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/* $OpenBSD: packet.c,v 1.14 2017/04/05 14:40:56 reyk 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/types.h> |
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#include <sys/socket.h> |
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#include <arpa/inet.h> |
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#include <net/if.h> |
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#include <net/if_enc.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 <string.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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u_int32_t checksum(unsigned char *, u_int32_t, u_int32_t); |
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u_int32_t wrapsum(u_int32_t); |
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u_int32_t |
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checksum(unsigned char *buf, u_int32_t nbytes, u_int32_t sum) |
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{ |
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u_int32_t 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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ssize_t |
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assemble_hw_header(unsigned char *buf, size_t buflen, |
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size_t offset, struct packet_ctx *pc, unsigned int intfhtype) |
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{ |
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struct ether_header eh; |
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switch (intfhtype) { |
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case HTYPE_ETHER: |
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if (buflen < offset + ETHER_HDR_LEN) |
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return (-1); |
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/* Use the supplied address or let the kernel fill it. */ |
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memcpy(eh.ether_shost, pc->pc_smac, ETHER_ADDR_LEN); |
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memcpy(eh.ether_dhost, pc->pc_dmac, ETHER_ADDR_LEN); |
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eh.ether_type = htons(ETHERTYPE_IP); |
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memcpy(&buf[offset], &eh, ETHER_HDR_LEN); |
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offset += ETHER_HDR_LEN; |
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break; |
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default: |
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return (-1); |
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} |
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return (offset); |
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} |
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ssize_t |
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assemble_udp_ip_header(unsigned char *buf, size_t buflen, size_t offset, |
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struct packet_ctx *pc, unsigned char *data, size_t datalen) |
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{ |
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struct ip ip; |
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struct udphdr udp; |
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if (buflen < offset + sizeof(ip) + sizeof(udp)) |
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return (-1); |
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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) + datalen); |
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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 = ss2sin(&pc->pc_src)->sin_addr.s_addr; |
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ip.ip_dst.s_addr = ss2sin(&pc->pc_dst)->sin_addr.s_addr; |
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ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0)); |
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memcpy(&buf[offset], &ip, sizeof(ip)); |
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offset += sizeof(ip); |
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udp.uh_sport = ss2sin(&pc->pc_src)->sin_port; |
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udp.uh_dport = ss2sin(&pc->pc_dst)->sin_port; |
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udp.uh_ulen = htons(sizeof(udp) + datalen); |
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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, datalen, 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[offset], &udp, sizeof(udp)); |
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offset += sizeof(udp); |
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return (offset); |
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} |
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ssize_t |
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decode_hw_header(unsigned char *buf, size_t buflen, |
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size_t offset, struct packet_ctx *pc, unsigned int intfhtype) |
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{ |
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u_int32_t ip_len; |
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struct ip *ip; |
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switch (intfhtype) { |
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case HTYPE_IPSEC_TUNNEL: |
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if (buflen < offset + ENC_HDRLEN + sizeof(*ip)) |
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return (-1); |
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offset += ENC_HDRLEN; |
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ip_len = (buf[offset] & 0xf) << 2; |
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if (buflen < offset + ip_len) |
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return (-1); |
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ip = (struct ip *)(buf + offset); |
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/* Encapsulated IP */ |
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if (ip->ip_p != IPPROTO_IPIP) |
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return (-1); |
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memset(pc->pc_dmac, 0xff, ETHER_ADDR_LEN); |
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offset += ip_len; |
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pc->pc_htype = ARPHRD_ETHER; |
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pc->pc_hlen = ETHER_ADDR_LEN; |
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break; |
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case HTYPE_ETHER: |
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if (buflen < offset + ETHER_HDR_LEN) |
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return (-1); |
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memcpy(pc->pc_dmac, buf + offset, ETHER_ADDR_LEN); |
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memcpy(pc->pc_smac, buf + offset + ETHER_ADDR_LEN, |
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ETHER_ADDR_LEN); |
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offset += ETHER_HDR_LEN; |
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pc->pc_htype = ARPHRD_ETHER; |
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pc->pc_hlen = ETHER_ADDR_LEN; |
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break; |
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default: |
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return (-1); |
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} |
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return (offset); |
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} |
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ssize_t |
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decode_udp_ip_header(unsigned char *buf, size_t buflen, |
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size_t offset, struct packet_ctx *pc) |
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{ |
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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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u_int32_t ip_len; |
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u_int32_t sum, usum; |
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static unsigned int ip_packets_seen; |
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static unsigned int ip_packets_bad_checksum; |
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static unsigned int udp_packets_seen; |
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static unsigned int udp_packets_bad_checksum; |
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static unsigned int udp_packets_length_checked; |
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static unsigned int udp_packets_length_overflow; |
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int len; |
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/* Assure that an entire IP header is within the buffer. */ |
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if (buflen < offset + sizeof(*ip)) |
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return (-1); |
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ip_len = (buf[offset] & 0xf) << 2; |
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if (buflen < offset + ip_len) |
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return (-1); |
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ip = (struct ip *)(buf + offset); |
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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(buf + offset, 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("%u bad IP checksums seen in %u 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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pc->pc_src.ss_len = sizeof(struct sockaddr_in); |
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pc->pc_src.ss_family = AF_INET; |
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memcpy(&ss2sin(&pc->pc_src)->sin_addr, &ip->ip_src, |
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sizeof(ss2sin(&pc->pc_src)->sin_addr)); |
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pc->pc_dst.ss_len = sizeof(struct sockaddr_in); |
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pc->pc_dst.ss_family = AF_INET; |
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memcpy(&ss2sin(&pc->pc_dst)->sin_addr, &ip->ip_dst, |
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sizeof(ss2sin(&pc->pc_dst)->sin_addr)); |
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#ifdef DEBUG |
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if (buflen != offset + ntohs(ip->ip_len)) |
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log_debug("ip length %d disagrees with bytes received %zd.", |
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ntohs(ip->ip_len), buflen - offset); |
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#endif |
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/* Assure that the entire IP packet is within the buffer. */ |
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if (buflen < offset + ntohs(ip->ip_len)) |
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return (-1); |
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/* Assure that the UDP header is within the buffer. */ |
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if (buflen < offset + ip_len + sizeof(*udp)) |
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return (-1); |
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udp = (struct udphdr *)(buf + offset + 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 (buflen < offset + ip_len + ntohs(udp->uh_ulen)) |
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return (-1); |
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data = buf + offset + 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("%u udp packets in %u 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 + buflen) |
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log_debug("accepting packet with data after udp payload."); |
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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 && udp_packets_bad_checksum != 0 && |
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(udp_packets_seen / udp_packets_bad_checksum) < 2) { |
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log_info("%u bad udp checksums in %u 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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ss2sin(&pc->pc_src)->sin_port = udp->uh_sport; |
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ss2sin(&pc->pc_dst)->sin_port = udp->uh_dport; |
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return (offset + ip_len + sizeof(*udp)); |
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} |