networking/udhcp/packet.c

   1 /* vi: set sw=4 ts=4: */
   2
   3 #include <netinet/in.h>
   4 #if (defined(__GLIBC__) && __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_recv_packet(struct dhcpMessage *packet, int fd)
  43 {
  44         int bytes;
  45         unsigned char *vendor;
  46
  47         memset(packet, 0, sizeof(*packet));
  48         bytes = safe_read(fd, packet, sizeof(*packet));
  49         if (bytes < 0) {
  50                 DEBUG("cannot read on listening socket, ignoring");
  51                 return bytes; /* returns -1 */
  52         }
  53
  54         if (packet->cookie != htonl(DHCP_MAGIC)) {
  55                 bb_error_msg("received bogus message, ignoring");
  56                 return -2;
  57         }
  58         DEBUG("Received a packet");
  59
  60         if (packet->op == BOOTREQUEST) {
  61                 vendor = get_option(packet, DHCP_VENDOR);
  62                 if (vendor) {
  63 #if 0
  64                         static const char broken_vendors[][8] = {
  65                                 "MSFT 98",
  66                                 ""
  67                         };
  68                         int i;
  69                         for (i = 0; broken_vendors[i][0]; i++) {
  70                                 if (vendor[OPT_LEN - 2] == (uint8_t)strlen(broken_vendors[i])
  71                                  && !strncmp((char*)vendor, broken_vendors[i], vendor[OPT_LEN - 2])
  72                                 ) {
  73                                         DEBUG("broken client (%s), forcing broadcast",
  74                                                 broken_vendors[i]);
  75                                         packet->flags |= htons(BROADCAST_FLAG);
  76                                 }
  77                         }
  78 #else
  79                         if (vendor[OPT_LEN - 2] == (uint8_t)(sizeof("MSFT 98")-1)
  80                          && memcmp(vendor, "MSFT 98", sizeof("MSFT 98")-1) == 0
  81                         ) {
  82                                 DEBUG("broken client (%s), forcing broadcast", "MSFT 98");
  83                                 packet->flags |= htons(BROADCAST_FLAG);
  84                         }
  85 #endif
  86                 }
  87         }
  88
  89         return bytes;
  90 }
  91
  92
  93 uint16_t udhcp_checksum(void *addr, int count)
  94 {
  95         /* Compute Internet Checksum for "count" bytes
  96          *         beginning at location "addr".
  97          */
  98         int32_t sum = 0;
  99         uint16_t *source = (uint16_t *) addr;
 100
 101         while (count > 1)  {
 102                 /*  This is the inner loop */
 103                 sum += *source++;
 104                 count -= 2;
 105         }
 106
 107         /*  Add left-over byte, if any */
 108         if (count > 0) {
 109                 /* Make sure that the left-over byte is added correctly both
 110                  * with little and big endian hosts */
 111                 uint16_t tmp = 0;
 112                 *(uint8_t*)&tmp = *(uint8_t*)source;
 113                 sum += tmp;
 114         }
 115         /*  Fold 32-bit sum to 16 bits */
 116         while (sum >> 16)
 117                 sum = (sum & 0xffff) + (sum >> 16);
 118
 119         return ~sum;
 120 }
 121
 122
 123 /* Construct a ip/udp header for a packet, send packet */
 124 int udhcp_send_raw_packet(struct dhcpMessage *payload,
 125                 uint32_t source_ip, int source_port,
 126                 uint32_t dest_ip, int dest_port, const uint8_t *dest_arp, int ifindex)
 127 {
 128         struct sockaddr_ll dest;
 129         struct udp_dhcp_packet packet;
 130         int fd;
 131         int result = -1;
 132         const char *msg;
 133
 134         enum {
 135                 IP_UPD_DHCP_SIZE = sizeof(struct udp_dhcp_packet) - CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS,
 136                 UPD_DHCP_SIZE    = IP_UPD_DHCP_SIZE - offsetof(struct udp_dhcp_packet, udp),
 137         };
 138
 139         fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
 140         if (fd < 0) {
 141                 msg = "socket(%s)";
 142                 goto ret_msg;
 143         }
 144
 145         memset(&dest, 0, sizeof(dest));
 146         memset(&packet, 0, sizeof(packet));
 147         packet.data = *payload; /* struct copy */
 148
 149         dest.sll_family = AF_PACKET;
 150         dest.sll_protocol = htons(ETH_P_IP);
 151         dest.sll_ifindex = ifindex;
 152         dest.sll_halen = 6;
 153         memcpy(dest.sll_addr, dest_arp, 6);
 154         if (bind(fd, (struct sockaddr *)&dest, sizeof(dest)) < 0) {
 155                 msg = "bind(%s)";
 156                 goto ret_close;
 157         }
 158
 159         packet.ip.protocol = IPPROTO_UDP;
 160         packet.ip.saddr = source_ip;
 161         packet.ip.daddr = dest_ip;
 162         packet.udp.source = htons(source_port);
 163         packet.udp.dest = htons(dest_port);
 164         /* size, excluding IP header: */
 165         packet.udp.len = htons(UPD_DHCP_SIZE);
 166         /* for UDP checksumming, ip.len is set to UDP packet len */
 167         packet.ip.tot_len = packet.udp.len;
 168         packet.udp.check = udhcp_checksum(&packet, IP_UPD_DHCP_SIZE);
 169         /* but for sending, it is set to IP packet len */
 170         packet.ip.tot_len = htons(IP_UPD_DHCP_SIZE);
 171         packet.ip.ihl = sizeof(packet.ip) >> 2;
 172         packet.ip.version = IPVERSION;
 173         packet.ip.ttl = IPDEFTTL;
 174         packet.ip.check = udhcp_checksum(&packet.ip, sizeof(packet.ip));
 175
 176         /* Currently we send full-sized DHCP packets (zero padded).
 177          * If you need to change this: last byte of the packet is
 178          * packet.data.options[end_option(packet.data.options)]
 179          */
 180         result = sendto(fd, &packet, IP_UPD_DHCP_SIZE, 0,
 181                                 (struct sockaddr *) &dest, sizeof(dest));
 182         msg = "sendto";
 183  ret_close:
 184         close(fd);
 185         if (result < 0) {
 186  ret_msg:
 187                 bb_perror_msg(msg, "PACKET");
 188         }
 189         return result;
 190 }
 191
 192
 193 /* Let the kernel do all the work for packet generation */
 194 int udhcp_send_kernel_packet(struct dhcpMessage *payload,
 195                 uint32_t source_ip, int source_port,
 196                 uint32_t dest_ip, int dest_port)
 197 {
 198         struct sockaddr_in client;
 199         int fd;
 200         int result = -1;
 201         const char *msg;
 202
 203         enum {
 204                 DHCP_SIZE = sizeof(struct dhcpMessage) - CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS,
 205         };
 206
 207         fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 208         if (fd < 0) {
 209                 msg = "socket(%s)";
 210                 goto ret_msg;
 211         }
 212         setsockopt_reuseaddr(fd);
 213
 214         memset(&client, 0, sizeof(client));
 215         client.sin_family = AF_INET;
 216         client.sin_port = htons(source_port);
 217         client.sin_addr.s_addr = source_ip;
 218         if (bind(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 219                 msg = "bind(%s)";
 220                 goto ret_close;
 221         }
 222
 223         memset(&client, 0, sizeof(client));
 224         client.sin_family = AF_INET;
 225         client.sin_port = htons(dest_port);
 226         client.sin_addr.s_addr = dest_ip;
 227         if (connect(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 228                 msg = "connect";
 229                 goto ret_close;
 230         }
 231
 232         /* Currently we send full-sized DHCP packets (see above) */
 233         result = safe_write(fd, payload, DHCP_SIZE);
 234         msg = "write";
 235  ret_close:
 236         close(fd);
 237         if (result < 0) {
 238  ret_msg:
 239                 bb_perror_msg(msg, "UDP");
 240         }
 241         return result;
 242 }