216 lines
6.5 KiB
C
216 lines
6.5 KiB
C
/* $OpenBSD: packet.c,v 1.45 2021/02/22 23:43:59 jsg 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/queue.h>
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#include <sys/socket.h>
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#include <net/if.h>
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#include <netinet/in.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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#include <signal.h>
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#include <stdio.h>
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#include <string.h>
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#include <unistd.h>
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#include "dhcp.h"
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#include "dhcpd.h"
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#include "log.h"
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uint32_t
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checksum(unsigned char *buf, uint32_t nbytes, uint32_t sum)
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{
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unsigned 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 += (uint16_t)ntohs(*((uint16_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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uint32_t
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wrapsum(uint32_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_eh_header(struct ether_addr shost, struct ether_header *eh)
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{
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memset(eh->ether_dhost, 0xff, sizeof(eh->ether_dhost));
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memcpy(eh->ether_shost, shost.ether_addr_octet,
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sizeof(eh->ether_shost));
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eh->ether_type = htons(ETHERTYPE_IP);
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}
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ssize_t
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decode_udp_ip_header(unsigned char *buf, uint32_t buflen,
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struct sockaddr_in *from)
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{
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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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struct ip *ip;
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struct udphdr *udp;
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unsigned char *data;
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int len;
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uint32_t ip_len;
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uint32_t sum, usum;
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/* Assure that an entire IP header is within the buffer. */
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if (sizeof(*ip) > buflen)
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return -1;
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ip_len = (*buf & 0xf) << 2;
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if (ip_len > buflen)
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return -1;
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ip = (struct ip *)(buf);
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ip_packets_seen++;
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/* Check the IP header checksum - it should be zero. */
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if (wrapsum(checksum((unsigned char *)ip, ip_len, 0)) != 0) {
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ip_packets_bad_checksum++;
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if (ip_packets_seen > 4 && ip_packets_bad_checksum != 0 &&
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(ip_packets_seen / ip_packets_bad_checksum) < 2) {
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log_debug("%s: %d bad IP checksums seen in %d packets",
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log_procname, ip_packets_bad_checksum,
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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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memcpy(&from->sin_addr, &ip->ip_src, sizeof(from->sin_addr));
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if (ntohs(ip->ip_len) != buflen)
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log_debug("%s: ip length %hu disagrees with bytes received %d",
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log_procname, ntohs(ip->ip_len), buflen);
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/* Assure that the entire IP packet is within the buffer. */
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if (ntohs(ip->ip_len) > buflen)
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return -1;
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/* Assure that the UDP header is within the buffer. */
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if (ip_len + sizeof(*udp) > buflen)
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return -1;
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udp = (struct udphdr *)(buf + ip_len);
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udp_packets_seen++;
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/* Assure that the entire UDP packet is within the buffer. */
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if (ip_len + ntohs(udp->uh_ulen) > buflen)
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return -1;
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data = buf + ip_len + sizeof(*udp);
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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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udp_packets_length_checked++;
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len = ntohs(udp->uh_ulen) - sizeof(*udp);
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if ((len < 0) || (len + data > buf + 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_overflow != 0 &&
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(udp_packets_length_checked /
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udp_packets_length_overflow) < 2) {
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log_debug("%s: %d udp packets in %d too long - dropped",
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log_procname, 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 + buflen)
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log_debug("%s: accepting packet with data after udp payload",
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log_procname);
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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 + (uint32_t)ntohs(udp->uh_ulen)))));
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udp_packets_seen++;
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if (usum != 0 && usum != sum) {
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udp_packets_bad_checksum++;
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if (udp_packets_seen > 4 && udp_packets_bad_checksum != 0 &&
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(udp_packets_seen / udp_packets_bad_checksum) < 2) {
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log_debug("%s: %d bad udp checksums in %d packets",
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log_procname, udp_packets_bad_checksum,
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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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