release/src/router/dnsmasq/contrib/wrt/dhcp_release.c

   1 /* Copyright (c) 2006 Simon Kelley
   2
   3    This program is free software; you can redistribute it and/or modify
   4    it under the terms of the GNU General Public License as published by
   5    the Free Software Foundation; version 2 dated June, 1991.
   6
   7    This program is distributed in the hope that it will be useful,
   8    but WITHOUT ANY WARRANTY; without even the implied warranty of
   9    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10    GNU General Public License for more details.
  11 */
  12
  13 /* dhcp_release <interface> <address> <MAC address> <client_id>
  14    MUST be run as root - will fail otherwise. */
  15
  16 /* Send a DHCPRELEASE message via the specified interface
  17    to tell the local DHCP server to delete a particular lease.
  18
  19    The interface argument is the interface in which a DHCP
  20    request _would_ be received if it was coming from the client,
  21    rather than being faked up here.
  22
  23    The address argument is a dotted-quad IP addresses and mandatory.
  24
  25    The MAC address is colon separated hex, and is mandatory. It may be
  26    prefixed by an address-type byte followed by -, eg
  27
  28    10-11:22:33:44:55:66
  29
  30    but if the address-type byte is missing it is assumed to be 1, the type
  31    for ethernet. This encoding is the one used in dnsmasq lease files.
  32
  33    The client-id is optional. If it is "*" then it treated as being missing.
  34 */
  35
  36 #include <sys/types.h>
  37 #include <netinet/in.h>
  38 #include <net/if.h>
  39 #include <arpa/inet.h>
  40 #include <sys/socket.h>
  41 #include <unistd.h>
  42 #include <stdio.h>
  43 #include <string.h>
  44 #include <stdlib.h>
  45 #include <net/if_arp.h>
  46 #include <sys/ioctl.h>
  47 #include <linux/types.h>
  48 #include <linux/netlink.h>
  49 #include <linux/rtnetlink.h>
  50 #include <errno.h>
  51
  52 #define DHCP_CHADDR_MAX          16
  53 #define BOOTREQUEST              1
  54 #define DHCP_COOKIE              0x63825363
  55 #define OPTION_SERVER_IDENTIFIER 54
  56 #define OPTION_CLIENT_ID         61
  57 #define OPTION_MESSAGE_TYPE      53
  58 #define OPTION_END               255
  59 #define DHCPRELEASE              7
  60 #define DHCP_SERVER_PORT         67
  61
  62 typedef unsigned char u8;
  63 typedef unsigned short u16;
  64 typedef unsigned int u32;
  65
  66 struct dhcp_packet {
  67   u8 op, htype, hlen, hops;
  68   u32 xid;
  69   u16 secs, flags;
  70   struct in_addr ciaddr, yiaddr, siaddr, giaddr;
  71   u8 chaddr[DHCP_CHADDR_MAX], sname[64], file[128];
  72   u32 cookie;
  73   unsigned char options[308];
  74 };
  75
  76 static struct iovec iov;
  77
  78 static int expand_buf(struct iovec *iov, size_t size)
  79 {
  80   void *new;
  81
  82   if (size <= iov->iov_len)
  83     return 1;
  84
  85   if (!(new = malloc(size)))
  86     {
  87       errno = ENOMEM;
  88       return 0;
  89     }
  90
  91   if (iov->iov_base)
  92     {
  93       memcpy(new, iov->iov_base, iov->iov_len);
  94       free(iov->iov_base);
  95     }
  96
  97   iov->iov_base = new;
  98   iov->iov_len = size;
  99
 100   return 1;
 101 }
 102
 103 static ssize_t netlink_recv(int fd)
 104 {
 105   struct msghdr msg;
 106   ssize_t rc;
 107
 108   msg.msg_control = NULL;
 109   msg.msg_controllen = 0;
 110   msg.msg_name = NULL;
 111   msg.msg_namelen = 0;
 112   msg.msg_iov = &iov;
 113   msg.msg_iovlen = 1;
 114
 115   while (1)
 116     {
 117       msg.msg_flags = 0;
 118       while ((rc = recvmsg(fd, &msg, MSG_PEEK)) == -1 && errno == EINTR);
 119
 120       /* 2.2.x doesn't suport MSG_PEEK at all, returning EOPNOTSUPP, so we just grab a
 121          big buffer and pray in that case. */
 122       if (rc == -1 && errno == EOPNOTSUPP)
 123         {
 124           if (!expand_buf(&iov, 2000))
 125             return -1;
 126           break;
 127         }
 128
 129       if (rc == -1 || !(msg.msg_flags & MSG_TRUNC))
 130         break;
 131
 132       if (!expand_buf(&iov, iov.iov_len + 100))
 133         return -1;
 134     }
 135
 136   /* finally, read it for real */
 137   while ((rc = recvmsg(fd, &msg, 0)) == -1 && errno == EINTR);
 138
 139   return rc;
 140 }
 141
 142 static int parse_hex(char *in, unsigned char *out, int maxlen, int *mac_type)
 143 {
 144   int i = 0;
 145   char *r;
 146
 147   if (mac_type)
 148     *mac_type = 0;
 149
 150   while (maxlen == -1 || i < maxlen)
 151     {
 152       for (r = in; *r != 0 && *r != ':' && *r != '-'; r++);
 153       if (*r == 0)
 154         maxlen = i;
 155
 156       if (r != in )
 157         {
 158           if (*r == '-' && i == 0 && mac_type)
 159            {
 160               *r = 0;
 161               *mac_type = strtol(in, NULL, 16);
 162               mac_type = NULL;
 163            }
 164           else
 165             {
 166               *r = 0;
 167               out[i] = strtol(in, NULL, 16);
 168               i++;
 169             }
 170         }
 171       in = r+1;
 172     }
 173     return i;
 174 }
 175
 176 static int is_same_net(struct in_addr a, struct in_addr b, struct in_addr mask)
 177 {
 178   return (a.s_addr & mask.s_addr) == (b.s_addr & mask.s_addr);
 179 }
 180
 181 static struct in_addr find_interface(struct in_addr client, int fd, unsigned int index)
 182 {
 183   struct sockaddr_nl addr;
 184   struct nlmsghdr *h;
 185   ssize_t len;
 186
 187   struct {
 188     struct nlmsghdr nlh;
 189     struct rtgenmsg g;
 190   } req;
 191
 192   addr.nl_family = AF_NETLINK;
 193   addr.nl_pad = 0;
 194   addr.nl_groups = 0;
 195   addr.nl_pid = 0; /* address to kernel */
 196
 197   req.nlh.nlmsg_len = sizeof(req);
 198   req.nlh.nlmsg_type = RTM_GETADDR;
 199   req.nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST | NLM_F_ACK;
 200   req.nlh.nlmsg_pid = 0;
 201   req.nlh.nlmsg_seq = 1;
 202   req.g.rtgen_family = AF_INET;
 203
 204   if (sendto(fd, (void *)&req, sizeof(req), 0,
 205              (struct sockaddr *)&addr, sizeof(addr)) == -1)
 206     {
 207       perror("sendto failed");
 208       exit(1);
 209     }
 210
 211   while (1)
 212     {
 213       if ((len = netlink_recv(fd)) == -1)
 214         {
 215           perror("netlink");
 216           exit(1);
 217         }
 218
 219       for (h = (struct nlmsghdr *)iov.iov_base; NLMSG_OK(h, (size_t)len); h = NLMSG_NEXT(h, len))
 220         if (h->nlmsg_type == NLMSG_DONE)
 221           exit(0);
 222         else if (h->nlmsg_type == RTM_NEWADDR)
 223           {
 224             struct ifaddrmsg *ifa = NLMSG_DATA(h);
 225             struct rtattr *rta;
 226             unsigned int len1 = h->nlmsg_len - NLMSG_LENGTH(sizeof(*ifa));
 227
 228             if (ifa->ifa_index == index && ifa->ifa_family == AF_INET)
 229               {
 230                 struct in_addr netmask, addr;
 231
 232                 netmask.s_addr = htonl(0xffffffff << (32 - ifa->ifa_prefixlen));
 233                 addr.s_addr = 0;
 234
 235                 for (rta = IFA_RTA(ifa); RTA_OK(rta, len1); rta = RTA_NEXT(rta, len1))
 236                   if (rta->rta_type == IFA_LOCAL)
 237                     addr = *((struct in_addr *)(rta+1));
 238
 239                 if (addr.s_addr && is_same_net(addr, client, netmask))
 240                   return addr;
 241               }
 242           }
 243     }
 244
 245   exit(0);
 246 }
 247
 248 int main(int argc, char **argv)
 249 {
 250   struct in_addr server, lease;
 251   int mac_type;
 252   struct dhcp_packet packet;
 253   unsigned char *p = packet.options;
 254   struct sockaddr_in dest;
 255   struct ifreq ifr;
 256   int fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 257   int nl = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
 258
 259   if (argc < 4 || argc > 5)
 260     {
 261       fprintf(stderr, "usage: dhcp_release <interface> <addr> <mac> [<client_id>]\n");
 262       exit(1);
 263     }
 264
 265   if (fd == -1 || nl == -1)
 266     {
 267       perror("cannot create socket");
 268       exit(1);
 269     }
 270
 271   /* This voodoo fakes up a packet coming from the correct interface, which really matters for
 272      a DHCP server */
 273   strcpy(ifr.ifr_name, argv[1]);
 274   if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, &ifr, sizeof(ifr)) == -1)
 275     {
 276       perror("cannot setup interface");
 277       exit(1);
 278     }
 279
 280
 281   lease.s_addr = inet_addr(argv[2]);
 282   server = find_interface(lease, nl, if_nametoindex(argv[1]));
 283
 284   memset(&packet, 0, sizeof(packet));
 285
 286   packet.hlen = parse_hex(argv[3], packet.chaddr, DHCP_CHADDR_MAX, &mac_type);
 287   if (mac_type == 0)
 288     packet.htype = ARPHRD_ETHER;
 289   else
 290     packet.htype = mac_type;
 291
 292   packet.op = BOOTREQUEST;
 293   packet.ciaddr = lease;
 294   packet.cookie = htonl(DHCP_COOKIE);
 295
 296   *(p++) = OPTION_MESSAGE_TYPE;
 297   *(p++) = 1;
 298   *(p++) = DHCPRELEASE;
 299
 300   *(p++) = OPTION_SERVER_IDENTIFIER;
 301   *(p++) = sizeof(server);
 302   memcpy(p, &server, sizeof(server));
 303   p += sizeof(server);
 304
 305   if (argc == 5 && strcmp(argv[4], "*") != 0)
 306     {
 307       unsigned int clid_len = parse_hex(argv[4], p+2, 255, NULL);
 308       *(p++) = OPTION_CLIENT_ID;
 309       *(p++) = clid_len;
 310       p += clid_len;
 311     }
 312
 313   *(p++) = OPTION_END;
 314
 315   dest.sin_family = AF_INET;
 316   dest.sin_port = ntohs(DHCP_SERVER_PORT);
 317   dest.sin_addr = server;
 318
 319   if (sendto(fd, &packet, sizeof(packet), 0,
 320              (struct sockaddr *)&dest, sizeof(dest)) == -1)
 321     {
 322       perror("sendto failed");
 323       exit(1);
 324     }
 325
 326   return 0;
 327 }