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/* $OpenBSD: packet.c,v 1.41 2017/09/17 21:20:23 krw 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_hw_header(unsigned char *buf, uint32_t buflen, struct ether_addr *from) |
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{ |
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struct ether_header eh; |
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if (buflen < sizeof(eh)) |
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return -1; |
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memcpy(&eh, buf, sizeof(eh)); |
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memcpy(from->ether_addr_octet, eh.ether_shost, ETHER_ADDR_LEN); |
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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, 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_info("%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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#ifdef DEBUG |
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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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#endif /* DEBUG */ |
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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_info("%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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#ifdef DEBUG |
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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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#endif /* DEBUG */ |
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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_info("%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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} |