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/* $OpenBSD: packet.c,v 1.9 2004/05/04 18:58:50 deraadt Exp $ */
/* Packet assembly code, originally contributed by Archie Cobbs. */
/*
* Copyright (c) 1995, 1996, 1999 The Internet Software Consortium.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of The Internet Software Consortium nor the names
* of its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
* CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* This software has been written for the Internet Software Consortium
* by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
* Enterprises. To learn more about the Internet Software Consortium,
* see ``http://www.vix.com/isc''. To learn more about Vixie
* Enterprises, see ``http://www.vix.com''.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "dhcpd.h"
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netinet/if_ether.h>
#define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t))
u_int32_t checksum(unsigned char *, unsigned, u_int32_t);
u_int32_t wrapsum(u_int32_t);
void assemble_ethernet_header(struct interface_info *, unsigned char *,
int *, struct hardware *);
ssize_t decode_ethernet_header(struct interface_info *, unsigned char *,
int bufix, struct hardware *);
u_int32_t
checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum)
{
int i;
/* Checksum all the pairs of bytes first... */
for (i = 0; i < (nbytes & ~1U); i += 2) {
sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
if (sum > 0xFFFF)
sum -= 0xFFFF;
}
/*
* If there's a single byte left over, checksum it, too.
* Network byte order is big-endian, so the remaining byte is
* the high byte.
*/
if (i < nbytes) {
sum += buf[i] << 8;
if (sum > 0xFFFF)
sum -= 0xFFFF;
}
return (sum);
}
u_int32_t
wrapsum(u_int32_t sum)
{
sum = ~sum & 0xFFFF;
return (htons(sum));
}
void
assemble_hw_header(struct interface_info *interface, unsigned char *buf,
int *bufix, struct hardware *to)
{
struct ether_header eh;
if (to != NULL && to->hlen == 6) /* XXX */
memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost));
else
memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost));
if (interface->hw_address.hlen == sizeof(eh.ether_shost))
memcpy(eh.ether_shost, interface->hw_address.haddr,
sizeof(eh.ether_shost));
else
memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost));
eh.ether_type = htons(ETHERTYPE_IP);
memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE);
*bufix += ETHER_HEADER_SIZE;
}
void
assemble_udp_ip_header(unsigned char *buf, int *bufix, u_int32_t from,
u_int32_t to, unsigned int port, unsigned char *data, int len)
{
struct ip ip;
struct udphdr udp;
ip.ip_v = 4;
ip.ip_hl = 5;
ip.ip_tos = IPTOS_LOWDELAY;
ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
ip.ip_id = 0;
ip.ip_off = 0;
ip.ip_ttl = 16;
ip.ip_p = IPPROTO_UDP;
ip.ip_sum = 0;
ip.ip_src.s_addr = from;
ip.ip_dst.s_addr = to;
ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0));
/*
* While the BPF -- used for broadcasts -- expects a "true" IP header
* with all the bytes in network byte order, the raw socket interface
* which is used for unicasts expects the ip_len field to be in host
* byte order. In both cases, the checksum has to be correct, so this
* is as good a place as any to turn the bytes around again.
*/
if (to != INADDR_BROADCAST)
ip.ip_len = ntohs(ip.ip_len);
memcpy(&buf[*bufix], &ip, sizeof(ip));
*bufix += sizeof(ip);
udp.uh_sport = htons(LOCAL_PORT); /* XXX */
udp.uh_dport = port; /* XXX */
udp.uh_ulen = htons(sizeof(udp) + len);
memset(&udp.uh_sum, 0, sizeof(udp.uh_sum));
udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
checksum(data, len, checksum((unsigned char *)&ip.ip_src,
2 * sizeof(ip.ip_src),
IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen)))));
memcpy(&buf[*bufix], &udp, sizeof(udp));
*bufix += sizeof(udp);
}
ssize_t
decode_hw_header(unsigned char *buf, int bufix, struct hardware *from)
{
struct ether_header eh;
memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE);
memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost));
from->htype = ARPHRD_ETHER;
from->hlen = sizeof(eh.ether_shost);
return (sizeof(eh));
}
ssize_t
decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from,
unsigned char *data, int buflen)
{
struct ip *ip;
struct udphdr *udp;
u_int32_t ip_len = (buf[bufix] & 0xf) << 2;
u_int32_t sum, usum;
static int ip_packets_seen;
static int ip_packets_bad_checksum;
static int udp_packets_seen;
static int udp_packets_bad_checksum;
static int udp_packets_length_checked;
static int udp_packets_length_overflow;
int len = 0;
ip = (struct ip *)(buf + bufix);
udp = (struct udphdr *)(buf + bufix + ip_len);
/* Check the IP header checksum - it should be zero. */
ip_packets_seen++;
if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) {
ip_packets_bad_checksum++;
if (ip_packets_seen > 4 &&
(ip_packets_seen / ip_packets_bad_checksum) < 2) {
note("%d bad IP checksums seen in %d packets",
ip_packets_bad_checksum, ip_packets_seen);
ip_packets_seen = ip_packets_bad_checksum = 0;
}
return (-1);
}
if (ntohs(ip->ip_len) != buflen)
debug("ip length %d disagrees with bytes received %d.",
ntohs(ip->ip_len), buflen);
memcpy(&from->sin_addr, &ip->ip_src, 4);
/*
* Compute UDP checksums, including the ``pseudo-header'', the
* UDP header and the data. If the UDP checksum field is zero,
* we're not supposed to do a checksum.
*/
if (!data) {
data = buf + bufix + ip_len + sizeof(*udp);
len = ntohs(udp->uh_ulen) - sizeof(*udp);
udp_packets_length_checked++;
if (len + data > buf + bufix + buflen) {
udp_packets_length_overflow++;
if (udp_packets_length_checked > 4 &&
(udp_packets_length_checked /
udp_packets_length_overflow) < 2) {
note("%d udp packets in %d too long - dropped",
udp_packets_length_overflow,
udp_packets_length_checked);
udp_packets_length_overflow =
udp_packets_length_checked = 0;
}
return (-1);
}
if (len + data != buf + bufix + buflen)
debug("accepting packet with data after udp payload.");
}
usum = udp->uh_sum;
udp->uh_sum = 0;
sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp),
checksum(data, len, checksum((unsigned char *)&ip->ip_src,
2 * sizeof(ip->ip_src),
IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen)))));
udp_packets_seen++;
if (usum && usum != sum) {
udp_packets_bad_checksum++;
if (udp_packets_seen > 4 &&
(udp_packets_seen / udp_packets_bad_checksum) < 2) {
note("%d bad udp checksums in %d packets",
udp_packets_bad_checksum, udp_packets_seen);
udp_packets_seen = udp_packets_bad_checksum = 0;
}
return (-1);
}
memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport));
return (ip_len + sizeof(*udp));
}
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