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9b683f8da6
packets instead of allowing the protocol stack to pick a random source port. This fixes the behaviour where dhclient would never transition from RENEWING to BOUND without going through REBINDING in networks which are paranoid about DHCP spoofing, such as most mainstream cable-broadband ISP networks. Reviewed by: brooks Obtained from: OpenBSD (partly - I'm not convinced their solution can work) MFC after: 1 week (pending re approval)
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 = 16;
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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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