freebsd-dev/sbin/dhclient/packet.c
Pedro F. Giffuni 8a16b7a18f General further adoption of SPDX licensing ID tags.
Mainly focus on files that use BSD 3-Clause license.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.
2017-11-20 19:49:47 +00:00

251 lines
7.4 KiB
C

/* $OpenBSD: packet.c,v 1.9 2004/05/04 18:58:50 deraadt Exp $ */
/* Packet assembly code, originally contributed by Archie Cobbs. */
/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 1995, 1996, 1999 The Internet Software Consortium.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of The Internet Software Consortium nor the names
* of its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
* CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* This software has been written for the Internet Software Consortium
* by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
* Enterprises. To learn more about the Internet Software Consortium,
* see ``http://www.vix.com/isc''. To learn more about Vixie
* Enterprises, see ``http://www.vix.com''.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "dhcpd.h"
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netinet/if_ether.h>
#define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t))
u_int32_t checksum(unsigned char *, unsigned, u_int32_t);
u_int32_t wrapsum(u_int32_t);
u_int32_t
checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum)
{
int i;
/* Checksum all the pairs of bytes first... */
for (i = 0; i < (nbytes & ~1U); i += 2) {
sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
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) {
sum += buf[i] << 8;
if (sum > 0xFFFF)
sum -= 0xFFFF;
}
return (sum);
}
u_int32_t
wrapsum(u_int32_t sum)
{
sum = ~sum & 0xFFFF;
return (htons(sum));
}
void
assemble_hw_header(struct interface_info *interface, unsigned char *buf,
int *bufix)
{
struct ether_header eh;
memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost));
if (interface->hw_address.hlen == sizeof(eh.ether_shost))
memcpy(eh.ether_shost, interface->hw_address.haddr,
sizeof(eh.ether_shost));
else
memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost));
eh.ether_type = htons(ETHERTYPE_IP);
memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE);
*bufix += ETHER_HEADER_SIZE;
}
void
assemble_udp_ip_header(unsigned char *buf, int *bufix, u_int32_t from,
u_int32_t to, unsigned int port, unsigned char *data, int len)
{
struct ip ip;
struct udphdr udp;
ip.ip_v = 4;
ip.ip_hl = 5;
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;
ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0));
memcpy(&buf[*bufix], &ip, sizeof(ip));
*bufix += sizeof(ip);
udp.uh_sport = htons(LOCAL_PORT); /* XXX */
udp.uh_dport = port; /* XXX */
udp.uh_ulen = htons(sizeof(udp) + len);
memset(&udp.uh_sum, 0, sizeof(udp.uh_sum));
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)))));
memcpy(&buf[*bufix], &udp, sizeof(udp));
*bufix += sizeof(udp);
}
ssize_t
decode_hw_header(unsigned char *buf, int bufix, struct hardware *from)
{
struct ether_header eh;
memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE);
memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost));
from->htype = ARPHRD_ETHER;
from->hlen = sizeof(eh.ether_shost);
return (sizeof(eh));
}
ssize_t
decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from,
unsigned char *data, int buflen)
{
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;
int len = 0;
ip = (struct ip *)(buf + bufix);
udp = (struct udphdr *)(buf + bufix + ip_len);
/* Check the IP header checksum - it should be zero. */
ip_packets_seen++;
if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) {
ip_packets_bad_checksum++;
if (ip_packets_seen > 4 &&
(ip_packets_seen / ip_packets_bad_checksum) < 2) {
note("%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);
}
if (ntohs(ip->ip_len) != buflen)
debug("ip length %d disagrees with bytes received %d.",
ntohs(ip->ip_len), buflen);
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.
*/
if (!data) {
data = buf + bufix + ip_len + sizeof(*udp);
len = ntohs(udp->uh_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) {
note("%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)
debug("accepting packet with data after udp payload.");
}
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)ntohs(udp->uh_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) {
note("%d bad udp checksums in %d packets",
udp_packets_bad_checksum, udp_packets_seen);
udp_packets_seen = udp_packets_bad_checksum = 0;
}
return (-1);
}
memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport));
return (ip_len + sizeof(*udp));
}