/* $OpenBSD: packet.c,v 1.7 2014/07/26 07:48:49 tobias Exp $ */ /* Packet assembly code, originally contributed by Archie Cobbs. */ /* * 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 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 "dhcpd.h" #include #include #include #include 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 hardware *to) { struct ether_header eh; if (to != NULL && to->hlen == 6) /* XXX */ memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost)); else memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost)); /* source address is filled in by the kernel */ memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost)); eh.ether_type = htons(ETHERTYPE_IP); memcpy(&buf[*bufix], &eh, ETHER_HDR_LEN); *bufix += ETHER_HDR_LEN; } void assemble_udp_ip_header(struct interface_info *interface, 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 = 16; 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 = server_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(struct interface_info *interface, unsigned char *buf, int bufix, struct hardware *from) { struct ether_header eh; memcpy(&eh, buf + bufix, ETHER_HDR_LEN); 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(struct interface_info *interface, unsigned char *buf, int bufix, struct sockaddr_in *from, int buflen) { struct ip *ip; struct udphdr *udp; unsigned char *data; 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; 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_bad_checksum != 0 && (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. */ data = buf + bufix + ip_len + sizeof(*udp); len = ntohs(udp->uh_ulen) - sizeof(*udp); udp_packets_length_checked++; if ((len < 0) || (len + data > buf + bufix + buflen)) { udp_packets_length_overflow++; if (udp_packets_length_checked > 4 && udp_packets_length_overflow != 0 && (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_bad_checksum != 0 && (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)); }