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         *opt = (uint8_t *)(message + 1);
  47
  48         if (*optlen < 4)
  49                 return -ENOBUFS;
  50         *optlen -= 4;
  51
  52         message->op = op;
  53         message->htype = ARPHRD_ETHER;
  54         message->hlen = ETHER_ADDR_LEN;
  55         message->xid = htobe32(xid);
  56
  57         (*opt)[0] = 0x63;
  58         (*opt)[1] = 0x82;
  59         (*opt)[2] = 0x53;
  60         (*opt)[3] = 0x63;
  61
  62         *opt += 4;
  63
  64         err = dhcp_option_append(opt, optlen, DHCP_OPTION_MESSAGE_TYPE, 1,
  65                                  &type);
  66         if (err < 0)
  67                 return err;
  68
  69         return 0;
  70 }
  71
  72 uint16_t dhcp_packet_checksum(void *buf, int len) {
  73         uint32_t sum;
  74         uint16_t *check;
  75         int i;
  76         uint8_t *odd;
  77
  78         sum = 0;
  79         check = buf;
  80
  81         for (i = 0; i < len / 2 ; i++)
  82                 sum += check[i];
  83
  84         if (len & 0x01) {
  85                 odd = buf;
  86                 sum += odd[len - 1];
  87         }
  88
  89         while (sum >> 16)
  90                 sum = (sum & 0xffff) + (sum >> 16);
  91
  92         return ~sum;
  93 }
  94
  95 void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
  96                                    uint16_t source_port, be32_t destination_addr,
  97                                    uint16_t destination_port, uint16_t len) {
  98         packet->ip.version = IPVERSION;
  99         packet->ip.ihl = DHCP_IP_SIZE / 4;
 100         packet->ip.tot_len = htobe16(len);
 101
 102         packet->ip.protocol = IPPROTO_UDP;
 103         packet->ip.saddr = source_addr;
 104         packet->ip.daddr = destination_addr;
 105
 106         packet->udp.source = htobe16(source_port);
 107         packet->udp.dest = htobe16(destination_port);
 108
 109         packet->udp.len = htobe16(len - DHCP_IP_SIZE);
 110
 111         packet->ip.check = packet->udp.len;
 112         packet->udp.check = dhcp_packet_checksum(&packet->ip.ttl, len - 8);
 113
 114         packet->ip.ttl = IPDEFTTL;
 115         packet->ip.check = 0;
 116         packet->ip.check = dhcp_packet_checksum(&packet->ip, DHCP_IP_SIZE);
 117 }
 118
 119 int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
 120         size_t hdrlen;
 121
 122         assert(packet);
 123
 124         /* IP */
 125
 126         if (len < DHCP_IP_SIZE) {
 127                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 128                                 " smaller than IP header (%u bytes)", len,
 129                                 DHCP_IP_SIZE);
 130                 return -EINVAL;
 131         }
 132
 133         if (packet->ip.ihl < 5) {
 134                 log_dhcp_client(client, "ignoring packet: IPv4 IHL (%u words) invalid",
 135                                 packet->ip.ihl);
 136                 return -EINVAL;
 137         }
 138
 139         hdrlen = packet->ip.ihl * 4;
 140         if (hdrlen < 20) {
 141                 log_dhcp_client(client, "ignoring packet: IPv4 IHL (%zu bytes) "
 142                                 "smaller than minimum (20 bytes)", hdrlen);
 143                 return -EINVAL;
 144         }
 145
 146         if (len < hdrlen) {
 147                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 148                                 "smaller than expected (%zu) by IP header", len,
 149                                 hdrlen);
 150                 return -EINVAL;
 151         }
 152
 153         if (dhcp_packet_checksum(&packet->ip, hdrlen)) {
 154                 log_dhcp_client(client, "ignoring packet: invalid IP checksum");
 155                 return -EINVAL;
 156         }
 157
 158         /* UDP */
 159
 160         if (len < DHCP_IP_UDP_SIZE) {
 161                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 162                                 " smaller than IP+UDP header (%u bytes)", len,
 163                                 DHCP_IP_UDP_SIZE);
 164                 return -EINVAL;
 165         }
 166
 167         if (len < hdrlen + be16toh(packet->udp.len)) {
 168                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 169                                 "smaller than expected (%zu) by UDP header", len,
 170                                 hdrlen + be16toh(packet->udp.len));
 171                 return -EINVAL;
 172         }
 173
 174         if (checksum && packet->udp.check) {
 175                 packet->ip.check = packet->udp.len;
 176                 packet->ip.ttl = 0;
 177
 178                 if (dhcp_packet_checksum(&packet->ip.ttl,
 179                                   be16toh(packet->udp.len) + 12)) {
 180                         log_dhcp_client(client, "ignoring packet: invalid UDP checksum");
 181                         return -EINVAL;
 182                 }
 183         }
 184
 185         if (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) {
 186                 log_dhcp_client(client, "ignoring packet: to port %u, which "
 187                                 "is not the DHCP client port (%u)",
 188                                 be16toh(packet->udp.dest), DHCP_PORT_CLIENT);
 189                 return -EINVAL;
 190         }
 191
 192         return 0;
 193 }