networking/udhcp/packet.c

   1 /* vi: set sw=4 ts=4: */
   2
   3 #include <netinet/in.h>
   4 #if (__GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION
   5 #include <netpacket/packet.h>
   6 #include <net/ethernet.h>
   7 #else
   8 #include <asm/types.h>
   9 #include <linux/if_packet.h>
  10 #include <linux/if_ether.h>
  11 #endif
  12
  13 #include "common.h"
  14 #include "dhcpd.h"
  15 #include "options.h"
  16
  17
  18 void udhcp_init_header(struct dhcpMessage *packet, char type)
  19 {
  20         memset(packet, 0, sizeof(struct dhcpMessage));
  21         switch (type) {
  22         case DHCPDISCOVER:
  23         case DHCPREQUEST:
  24         case DHCPRELEASE:
  25         case DHCPINFORM:
  26                 packet->op = BOOTREQUEST;
  27                 break;
  28         case DHCPOFFER:
  29         case DHCPACK:
  30         case DHCPNAK:
  31                 packet->op = BOOTREPLY;
  32         }
  33         packet->htype = ETH_10MB;
  34         packet->hlen = ETH_10MB_LEN;
  35         packet->cookie = htonl(DHCP_MAGIC);
  36         packet->options[0] = DHCP_END;
  37         add_simple_option(packet->options, DHCP_MESSAGE_TYPE, type);
  38 }
  39
  40
  41 /* read a packet from socket fd, return -1 on read error, -2 on packet error */
  42 int udhcp_get_packet(struct dhcpMessage *packet, int fd)
  43 {
  44         static const char broken_vendors[][8] = {
  45                 "MSFT 98",
  46                 ""
  47         };
  48         int bytes;
  49         int i;
  50         char unsigned *vendor;
  51
  52         memset(packet, 0, sizeof(struct dhcpMessage));
  53         bytes = read(fd, packet, sizeof(struct dhcpMessage));
  54         if (bytes < 0) {
  55                 DEBUG("cannot read on listening socket, ignoring");
  56                 return -1;
  57         }
  58
  59         if (ntohl(packet->cookie) != DHCP_MAGIC) {
  60                 bb_error_msg("received bogus message, ignoring");
  61                 return -2;
  62         }
  63         DEBUG("Received a packet");
  64
  65         if (packet->op == BOOTREQUEST && (vendor = get_option(packet, DHCP_VENDOR))) {
  66                 for (i = 0; broken_vendors[i][0]; i++) {
  67                         if (vendor[OPT_LEN - 2] == (uint8_t)strlen(broken_vendors[i])
  68                          && !strncmp((char*)vendor, broken_vendors[i], vendor[OPT_LEN - 2])
  69                         ) {
  70                                 DEBUG("broken client (%s), forcing broadcast",
  71                                         broken_vendors[i]);
  72                                 packet->flags |= htons(BROADCAST_FLAG);
  73                         }
  74                 }
  75         }
  76
  77         return bytes;
  78 }
  79
  80
  81 uint16_t udhcp_checksum(void *addr, int count)
  82 {
  83         /* Compute Internet Checksum for "count" bytes
  84          *         beginning at location "addr".
  85          */
  86         int32_t sum = 0;
  87         uint16_t *source = (uint16_t *) addr;
  88
  89         while (count > 1)  {
  90                 /*  This is the inner loop */
  91                 sum += *source++;
  92                 count -= 2;
  93         }
  94
  95         /*  Add left-over byte, if any */
  96         if (count > 0) {
  97                 /* Make sure that the left-over byte is added correctly both
  98                  * with little and big endian hosts */
  99                 uint16_t tmp = 0;
 100                 *(uint8_t *) (&tmp) = * (uint8_t *) source;
 101                 sum += tmp;
 102         }
 103         /*  Fold 32-bit sum to 16 bits */
 104         while (sum >> 16)
 105                 sum = (sum & 0xffff) + (sum >> 16);
 106
 107         return ~sum;
 108 }
 109
 110
 111 /* Construct a ip/udp header for a packet, and specify the source and dest hardware address */
 112 int udhcp_raw_packet(struct dhcpMessage *payload,
 113                 uint32_t source_ip, int source_port,
 114                 uint32_t dest_ip, int dest_port, uint8_t *dest_arp, int ifindex)
 115 {
 116         int fd;
 117         int result;
 118         struct sockaddr_ll dest;
 119         struct udp_dhcp_packet packet;
 120
 121         fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
 122         if (fd < 0) {
 123                 bb_perror_msg("socket");
 124                 return -1;
 125         }
 126
 127         memset(&dest, 0, sizeof(dest));
 128         memset(&packet, 0, sizeof(packet));
 129
 130         dest.sll_family = AF_PACKET;
 131         dest.sll_protocol = htons(ETH_P_IP);
 132         dest.sll_ifindex = ifindex;
 133         dest.sll_halen = 6;
 134         memcpy(dest.sll_addr, dest_arp, 6);
 135         if (bind(fd, (struct sockaddr *)&dest, sizeof(struct sockaddr_ll)) < 0) {
 136                 bb_perror_msg("bind");
 137                 close(fd);
 138                 return -1;
 139         }
 140
 141         packet.ip.protocol = IPPROTO_UDP;
 142         packet.ip.saddr = source_ip;
 143         packet.ip.daddr = dest_ip;
 144         packet.udp.source = htons(source_port);
 145         packet.udp.dest = htons(dest_port);
 146         packet.udp.len = htons(sizeof(packet.udp) + sizeof(struct dhcpMessage)); /* cheat on the psuedo-header */
 147         packet.ip.tot_len = packet.udp.len;
 148         memcpy(&(packet.data), payload, sizeof(struct dhcpMessage));
 149         packet.udp.check = udhcp_checksum(&packet, sizeof(struct udp_dhcp_packet));
 150
 151         packet.ip.tot_len = htons(sizeof(struct udp_dhcp_packet));
 152         packet.ip.ihl = sizeof(packet.ip) >> 2;
 153         packet.ip.version = IPVERSION;
 154         packet.ip.ttl = IPDEFTTL;
 155         packet.ip.check = udhcp_checksum(&(packet.ip), sizeof(packet.ip));
 156
 157         result = sendto(fd, &packet, sizeof(struct udp_dhcp_packet), 0,
 158                         (struct sockaddr *) &dest, sizeof(dest));
 159         if (result <= 0) {
 160                 bb_perror_msg("sendto");
 161         }
 162         close(fd);
 163         return result;
 164 }
 165
 166
 167 /* Let the kernel do all the work for packet generation */
 168 int udhcp_kernel_packet(struct dhcpMessage *payload,
 169                 uint32_t source_ip, int source_port,
 170                 uint32_t dest_ip, int dest_port)
 171 {
 172         int n = 1;
 173         int fd, result;
 174         struct sockaddr_in client;
 175
 176         fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 177         if (fd < 0)
 178                 return -1;
 179
 180         if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (char *) &n, sizeof(n)) == -1) {
 181                 close(fd);
 182                 return -1;
 183         }
 184
 185         memset(&client, 0, sizeof(client));
 186         client.sin_family = AF_INET;
 187         client.sin_port = htons(source_port);
 188         client.sin_addr.s_addr = source_ip;
 189
 190         if (bind(fd, (struct sockaddr *)&client, sizeof(struct sockaddr)) == -1) {
 191                 close(fd);
 192                 return -1;
 193         }
 194
 195         memset(&client, 0, sizeof(client));
 196         client.sin_family = AF_INET;
 197         client.sin_port = htons(dest_port);
 198         client.sin_addr.s_addr = dest_ip;
 199
 200         if (connect(fd, (struct sockaddr *)&client, sizeof(struct sockaddr)) == -1) {
 201                 close(fd);
 202                 return -1;
 203         }
 204
 205         result = write(fd, payload, sizeof(struct dhcpMessage));
 206         close(fd);
 207         return result;
 208 }