/* packet-null.c * Routines for null packet disassembly * * $Id: packet-null.c,v 1.63 2003/12/17 23:35:29 ulfl 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 "prefs.h" #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 - * stuff the AF_ value for the protocol, in *host* byte order, in the * first four bytes. (BSD drivers that use DLT_LOOP, such as recent * OpenBSD loopback drivers, stuff it in *network* byte order in the * first four bytes.) * * However, the IRIX and UNICOS/mp snoop socket mechanism supplies, * on loopback devices, a 4-byte header that has a 2 byte (big-endian) * AF_ value and 2 bytes of 0, so it's * * 0000AAAA * * when read on a little-endian machine and * * AAAA0000 * * when read on a big-endian machine. The current CVS version of libpcap * compensates for this by converting it to standard 4-byte format before * processing the packet, but snoop captures from IRIX or UNICOS/mp * have the 2-byte+2-byte header, as might tcpdump or libpcap captures * with older versions of libpcap. * * AF_ values are small integers, and probably fit in 8 bits (current * values on the BSDs do), and have their upper 24 bits zero. * This means that, in practice, if you look at the header as a 32-bit * integer in host byte order: * * on a little-endian machine: * * a little-endian DLT_NULL header looks like * * 000000AA * * a big-endian DLT_NULL header, or a DLT_LOOP header, looks * like * * AA000000 * * an IRIX or UNICOS/mp DLT_NULL header looks like * * 0000AA00 * * on a big-endian machine: * * a big-endian DLT_NULL header, or a DLT_LOOP header, looks * like * * 000000AA * * a little-endian DLT_NULL header looks like * * AA000000 * * an IRIX or UNICOS/mp DLT_NULL header looks like * * 00AA0000 * * 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 * * If we treat that as a 32-bit host-byte-order value, it looks like * * PPPP03FF * * where PPPP is a byte-swapped PPP protocol type if we read it on * a little-endian machine and * * FF03PPPP * * where PPPP is a PPP protocol type if we read it on a big-endian * machine. 0x0000 does not appear to be a valid PPP protocol type * value, so at least one of those hex digits is guaranteed not to * be 0. * * Old versions of libpcap for Linux used DLT_NULL for loopback devices, * but not any other devices. (Current versions use DLT_EN10MB for it.) * The Linux loopback driver puts an *Ethernet* header at the beginning * of loopback packets, with fake source and destination addresses and * the appropriate Ethernet type value; however, those older versions of * libpcap for Linux compensated 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 * * EEEE0000 * * where EEEE is a byte-swapped Ethernet type, and if we're reading it * on a big-endian machine, it looks like * * 0000EEEE * * where EEEE is an Ethernet type. * * If the first 2 bytes of the header are FF 03: * * it can't be a big-endian BSD DLT_NULL header, or a DLT_LOOP * header, as AF_ values are small so the first 2 bytes of the * header would be 0; * * it can't be a little-endian BSD DLT_NULL header, as the * resulting AF_ value would be >= 0x03FF, which is too big * for an AF_ value; * * it can't be an IRIX or UNICOS/mp DLT_NULL header, as the * resulting AF_ value with be 0x03FF. * * So the first thing we do is check the first two bytes of the * header; if it's FF 03, we treat the packet as a PPP frame. * * Otherwise, if the upper 16 bits are non-zero, either: * * it's a BSD DLT_NULL or DLT_LOOP header whose AF_ value * is not in our byte order; * * it's an IRIX or UNICOS/mp DLT_NULL header being read on * a big-endian machine; * * it's a Linux DLT_NULL header being read on a little-endian * machine. * * In all those cases except for the IRIX or UNICOS/mp DLT_NULL header, * we should byte-swap it (if it's a Linux DLT_NULL header, that'll * put the Ethernet type in the right byte order). In the case * of the IRIX or UNICOS/mp DLT_NULL header, we should just get * the upper 16 bits as an AF_ value. * * If it's a BSD DLT_NULL or DLT_LOOP header whose AF_ value is not * in our byte order, then the upper 2 hex digits would be non-zero * and the next 2 hex digits down would be zero, as AF_ values fit in * 8 bits, and the upper 2 hex digits are the *lower* 8 bits of the value. * * If it's an IRIX or UNICOS/mp DLT_NULL header, the upper 2 hex digits * would be zero and the next 2 hex digits down would be non-zero, as * the upper 16 bits are a big-endian AF_ value. Furthermore, the * next 2 hex digits down are likely to be < 0x60, as 0x60 is 96, * and, so far, we're far from requiring AF_ values that high. * * If it's a Linux DLT_NULL header, the third hex digit from the top * will be >= 6, as Ethernet types are >= 1536, or 0x0600, and * it's byte-swapped, so the second 2 hex digits from the top are * >= 0x60. * * So, if the upper 16 bits are non-zero: * * if the upper 2 hex digits are 0 and the next 2 hex digits are * in the range 0x00-0x5F, we treat it as a big-endian IRIX or * UNICOS/mp DLT_NULL header; * * otherwise, we byte-swap it and do the next stage. * * If the upper 16 bits are zero, either: * * it's a BSD DLT_NULLor DLT_LOOP header whose AF_ value is in * our byte order; * * it's an IRIX or UNICOS/mp DLT_NULL header being read on * a little-endian machine; * * it's a Linux DLT_NULL header being read on a big-endian * machine. * * In all of those cases except for the IRIX or UNICOS/mp DLT_NULL header, * we should *not* byte-swap it. In the case of the IRIX or UNICOS/mp * DLT_NULL header, we should extract the AF_ value and byte-swap it. * * If it's a BSD DLT_NULL or DLT_LOOP header whose AF_ value is * in our byte order, the upper 6 hex digits would all be zero. * * If it's an IRIX or UNICOS/mp DLT_NULL header, the upper 4 hex * digits would be zero and the next 2 hex digits would not be zero. * Furthermore, the third hex digit from the bottom would be < */ 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, (const char *)&pd[0], sizeof(null_header)); if ((null_header & 0xFFFF0000) != 0) { /* * It is possible that the AF_ type was only a 16 bit value. * IRIX and UNICOS/mp loopback snoop use a 4 byte header with * AF_ type in the first 2 bytes! * BSD AF_ types will always have the upper 8 bits as 0. */ if ((null_header & 0xFF000000) == 0 && (null_header & 0x00FF0000) < 0x00060000) { /* * Looks like a IRIX or UNICOS/mp loopback header, in the * correct byte order. Set the null header value to the * AF_ type, which is in the upper 16 bits of "null_header". */ null_header >>= 16; } else { /* Byte-swap it. */ null_header = BSWAP32(null_header); } } else { /* * Check for an IRIX or UNICOS/mp snoop header. */ if ((null_header & 0x000000FF) == 0 && (null_header & 0x0000FF00) < 0x00000600) { /* * Looks like a IRIX or UNICOS/mp loopback header, in the * wrong byte order. Set the null header value to the AF_ * type; that's in the lower 16 bits of "null_header", but * is byte-swapped. */ null_header = BSWAP16(null_header & 0xFFFF); } } /* * 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((guint16) 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) { /* * It is possible that the AF_ type was only a 16 bit value. * IRIX and UNICOS/mp loopback snoop use a 4 byte header with * AF_ type in the first 2 bytes! * BSD AF_ types will always have the upper 8 bits as 0. */ if ((null_header & 0xFF000000) == 0 && (null_header & 0x00FF0000) < 0x00060000) { /* * Looks like a IRIX or UNICOS/mp loopback header, in the * correct byte order. Set the null header value to the * AF_ type, which is in the upper 16 bits of "null_header". */ null_header >>= 16; } else { /* Byte-swap it. */ null_header = BSWAP32(null_header); } } else { /* * Check for an IRIX or UNICOS/mp snoop header. */ if ((null_header & 0x000000FF) == 0 && (null_header & 0x0000FF00) < 0x00000600) { /* * Looks like a IRIX or UNICOS/mp loopback header, in the * wrong byte order. Set the null header value to the AF_ * type; that's in the lower 16 bits of "null_header", but * is byte-swapped. */ null_header = BSWAP16(null_header & 0xFFFF); } } /* * 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((guint16) null_header, tvb, 4, pinfo, tree, fh_tree, hf_null_etype, -1, 0); } 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_DEC, 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); }