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/***
This file is part of systemd.
Copyright (C) 2013 Intel Corporation. All rights reserved.
Copyright (C) 2014 Tom Gundersen
systemd 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.
systemd 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 systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <net/ethernet.h>
#include <net/if_arp.h>
#include <sys/param.h>
#include "util.h"
#include "list.h"
#include "dhcp-protocol.h"
#include "dhcp-lease.h"
#include "dhcp-internal.h"
#include "sd-dhcp-client.h"
#define DHCP_CLIENT_MIN_OPTIONS_SIZE 312
int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid,
uint8_t type, uint16_t secs, uint8_t **opt,
size_t *optlen) {
int err;
*opt = (uint8_t *)(message + 1);
if (*optlen < 4)
return -ENOBUFS;
*optlen -= 4;
message->op = op;
message->htype = ARPHRD_ETHER;
message->hlen = ETHER_ADDR_LEN;
message->xid = htobe32(xid);
/* Although 'secs' field is a SHOULD in RFC 2131, certain DHCP servers
refuse to issue an DHCP lease if 'secs' is set to zero */
message->secs = htobe16(secs);
(*opt)[0] = 0x63;
(*opt)[1] = 0x82;
(*opt)[2] = 0x53;
(*opt)[3] = 0x63;
*opt += 4;
err = dhcp_option_append(opt, optlen, DHCP_OPTION_MESSAGE_TYPE, 1,
&type);
if (err < 0)
return err;
return 0;
}
static uint16_t dhcp_checksum(void *buf, int len) {
uint32_t sum;
uint16_t *check;
int i;
uint8_t *odd;
sum = 0;
check = buf;
for (i = 0; i < len / 2 ; i++)
sum += check[i];
if (len & 0x01) {
odd = buf;
sum += odd[len - 1];
}
while (sum >> 16)
sum = (sum & 0xffff) + (sum >> 16);
return ~sum;
}
void dhcp_packet_append_ip_headers(DHCPPacket *packet, uint16_t len) {
packet->ip.version = IPVERSION;
packet->ip.ihl = DHCP_IP_SIZE / 4;
packet->ip.tot_len = htobe16(len);
packet->ip.protocol = IPPROTO_UDP;
packet->ip.saddr = INADDR_ANY;
packet->ip.daddr = INADDR_BROADCAST;
packet->udp.source = htobe16(DHCP_PORT_CLIENT);
packet->udp.dest = htobe16(DHCP_PORT_SERVER);
packet->udp.len = htobe16(len - DHCP_IP_SIZE);
packet->ip.check = packet->udp.len;
packet->udp.check = dhcp_checksum(&packet->ip.ttl, len - 8);
packet->ip.ttl = IPDEFTTL;
packet->ip.check = 0;
packet->ip.check = dhcp_checksum(&packet->ip, DHCP_IP_SIZE);
}
int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len) {
size_t hdrlen;
assert(packet);
/* IP */
if (len < DHCP_IP_SIZE) {
log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
" smaller than IP header (%u bytes)", len,
DHCP_IP_SIZE);
return -EINVAL;
}
if (packet->ip.ihl < 5) {
log_dhcp_client(client, "ignoring packet: IPv4 IHL (%u words) invalid",
packet->ip.ihl);
return -EINVAL;
}
hdrlen = packet->ip.ihl * 4;
if (hdrlen < 20) {
log_dhcp_client(client, "ignoring packet: IPv4 IHL (%zu bytes) "
"smaller than minimum (20 bytes)", hdrlen);
return -EINVAL;
}
if (len < hdrlen) {
log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
"smaller than expected (%zu) by IP header", len,
hdrlen);
return -EINVAL;
}
if (dhcp_checksum(&packet->ip, hdrlen)) {
log_dhcp_client(client, "ignoring packet: invalid IP checksum");
return -EINVAL;
}
/* UDP */
if (len < DHCP_IP_UDP_SIZE) {
log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
" smaller than IP+UDP header (%u bytes)", len,
DHCP_IP_UDP_SIZE);
return -EINVAL;
}
if (hdrlen + be16toh(packet->udp.len) > len) {
log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
"smaller than expected (%zu) by UDP header", len,
hdrlen + be16toh(packet->udp.len));
return -EINVAL;
}
if (packet->udp.check) {
packet->ip.check = packet->udp.len;
packet->ip.ttl = 0;
if (dhcp_checksum(&packet->ip.ttl,
be16toh(packet->udp.len) + 12)) {
log_dhcp_client(client, "ignoring packet: invalid UDP checksum");
return -EINVAL;
}
}
if (be16toh(packet->udp.source) != DHCP_PORT_SERVER ||
be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) {
log_dhcp_client(client, "ignoring packet: wrong ports (source: %u, destination: %u)",
be16toh(packet->udp.source), be16toh(packet->udp.dest));
return -EINVAL;
}
return 0;
}
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