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 FAST_FUNC udhcp_init_header(struct dhcpMessage *packet, char type)
  19 {
  20         memset(packet, 0, sizeof(struct dhcpMessage));
  21         packet->op = BOOTREQUEST;
  22         switch (type) {
  23         case DHCPOFFER:
  24         case DHCPACK:
  25         case DHCPNAK:
  26                 packet->op = BOOTREPLY;
  27         }
  28         packet->htype = ETH_10MB;
  29         packet->hlen = ETH_10MB_LEN;
  30         packet->cookie = htonl(DHCP_MAGIC);
  31         packet->options[0] = DHCP_END;
  32         add_simple_option(packet->options, DHCP_MESSAGE_TYPE, type);
  33 }
  34
  35
  36 /* read a packet from socket fd, return -1 on read error, -2 on packet error */
  37 int FAST_FUNC udhcp_recv_kernel_packet(struct dhcpMessage *packet, int fd)
  38 {
  39         int bytes;
  40         unsigned char *vendor;
  41
  42         memset(packet, 0, sizeof(*packet));
  43         bytes = safe_read(fd, packet, sizeof(*packet));
  44         if (bytes < 0) {
  45                 DEBUG("cannot read on listening socket, ignoring");
  46                 return bytes; /* returns -1 */
  47         }
  48
  49         if (packet->cookie != htonl(DHCP_MAGIC)) {
  50                 bb_error_msg("received bogus message, ignoring");
  51                 return -2;
  52         }
  53         DEBUG("Received a packet");
  54
  55         if (packet->op == BOOTREQUEST) {
  56                 vendor = get_option(packet, DHCP_VENDOR);
  57                 if (vendor) {
  58 #if 0
  59                         static const char broken_vendors[][8] = {
  60                                 "MSFT 98",
  61                                 ""
  62                         };
  63                         int i;
  64                         for (i = 0; broken_vendors[i][0]; i++) {
  65                                 if (vendor[OPT_LEN - 2] == (uint8_t)strlen(broken_vendors[i])
  66                                  && !strncmp((char*)vendor, broken_vendors[i], vendor[OPT_LEN - 2])
  67                                 ) {
  68                                         DEBUG("broken client (%s), forcing broadcast",
  69                                                 broken_vendors[i]);
  70                                         packet->flags |= htons(BROADCAST_FLAG);
  71                                 }
  72                         }
  73 #else
  74                         if (vendor[OPT_LEN - 2] == (uint8_t)(sizeof("MSFT 98")-1)
  75                          && memcmp(vendor, "MSFT 98", sizeof("MSFT 98")-1) == 0
  76                         ) {
  77                                 DEBUG("broken client (%s), forcing broadcast", "MSFT 98");
  78                                 packet->flags |= htons(BROADCAST_FLAG);
  79                         }
  80 #endif
  81                 }
  82         }
  83
  84         return bytes;
  85 }
  86
  87
  88 uint16_t FAST_FUNC udhcp_checksum(void *addr, int count)
  89 {
  90         /* Compute Internet Checksum for "count" bytes
  91          *         beginning at location "addr".
  92          */
  93         int32_t sum = 0;
  94         uint16_t *source = (uint16_t *) addr;
  95
  96         while (count > 1)  {
  97                 /*  This is the inner loop */
  98                 sum += *source++;
  99                 count -= 2;
 100         }
 101
 102         /*  Add left-over byte, if any */
 103         if (count > 0) {
 104                 /* Make sure that the left-over byte is added correctly both
 105                  * with little and big endian hosts */
 106                 uint16_t tmp = 0;
 107                 *(uint8_t*)&tmp = *(uint8_t*)source;
 108                 sum += tmp;
 109         }
 110         /*  Fold 32-bit sum to 16 bits */
 111         while (sum >> 16)
 112                 sum = (sum & 0xffff) + (sum >> 16);
 113
 114         return ~sum;
 115 }
 116
 117
 118 /* Construct a ip/udp header for a packet, send packet */
 119 int FAST_FUNC udhcp_send_raw_packet(struct dhcpMessage *payload,
 120                 uint32_t source_ip, int source_port,
 121                 uint32_t dest_ip, int dest_port, const uint8_t *dest_arp,
 122                 int ifindex)
 123 {
 124         struct sockaddr_ll dest;
 125         struct udp_dhcp_packet packet;
 126         int fd;
 127         int result = -1;
 128         const char *msg;
 129
 130         enum {
 131                 IP_UPD_DHCP_SIZE = sizeof(struct udp_dhcp_packet) - CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS,
 132                 UPD_DHCP_SIZE    = IP_UPD_DHCP_SIZE - offsetof(struct udp_dhcp_packet, udp),
 133         };
 134
 135         fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
 136         if (fd < 0) {
 137                 msg = "socket(%s)";
 138                 goto ret_msg;
 139         }
 140
 141         memset(&dest, 0, sizeof(dest));
 142         memset(&packet, 0, sizeof(packet));
 143         packet.data = *payload; /* struct copy */
 144
 145         dest.sll_family = AF_PACKET;
 146         dest.sll_protocol = htons(ETH_P_IP);
 147         dest.sll_ifindex = ifindex;
 148         dest.sll_halen = 6;
 149         memcpy(dest.sll_addr, dest_arp, 6);
 150         if (bind(fd, (struct sockaddr *)&dest, sizeof(dest)) < 0) {
 151                 msg = "bind(%s)";
 152                 goto ret_close;
 153         }
 154
 155         packet.ip.protocol = IPPROTO_UDP;
 156         packet.ip.saddr = source_ip;
 157         packet.ip.daddr = dest_ip;
 158         packet.udp.source = htons(source_port);
 159         packet.udp.dest = htons(dest_port);
 160         /* size, excluding IP header: */
 161         packet.udp.len = htons(UPD_DHCP_SIZE);
 162         /* for UDP checksumming, ip.len is set to UDP packet len */
 163         packet.ip.tot_len = packet.udp.len;
 164         packet.udp.check = udhcp_checksum(&packet, IP_UPD_DHCP_SIZE);
 165         /* but for sending, it is set to IP packet len */
 166         packet.ip.tot_len = htons(IP_UPD_DHCP_SIZE);
 167         packet.ip.ihl = sizeof(packet.ip) >> 2;
 168         packet.ip.version = IPVERSION;
 169         packet.ip.ttl = IPDEFTTL;
 170         packet.ip.check = udhcp_checksum(&packet.ip, sizeof(packet.ip));
 171
 172         /* Currently we send full-sized DHCP packets (zero padded).
 173          * If you need to change this: last byte of the packet is
 174          * packet.data.options[end_option(packet.data.options)]
 175          */
 176         result = sendto(fd, &packet, IP_UPD_DHCP_SIZE, 0,
 177                                 (struct sockaddr *) &dest, sizeof(dest));
 178         msg = "sendto";
 179  ret_close:
 180         close(fd);
 181         if (result < 0) {
 182  ret_msg:
 183                 bb_perror_msg(msg, "PACKET");
 184         }
 185         return result;
 186 }
 187
 188
 189 /* Let the kernel do all the work for packet generation */
 190 int FAST_FUNC udhcp_send_kernel_packet(struct dhcpMessage *payload,
 191                 uint32_t source_ip, int source_port,
 192                 uint32_t dest_ip, int dest_port)
 193 {
 194         struct sockaddr_in client;
 195         int fd;
 196         int result = -1;
 197         const char *msg;
 198
 199         enum {
 200                 DHCP_SIZE = sizeof(struct dhcpMessage) - CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS,
 201         };
 202
 203         fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 204         if (fd < 0) {
 205                 msg = "socket(%s)";
 206                 goto ret_msg;
 207         }
 208         setsockopt_reuseaddr(fd);
 209
 210         memset(&client, 0, sizeof(client));
 211         client.sin_family = AF_INET;
 212         client.sin_port = htons(source_port);
 213         client.sin_addr.s_addr = source_ip;
 214         if (bind(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 215                 msg = "bind(%s)";
 216                 goto ret_close;
 217         }
 218
 219         memset(&client, 0, sizeof(client));
 220         client.sin_family = AF_INET;
 221         client.sin_port = htons(dest_port);
 222         client.sin_addr.s_addr = dest_ip;
 223         if (connect(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 224                 msg = "connect";
 225                 goto ret_close;
 226         }
 227
 228         /* Currently we send full-sized DHCP packets (see above) */
 229         result = safe_write(fd, payload, DHCP_SIZE);
 230         msg = "write";
 231  ret_close:
 232         close(fd);
 233         if (result < 0) {
 234  ret_msg:
 235                 bb_perror_msg(msg, "UDP");
 236         }
 237         return result;
 238 }