src/libsystemd-network/dhcp-packet.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright (C) 2013 Intel Corporation. All rights reserved.
   5   Copyright (C) 2014 Tom Gundersen
   6
   7   systemd is free software; you can redistribute it and/or modify it
   8   under the terms of the GNU Lesser General Public License as published by
   9   the Free Software Foundation; either version 2.1 of the License, or
  10   (at your option) any later version.
  11
  12   systemd is distributed in the hope that it will be useful, but
  13   WITHOUT ANY WARRANTY; without even the implied warranty of
  14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15   Lesser General Public License for more details.
  16
  17   You should have received a copy of the GNU Lesser General Public License
  18   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  19 ***/
  20
  21 #include <stdlib.h>
  22 #include <errno.h>
  23 #include <string.h>
  24 #include <stdio.h>
  25 #include <net/ethernet.h>
  26 #include <net/if_arp.h>
  27 #include <sys/param.h>
  28
  29 #include "util.h"
  30 #include "list.h"
  31
  32 #include "dhcp-protocol.h"
  33 #include "dhcp-lease-internal.h"
  34 #include "dhcp-internal.h"
  35 #include "sd-dhcp-lease.h"
  36 #include "sd-dhcp-client.h"
  37
  38 #define DHCP_CLIENT_MIN_OPTIONS_SIZE            312
  39
  40 int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid,
  41                       uint8_t type, uint8_t **opt, size_t *optlen) {
  42         int err;
  43
  44         assert(op == BOOTREQUEST || op == BOOTREPLY);
  45
  46         message->op = op;
  47         message->htype = ARPHRD_ETHER;
  48         message->hlen = ETHER_ADDR_LEN;
  49         message->xid = htobe32(xid);
  50         message->magic = htobe32(DHCP_MAGIC_COOKIE);
  51
  52         *opt = (uint8_t *)(message + 1);
  53
  54         err = dhcp_option_append(opt, optlen, DHCP_OPTION_MESSAGE_TYPE, 1,
  55                                  &type);
  56         if (err < 0)
  57                 return err;
  58
  59         return 0;
  60 }
  61
  62 uint16_t dhcp_packet_checksum(void *buf, int len) {
  63         uint32_t sum;
  64         uint16_t *check;
  65         int i;
  66         uint8_t *odd;
  67
  68         sum = 0;
  69         check = buf;
  70
  71         for (i = 0; i < len / 2 ; i++)
  72                 sum += check[i];
  73
  74         if (len & 0x01) {
  75                 odd = buf;
  76                 sum += odd[len - 1];
  77         }
  78
  79         while (sum >> 16)
  80                 sum = (sum & 0xffff) + (sum >> 16);
  81
  82         return ~sum;
  83 }
  84
  85 void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
  86                                    uint16_t source_port, be32_t destination_addr,
  87                                    uint16_t destination_port, uint16_t len) {
  88         packet->ip.version = IPVERSION;
  89         packet->ip.ihl = DHCP_IP_SIZE / 4;
  90         packet->ip.tot_len = htobe16(len);
  91
  92         packet->ip.protocol = IPPROTO_UDP;
  93         packet->ip.saddr = source_addr;
  94         packet->ip.daddr = destination_addr;
  95
  96         packet->udp.source = htobe16(source_port);
  97         packet->udp.dest = htobe16(destination_port);
  98
  99         packet->udp.len = htobe16(len - DHCP_IP_SIZE);
 100
 101         packet->ip.check = packet->udp.len;
 102         packet->udp.check = dhcp_packet_checksum(&packet->ip.ttl, len - 8);
 103
 104         packet->ip.ttl = IPDEFTTL;
 105         packet->ip.check = 0;
 106         packet->ip.check = dhcp_packet_checksum(&packet->ip, DHCP_IP_SIZE);
 107 }
 108
 109 int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
 110         size_t hdrlen;
 111
 112         assert(packet);
 113
 114         /* IP */
 115
 116         if (packet->ip.version != IPVERSION) {
 117                 log_dhcp_client(client, "ignoring packet: not IPv4");
 118                 return -EINVAL;
 119         }
 120
 121         if (packet->ip.ihl < 5) {
 122                 log_dhcp_client(client, "ignoring packet: IPv4 IHL (%u words) invalid",
 123                                 packet->ip.ihl);
 124                 return -EINVAL;
 125         }
 126
 127         hdrlen = packet->ip.ihl * 4;
 128         if (hdrlen < 20) {
 129                 log_dhcp_client(client, "ignoring packet: IPv4 IHL (%zu bytes) "
 130                                 "smaller than minimum (20 bytes)", hdrlen);
 131                 return -EINVAL;
 132         }
 133
 134         if (len < hdrlen) {
 135                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 136                                 "smaller than expected (%zu) by IP header", len,
 137                                 hdrlen);
 138                 return -EINVAL;
 139         }
 140
 141         /* UDP */
 142
 143         if (packet->ip.protocol != IPPROTO_UDP) {
 144                 log_dhcp_client(client, "ignoring packet: not UDP");
 145                 return -EINVAL;
 146         }
 147
 148         if (len < hdrlen + be16toh(packet->udp.len)) {
 149                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 150                                 "smaller than expected (%zu) by UDP header", len,
 151                                 hdrlen + be16toh(packet->udp.len));
 152                 return -EINVAL;
 153         }
 154
 155         if (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) {
 156                 log_dhcp_client(client, "ignoring packet: to port %u, which "
 157                                 "is not the DHCP client port (%u)",
 158                                 be16toh(packet->udp.dest), DHCP_PORT_CLIENT);
 159                 return -EINVAL;
 160         }
 161
 162         /* checksums - computing these is relatively expensive, so only do it
 163            if all the other checks have passed
 164          */
 165
 166         if (dhcp_packet_checksum(&packet->ip, hdrlen)) {
 167                 log_dhcp_client(client, "ignoring packet: invalid IP checksum");
 168                 return -EINVAL;
 169         }
 170
 171         if (checksum && packet->udp.check) {
 172                 packet->ip.check = packet->udp.len;
 173                 packet->ip.ttl = 0;
 174
 175                 if (dhcp_packet_checksum(&packet->ip.ttl,
 176                                   be16toh(packet->udp.len) + 12)) {
 177                         log_dhcp_client(client, "ignoring packet: invalid UDP checksum");
 178                         return -EINVAL;
 179                 }
 180         }
 181
 182         return 0;
 183 }