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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 <errno.h>
#include <net/ethernet.h>
#include <net/if_arp.h>
#include <string.h>
#include "dhcp-internal.h"
#include "dhcp-protocol.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 arp_type, size_t optlen,
size_t *optoffset) {
size_t offset = 0;
int r;
assert(op == BOOTREQUEST || op == BOOTREPLY);
assert(arp_type == ARPHRD_ETHER || arp_type == ARPHRD_INFINIBAND);
message->op = op;
message->htype = arp_type;
message->hlen = (arp_type == ARPHRD_ETHER) ? ETHER_ADDR_LEN : 0;
message->xid = htobe32(xid);
message->magic = htobe32(DHCP_MAGIC_COOKIE);
r = dhcp_option_append(message, optlen, &offset, 0,
DHCP_OPTION_MESSAGE_TYPE, 1, &type);
if (r < 0)
return r;
*optoffset = offset;
return 0;
}
uint16_t dhcp_packet_checksum(uint8_t *buf, size_t len) {
uint64_t *buf_64 = (uint64_t*)buf;
uint64_t *end_64 = buf_64 + (len / sizeof(uint64_t));
uint64_t sum = 0;
/* See RFC1071 */
while (buf_64 < end_64) {
sum += *buf_64;
if (sum < *buf_64)
/* wrap around in one's complement */
sum++;
buf_64 ++;
}
if (len % sizeof(uint64_t)) {
/* If the buffer is not aligned to 64-bit, we need
to zero-pad the last few bytes and add them in */
uint64_t buf_tail = 0;
memcpy(&buf_tail, buf_64, len % sizeof(uint64_t));
sum += buf_tail;
if (sum < buf_tail)
/* wrap around */
sum++;
}
while (sum >> 16)
sum = (sum & 0xffff) + (sum >> 16);
return ~sum;
}
void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
uint16_t source_port, be32_t destination_addr,
uint16_t destination_port, uint16_t len) {
packet->ip.version = IPVERSION;
packet->ip.ihl = DHCP_IP_SIZE / 4;
packet->ip.tot_len = htobe16(len);
packet->ip.tos = IPTOS_CLASS_CS6;
packet->ip.protocol = IPPROTO_UDP;
packet->ip.saddr = source_addr;
packet->ip.daddr = destination_addr;
packet->udp.source = htobe16(source_port);
packet->udp.dest = htobe16(destination_port);
packet->udp.len = htobe16(len - DHCP_IP_SIZE);
packet->ip.check = packet->udp.len;
packet->udp.check = dhcp_packet_checksum((uint8_t*)&packet->ip.ttl, len - 8);
packet->ip.ttl = IPDEFTTL;
packet->ip.check = 0;
packet->ip.check = dhcp_packet_checksum((uint8_t*)&packet->ip, DHCP_IP_SIZE);
}
int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
size_t hdrlen;
assert(packet);
/* IP */
if (packet->ip.version != IPVERSION) {
log_debug("ignoring packet: not IPv4");
return -EINVAL;
}
if (packet->ip.ihl < 5) {
log_debug("ignoring packet: IPv4 IHL (%u words) invalid",
packet->ip.ihl);
return -EINVAL;
}
hdrlen = packet->ip.ihl * 4;
if (hdrlen < 20) {
log_debug("ignoring packet: IPv4 IHL (%zu bytes) "
"smaller than minimum (20 bytes)", hdrlen);
return -EINVAL;
}
if (len < hdrlen) {
log_debug("ignoring packet: packet (%zu bytes) "
"smaller than expected (%zu) by IP header", len,
hdrlen);
return -EINVAL;
}
/* UDP */
if (packet->ip.protocol != IPPROTO_UDP) {
log_debug("ignoring packet: not UDP");
return -EINVAL;
}
if (len < hdrlen + be16toh(packet->udp.len)) {
log_debug("ignoring packet: packet (%zu bytes) "
"smaller than expected (%zu) by UDP header", len,
hdrlen + be16toh(packet->udp.len));
return -EINVAL;
}
if (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) {
log_debug("ignoring packet: to port %u, which "
"is not the DHCP client port (%u)",
be16toh(packet->udp.dest), DHCP_PORT_CLIENT);
return -EINVAL;
}
/* checksums - computing these is relatively expensive, so only do it
if all the other checks have passed
*/
if (dhcp_packet_checksum((uint8_t*)&packet->ip, hdrlen)) {
log_debug("ignoring packet: invalid IP checksum");
return -EINVAL;
}
if (checksum && packet->udp.check) {
packet->ip.check = packet->udp.len;
packet->ip.ttl = 0;
if (dhcp_packet_checksum((uint8_t*)&packet->ip.ttl,
be16toh(packet->udp.len) + 12)) {
log_debug("ignoring packet: invalid UDP checksum");
return -EINVAL;
}
}
return 0;
}
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