networking/udhcp/packet.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Packet ops
   4  *
   5  * Rewrite by Russ Dill <Russ.Dill@asu.edu> July 2001
   6  *
   7  * Licensed under GPLv2, see file LICENSE in this source tree.
   8  */
   9 #include "common.h"
  10 #include "dhcpd.h"
  11 #include <netinet/in.h>
  12 #include <netinet/if_ether.h>
  13 #include <netpacket/packet.h>
  14
  15 void FAST_FUNC udhcp_init_header(struct dhcp_packet *packet, char type)
  16 {
  17         memset(packet, 0, sizeof(*packet));
  18         packet->op = BOOTREQUEST; /* if client to a server */
  19         switch (type) {
  20         case DHCPOFFER:
  21         case DHCPACK:
  22         case DHCPNAK:
  23                 packet->op = BOOTREPLY; /* if server to client */
  24         }
  25         packet->htype = 1; /* ethernet */
  26         packet->hlen = 6;
  27         packet->cookie = htonl(DHCP_MAGIC);
  28         if (DHCP_END != 0)
  29                 packet->options[0] = DHCP_END;
  30         udhcp_add_simple_option(packet, DHCP_MESSAGE_TYPE, type);
  31 }
  32
  33 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 2
  34 void FAST_FUNC udhcp_dump_packet(struct dhcp_packet *packet)
  35 {
  36         char buf[sizeof(packet->chaddr)*2 + 1];
  37
  38         if (dhcp_verbose < 2)
  39                 return;
  40
  41         bb_info_msg(
  42                 //" op %x"
  43                 //" htype %x"
  44                 " hlen %x"
  45                 //" hops %x"
  46                 " xid %x"
  47                 //" secs %x"
  48                 //" flags %x"
  49                 " ciaddr %x"
  50                 " yiaddr %x"
  51                 " siaddr %x"
  52                 " giaddr %x"
  53                 //" chaddr %s"
  54                 //" sname %s"
  55                 //" file %s"
  56                 //" cookie %x"
  57                 //" options %s"
  58                 //, packet->op
  59                 //, packet->htype
  60                 , packet->hlen
  61                 //, packet->hops
  62                 , packet->xid
  63                 //, packet->secs
  64                 //, packet->flags
  65                 , packet->ciaddr
  66                 , packet->yiaddr
  67                 , packet->siaddr_nip
  68                 , packet->gateway_nip
  69                 //, packet->chaddr[16]
  70                 //, packet->sname[64]
  71                 //, packet->file[128]
  72                 //, packet->cookie
  73                 //, packet->options[]
  74         );
  75         *bin2hex(buf, (void *) packet->chaddr, sizeof(packet->chaddr)) = '\0';
  76         bb_info_msg(" chaddr %s", buf);
  77 }
  78 #endif
  79
  80 /* Read a packet from socket fd, return -1 on read error, -2 on packet error */
  81 int FAST_FUNC udhcp_recv_kernel_packet(struct dhcp_packet *packet, int fd)
  82 {
  83         int bytes;
  84         unsigned char *vendor;
  85
  86         memset(packet, 0, sizeof(*packet));
  87         bytes = safe_read(fd, packet, sizeof(*packet));
  88         if (bytes < 0) {
  89                 log1("Packet read error, ignoring");
  90                 return bytes; /* returns -1 */
  91         }
  92
  93         if (packet->cookie != htonl(DHCP_MAGIC)) {
  94                 bb_info_msg("Packet with bad magic, ignoring");
  95                 return -2;
  96         }
  97         log1("Received a packet");
  98         udhcp_dump_packet(packet);
  99
 100         if (packet->op == BOOTREQUEST) {
 101                 vendor = udhcp_get_option(packet, DHCP_VENDOR);
 102                 if (vendor) {
 103 #if 0
 104                         static const char broken_vendors[][8] = {
 105                                 "MSFT 98",
 106                                 ""
 107                         };
 108                         int i;
 109                         for (i = 0; broken_vendors[i][0]; i++) {
 110                                 if (vendor[OPT_LEN - OPT_DATA] == (uint8_t)strlen(broken_vendors[i])
 111                                  && strncmp((char*)vendor, broken_vendors[i], vendor[OPT_LEN - OPT_DATA]) == 0
 112                                 ) {
 113                                         log1("Broken client (%s), forcing broadcast replies",
 114                                                 broken_vendors[i]);
 115                                         packet->flags |= htons(BROADCAST_FLAG);
 116                                 }
 117                         }
 118 #else
 119                         if (vendor[OPT_LEN - OPT_DATA] == (uint8_t)(sizeof("MSFT 98")-1)
 120                          && memcmp(vendor, "MSFT 98", sizeof("MSFT 98")-1) == 0
 121                         ) {
 122                                 log1("Broken client (%s), forcing broadcast replies", "MSFT 98");
 123                                 packet->flags |= htons(BROADCAST_FLAG);
 124                         }
 125 #endif
 126                 }
 127         }
 128
 129         return bytes;
 130 }
 131
 132 uint16_t FAST_FUNC udhcp_checksum(void *addr, int count)
 133 {
 134         /* Compute Internet Checksum for "count" bytes
 135          * beginning at location "addr".
 136          */
 137         int32_t sum = 0;
 138         uint16_t *source = (uint16_t *) addr;
 139
 140         while (count > 1)  {
 141                 /*  This is the inner loop */
 142                 sum += *source++;
 143                 count -= 2;
 144         }
 145
 146         /*  Add left-over byte, if any */
 147         if (count > 0) {
 148                 /* Make sure that the left-over byte is added correctly both
 149                  * with little and big endian hosts */
 150                 uint16_t tmp = 0;
 151                 *(uint8_t*)&tmp = *(uint8_t*)source;
 152                 sum += tmp;
 153         }
 154         /*  Fold 32-bit sum to 16 bits */
 155         while (sum >> 16)
 156                 sum = (sum & 0xffff) + (sum >> 16);
 157
 158         return ~sum;
 159 }
 160
 161 /* Construct a ip/udp header for a packet, send packet */
 162 int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
 163                 uint32_t source_nip, int source_port,
 164                 uint32_t dest_nip, int dest_port, const uint8_t *dest_arp,
 165                 int ifindex)
 166 {
 167         struct sockaddr_ll dest_sll;
 168         struct ip_udp_dhcp_packet packet;
 169         unsigned padding;
 170         int fd;
 171         int result = -1;
 172         const char *msg;
 173
 174         fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
 175         if (fd < 0) {
 176                 msg = "socket(%s)";
 177                 goto ret_msg;
 178         }
 179
 180         memset(&dest_sll, 0, sizeof(dest_sll));
 181         memset(&packet, 0, offsetof(struct ip_udp_dhcp_packet, data));
 182         packet.data = *dhcp_pkt; /* struct copy */
 183
 184         dest_sll.sll_family = AF_PACKET;
 185         dest_sll.sll_protocol = htons(ETH_P_IP);
 186         dest_sll.sll_ifindex = ifindex;
 187         dest_sll.sll_halen = 6;
 188         memcpy(dest_sll.sll_addr, dest_arp, 6);
 189
 190         if (bind(fd, (struct sockaddr *)&dest_sll, sizeof(dest_sll)) < 0) {
 191                 msg = "bind(%s)";
 192                 goto ret_close;
 193         }
 194
 195         /* We were sending full-sized DHCP packets (zero padded),
 196          * but some badly configured servers were seen dropping them.
 197          * Apparently they drop all DHCP packets >576 *ethernet* octets big,
 198          * whereas they may only drop packets >576 *IP* octets big
 199          * (which for typical Ethernet II means 590 octets: 6+6+2 + 576).
 200          *
 201          * In order to work with those buggy servers,
 202          * we truncate packets after end option byte.
 203          */
 204         padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(packet.data.options);
 205
 206         packet.ip.protocol = IPPROTO_UDP;
 207         packet.ip.saddr = source_nip;
 208         packet.ip.daddr = dest_nip;
 209         packet.udp.source = htons(source_port);
 210         packet.udp.dest = htons(dest_port);
 211         /* size, excluding IP header: */
 212         packet.udp.len = htons(UDP_DHCP_SIZE - padding);
 213         /* for UDP checksumming, ip.len is set to UDP packet len */
 214         packet.ip.tot_len = packet.udp.len;
 215         packet.udp.check = udhcp_checksum(&packet, IP_UDP_DHCP_SIZE - padding);
 216         /* but for sending, it is set to IP packet len */
 217         packet.ip.tot_len = htons(IP_UDP_DHCP_SIZE - padding);
 218         packet.ip.ihl = sizeof(packet.ip) >> 2;
 219         packet.ip.version = IPVERSION;
 220         packet.ip.ttl = IPDEFTTL;
 221         packet.ip.check = udhcp_checksum(&packet.ip, sizeof(packet.ip));
 222
 223         udhcp_dump_packet(dhcp_pkt);
 224         result = sendto(fd, &packet, IP_UDP_DHCP_SIZE - padding, /*flags:*/ 0,
 225                         (struct sockaddr *) &dest_sll, sizeof(dest_sll));
 226         msg = "sendto";
 227  ret_close:
 228         close(fd);
 229         if (result < 0) {
 230  ret_msg:
 231                 bb_perror_msg(msg, "PACKET");
 232         }
 233         return result;
 234 }
 235
 236 /* Let the kernel do all the work for packet generation */
 237 int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
 238                 uint32_t source_nip, int source_port,
 239                 uint32_t dest_nip, int dest_port)
 240 {
 241         struct sockaddr_in client;
 242         unsigned padding;
 243         int fd;
 244         int result = -1;
 245         const char *msg;
 246
 247         fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 248         if (fd < 0) {
 249                 msg = "socket(%s)";
 250                 goto ret_msg;
 251         }
 252         setsockopt_reuseaddr(fd);
 253
 254         memset(&client, 0, sizeof(client));
 255         client.sin_family = AF_INET;
 256         client.sin_port = htons(source_port);
 257         client.sin_addr.s_addr = source_nip;
 258         if (bind(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 259                 msg = "bind(%s)";
 260                 goto ret_close;
 261         }
 262
 263         memset(&client, 0, sizeof(client));
 264         client.sin_family = AF_INET;
 265         client.sin_port = htons(dest_port);
 266         client.sin_addr.s_addr = dest_nip;
 267         if (connect(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 268                 msg = "connect";
 269                 goto ret_close;
 270         }
 271
 272         udhcp_dump_packet(dhcp_pkt);
 273
 274         padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(dhcp_pkt->options);
 275         result = safe_write(fd, dhcp_pkt, DHCP_SIZE - padding);
 276         msg = "write";
 277  ret_close:
 278         close(fd);
 279         if (result < 0) {
 280  ret_msg:
 281                 bb_perror_msg(msg, "UDP");
 282         }
 283         return result;
 284 }