usr.sbin/vknetd/filter.c

   1 /*
   2  * Copyright (c) 2008 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@backplane.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  * $DragonFly: src/usr.sbin/vknetd/filter.c,v 1.2 2008/05/27 22:47:16 dillon Exp $
  35  */
  36 /*
  37  * Bridging code (serialized)
  38  */
  39 #include "vknetd.h"
  40 #include <netinet/ip.h>
  41 #include <netinet/udp.h>
  42
  43 /*
  44  * Return on-zero if the packet should be passed through, zero if it should
  45  * be discarded.
  46  */
  47 int
  48 filter_ok(u_int8_t *pkt, int bytes)
  49 {
  50         struct ip *ip;
  51         u_int16_t ether_type;
  52
  53         if (bytes < 12 + 2 + 20)
  54                 return(0);
  55
  56         /*
  57          * Allow only ARP and IP packetes
  58          */
  59         ether_type = ntohs(*(u_int16_t *)(pkt + 12));
  60         if (ether_type == ETHERTYPE_ARP)
  61                 return(1);
  62         if (ether_type != ETHERTYPE_IP)
  63                 return(0);
  64
  65         /*
  66          * Allow only ICMP, TCP, and UDP protocols.
  67          */
  68         ip = (void *)(pkt + 14);
  69
  70         switch(ip->ip_p) {
  71         case 1:         /* ICMP */
  72                 /* XXX fix me */
  73                 break;
  74         case 17:        /* UDP */
  75         case 6:         /* TCP */
  76                 /*
  77                  * ip_src must represent our network or be 0.
  78                  * 0 is a special case, mainly so bootp (dhclient) gets
  79                  * through.
  80                  */
  81                 if (ip->ip_src.s_addr == 0)
  82                         break;
  83                 if (SecureOpt &&
  84                     (ip->ip_src.s_addr & NetMask.s_addr) !=
  85                     (NetAddress.s_addr & NetMask.s_addr)) {
  86                         fprintf(stderr, "Filtered Address: %08x\n",
  87                                 ntohl(ip->ip_src.s_addr));
  88                         return(0);
  89                 }
  90                 break;
  91         default:
  92                 if (SecureOpt)
  93                         return(0);
  94                 break;
  95         }
  96         return(1);
  97 }
  98