340 lines
9.4 KiB
C
340 lines
9.4 KiB
C
/* packet.c
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Packet assembly code, originally contributed by Archie Cobbs. */
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/*
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* Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
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* Copyright (c) 1996-2003 by Internet Software Consortium
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
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* OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*
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* Internet Systems Consortium, Inc.
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* 950 Charter Street
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* Redwood City, CA 94063
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* <info@isc.org>
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* http://www.isc.org/
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*
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* This code was originally contributed by Archie Cobbs, and is still
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* very similar to that contribution, although the packet checksum code
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* has been hacked significantly with the help of quite a few ISC DHCP
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* users, without whose gracious and thorough help the checksum code would
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* still be disabled.
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*/
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#ifndef lint
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static char copyright[] =
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"$Id: packet.c,v 1.40.2.3 2004/06/10 17:59:19 dhankins Exp $ Copyright (c) 2004 Internet Systems Consortium. All rights reserved.\n";
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#endif /* not lint */
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#include "dhcpd.h"
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#if defined (PACKET_ASSEMBLY) || defined (PACKET_DECODING)
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#include "includes/netinet/ip.h"
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#include "includes/netinet/udp.h"
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#include "includes/netinet/if_ether.h"
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#endif /* PACKET_ASSEMBLY || PACKET_DECODING */
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/* Compute the easy part of the checksum on a range of bytes. */
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u_int32_t checksum (buf, nbytes, sum)
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unsigned char *buf;
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unsigned nbytes;
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u_int32_t sum;
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{
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unsigned i;
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#ifdef DEBUG_CHECKSUM
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log_debug ("checksum (%x %d %x)", buf, nbytes, sum);
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#endif
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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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#ifdef DEBUG_CHECKSUM_VERBOSE
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log_debug ("sum = %x", sum);
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#endif
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sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
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/* Add carry. */
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if (sum > 0xFFFF)
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sum -= 0xFFFF;
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}
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/* If there's a single byte left over, checksum it, too. Network
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byte order is big-endian, so the remaining byte is the high byte. */
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if (i < nbytes) {
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#ifdef DEBUG_CHECKSUM_VERBOSE
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log_debug ("sum = %x", sum);
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#endif
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sum += buf [i] << 8;
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/* Add carry. */
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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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/* Finish computing the checksum, and then put it into network byte order. */
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u_int32_t wrapsum (sum)
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u_int32_t sum;
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{
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#ifdef DEBUG_CHECKSUM
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log_debug ("wrapsum (%x)", sum);
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#endif
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sum = ~sum & 0xFFFF;
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#ifdef DEBUG_CHECKSUM_VERBOSE
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log_debug ("sum = %x", sum);
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#endif
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#ifdef DEBUG_CHECKSUM
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log_debug ("wrapsum returns %x", htons (sum));
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#endif
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return htons(sum);
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}
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#ifdef PACKET_ASSEMBLY
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void assemble_hw_header (interface, buf, bufix, to)
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struct interface_info *interface;
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unsigned char *buf;
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unsigned *bufix;
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struct hardware *to;
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{
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#if defined (HAVE_TR_SUPPORT)
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if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
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assemble_tr_header (interface, buf, bufix, to);
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else
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#endif
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#if defined (DEC_FDDI)
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if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
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assemble_fddi_header (interface, buf, bufix, to);
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else
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#endif
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assemble_ethernet_header (interface, buf, bufix, to);
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}
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/* UDP header and IP header assembled together for convenience. */
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void assemble_udp_ip_header (interface, buf, bufix,
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from, to, port, data, len)
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struct interface_info *interface;
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unsigned char *buf;
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unsigned *bufix;
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u_int32_t from;
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u_int32_t to;
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u_int32_t port;
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unsigned char *data;
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unsigned len;
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{
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struct ip ip;
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struct udphdr udp;
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/* Fill out the IP header */
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IP_V_SET (&ip, 4);
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IP_HL_SET (&ip, 20);
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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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/* Checksum the IP header... */
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ip.ip_sum = wrapsum (checksum ((unsigned char *)&ip, sizeof ip, 0));
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/* Copy the ip header into the buffer... */
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memcpy (&buf [*bufix], &ip, sizeof ip);
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*bufix += sizeof ip;
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/* Fill out the UDP header */
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udp.uh_sport = 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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/* Compute UDP checksums, including the ``pseudo-header'', the UDP
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header and the data. */
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udp.uh_sum =
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wrapsum (checksum ((unsigned char *)&udp, sizeof udp,
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checksum (data, len,
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checksum ((unsigned char *)
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&ip.ip_src,
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2 * sizeof ip.ip_src,
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IPPROTO_UDP +
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(u_int32_t)
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ntohs (udp.uh_ulen)))));
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/* Copy the udp header into the buffer... */
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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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#endif /* PACKET_ASSEMBLY */
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#ifdef PACKET_DECODING
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/* Decode a hardware header... */
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/* XXX currently only supports ethernet; doesn't check for other types. */
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ssize_t decode_hw_header (interface, buf, bufix, from)
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struct interface_info *interface;
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unsigned char *buf;
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unsigned bufix;
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struct hardware *from;
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{
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#if defined (HAVE_TR_SUPPORT)
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if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
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return decode_tr_header (interface, buf, bufix, from);
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else
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#endif
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#if defined (DEC_FDDI)
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if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
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return decode_fddi_header (interface, buf, bufix, from);
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else
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#endif
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return decode_ethernet_header (interface, buf, bufix, from);
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}
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/* UDP header and IP header decoded together for convenience. */
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ssize_t decode_udp_ip_header (interface, buf, bufix, from, data, buflen)
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struct interface_info *interface;
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unsigned char *buf;
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unsigned bufix;
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struct sockaddr_in *from;
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unsigned char *data;
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unsigned 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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unsigned len;
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unsigned ulen;
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int ignore = 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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#ifdef USERLAND_FILTER
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/* Is it a UDP packet? */
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if (ip -> ip_p != IPPROTO_UDP)
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return -1;
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/* Is it to the port we're serving? */
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if (udp -> uh_dport != local_port)
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return -1;
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#endif /* USERLAND_FILTER */
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ulen = ntohs (udp -> uh_ulen);
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if (ulen < sizeof *udp ||
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((unsigned char *)udp) + ulen > buf + bufix + buflen) {
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log_info ("bogus UDP packet length: %d", ulen);
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return -1;
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}
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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))) {
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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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log_info ("%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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/* Check the IP packet length. */
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if (ntohs (ip -> ip_len) != buflen) {
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if ((ntohs (ip -> ip_len + 2) & ~1) == buflen)
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ignore = 1;
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else
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log_debug ("ip length %d disagrees with bytes received %d.",
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ntohs (ip -> ip_len), buflen);
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}
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/* Copy out the IP source address... */
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memcpy (&from -> sin_addr, &ip -> ip_src, 4);
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/* Compute UDP checksums, including the ``pseudo-header'', the UDP
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header and the data. If the UDP checksum field is zero, we're
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not supposed to do a checksum. */
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if (!data) {
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data = buf + bufix + ip_len + sizeof *udp;
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len = 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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log_info ("%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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len + data != buf + bufix + buflen && !ignore)
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log_debug ("accepting packet with data after udp payload.");
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if (len + data > buf + bufix + buflen) {
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log_debug ("dropping packet with bogus uh_ulen %ld",
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(long)(len + sizeof *udp));
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return -1;
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}
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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,
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checksum ((unsigned char *)
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&ip -> ip_src,
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2 * sizeof ip -> ip_src,
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IPPROTO_UDP +
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(u_int32_t)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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log_info ("%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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/* Copy out the port... */
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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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#endif /* PACKET_DECODING */
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