268 lines
8.1 KiB
C
268 lines
8.1 KiB
C
/* $OpenBSD: packet.c,v 1.9 2004/05/04 18:58:50 deraadt Exp $ */
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/* Packet assembly code, originally contributed by Archie Cobbs. */
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/*
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* Copyright (c) 1995, 1996, 1999 The Internet Software Consortium.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of The Internet Software Consortium nor the names
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* of its contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
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* CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* This software has been written for the Internet Software Consortium
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* by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
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* Enterprises. To learn more about the Internet Software Consortium,
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* see ``http://www.vix.com/isc''. To learn more about Vixie
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* Enterprises, see ``http://www.vix.com''.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include "dhcpd.h"
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#include <netinet/in_systm.h>
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#include <netinet/ip.h>
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#include <netinet/udp.h>
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#include <netinet/if_ether.h>
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#define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t))
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u_int32_t checksum(unsigned char *, unsigned, u_int32_t);
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u_int32_t wrapsum(u_int32_t);
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void assemble_ethernet_header(struct interface_info *, unsigned char *,
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int *, struct hardware *);
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ssize_t decode_ethernet_header(struct interface_info *, unsigned char *,
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int bufix, struct hardware *);
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u_int32_t
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checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum)
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{
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int i;
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/* Checksum all the pairs of bytes first... */
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for (i = 0; i < (nbytes & ~1U); i += 2) {
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sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
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if (sum > 0xFFFF)
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sum -= 0xFFFF;
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}
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/*
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* If there's a single byte left over, checksum it, too.
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* Network byte order is big-endian, so the remaining byte is
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* the high byte.
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*/
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if (i < nbytes) {
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sum += buf[i] << 8;
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if (sum > 0xFFFF)
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sum -= 0xFFFF;
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}
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return (sum);
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}
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u_int32_t
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wrapsum(u_int32_t sum)
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{
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sum = ~sum & 0xFFFF;
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return (htons(sum));
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}
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void
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assemble_hw_header(struct interface_info *interface, unsigned char *buf,
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int *bufix, struct hardware *to)
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{
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struct ether_header eh;
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if (to != NULL && to->hlen == 6) /* XXX */
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memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost));
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else
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memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost));
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if (interface->hw_address.hlen == sizeof(eh.ether_shost))
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memcpy(eh.ether_shost, interface->hw_address.haddr,
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sizeof(eh.ether_shost));
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else
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memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost));
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eh.ether_type = htons(ETHERTYPE_IP);
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memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE);
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*bufix += ETHER_HEADER_SIZE;
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}
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void
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assemble_udp_ip_header(unsigned char *buf, int *bufix, u_int32_t from,
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u_int32_t to, unsigned int port, unsigned char *data, int len)
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{
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struct ip ip;
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struct udphdr udp;
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ip.ip_v = 4;
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ip.ip_hl = 5;
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ip.ip_tos = IPTOS_LOWDELAY;
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ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
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ip.ip_id = 0;
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ip.ip_off = 0;
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ip.ip_ttl = 128;
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ip.ip_p = IPPROTO_UDP;
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ip.ip_sum = 0;
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ip.ip_src.s_addr = from;
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ip.ip_dst.s_addr = to;
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ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0));
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/*
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* While the BPF -- used for broadcasts -- expects a "true" IP header
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* with all the bytes in network byte order, the raw socket interface
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* which is used for unicasts expects the ip_len field to be in host
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* byte order. In both cases, the checksum has to be correct, so this
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* is as good a place as any to turn the bytes around again.
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*/
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if (to != INADDR_BROADCAST)
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ip.ip_len = ntohs(ip.ip_len);
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memcpy(&buf[*bufix], &ip, sizeof(ip));
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*bufix += sizeof(ip);
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udp.uh_sport = htons(LOCAL_PORT); /* XXX */
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udp.uh_dport = port; /* XXX */
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udp.uh_ulen = htons(sizeof(udp) + len);
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memset(&udp.uh_sum, 0, sizeof(udp.uh_sum));
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udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
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checksum(data, len, checksum((unsigned char *)&ip.ip_src,
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2 * sizeof(ip.ip_src),
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IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen)))));
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memcpy(&buf[*bufix], &udp, sizeof(udp));
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*bufix += sizeof(udp);
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}
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ssize_t
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decode_hw_header(unsigned char *buf, int bufix, struct hardware *from)
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{
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struct ether_header eh;
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memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE);
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memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost));
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from->htype = ARPHRD_ETHER;
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from->hlen = sizeof(eh.ether_shost);
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return (sizeof(eh));
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}
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ssize_t
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decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from,
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unsigned char *data, int buflen)
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{
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struct ip *ip;
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struct udphdr *udp;
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u_int32_t ip_len = (buf[bufix] & 0xf) << 2;
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u_int32_t sum, usum;
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static int ip_packets_seen;
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static int ip_packets_bad_checksum;
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static int udp_packets_seen;
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static int udp_packets_bad_checksum;
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static int udp_packets_length_checked;
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static int udp_packets_length_overflow;
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int len = 0;
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ip = (struct ip *)(buf + bufix);
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udp = (struct udphdr *)(buf + bufix + ip_len);
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/* Check the IP header checksum - it should be zero. */
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ip_packets_seen++;
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if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) {
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ip_packets_bad_checksum++;
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if (ip_packets_seen > 4 &&
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(ip_packets_seen / ip_packets_bad_checksum) < 2) {
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note("%d bad IP checksums seen in %d packets",
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ip_packets_bad_checksum, ip_packets_seen);
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ip_packets_seen = ip_packets_bad_checksum = 0;
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}
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return (-1);
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}
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if (ntohs(ip->ip_len) != buflen)
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debug("ip length %d disagrees with bytes received %d.",
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ntohs(ip->ip_len), buflen);
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memcpy(&from->sin_addr, &ip->ip_src, 4);
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/*
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* Compute UDP checksums, including the ``pseudo-header'', the
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* UDP header and the data. If the UDP checksum field is zero,
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* we're not supposed to do a checksum.
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*/
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if (!data) {
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data = buf + bufix + ip_len + sizeof(*udp);
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len = ntohs(udp->uh_ulen) - sizeof(*udp);
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udp_packets_length_checked++;
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if (len + data > buf + bufix + buflen) {
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udp_packets_length_overflow++;
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if (udp_packets_length_checked > 4 &&
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(udp_packets_length_checked /
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udp_packets_length_overflow) < 2) {
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note("%d udp packets in %d too long - dropped",
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udp_packets_length_overflow,
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udp_packets_length_checked);
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udp_packets_length_overflow =
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udp_packets_length_checked = 0;
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}
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return (-1);
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}
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if (len + data != buf + bufix + buflen)
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debug("accepting packet with data after udp payload.");
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}
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usum = udp->uh_sum;
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udp->uh_sum = 0;
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sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp),
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checksum(data, len, checksum((unsigned char *)&ip->ip_src,
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2 * sizeof(ip->ip_src),
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IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen)))));
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udp_packets_seen++;
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if (usum && usum != sum) {
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udp_packets_bad_checksum++;
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if (udp_packets_seen > 4 &&
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(udp_packets_seen / udp_packets_bad_checksum) < 2) {
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note("%d bad udp checksums in %d packets",
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udp_packets_bad_checksum, udp_packets_seen);
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udp_packets_seen = udp_packets_bad_checksum = 0;
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}
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return (-1);
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}
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memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport));
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return (ip_len + sizeof(*udp));
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}
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