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
  85         memset(packet, 0, sizeof(*packet));
  86         bytes = safe_read(fd, packet, sizeof(*packet));
  87         if (bytes < 0) {
  88                 log1("Packet read error, ignoring");
  89                 return bytes; /* returns -1 */
  90         }
  91
  92         if (bytes < offsetof(struct dhcp_packet, options)
  93          || packet->cookie != htonl(DHCP_MAGIC)
  94         ) {
  95                 bb_info_msg("Packet with bad magic, ignoring");
  96                 return -2;
  97         }
  98         log1("Received a packet");
  99         udhcp_dump_packet(packet);
 100
 101         return bytes;
 102 }
 103
 104 /* Construct a ip/udp header for a packet, send packet */
 105 int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
 106                 uint32_t source_nip, int source_port,
 107                 uint32_t dest_nip, int dest_port, const uint8_t *dest_arp,
 108                 int ifindex)
 109 {
 110         struct sockaddr_ll dest_sll;
 111         struct ip_udp_dhcp_packet packet;
 112         unsigned padding;
 113         int fd;
 114         int result = -1;
 115         const char *msg;
 116
 117         fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
 118         if (fd < 0) {
 119                 msg = "socket(%s)";
 120                 goto ret_msg;
 121         }
 122
 123         memset(&dest_sll, 0, sizeof(dest_sll));
 124         memset(&packet, 0, offsetof(struct ip_udp_dhcp_packet, data));
 125         packet.data = *dhcp_pkt; /* struct copy */
 126
 127         dest_sll.sll_family = AF_PACKET;
 128         dest_sll.sll_protocol = htons(ETH_P_IP);
 129         dest_sll.sll_ifindex = ifindex;
 130         dest_sll.sll_halen = 6;
 131         memcpy(dest_sll.sll_addr, dest_arp, 6);
 132
 133         if (bind(fd, (struct sockaddr *)&dest_sll, sizeof(dest_sll)) < 0) {
 134                 msg = "bind(%s)";
 135                 goto ret_close;
 136         }
 137
 138         /* We were sending full-sized DHCP packets (zero padded),
 139          * but some badly configured servers were seen dropping them.
 140          * Apparently they drop all DHCP packets >576 *ethernet* octets big,
 141          * whereas they may only drop packets >576 *IP* octets big
 142          * (which for typical Ethernet II means 590 octets: 6+6+2 + 576).
 143          *
 144          * In order to work with those buggy servers,
 145          * we truncate packets after end option byte.
 146          *
 147          * However, RFC 1542 says "The IP Total Length and UDP Length
 148          * must be large enough to contain the minimal BOOTP header of 300 octets".
 149          * Thus, we retain enough padding to not go below 300 BOOTP bytes.
 150          * Some devices have filters which drop DHCP packets shorter than that.
 151          */
 152         padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(packet.data.options);
 153         if (padding > DHCP_SIZE - 300)
 154                 padding = DHCP_SIZE - 300;
 155
 156         packet.ip.protocol = IPPROTO_UDP;
 157         packet.ip.saddr = source_nip;
 158         packet.ip.daddr = dest_nip;
 159         packet.udp.source = htons(source_port);
 160         packet.udp.dest = htons(dest_port);
 161         /* size, excluding IP header: */
 162         packet.udp.len = htons(UDP_DHCP_SIZE - padding);
 163         /* for UDP checksumming, ip.len is set to UDP packet len */
 164         packet.ip.tot_len = packet.udp.len;
 165         packet.udp.check = inet_cksum((uint16_t *)&packet,
 166                         IP_UDP_DHCP_SIZE - padding);
 167         /* but for sending, it is set to IP packet len */
 168         packet.ip.tot_len = htons(IP_UDP_DHCP_SIZE - padding);
 169         packet.ip.ihl = sizeof(packet.ip) >> 2;
 170         packet.ip.version = IPVERSION;
 171         packet.ip.ttl = IPDEFTTL;
 172         packet.ip.check = inet_cksum((uint16_t *)&packet.ip, sizeof(packet.ip));
 173
 174         udhcp_dump_packet(dhcp_pkt);
 175         result = sendto(fd, &packet, IP_UDP_DHCP_SIZE - padding, /*flags:*/ 0,
 176                         (struct sockaddr *) &dest_sll, sizeof(dest_sll));
 177         msg = "sendto";
 178  ret_close:
 179         close(fd);
 180         if (result < 0) {
 181  ret_msg:
 182                 bb_perror_msg(msg, "PACKET");
 183         }
 184         return result;
 185 }
 186
 187 /* Let the kernel do all the work for packet generation */
 188 int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
 189                 uint32_t source_nip, int source_port,
 190                 uint32_t dest_nip, int dest_port)
 191 {
 192         struct sockaddr_in sa;
 193         unsigned padding;
 194         int fd;
 195         int result = -1;
 196         const char *msg;
 197
 198         fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 199         if (fd < 0) {
 200                 msg = "socket(%s)";
 201                 goto ret_msg;
 202         }
 203         setsockopt_reuseaddr(fd);
 204
 205         memset(&sa, 0, sizeof(sa));
 206         sa.sin_family = AF_INET;
 207         sa.sin_port = htons(source_port);
 208         sa.sin_addr.s_addr = source_nip;
 209         if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
 210                 msg = "bind(%s)";
 211                 goto ret_close;
 212         }
 213
 214         memset(&sa, 0, sizeof(sa));
 215         sa.sin_family = AF_INET;
 216         sa.sin_port = htons(dest_port);
 217         sa.sin_addr.s_addr = dest_nip;
 218         if (connect(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
 219                 msg = "connect";
 220                 goto ret_close;
 221         }
 222
 223         udhcp_dump_packet(dhcp_pkt);
 224         padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(dhcp_pkt->options);
 225         if (padding > DHCP_SIZE - 300)
 226                 padding = DHCP_SIZE - 300;
 227         result = safe_write(fd, dhcp_pkt, DHCP_SIZE - padding);
 228         msg = "write";
 229  ret_close:
 230         close(fd);
 231         if (result < 0) {
 232  ret_msg:
 233                 bb_perror_msg(msg, "UDP");
 234         }
 235         return result;
 236 }