/* packet.c
Packet assembly code, originally contributed by Archie Cobbs. */
/*
* Copyright (c) 2009,2012 by Internet Systems Consortium, Inc. ("ISC")
* Copyright (c) 2004,2005,2007 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>
* https://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.
*/
#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;
{
switch (interface->hw_address.hbuf[0]) {
#if defined(HAVE_TR_SUPPORT)
case HTYPE_IEEE802:
assemble_tr_header(interface, buf, bufix, to);
break;
#endif
#if defined (DEC_FDDI)
case HTYPE_FDDI:
assemble_fddi_header(interface, buf, bufix, to);
break;
#endif
case HTYPE_INFINIBAND:
log_error("Attempt to assemble hw header for infiniband");
break;
case HTYPE_ETHER:
default:
assemble_ethernet_header(interface, buf, bufix, to);
break;
}
}
/* 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;
memset (&ip, 0, sizeof ip);
/* 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 = 128;
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... */
/* Support for ethernet, TR and FDDI
* Doesn't support infiniband yet as the supported oses shouldn't get here
*/
ssize_t decode_hw_header (interface, buf, bufix, from)
struct interface_info *interface;
unsigned char *buf;
unsigned bufix;
struct hardware *from;
{
switch(interface->hw_address.hbuf[0]) {
#if defined (HAVE_TR_SUPPORT)
case HTYPE_IEEE802:
return (decode_tr_header(interface, buf, bufix, from));
#endif
#if defined (DEC_FDDI)
case HTYPE_FDDI:
return (decode_fddi_header(interface, buf, bufix, from));
#endif
case HTYPE_INFINIBAND:
log_error("Attempt to decode hw header for infiniband");
return (0);
case HTYPE_ETHER:
default:
return (decode_ethernet_header(interface, buf, bufix, from));
}
}
/* UDP header and IP header decoded together for convenience. */
ssize_t
decode_udp_ip_header(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;
unsigned char *upp, *endbuf;
u_int32_t ip_len, ulen, pkt_len;
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;
/* Designate the end of the input buffer for bounds checks. */
endbuf = buf + bufix + buflen;
/* Assure there is at least an IP header there. */
if ((buf + bufix + sizeof(ip)) > endbuf)
return -1;
/* Copy the IP header into a stack aligned structure for inspection.
* There may be bits in the IP header that we're not decoding, so we
* copy out the bits we grok and skip ahead by ip.ip_hl * 4.
*/
upp = buf + bufix;
memcpy(&ip, upp, sizeof(ip));
ip_len = (*upp & 0x0f) << 2;
upp += ip_len;
/* Check the IP packet length. */
pkt_len = ntohs(ip.ip_len);
if (pkt_len > buflen)
return -1;
/* Assure after ip_len bytes that there is enough room for a UDP header. */
if ((upp + sizeof(udp)) > endbuf)
return -1;
/* Copy the UDP header into a stack aligned structure for inspection. */
memcpy(&udp, upp, sizeof(udp));
#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))
return -1;
udp_packets_length_checked++;
if ((upp + ulen) > endbuf) {
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 = 0;
udp_packets_length_checked = 0;
}
return -1;
}
if ((ulen < sizeof(udp)) || ((upp + ulen) > endbuf))
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;
}
/* 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 = upp + sizeof(udp);
len = ulen - sizeof(udp);
usum = udp.uh_sum;
udp.uh_sum = 0;
/* XXX: We have to pass &udp, because we have to zero the checksum
* field before calculating the sum...'upp' isn't zeroed.
*/
sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
checksum(data, len,
checksum((unsigned char *)&ip.ip_src,
8, IPPROTO_UDP + 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);
/* Save the length of the UDP payload. */
if (rbuflen != NULL)
*rbuflen = len;
/* Return the index to the UDP payload. */
return ip_len + sizeof udp;
}
#endif /* PACKET_DECODING */
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