Annotation of embedaddon/dhcp/common/packet.c, revision 1.1
1.1 ! misho 1: /* packet.c
! 2:
! 3: Packet assembly code, originally contributed by Archie Cobbs. */
! 4:
! 5: /*
! 6: * Copyright (c) 2004,2005,2007,2009 by Internet Systems Consortium, Inc. ("ISC")
! 7: * Copyright (c) 1996-2003 by Internet Software Consortium
! 8: *
! 9: * Permission to use, copy, modify, and distribute this software for any
! 10: * purpose with or without fee is hereby granted, provided that the above
! 11: * copyright notice and this permission notice appear in all copies.
! 12: *
! 13: * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
! 14: * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
! 15: * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
! 16: * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
! 17: * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
! 18: * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
! 19: * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
! 20: *
! 21: * Internet Systems Consortium, Inc.
! 22: * 950 Charter Street
! 23: * Redwood City, CA 94063
! 24: * <info@isc.org>
! 25: * https://www.isc.org/
! 26: *
! 27: * This code was originally contributed by Archie Cobbs, and is still
! 28: * very similar to that contribution, although the packet checksum code
! 29: * has been hacked significantly with the help of quite a few ISC DHCP
! 30: * users, without whose gracious and thorough help the checksum code would
! 31: * still be disabled.
! 32: */
! 33:
! 34: #include "dhcpd.h"
! 35:
! 36: #if defined (PACKET_ASSEMBLY) || defined (PACKET_DECODING)
! 37: #include "includes/netinet/ip.h"
! 38: #include "includes/netinet/udp.h"
! 39: #include "includes/netinet/if_ether.h"
! 40: #endif /* PACKET_ASSEMBLY || PACKET_DECODING */
! 41:
! 42: /* Compute the easy part of the checksum on a range of bytes. */
! 43:
! 44: u_int32_t checksum (buf, nbytes, sum)
! 45: unsigned char *buf;
! 46: unsigned nbytes;
! 47: u_int32_t sum;
! 48: {
! 49: unsigned i;
! 50:
! 51: #ifdef DEBUG_CHECKSUM
! 52: log_debug ("checksum (%x %d %x)", buf, nbytes, sum);
! 53: #endif
! 54:
! 55: /* Checksum all the pairs of bytes first... */
! 56: for (i = 0; i < (nbytes & ~1U); i += 2) {
! 57: #ifdef DEBUG_CHECKSUM_VERBOSE
! 58: log_debug ("sum = %x", sum);
! 59: #endif
! 60: sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
! 61: /* Add carry. */
! 62: if (sum > 0xFFFF)
! 63: sum -= 0xFFFF;
! 64: }
! 65:
! 66: /* If there's a single byte left over, checksum it, too. Network
! 67: byte order is big-endian, so the remaining byte is the high byte. */
! 68: if (i < nbytes) {
! 69: #ifdef DEBUG_CHECKSUM_VERBOSE
! 70: log_debug ("sum = %x", sum);
! 71: #endif
! 72: sum += buf [i] << 8;
! 73: /* Add carry. */
! 74: if (sum > 0xFFFF)
! 75: sum -= 0xFFFF;
! 76: }
! 77:
! 78: return sum;
! 79: }
! 80:
! 81: /* Finish computing the checksum, and then put it into network byte order. */
! 82:
! 83: u_int32_t wrapsum (sum)
! 84: u_int32_t sum;
! 85: {
! 86: #ifdef DEBUG_CHECKSUM
! 87: log_debug ("wrapsum (%x)", sum);
! 88: #endif
! 89:
! 90: sum = ~sum & 0xFFFF;
! 91: #ifdef DEBUG_CHECKSUM_VERBOSE
! 92: log_debug ("sum = %x", sum);
! 93: #endif
! 94:
! 95: #ifdef DEBUG_CHECKSUM
! 96: log_debug ("wrapsum returns %x", htons (sum));
! 97: #endif
! 98: return htons(sum);
! 99: }
! 100:
! 101: #ifdef PACKET_ASSEMBLY
! 102: void assemble_hw_header (interface, buf, bufix, to)
! 103: struct interface_info *interface;
! 104: unsigned char *buf;
! 105: unsigned *bufix;
! 106: struct hardware *to;
! 107: {
! 108: #if defined (HAVE_TR_SUPPORT)
! 109: if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
! 110: assemble_tr_header (interface, buf, bufix, to);
! 111: else
! 112: #endif
! 113: #if defined (DEC_FDDI)
! 114: if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
! 115: assemble_fddi_header (interface, buf, bufix, to);
! 116: else
! 117: #endif
! 118: assemble_ethernet_header (interface, buf, bufix, to);
! 119:
! 120: }
! 121:
! 122: /* UDP header and IP header assembled together for convenience. */
! 123:
! 124: void assemble_udp_ip_header (interface, buf, bufix,
! 125: from, to, port, data, len)
! 126: struct interface_info *interface;
! 127: unsigned char *buf;
! 128: unsigned *bufix;
! 129: u_int32_t from;
! 130: u_int32_t to;
! 131: u_int32_t port;
! 132: unsigned char *data;
! 133: unsigned len;
! 134: {
! 135: struct ip ip;
! 136: struct udphdr udp;
! 137:
! 138: memset (&ip, 0, sizeof ip);
! 139:
! 140: /* Fill out the IP header */
! 141: IP_V_SET (&ip, 4);
! 142: IP_HL_SET (&ip, 20);
! 143: ip.ip_tos = IPTOS_LOWDELAY;
! 144: ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
! 145: ip.ip_id = 0;
! 146: ip.ip_off = 0;
! 147: ip.ip_ttl = 128;
! 148: ip.ip_p = IPPROTO_UDP;
! 149: ip.ip_sum = 0;
! 150: ip.ip_src.s_addr = from;
! 151: ip.ip_dst.s_addr = to;
! 152:
! 153: /* Checksum the IP header... */
! 154: ip.ip_sum = wrapsum (checksum ((unsigned char *)&ip, sizeof ip, 0));
! 155:
! 156: /* Copy the ip header into the buffer... */
! 157: memcpy (&buf [*bufix], &ip, sizeof ip);
! 158: *bufix += sizeof ip;
! 159:
! 160: /* Fill out the UDP header */
! 161: udp.uh_sport = local_port; /* XXX */
! 162: udp.uh_dport = port; /* XXX */
! 163: udp.uh_ulen = htons(sizeof(udp) + len);
! 164: memset (&udp.uh_sum, 0, sizeof udp.uh_sum);
! 165:
! 166: /* Compute UDP checksums, including the ``pseudo-header'', the UDP
! 167: header and the data. */
! 168:
! 169: udp.uh_sum =
! 170: wrapsum (checksum ((unsigned char *)&udp, sizeof udp,
! 171: checksum (data, len,
! 172: checksum ((unsigned char *)
! 173: &ip.ip_src,
! 174: 2 * sizeof ip.ip_src,
! 175: IPPROTO_UDP +
! 176: (u_int32_t)
! 177: ntohs (udp.uh_ulen)))));
! 178:
! 179: /* Copy the udp header into the buffer... */
! 180: memcpy (&buf [*bufix], &udp, sizeof udp);
! 181: *bufix += sizeof udp;
! 182: }
! 183: #endif /* PACKET_ASSEMBLY */
! 184:
! 185: #ifdef PACKET_DECODING
! 186: /* Decode a hardware header... */
! 187: /* XXX currently only supports ethernet; doesn't check for other types. */
! 188:
! 189: ssize_t decode_hw_header (interface, buf, bufix, from)
! 190: struct interface_info *interface;
! 191: unsigned char *buf;
! 192: unsigned bufix;
! 193: struct hardware *from;
! 194: {
! 195: #if defined (HAVE_TR_SUPPORT)
! 196: if (interface -> hw_address.hbuf [0] == HTYPE_IEEE802)
! 197: return decode_tr_header (interface, buf, bufix, from);
! 198: else
! 199: #endif
! 200: #if defined (DEC_FDDI)
! 201: if (interface -> hw_address.hbuf [0] == HTYPE_FDDI)
! 202: return decode_fddi_header (interface, buf, bufix, from);
! 203: else
! 204: #endif
! 205: return decode_ethernet_header (interface, buf, bufix, from);
! 206: }
! 207:
! 208: /* UDP header and IP header decoded together for convenience. */
! 209:
! 210: ssize_t
! 211: decode_udp_ip_header(struct interface_info *interface,
! 212: unsigned char *buf, unsigned bufix,
! 213: struct sockaddr_in *from, unsigned buflen,
! 214: unsigned *rbuflen)
! 215: {
! 216: unsigned char *data;
! 217: struct ip ip;
! 218: struct udphdr udp;
! 219: unsigned char *upp, *endbuf;
! 220: u_int32_t ip_len, ulen, pkt_len;
! 221: u_int32_t sum, usum;
! 222: static int ip_packets_seen;
! 223: static int ip_packets_bad_checksum;
! 224: static int udp_packets_seen;
! 225: static int udp_packets_bad_checksum;
! 226: static int udp_packets_length_checked;
! 227: static int udp_packets_length_overflow;
! 228: unsigned len;
! 229:
! 230: /* Designate the end of the input buffer for bounds checks. */
! 231: endbuf = buf + bufix + buflen;
! 232:
! 233: /* Assure there is at least an IP header there. */
! 234: if ((buf + bufix + sizeof(ip)) > endbuf)
! 235: return -1;
! 236:
! 237: /* Copy the IP header into a stack aligned structure for inspection.
! 238: * There may be bits in the IP header that we're not decoding, so we
! 239: * copy out the bits we grok and skip ahead by ip.ip_hl * 4.
! 240: */
! 241: upp = buf + bufix;
! 242: memcpy(&ip, upp, sizeof(ip));
! 243: ip_len = (*upp & 0x0f) << 2;
! 244: upp += ip_len;
! 245:
! 246: /* Check the IP packet length. */
! 247: pkt_len = ntohs(ip.ip_len);
! 248: if (pkt_len > buflen)
! 249: return -1;
! 250:
! 251: /* Assure after ip_len bytes that there is enough room for a UDP header. */
! 252: if ((upp + sizeof(udp)) > endbuf)
! 253: return -1;
! 254:
! 255: /* Copy the UDP header into a stack aligned structure for inspection. */
! 256: memcpy(&udp, upp, sizeof(udp));
! 257:
! 258: #ifdef USERLAND_FILTER
! 259: /* Is it a UDP packet? */
! 260: if (ip.ip_p != IPPROTO_UDP)
! 261: return -1;
! 262:
! 263: /* Is it to the port we're serving? */
! 264: if (udp.uh_dport != local_port)
! 265: return -1;
! 266: #endif /* USERLAND_FILTER */
! 267:
! 268: ulen = ntohs(udp.uh_ulen);
! 269: if (ulen < sizeof(udp))
! 270: return -1;
! 271:
! 272: udp_packets_length_checked++;
! 273: if ((upp + ulen) > endbuf) {
! 274: udp_packets_length_overflow++;
! 275: if ((udp_packets_length_checked > 4) &&
! 276: ((udp_packets_length_checked /
! 277: udp_packets_length_overflow) < 2)) {
! 278: log_info("%d udp packets in %d too long - dropped",
! 279: udp_packets_length_overflow,
! 280: udp_packets_length_checked);
! 281: udp_packets_length_overflow = 0;
! 282: udp_packets_length_checked = 0;
! 283: }
! 284: return -1;
! 285: }
! 286:
! 287: if ((ulen < sizeof(udp)) || ((upp + ulen) > endbuf))
! 288: return -1;
! 289:
! 290: /* Check the IP header checksum - it should be zero. */
! 291: ++ip_packets_seen;
! 292: if (wrapsum (checksum (buf + bufix, ip_len, 0))) {
! 293: ++ip_packets_bad_checksum;
! 294: if (ip_packets_seen > 4 &&
! 295: (ip_packets_seen / ip_packets_bad_checksum) < 2) {
! 296: log_info ("%d bad IP checksums seen in %d packets",
! 297: ip_packets_bad_checksum, ip_packets_seen);
! 298: ip_packets_seen = ip_packets_bad_checksum = 0;
! 299: }
! 300: return -1;
! 301: }
! 302:
! 303: /* Copy out the IP source address... */
! 304: memcpy(&from->sin_addr, &ip.ip_src, 4);
! 305:
! 306: /* Compute UDP checksums, including the ``pseudo-header'', the UDP
! 307: header and the data. If the UDP checksum field is zero, we're
! 308: not supposed to do a checksum. */
! 309:
! 310: data = upp + sizeof(udp);
! 311: len = ulen - sizeof(udp);
! 312:
! 313: usum = udp.uh_sum;
! 314: udp.uh_sum = 0;
! 315:
! 316: /* XXX: We have to pass &udp, because we have to zero the checksum
! 317: * field before calculating the sum...'upp' isn't zeroed.
! 318: */
! 319: sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
! 320: checksum(data, len,
! 321: checksum((unsigned char *)&ip.ip_src,
! 322: 8, IPPROTO_UDP + ulen))));
! 323:
! 324: udp_packets_seen++;
! 325: if (usum && usum != sum) {
! 326: udp_packets_bad_checksum++;
! 327: if (udp_packets_seen > 4 &&
! 328: (udp_packets_seen / udp_packets_bad_checksum) < 2) {
! 329: log_info ("%d bad udp checksums in %d packets",
! 330: udp_packets_bad_checksum, udp_packets_seen);
! 331: udp_packets_seen = udp_packets_bad_checksum = 0;
! 332: }
! 333: return -1;
! 334: }
! 335:
! 336: /* Copy out the port... */
! 337: memcpy (&from -> sin_port, &udp.uh_sport, sizeof udp.uh_sport);
! 338:
! 339: /* Save the length of the UDP payload. */
! 340: if (rbuflen != NULL)
! 341: *rbuflen = len;
! 342:
! 343: /* Return the index to the UDP payload. */
! 344: return ip_len + sizeof udp;
! 345: }
! 346: #endif /* PACKET_DECODING */
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