/* packet-null.c * Routines for null packet disassembly * * $Id: packet-null.c,v 1.55 2002/08/03 19:49:30 guy Exp $ * * Ethereal - Network traffic analyzer * By Gerald Combs * * This file created by Mike Hall * Copyright 1998 * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #ifdef HAVE_CONFIG_H # include "config.h" #endif #include #include #include #include "packet-null.h" #include #include "packet-ip.h" #include "packet-ipx.h" #include "packet-osi.h" #include "packet-ppp.h" #include "etypes.h" #include "aftypes.h" static dissector_table_t null_dissector_table; /* protocols and header fields */ static int proto_null = -1; static int hf_null_etype = -1; static int hf_null_family = -1; static gint ett_null = -1; /* Null/loopback structs and definitions */ /* Family values. */ static const value_string family_vals[] = { {BSD_AF_INET, "IP" }, {BSD_AF_ISO, "OSI" }, {BSD_AF_APPLETALK, "Appletalk" }, {BSD_AF_IPX, "Netware IPX/SPX"}, {BSD_AF_INET6_BSD, "IPv6" }, {BSD_AF_INET6_FREEBSD, "IPv6" }, {BSD_AF_INET6_DARWIN, "IPv6" }, {0, NULL } }; static dissector_handle_t ppp_hdlc_handle; static dissector_handle_t data_handle; void capture_null( const guchar *pd, int len, packet_counts *ld ) { guint32 null_header; /* * BSD drivers that use DLT_NULL - including the FreeBSD 3.2 ISDN-for-BSD * drivers, as well as the 4.4-Lite and FreeBSD loopback drivers - * appear to stuff the AF_ value for the protocol, in *host* byte * order, in the first four bytes. * * However, according to Gerald Combs, a FreeBSD ISDN PPP dump that * Andreas Klemm sent to ethereal-dev has a packet type of DLT_NULL, * and the family bits look like PPP's protocol field. (Was this an * older, or different, ISDN driver?) Looking at what appears to be * that capture file, it appears that it's using PPP in HDLC framing, * RFC 1549, wherein the first two octets of the frame are 0xFF * (address) and 0x03 (control), so the header bytes are, in order: * * 0xFF * 0x03 * high-order byte of a PPP protocol field * low-order byte of a PPP protocol field * * when reading it on a little-endian machine; that means it's * PPPP03FF, where PPPP is a byte-swapped PPP protocol field. * * "libpcap" for Linux uses DLT_NULL only for the loopback device. * The loopback driver in Linux 2.0.36, at least, puts an *Ethernet* * header at the beginning of loopback packets; however, "libpcap" * for Linux compensates for this by skipping the source and * destination MAC addresses, replacing them with 2 bytes of 0. * This means that if we're reading the capture on a little-endian * machine, the header, treated as a 32-bit integer, looks like * * EEEEEEEEEEEEEEEE0000000000000000 * * where "EEEEEEEEEEEEEEEE" is the Ethernet type, and if we're reading * it on a big-endian machine, it looks like * * 0000000000000000EEEEEEEEEEEEEEEE * * The Ethernet type might or might not be byte-swapped; I haven't * bothered thinking about that yet. * * AF_ values are (relatively) small integers, and shouldn't have their * upper 16 bits zero; Ethernet types have to fit in 16 bits and * thus must have their upper 16 bits zero. Therefore, if the upper * 16 bits of the field aren't zero, it's in the wrong byte order. * * Ethernet types are bigger than 1536, and AF_ values are smaller * than 1536, so we needn't worry about one being mistaken for * the other. (There may be a problem if the 16-bit Ethernet * type is byte-swapped as a 16-bit quantity, but if when treated * as a 32-bit quantity its upper 16 bits are zero, but I'll think * about that one later.) * * As for the PPP protocol field values: * * 0x0000 does not appear to be a valid PPP protocol field value, * so the upper 16 bits will be non-zero, and we'll byte swap it. * It'll then be * * 0xFF03PPPP * * where PPPP is a non-byte-swapped PPP protocol field; we'll * check for the upper 16 bits of the byte-swapped field being * non-zero and, if so, assume the lower 16 bits are a PPP * protocol field (AF_ and Ethernet protocol fields should leave * the upper 16 bits zero - unless somebody stuff something else * there; see below). * * So, to compensate for this mess, we: * * check if the first two octets are 0xFF and 0x03 and, if so, * treat it as a PPP frame; * * otherwise, byte-swap the value if its upper 16 bits aren't zero, * and compare the lower 16 bits of the value against Ethernet * and AF_ types. * * If, as implied by an earlier version of the "e_nullhdr" structure, * the family is only 16 bits, and there are "next" and "len" fields * before it, that all goes completely to hell. (Note that, for * the BSD header, we could byte-swap it if the capture was written * on a machine with the opposite byte-order to ours - the "libpcap" * header lets us determine that - but it's more of a mess for Linux, * given that the effect of inserting the two 0 bytes depends only * on the byte order of the machine reading the file.) */ if (!BYTES_ARE_IN_FRAME(0, len, 2)) { ld->other++; return; } if (pd[0] == 0xFF && pd[1] == 0x03) { /* * Hand it to PPP. */ capture_ppp_hdlc(pd, 0, len, ld); } else { /* * Treat it as a normal DLT_NULL header. */ if (!BYTES_ARE_IN_FRAME(0, len, (int)sizeof(null_header))) { ld->other++; return; } memcpy((char *)&null_header, (char *)&pd[0], sizeof(null_header)); if ((null_header & 0xFFFF0000) != 0) { /* Byte-swap it. */ null_header = BSWAP32(null_header); } /* * The null header value must be greater than the IEEE 802.3 maximum * frame length to be a valid Ethernet type; if it is, hand it * to "ethertype()", otherwise treat it as a BSD AF_type (we wire * in the values of the BSD AF_ types, because the values * in the file will be BSD values, and the OS on which * we're building this might not have the same values or * might not have them defined at all; XXX - what if different * BSD derivatives have different values?). */ if (null_header > IEEE_802_3_MAX_LEN) capture_ethertype(null_header, pd, 4, len, ld); else { switch (null_header) { case BSD_AF_INET: capture_ip(pd, 4, len, ld); break; default: ld->other++; break; } } } } static void dissect_null(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree) { guint32 null_header; proto_tree *fh_tree; proto_item *ti; tvbuff_t *next_tvb; /* * See comment in "capture_null()" for an explanation of what we're * doing. */ if (tvb_get_ntohs(tvb, 0) == 0xFF03) { /* * Hand it to PPP. */ call_dissector(ppp_hdlc_handle, tvb, pinfo, tree); } else { /* load the top pane info. This should be overwritten by the next protocol in the stack */ if(check_col(pinfo->cinfo, COL_RES_DL_SRC)) col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "N/A" ); if(check_col(pinfo->cinfo, COL_RES_DL_DST)) col_set_str(pinfo->cinfo, COL_RES_DL_DST, "N/A" ); if(check_col(pinfo->cinfo, COL_PROTOCOL)) col_set_str(pinfo->cinfo, COL_PROTOCOL, "N/A" ); if(check_col(pinfo->cinfo, COL_INFO)) col_set_str(pinfo->cinfo, COL_INFO, "Null/Loopback" ); /* * Treat it as a normal DLT_NULL header. */ tvb_memcpy(tvb, (guint8 *)&null_header, 0, sizeof(null_header)); if ((null_header & 0xFFFF0000) != 0) { /* Byte-swap it. */ null_header = BSWAP32(null_header); } /* * The null header value must be greater than the IEEE 802.3 maximum * frame length to be a valid Ethernet type; if it is, hand it * to "ethertype()", otherwise treat it as a BSD AF_type (we wire * in the values of the BSD AF_ types, because the values * in the file will be BSD values, and the OS on which * we're building this might not have the same values or * might not have them defined at all; XXX - what if different * BSD derivatives have different values?). */ if (null_header > IEEE_802_3_MAX_LEN) { if (tree) { ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, FALSE); fh_tree = proto_item_add_subtree(ti, ett_null); } else fh_tree = NULL; ethertype(null_header, tvb, 4, pinfo, tree, fh_tree, hf_null_etype, -1); } else { /* populate a tree in the second pane with the status of the link layer (ie none) */ if (tree) { ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, FALSE); fh_tree = proto_item_add_subtree(ti, ett_null); proto_tree_add_uint(fh_tree, hf_null_family, tvb, 0, 4, null_header); } next_tvb = tvb_new_subset(tvb, 4, -1, -1); if (!dissector_try_port(null_dissector_table, null_header, next_tvb, pinfo, tree)) { /* No sub-dissector found. Label rest of packet as "Data" */ call_dissector(data_handle,next_tvb, pinfo, tree); } } } } void proto_register_null(void) { static hf_register_info hf[] = { /* registered here but handled in ethertype.c */ { &hf_null_etype, { "Type", "null.type", FT_UINT16, BASE_HEX, VALS(etype_vals), 0x0, "", HFILL }}, { &hf_null_family, { "Family", "null.family", FT_UINT32, BASE_HEX, VALS(family_vals), 0x0, "", HFILL }} }; static gint *ett[] = { &ett_null, }; proto_null = proto_register_protocol("Null/Loopback", "Null", "null"); proto_register_field_array(proto_null, hf, array_length(hf)); proto_register_subtree_array(ett, array_length(ett)); /* subdissector code */ null_dissector_table = register_dissector_table("null.type", "BSD AF_ type", FT_UINT32, BASE_DEC); } void proto_reg_handoff_null(void) { dissector_handle_t null_handle; /* * Get a handle for the PPP-in-HDLC-like-framing dissector. */ ppp_hdlc_handle = find_dissector("ppp_hdlc"); data_handle = find_dissector("data"); null_handle = create_dissector_handle(dissect_null, proto_null); dissector_add("wtap_encap", WTAP_ENCAP_NULL, null_handle); }