dhcp.c

   1 /*
   2  *   Copyright (C) 2010 Felix Fietkau <nbd@openwrt.org>
   3  *
   4  *   This program is free software; you can redistribute it and/or modify
   5  *   it under the terms of the GNU General Public License v2 as published by
   6  *   the Free Software Foundation.
   7  *
   8  *   This program is distributed in the hope that it will be useful,
   9  *   but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  *   GNU General Public License for more details.
  12  *
  13  *   You should have received a copy of the GNU General Public License
  14  *   along with this program; if not, write to the Free Software
  15  *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
  16  */
  17
  18 #include <sys/socket.h>
  19 #include <stdio.h>
  20 #include <string.h>
  21 #include <errno.h>
  22 #include <unistd.h>
  23 #include <fcntl.h>
  24
  25 #include "relayd.h"
  26
  27 struct ip_packet {
  28         struct ether_header eth;
  29         struct iphdr iph;
  30 } __packed;
  31
  32 struct dhcp_header {
  33         uint8_t op, htype, hlen, hops;
  34         uint32_t xit;
  35         uint16_t secs, flags;
  36         struct in_addr ciaddr, yiaddr, siaddr, giaddr;
  37         unsigned char chaddr[16];
  38         unsigned char sname[64];
  39         unsigned char file[128];
  40 } __packed;
  41
  42 static uint16_t
  43 chksum(uint16_t sum, const uint8_t *data, uint16_t len)
  44 {
  45         const uint8_t *last;
  46         uint16_t t;
  47
  48         last = data + len - 1;
  49
  50         while(data < last) {
  51                 t = (data[0] << 8) + data[1];
  52                 sum += t;
  53                 if(sum < t)
  54                         sum++;
  55                 data += 2;
  56         }
  57
  58         if(data == last) {
  59                 t = (data[0] << 8) + 0;
  60                 sum += t;
  61                 if(sum < t)
  62                         sum++;
  63         }
  64
  65         return sum;
  66 }
  67
  68 bool relayd_handle_dhcp_packet(struct relayd_interface *rif, void *data, int len, bool forward)
  69 {
  70         struct ip_packet *pkt = data;
  71         struct udphdr *udp;
  72         struct dhcp_header *dhcp;
  73         int udplen;
  74         uint16_t sum;
  75
  76         if (pkt->eth.ether_type != htons(ETH_P_IP))
  77                 return false;
  78
  79         if (pkt->iph.version != 4)
  80                 return false;
  81
  82         if (pkt->iph.protocol != IPPROTO_UDP)
  83                 return false;
  84
  85         udp = (void *) ((char *) &pkt->iph + (pkt->iph.ihl << 2));
  86         dhcp = (void *) (udp + 1);
  87
  88         udplen = ntohs(udp->len);
  89         if (udplen > len - ((char *) udp - (char *) data))
  90                 return false;
  91
  92         if (udp->dest != htons(67) && udp->source != htons(67))
  93                 return false;
  94
  95         if (dhcp->op != 1 && dhcp->op != 2)
  96                 return false;
  97
  98         if (!forward)
  99                 return true;
 100
 101         if (dhcp->op == 2)
 102                 relayd_refresh_host(rif, pkt->eth.ether_shost, (void *) &pkt->iph.saddr);
 103
 104         DPRINTF(2, "%s: handling DHCP %s\n", rif->ifname, (dhcp->op == 1 ? "request" : "response"));
 105
 106         dhcp->flags |= htons(DHCP_FLAG_BROADCAST);
 107
 108         udp->check = 0;
 109         sum = udplen + IPPROTO_UDP;
 110         sum = chksum(sum, (void *) &pkt->iph.saddr, 8);
 111         sum = chksum(sum, (void *) udp, udplen);
 112         if (sum == 0)
 113                 sum = 0xffff;
 114
 115         udp->check = htons(~sum);
 116
 117         relayd_forward_bcast_packet(rif, data, len);
 118
 119         return true;
 120 }
 121
 122