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NetBSD/dist/dhcp/common/packet.c

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/* packet.c
Packet assembly code, originally contributed by Archie Cobbs. */
/*
* Copyright (c) 2004-2005 by Internet Systems Consortium, Inc. ("ISC")
* Copyright (c) 1996-2003 by Internet Software Consortium
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
* OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
* Internet Systems Consortium, Inc.
* 950 Charter Street
* Redwood City, CA 94063
* <info@isc.org>
* http://www.isc.org/
*
* This code was originally contributed by Archie Cobbs, and is still
* very similar to that contribution, although the packet checksum code
* has been hacked significantly with the help of quite a few ISC DHCP
* users, without whose gracious and thorough help the checksum code would
* still be disabled.
*/
#ifndef lint
static char copyright[] =
"$Id: packet.c,v 1.7 2005/08/11 17:13:21 drochner Exp $ Copyright (c) 2004-2005 Internet Systems Consortium. All rights reserved.\n";
#endif /* not lint */
#include "dhcpd.h"
#if defined (PACKET_ASSEMBLY) || defined (PACKET_DECODING)
#include "includes/netinet/ip.h"
#include "includes/netinet/udp.h"
#include "includes/netinet/if_ether.h"
#endif /* PACKET_ASSEMBLY || PACKET_DECODING */
/* Compute the easy part of the checksum on a range of bytes. */
u_int32_t checksum (buf, nbytes, sum)
unsigned char *buf;
unsigned nbytes;
u_int32_t sum;
{
unsigned i;
#ifdef DEBUG_CHECKSUM
log_debug ("checksum (%x %d %x)", buf, nbytes, sum);
#endif
/* Checksum all the pairs of bytes first... */
for (i = 0; i < (nbytes & ~1U); i += 2) {
#ifdef DEBUG_CHECKSUM_VERBOSE
log_debug ("sum = %x", sum);
#endif
sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
/* Add carry. */
if (sum > 0xFFFF)
sum -= 0xFFFF;
}
/* If there's a single byte left over, checksum it, too. Network
byte order is big-endian, so the remaining byte is the high byte. */
if (i < nbytes) {
#ifdef DEBUG_CHECKSUM_VERBOSE
log_debug ("sum = %x", sum);
#endif
sum += buf [i] << 8;
/* Add carry. */
if (sum > 0xFFFF)
sum -= 0xFFFF;
}
return sum;
}
/* Finish computing the checksum, and then put it into network byte order. */
u_int32_t wrapsum (sum)
u_int32_t sum;
{
#ifdef DEBUG_CHECKSUM
log_debug ("wrapsum (%x)", sum);
#endif
sum = ~sum & 0xFFFF;
#ifdef DEBUG_CHECKSUM_VERBOSE
log_debug ("sum = %x", sum);
#endif
#ifdef DEBUG_CHECKSUM
log_debug ("wrapsum returns %x", htons (sum));
#endif
return htons(sum);
}
#ifdef PACKET_ASSEMBLY
void assemble_hw_header (interface, buf, bufix, to)
struct interface_info *interface;
unsigned char *buf;
unsigned *bufix;
struct hardware *to;
{
#if defined (HAVE_TR_SUPPORT)
if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
assemble_tr_header (interface, buf, bufix, to);
else
#endif
#if defined (DEC_FDDI) || defined (NETBSD_FDDI)
if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
assemble_fddi_header (interface, buf, bufix, to);
else
#endif
assemble_ethernet_header (interface, buf, bufix, to);
}
/* UDP header and IP header assembled together for convenience. */
void assemble_udp_ip_header (interface, buf, bufix,
from, to, port, data, len)
struct interface_info *interface;
unsigned char *buf;
unsigned *bufix;
u_int32_t from;
u_int32_t to;
u_int32_t port;
unsigned char *data;
unsigned len;
{
struct ip ip;
struct udphdr udp;
/* Fill out the IP header */
IP_V_SET (&ip, 4);
IP_HL_SET (&ip, 20);
ip.ip_tos = IPTOS_LOWDELAY;
ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
ip.ip_id = 0;
ip.ip_off = 0;
ip.ip_ttl = 32;
ip.ip_p = IPPROTO_UDP;
ip.ip_sum = 0;
ip.ip_src.s_addr = from;
ip.ip_dst.s_addr = to;
/* Checksum the IP header... */
ip.ip_sum = wrapsum (checksum ((unsigned char *)&ip, sizeof ip, 0));
/* Copy the ip header into the buffer... */
memcpy (&buf [*bufix], &ip, sizeof ip);
*bufix += sizeof ip;
/* Fill out the UDP header */
udp.uh_sport = local_port; /* XXX */
udp.uh_dport = port; /* XXX */
udp.uh_ulen = htons(sizeof(udp) + len);
memset (&udp.uh_sum, 0, sizeof udp.uh_sum);
/* Compute UDP checksums, including the ``pseudo-header'', the UDP
header and the data. */
udp.uh_sum =
wrapsum (checksum ((unsigned char *)&udp, sizeof udp,
checksum (data, len,
checksum ((unsigned char *)
&ip.ip_src,
2 * sizeof ip.ip_src,
IPPROTO_UDP +
(u_int32_t)
ntohs (udp.uh_ulen)))));
/* Copy the udp header into the buffer... */
memcpy (&buf [*bufix], &udp, sizeof udp);
*bufix += sizeof udp;
}
#endif /* PACKET_ASSEMBLY */
#ifdef PACKET_DECODING
/* Decode a hardware header... */
/* XXX currently only supports ethernet; doesn't check for other types. */
ssize_t decode_hw_header (interface, buf, bufix, from)
struct interface_info *interface;
unsigned char *buf;
unsigned bufix;
struct hardware *from;
{
#if defined (HAVE_TR_SUPPORT)
if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
return decode_tr_header (interface, buf, bufix, from);
else
#endif
#if defined (DEC_FDDI) || defined (NETBSD_FDDI)
if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
return decode_fddi_header (interface, buf, bufix, from);
else
#endif
return decode_ethernet_header (interface, buf, bufix, from);
}
/* UDP header and IP header decoded together for convenience. */
ssize_t decode_udp_ip_header (interface, buf, bufix, from, buflen, rbuflen)
struct interface_info *interface;
unsigned char *buf;
unsigned bufix;
struct sockaddr_in *from;
unsigned buflen;
unsigned *rbuflen;
{
unsigned char *data;
struct ip ip;
struct udphdr *udp;
u_int32_t ip_len = (buf [bufix] & 0xf) << 2;
u_int32_t sum, usum;
static int ip_packets_seen;
static int ip_packets_bad_checksum;
static int udp_packets_seen;
static int udp_packets_bad_checksum;
static int udp_packets_length_checked;
static int udp_packets_length_overflow;
unsigned len;
unsigned ulen;
int ignore = 0;
memcpy(&ip, buf + bufix, sizeof (struct ip));
udp = (struct udphdr *)(buf + bufix + ip_len);
len = 0; /* XXXGCC -Wuninitialized */
#ifdef USERLAND_FILTER
/* Is it a UDP packet? */
if (ip.ip_p != IPPROTO_UDP)
return -1;
/* Is it to the port we're serving? */
if (udp -> uh_dport != local_port)
return -1;
#endif /* USERLAND_FILTER */
ulen = ntohs (udp -> uh_ulen);
if (ulen < sizeof *udp ||
((unsigned char *)udp) + ulen > buf + bufix + buflen) {
log_info ("bogus UDP packet length: %d", ulen);
return -1;
}
/* Check the IP header checksum - it should be zero. */
++ip_packets_seen;
if (wrapsum (checksum (buf + bufix, ip_len, 0))) {
++ip_packets_bad_checksum;
if (ip_packets_seen > 4 &&
(ip_packets_seen / ip_packets_bad_checksum) < 2) {
log_info ("%d bad IP checksums seen in %d packets",
ip_packets_bad_checksum, ip_packets_seen);
ip_packets_seen = ip_packets_bad_checksum = 0;
}
return -1;
}
/* Check the IP packet length. */
if (ntohs (ip.ip_len) != buflen) {
if ((ntohs (ip.ip_len + 2) & ~1) == buflen)
ignore = 1;
else
log_debug ("ip length %d disagrees with bytes received %d.",
ntohs (ip.ip_len), buflen);
}
/* Copy out the IP source address... */
memcpy (&from -> sin_addr, &ip.ip_src, 4);
/* Compute UDP checksums, including the ``pseudo-header'', the UDP
header and the data. If the UDP checksum field is zero, we're
not supposed to do a checksum. */
data = buf + bufix + ip_len + sizeof *udp;
len = ulen - sizeof *udp;
++udp_packets_length_checked;
if (len + data > buf + bufix + buflen) {
++udp_packets_length_overflow;
if (udp_packets_length_checked > 4 &&
(udp_packets_length_checked /
udp_packets_length_overflow) < 2) {
log_info ("%d udp packets in %d too long - dropped",
udp_packets_length_overflow,
udp_packets_length_checked);
udp_packets_length_overflow =
udp_packets_length_checked = 0;
}
return -1;
}
if (len + data < buf + bufix + buflen &&
len + data != buf + bufix + buflen && !ignore)
log_debug ("accepting packet with data after udp payload.");
if (len + data > buf + bufix + buflen) {
log_debug ("dropping packet with bogus uh_ulen %ld",
(long)(len + sizeof *udp));
return -1;
}
usum = udp -> uh_sum;
udp -> uh_sum = 0;
sum = wrapsum (checksum ((unsigned char *)udp, sizeof *udp,
checksum (data, len,
checksum ((unsigned char *)
&ip.ip_src,
2 * sizeof ip.ip_src,
IPPROTO_UDP +
(u_int32_t)ulen))));
udp_packets_seen++;
if (usum && usum != sum) {
udp_packets_bad_checksum++;
if (udp_packets_seen > 4 &&
(udp_packets_seen / udp_packets_bad_checksum) < 2) {
log_info ("%d bad udp checksums in %d packets",
udp_packets_bad_checksum, udp_packets_seen);
udp_packets_seen = udp_packets_bad_checksum = 0;
}
return -1;
}
/* Copy out the port... */
memcpy (&from -> sin_port, &udp -> uh_sport, sizeof udp -> uh_sport);
*rbuflen = ntohs (ip.ip_len) - ip_len - sizeof *udp;
return ip_len + sizeof *udp;
}
#endif /* PACKET_DECODING */
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