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/* $OpenBSD: packet.c,v 1.45 2021/02/22 23:43:59 jsg 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/queue.h>
#include <sys/socket.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netinet/if_ether.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include "dhcp.h"
#include "dhcpd.h"
#include "log.h"
uint32_t
checksum(unsigned char *buf, uint32_t nbytes, uint32_t sum)
{
unsigned int i;
/* Checksum all the pairs of bytes first. */
for (i = 0; i < (nbytes & ~1U); i += 2) {
sum += (uint16_t)ntohs(*((uint16_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;
}
uint32_t
wrapsum(uint32_t sum)
{
sum = ~sum & 0xFFFF;
return htons(sum);
}
void
assemble_eh_header(struct ether_addr shost, struct ether_header *eh)
{
memset(eh->ether_dhost, 0xff, sizeof(eh->ether_dhost));
memcpy(eh->ether_shost, shost.ether_addr_octet,
sizeof(eh->ether_shost));
eh->ether_type = htons(ETHERTYPE_IP);
}
ssize_t
decode_udp_ip_header(unsigned char *buf, uint32_t buflen,
struct sockaddr_in *from)
{
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;
struct ip *ip;
struct udphdr *udp;
unsigned char *data;
int len;
uint32_t ip_len;
uint32_t sum, usum;
/* Assure that an entire IP header is within the buffer. */
if (sizeof(*ip) > buflen)
return -1;
ip_len = (*buf & 0xf) << 2;
if (ip_len > buflen)
return -1;
ip = (struct ip *)(buf);
ip_packets_seen++;
/* Check the IP header checksum - it should be zero. */
if (wrapsum(checksum((unsigned char *)ip, ip_len, 0)) != 0) {
ip_packets_bad_checksum++;
if (ip_packets_seen > 4 && ip_packets_bad_checksum != 0 &&
(ip_packets_seen / ip_packets_bad_checksum) < 2) {
log_debug("%s: %d bad IP checksums seen in %d packets",
log_procname, ip_packets_bad_checksum,
ip_packets_seen);
ip_packets_seen = ip_packets_bad_checksum = 0;
}
return -1;
}
memcpy(&from->sin_addr, &ip->ip_src, sizeof(from->sin_addr));
if (ntohs(ip->ip_len) != buflen)
log_debug("%s: ip length %hu disagrees with bytes received %d",
log_procname, ntohs(ip->ip_len), buflen);
/* Assure that the entire IP packet is within the buffer. */
if (ntohs(ip->ip_len) > buflen)
return -1;
/* Assure that the UDP header is within the buffer. */
if (ip_len + sizeof(*udp) > buflen)
return -1;
udp = (struct udphdr *)(buf + ip_len);
udp_packets_seen++;
/* Assure that the entire UDP packet is within the buffer. */
if (ip_len + ntohs(udp->uh_ulen) > buflen)
return -1;
data = buf + ip_len + sizeof(*udp);
/*
* 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.
*/
udp_packets_length_checked++;
len = ntohs(udp->uh_ulen) - sizeof(*udp);
if ((len < 0) || (len + data > buf + buflen)) {
udp_packets_length_overflow++;
if (udp_packets_length_checked > 4 &&
udp_packets_length_overflow != 0 &&
(udp_packets_length_checked /
udp_packets_length_overflow) < 2) {
log_debug("%s: %d udp packets in %d too long - dropped",
log_procname, udp_packets_length_overflow,
udp_packets_length_checked);
udp_packets_length_overflow =
udp_packets_length_checked = 0;
}
return -1;
}
if (len + data != buf + buflen)
log_debug("%s: accepting packet with data after udp payload",
log_procname);
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 + (uint32_t)ntohs(udp->uh_ulen)))));
udp_packets_seen++;
if (usum != 0 && usum != sum) {
udp_packets_bad_checksum++;
if (udp_packets_seen > 4 && udp_packets_bad_checksum != 0 &&
(udp_packets_seen / udp_packets_bad_checksum) < 2) {
log_debug("%s: %d bad udp checksums in %d packets",
log_procname, 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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