networking/udhcp/packet.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * packet.c -- packet ops
   4  * Rewrite by Russ Dill <Russ.Dill@asu.edu> July 2001
   5  *
   6  * Licensed under GPLv2, see file LICENSE in this tarball for details.
   7  */
   8 #include <netinet/in.h>
   9 #if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION
  10 #include <netpacket/packet.h>
  11 #include <net/ethernet.h>
  12 #else
  13 #include <asm/types.h>
  14 #include <linux/if_packet.h>
  15 #include <linux/if_ether.h>
  16 #endif
  17
  18 #include "common.h"
  19 #include "dhcpd.h"
  20 #include "options.h"
  21
  22 void FAST_FUNC udhcp_init_header(struct dhcp_packet *packet, char type)
  23 {
  24         memset(packet, 0, sizeof(struct dhcp_packet));
  25         packet->op = BOOTREQUEST; /* if client to a server */
  26         switch (type) {
  27         case DHCPOFFER:
  28         case DHCPACK:
  29         case DHCPNAK:
  30                 packet->op = BOOTREPLY; /* if server to client */
  31         }
  32         packet->htype = ETH_10MB;
  33         packet->hlen = ETH_10MB_LEN;
  34         packet->cookie = htonl(DHCP_MAGIC);
  35         packet->options[0] = DHCP_END;
  36         add_simple_option(packet->options, DHCP_MESSAGE_TYPE, type);
  37 }
  38
  39 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 2
  40 void FAST_FUNC udhcp_dump_packet(struct dhcp_packet *packet)
  41 {
  42         char buf[sizeof(packet->chaddr)*2 + 1];
  43
  44         if (dhcp_verbose < 2)
  45                 return;
  46
  47         bb_info_msg(
  48                 //" op %x"
  49                 //" htype %x"
  50                 " hlen %x"
  51                 //" hops %x"
  52                 " xid %x"
  53                 //" secs %x"
  54                 //" flags %x"
  55                 " ciaddr %x"
  56                 " yiaddr %x"
  57                 " siaddr %x"
  58                 " giaddr %x"
  59                 //" chaddr %s"
  60                 //" sname %s"
  61                 //" file %s"
  62                 //" cookie %x"
  63                 //" options %s"
  64                 //, packet->op
  65                 //, packet->htype
  66                 , packet->hlen
  67                 //, packet->hops
  68                 , packet->xid
  69                 //, packet->secs
  70                 //, packet->flags
  71                 , packet->ciaddr
  72                 , packet->yiaddr
  73                 , packet->siaddr_nip
  74                 , packet->gateway_nip
  75                 //, packet->chaddr[16]
  76                 //, packet->sname[64]
  77                 //, packet->file[128]
  78                 //, packet->cookie
  79                 //, packet->options[]
  80         );
  81         *bin2hex(buf, (void *) packet->chaddr, sizeof(packet->chaddr)) = '\0';
  82         bb_info_msg(" chaddr %s", buf);
  83 }
  84 #endif
  85
  86 /* Read a packet from socket fd, return -1 on read error, -2 on packet error */
  87 int FAST_FUNC udhcp_recv_kernel_packet(struct dhcp_packet *packet, int fd)
  88 {
  89         int bytes;
  90         unsigned char *vendor;
  91
  92         memset(packet, 0, sizeof(*packet));
  93         bytes = safe_read(fd, packet, sizeof(*packet));
  94         if (bytes < 0) {
  95                 log1("Packet read error, ignoring");
  96                 return bytes; /* returns -1 */
  97         }
  98
  99         if (packet->cookie != htonl(DHCP_MAGIC)) {
 100                 bb_info_msg("Packet with bad magic, ignoring");
 101                 return -2;
 102         }
 103         log1("Received a packet");
 104         udhcp_dump_packet(packet);
 105
 106         if (packet->op == BOOTREQUEST) {
 107                 vendor = get_option(packet, DHCP_VENDOR);
 108                 if (vendor) {
 109 #if 0
 110                         static const char broken_vendors[][8] = {
 111                                 "MSFT 98",
 112                                 ""
 113                         };
 114                         int i;
 115                         for (i = 0; broken_vendors[i][0]; i++) {
 116                                 if (vendor[OPT_LEN - 2] == (uint8_t)strlen(broken_vendors[i])
 117                                  && !strncmp((char*)vendor, broken_vendors[i], vendor[OPT_LEN - 2])
 118                                 ) {
 119                                         log1("Broken client (%s), forcing broadcast replies",
 120                                                 broken_vendors[i]);
 121                                         packet->flags |= htons(BROADCAST_FLAG);
 122                                 }
 123                         }
 124 #else
 125                         if (vendor[OPT_LEN - 2] == (uint8_t)(sizeof("MSFT 98")-1)
 126                          && memcmp(vendor, "MSFT 98", sizeof("MSFT 98")-1) == 0
 127                         ) {
 128                                 log1("Broken client (%s), forcing broadcast replies", "MSFT 98");
 129                                 packet->flags |= htons(BROADCAST_FLAG);
 130                         }
 131 #endif
 132                 }
 133         }
 134
 135         return bytes;
 136 }
 137
 138 uint16_t FAST_FUNC udhcp_checksum(void *addr, int count)
 139 {
 140         /* Compute Internet Checksum for "count" bytes
 141          * beginning at location "addr".
 142          */
 143         int32_t sum = 0;
 144         uint16_t *source = (uint16_t *) addr;
 145
 146         while (count > 1)  {
 147                 /*  This is the inner loop */
 148                 sum += *source++;
 149                 count -= 2;
 150         }
 151
 152         /*  Add left-over byte, if any */
 153         if (count > 0) {
 154                 /* Make sure that the left-over byte is added correctly both
 155                  * with little and big endian hosts */
 156                 uint16_t tmp = 0;
 157                 *(uint8_t*)&tmp = *(uint8_t*)source;
 158                 sum += tmp;
 159         }
 160         /*  Fold 32-bit sum to 16 bits */
 161         while (sum >> 16)
 162                 sum = (sum & 0xffff) + (sum >> 16);
 163
 164         return ~sum;
 165 }
 166
 167 /* Construct a ip/udp header for a packet, send packet */
 168 int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
 169                 uint32_t source_ip, int source_port,
 170                 uint32_t dest_ip, int dest_port, const uint8_t *dest_arp,
 171                 int ifindex)
 172 {
 173         struct sockaddr_ll dest;
 174         struct ip_udp_dhcp_packet packet;
 175         int fd;
 176         int result = -1;
 177         const char *msg;
 178
 179         enum {
 180                 IP_UPD_DHCP_SIZE = sizeof(struct ip_udp_dhcp_packet) - CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS,
 181                 UPD_DHCP_SIZE    = IP_UPD_DHCP_SIZE - offsetof(struct ip_udp_dhcp_packet, udp),
 182         };
 183
 184         fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
 185         if (fd < 0) {
 186                 msg = "socket(%s)";
 187                 goto ret_msg;
 188         }
 189
 190         memset(&dest, 0, sizeof(dest));
 191         memset(&packet, 0, sizeof(packet));
 192         packet.data = *dhcp_pkt; /* struct copy */
 193
 194         dest.sll_family = AF_PACKET;
 195         dest.sll_protocol = htons(ETH_P_IP);
 196         dest.sll_ifindex = ifindex;
 197         dest.sll_halen = 6;
 198         memcpy(dest.sll_addr, dest_arp, 6);
 199         if (bind(fd, (struct sockaddr *)&dest, sizeof(dest)) < 0) {
 200                 msg = "bind(%s)";
 201                 goto ret_close;
 202         }
 203
 204         packet.ip.protocol = IPPROTO_UDP;
 205         packet.ip.saddr = source_ip;
 206         packet.ip.daddr = dest_ip;
 207         packet.udp.source = htons(source_port);
 208         packet.udp.dest = htons(dest_port);
 209         /* size, excluding IP header: */
 210         packet.udp.len = htons(UPD_DHCP_SIZE);
 211         /* for UDP checksumming, ip.len is set to UDP packet len */
 212         packet.ip.tot_len = packet.udp.len;
 213         packet.udp.check = udhcp_checksum(&packet, IP_UPD_DHCP_SIZE);
 214         /* but for sending, it is set to IP packet len */
 215         packet.ip.tot_len = htons(IP_UPD_DHCP_SIZE);
 216         packet.ip.ihl = sizeof(packet.ip) >> 2;
 217         packet.ip.version = IPVERSION;
 218         packet.ip.ttl = IPDEFTTL;
 219         packet.ip.check = udhcp_checksum(&packet.ip, sizeof(packet.ip));
 220
 221         /* Currently we send full-sized DHCP packets (zero padded).
 222          * If you need to change this: last byte of the packet is
 223          * packet.data.options[end_option(packet.data.options)]
 224          */
 225         udhcp_dump_packet(dhcp_pkt);
 226         result = sendto(fd, &packet, IP_UPD_DHCP_SIZE, 0,
 227                                 (struct sockaddr *) &dest, sizeof(dest));
 228         msg = "sendto";
 229  ret_close:
 230         close(fd);
 231         if (result < 0) {
 232  ret_msg:
 233                 bb_perror_msg(msg, "PACKET");
 234         }
 235         return result;
 236 }
 237
 238 /* Let the kernel do all the work for packet generation */
 239 int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
 240                 uint32_t source_ip, int source_port,
 241                 uint32_t dest_ip, int dest_port)
 242 {
 243         struct sockaddr_in client;
 244         int fd;
 245         int result = -1;
 246         const char *msg;
 247
 248         enum {
 249                 DHCP_SIZE = sizeof(struct dhcp_packet) - CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS,
 250         };
 251
 252         fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 253         if (fd < 0) {
 254                 msg = "socket(%s)";
 255                 goto ret_msg;
 256         }
 257         setsockopt_reuseaddr(fd);
 258
 259         memset(&client, 0, sizeof(client));
 260         client.sin_family = AF_INET;
 261         client.sin_port = htons(source_port);
 262         client.sin_addr.s_addr = source_ip;
 263         if (bind(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 264                 msg = "bind(%s)";
 265                 goto ret_close;
 266         }
 267
 268         memset(&client, 0, sizeof(client));
 269         client.sin_family = AF_INET;
 270         client.sin_port = htons(dest_port);
 271         client.sin_addr.s_addr = dest_ip;
 272         if (connect(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 273                 msg = "connect";
 274                 goto ret_close;
 275         }
 276
 277         /* Currently we send full-sized DHCP packets (see above) */
 278         udhcp_dump_packet(dhcp_pkt);
 279         result = safe_write(fd, dhcp_pkt, DHCP_SIZE);
 280         msg = "write";
 281  ret_close:
 282         close(fd);
 283         if (result < 0) {
 284  ret_msg:
 285                 bb_perror_msg(msg, "UDP");
 286         }
 287         return result;
 288 }