP_CODE_BOOTREQUEST;
		break;
	}

	message->htype = 1;
	message->hlen = 6;
	message->magic = htonl(DHCP_MAGIC);
	message->options[0] = DHCP_OPTION_END;
}

#define LEN_CHECK(builder, next) \
	if ((builder)->pos - (builder)->start + (next) > (builder)->max) \
		return false;

bool _dhcp_message_builder_append(struct dhcp_message_builder *builder,
					uint8_t code, size_t optlen,
					const void *optval)
{
	switch (code) {
	case DHCP_OPTION_PAD:
	case DHCP_OPTION_END:
		LEN_CHECK(builder, 1U);

		builder->pos[0] = code;
		builder->pos += 1;
		break;
	default:
		LEN_CHECK(builder, optlen + 2);

		builder->pos[0] = code;
		builder->pos[1] = optlen;

		if (optlen)
			memcpy(builder->pos + 2, optval, optlen);

		builder->pos += optlen + 2;
		break;
	}

	return true;
}

bool _dhcp_message_builder_append_prl(struct dhcp_message_builder *builder,
					const unsigned long *reqopts)
{
	uint8_t optlen = 0;
	unsigned int i;
	unsigned int j;

	for (i = 0; i < 256 / BITS_PER_LONG; i++)
		optlen += __builtin_popcountl(reqopts[i]);

	/*
	 * This function assumes that there's enough space to put the PRL
	 * into the buffer without resorting to file or sname overloading
	 */
	LEN_CHECK(builder, optlen + 2U);

	i = 0;
	builder->pos[i++] = DHCP_OPTION_PARAMETER_REQUEST_LIST;
	builder->pos[i++] = optlen;

	for (j = 0; j < 256; j++) {
		if (reqopts[j / BITS_PER_LONG] & 1UL << (j % BITS_PER_LONG)) {
			builder->pos[i++] = j;
		}
	}

	builder->pos += optlen + 2;

	return true;
}

bool _dhcp_message_builder_init(struct dhcp_message_builder *builder,
				struct dhcp_message *message,
				size_t len, uint8_t type)
{
	if (!builder || !message || !len)
		return false;

	builder->max = len;
	builder->pos = (uint8_t *) message->options;
	builder->start = (uint8_t *) message;

	dhcp_init_header(message, type);

	return _dhcp_message_builder_append(builder, DHCP_OPTION_MESSAGE_TYPE,
						1, &type);
}

static inline int dhcp_message_optimize(struct dhcp_message *message,
					const uint8_t *end)
{
	/*
	 * Don't bother sending a full sized dhcp_message as it is most likely
	 * mostly zeros.  Instead truncate it at DHCP_OPTION_END and align to
	 * the nearest 4 byte boundary.  Many implementations expect a packet
	 * of a certain size or it is filtered, so we cap the length in
	 * accordance to RFC 1542:
	 * "The IP Total Length and UDP Length must be large enough to contain
	 * the minimal BOOTP header of 300 octets"
	 */
	size_t len = align_len(end - (uint8_t *) message, 4);
	if (len < 300)
		len = 300;

	return len;
}

uint8_t *_dhcp_message_builder_finalize(struct dhcp_message_builder *builder,
					size_t *outlen)
{
	_dhcp_message_builder_append(builder, DHCP_OPTION_END, 0, NULL);

	*outlen = dhcp_message_optimize((struct dhcp_message *)builder->start,
				builder->pos);

	return builder->start;
}

bool _dhcp_message_iter_init(struct dhcp_message_iter *iter,
				const struct dhcp_message *message, size_t len)
{
	if (!message)
		return false;

	if (len < sizeof(struct dhcp_message))
		return false;

	if (L_BE32_TO_CPU(message->magic) != DHCP_MAGIC)
		return false;

	memset(iter, 0, sizeof(*iter));
	iter->message = message;
	iter->message_len = len;
	iter->max = len - sizeof(struct dhcp_message);
	iter->options = message->options;
	iter->can_overload = true;

	return true;
}

static bool next_option(struct dhcp_message_iter *iter,
				uint8_t *t, uint8_t *l, const void **v)
{
	uint8_t type;
	uint8_t len;

	while (iter->pos < iter->max) {
		type = iter->options[iter->pos];

		switch (type) {
		case DHCP_OPTION_PAD:
			iter->pos += 1;
			continue;
		case DHCP_OPTION_END:
			return false;
		default:
			break;
		}

		if (iter->pos + 2 >= iter->max)
			return false;

		len = iter->options[iter->pos + 1];

		if (iter->pos + 2 + len > iter->max)
			return false;

		*t = type;
		*l = len;
		*v = &iter->options[iter->pos + 2];

		iter->pos += 2 + len;
		return true;
	}

	return false;
}

bool _dhcp_message_iter_next(struct dhcp_message_iter *iter, uint8_t *type,
				uint8_t *len, const void **data)
{
	bool r;
	uint8_t t, l;
	const void *v;

	do {
		r = next_option(iter, &t, &l, &v);
		if (!r) {
			iter->can_overload = false;

			if (iter->overload_file) {
				iter->options = iter->message->file;
				iter->pos = 0;
				iter->max = sizeof(iter->message->file);
				iter->overload_file = false;
				continue;
			}

			if (iter->overload_sname) {
				iter->options = iter->message->sname;
				iter->pos = 0;
				iter->max = sizeof(iter->message->sname);
				iter->overload_sname = false;
				continue;
			}

			return r;
		}

		switch (t) {
		case DHCP_OPTION_OVERLOAD:
			if (l != 1)
				continue;

			if (!iter->can_overload)
				continue;

			if (l_get_u8(v) & DHCP_OVERLOAD_FILE)
				iter->overload_file = true;

			if (l_get_u8(v) & DHCP_OVERLOAD_SNAME)
				iter->overload_sname = true;

			continue;
		default:
			if (type)
				*type = t;

			if (len)
				*len = l;

			if (data)
				*data = v;
			return r;
		}
	} while (true);

	return false;
}

int _dhcp_option_append(uint8_t **buf, size_t *buflen, uint8_t code,
					size_t optlen, const void *optval)
{
	if (!buf || !buflen)
		return -EINVAL;

	switch (code) {

	case DHCP_OPTION_PAD:
	case DHCP_OPTION_END:
		if (*buflen < 1)
			return -ENOBUFS;

		(*buf)[0] = code;
		*buf += 1;
		*buflen -= 1;
		break;

	default:
		if (*buflen < optlen + 2)
			return -ENOBUFS;

		if (!optval)
			return -EINVAL;

		(*buf)[0] = code;
		(*buf)[1] = optlen;
		memcpy(&(*buf)[2], optval, optlen);

		*buf += optlen + 2;
		*buflen -= (optlen + 2);

		break;
	}

	return 0;
}