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 <netinet/in.h>
  10 #if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION
  11 # include <netpacket/packet.h>
  12 # include <net/ethernet.h>
  13 #else
  14 # include <asm/types.h>
  15 # include <linux/if_packet.h>
  16 # include <linux/if_ether.h>
  17 #endif
  18
  19 #include "common.h"
  20 #include "dhcpd.h"
  21
  22 void FAST_FUNC udhcp_init_header(struct dhcp_packet *packet, char type)
  23 {
  24         memset(packet, 0, sizeof(*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 = 1; /* ethernet */
  33         packet->hlen = 6;
  34         packet->cookie = htonl(DHCP_MAGIC);
  35         if (DHCP_END != 0)
  36                 packet->options[0] = DHCP_END;
  37         udhcp_add_simple_option(packet, DHCP_MESSAGE_TYPE, type);
  38 }
  39
  40 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 2
  41 void FAST_FUNC udhcp_dump_packet(struct dhcp_packet *packet)
  42 {
  43         char buf[sizeof(packet->chaddr)*2 + 1];
  44
  45         if (dhcp_verbose < 2)
  46                 return;
  47
  48         bb_info_msg(
  49                 //" op %x"
  50                 //" htype %x"
  51                 " hlen %x"
  52                 //" hops %x"
  53                 " xid %x"
  54                 //" secs %x"
  55                 //" flags %x"
  56                 " ciaddr %x"
  57                 " yiaddr %x"
  58                 " siaddr %x"
  59                 " giaddr %x"
  60                 //" chaddr %s"
  61                 //" sname %s"
  62                 //" file %s"
  63                 //" cookie %x"
  64                 //" options %s"
  65                 //, packet->op
  66                 //, packet->htype
  67                 , packet->hlen
  68                 //, packet->hops
  69                 , packet->xid
  70                 //, packet->secs
  71                 //, packet->flags
  72                 , packet->ciaddr
  73                 , packet->yiaddr
  74                 , packet->siaddr_nip
  75                 , packet->gateway_nip
  76                 //, packet->chaddr[16]
  77                 //, packet->sname[64]
  78                 //, packet->file[128]
  79                 //, packet->cookie
  80                 //, packet->options[]
  81         );
  82         *bin2hex(buf, (void *) packet->chaddr, sizeof(packet->chaddr)) = '\0';
  83         bb_info_msg(" chaddr %s", buf);
  84 }
  85 #endif
  86
  87 /* Read a packet from socket fd, return -1 on read error, -2 on packet error */
  88 int FAST_FUNC udhcp_recv_kernel_packet(struct dhcp_packet *packet, int fd)
  89 {
  90         int bytes;
  91         unsigned char *vendor;
  92
  93         memset(packet, 0, sizeof(*packet));
  94         bytes = safe_read(fd, packet, sizeof(*packet));
  95         if (bytes < 0) {
  96                 log1("Packet read error, ignoring");
  97                 return bytes; /* returns -1 */
  98         }
  99
 100         if (packet->cookie != htonl(DHCP_MAGIC)) {
 101                 bb_info_msg("Packet with bad magic, ignoring");
 102                 return -2;
 103         }
 104         log1("Received a packet");
 105         udhcp_dump_packet(packet);
 106
 107         if (packet->op == BOOTREQUEST) {
 108                 vendor = udhcp_get_option(packet, DHCP_VENDOR);
 109                 if (vendor) {
 110 #if 0
 111                         static const char broken_vendors[][8] = {
 112                                 "MSFT 98",
 113                                 ""
 114                         };
 115                         int i;
 116                         for (i = 0; broken_vendors[i][0]; i++) {
 117                                 if (vendor[OPT_LEN - OPT_DATA] == (uint8_t)strlen(broken_vendors[i])
 118                                  && strncmp((char*)vendor, broken_vendors[i], vendor[OPT_LEN - OPT_DATA]) == 0
 119                                 ) {
 120                                         log1("Broken client (%s), forcing broadcast replies",
 121                                                 broken_vendors[i]);
 122                                         packet->flags |= htons(BROADCAST_FLAG);
 123                                 }
 124                         }
 125 #else
 126                         if (vendor[OPT_LEN - OPT_DATA] == (uint8_t)(sizeof("MSFT 98")-1)
 127                          && memcmp(vendor, "MSFT 98", sizeof("MSFT 98")-1) == 0
 128                         ) {
 129                                 log1("Broken client (%s), forcing broadcast replies", "MSFT 98");
 130                                 packet->flags |= htons(BROADCAST_FLAG);
 131                         }
 132 #endif
 133                 }
 134         }
 135
 136         return bytes;
 137 }
 138
 139 uint16_t FAST_FUNC udhcp_checksum(void *addr, int count)
 140 {
 141         /* Compute Internet Checksum for "count" bytes
 142          * beginning at location "addr".
 143          */
 144         int32_t sum = 0;
 145         uint16_t *source = (uint16_t *) addr;
 146
 147         while (count > 1)  {
 148                 /*  This is the inner loop */
 149                 sum += *source++;
 150                 count -= 2;
 151         }
 152
 153         /*  Add left-over byte, if any */
 154         if (count > 0) {
 155                 /* Make sure that the left-over byte is added correctly both
 156                  * with little and big endian hosts */
 157                 uint16_t tmp = 0;
 158                 *(uint8_t*)&tmp = *(uint8_t*)source;
 159                 sum += tmp;
 160         }
 161         /*  Fold 32-bit sum to 16 bits */
 162         while (sum >> 16)
 163                 sum = (sum & 0xffff) + (sum >> 16);
 164
 165         return ~sum;
 166 }
 167
 168 /* Construct a ip/udp header for a packet, send packet */
 169 int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
 170                 uint32_t source_nip, int source_port,
 171                 uint32_t dest_nip, int dest_port, const uint8_t *dest_arp,
 172                 int ifindex)
 173 {
 174         struct sockaddr_ll dest_sll;
 175         struct ip_udp_dhcp_packet packet;
 176         unsigned padding;
 177         int fd;
 178         int result = -1;
 179         const char *msg;
 180
 181         fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
 182         if (fd < 0) {
 183                 msg = "socket(%s)";
 184                 goto ret_msg;
 185         }
 186
 187         memset(&dest_sll, 0, sizeof(dest_sll));
 188         memset(&packet, 0, offsetof(struct ip_udp_dhcp_packet, data));
 189         packet.data = *dhcp_pkt; /* struct copy */
 190
 191         dest_sll.sll_family = AF_PACKET;
 192         dest_sll.sll_protocol = htons(ETH_P_IP);
 193         dest_sll.sll_ifindex = ifindex;
 194         dest_sll.sll_halen = 6;
 195         memcpy(dest_sll.sll_addr, dest_arp, 6);
 196
 197         if (bind(fd, (struct sockaddr *)&dest_sll, sizeof(dest_sll)) < 0) {
 198                 msg = "bind(%s)";
 199                 goto ret_close;
 200         }
 201
 202         /* We were sending full-sized DHCP packets (zero padded),
 203          * but some badly configured servers were seen dropping them.
 204          * Apparently they drop all DHCP packets >576 *ethernet* octets big,
 205          * whereas they may only drop packets >576 *IP* octets big
 206          * (which for typical Ethernet II means 590 octets: 6+6+2 + 576).
 207          *
 208          * In order to work with those buggy servers,
 209          * we truncate packets after end option byte.
 210          */
 211         padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(packet.data.options);
 212
 213         packet.ip.protocol = IPPROTO_UDP;
 214         packet.ip.saddr = source_nip;
 215         packet.ip.daddr = dest_nip;
 216         packet.udp.source = htons(source_port);
 217         packet.udp.dest = htons(dest_port);
 218         /* size, excluding IP header: */
 219         packet.udp.len = htons(UDP_DHCP_SIZE - padding);
 220         /* for UDP checksumming, ip.len is set to UDP packet len */
 221         packet.ip.tot_len = packet.udp.len;
 222         packet.udp.check = udhcp_checksum(&packet, IP_UDP_DHCP_SIZE - padding);
 223         /* but for sending, it is set to IP packet len */
 224         packet.ip.tot_len = htons(IP_UDP_DHCP_SIZE - padding);
 225         packet.ip.ihl = sizeof(packet.ip) >> 2;
 226         packet.ip.version = IPVERSION;
 227         packet.ip.ttl = IPDEFTTL;
 228         packet.ip.check = udhcp_checksum(&packet.ip, sizeof(packet.ip));
 229
 230         udhcp_dump_packet(dhcp_pkt);
 231         result = sendto(fd, &packet, IP_UDP_DHCP_SIZE - padding, /*flags:*/ 0,
 232                         (struct sockaddr *) &dest_sll, sizeof(dest_sll));
 233         msg = "sendto";
 234  ret_close:
 235         close(fd);
 236         if (result < 0) {
 237  ret_msg:
 238                 bb_perror_msg(msg, "PACKET");
 239         }
 240         return result;
 241 }
 242
 243 /* Let the kernel do all the work for packet generation */
 244 int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
 245                 uint32_t source_nip, int source_port,
 246                 uint32_t dest_nip, int dest_port)
 247 {
 248         struct sockaddr_in client;
 249         unsigned padding;
 250         int fd;
 251         int result = -1;
 252         const char *msg;
 253
 254         fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 255         if (fd < 0) {
 256                 msg = "socket(%s)";
 257                 goto ret_msg;
 258         }
 259         setsockopt_reuseaddr(fd);
 260
 261         memset(&client, 0, sizeof(client));
 262         client.sin_family = AF_INET;
 263         client.sin_port = htons(source_port);
 264         client.sin_addr.s_addr = source_nip;
 265         if (bind(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 266                 msg = "bind(%s)";
 267                 goto ret_close;
 268         }
 269
 270         memset(&client, 0, sizeof(client));
 271         client.sin_family = AF_INET;
 272         client.sin_port = htons(dest_port);
 273         client.sin_addr.s_addr = dest_nip;
 274         if (connect(fd, (struct sockaddr *)&client, sizeof(client)) == -1) {
 275                 msg = "connect";
 276                 goto ret_close;
 277         }
 278
 279         udhcp_dump_packet(dhcp_pkt);
 280
 281         padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(dhcp_pkt->options);
 282         result = safe_write(fd, dhcp_pkt, DHCP_SIZE - padding);
 283         msg = "write";
 284  ret_close:
 285         close(fd);
 286         if (result < 0) {
 287  ret_msg:
 288                 bb_perror_msg(msg, "UDP");
 289         }
 290         return result;
 291 }