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wireshark/epan/dissectors/packet-null.c

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/* packet-null.c
* Routines for null packet disassembly
*
* Wireshark - Network traffic analyzer
* By Gerald Combs <gerald@wireshark.org>
*
* This file created by Mike Hall <mlh@io.com>
* 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "config.h"
#include <wsutil/pint.h>
#include <epan/packet.h>
#include <epan/capture_dissectors.h>
#include "packet-ip.h"
#include "packet-ppp.h"
#include <epan/etypes.h>
#include <epan/aftypes.h>
#include <wiretap/wtap.h>
void proto_register_null(void);
void proto_reg_handoff_null(void);
static dissector_table_t null_dissector_table;
static dissector_table_t ethertype_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 capture_dissector_handle_t ppp_hdlc_cap_handle;
static gboolean
capture_null( const guchar *pd, int offset _U_, int len, capture_packet_info_t *cpinfo, const union wtap_pseudo_header *pseudo_header _U_ )
{
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.
*
* 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 wireshark-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 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 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_NULL 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 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))
return FALSE;
if (pd[0] == 0xFF && pd[1] == 0x03) {
/*
* Hand it to PPP.
*/
return call_capture_dissector(ppp_hdlc_cap_handle, pd, 0, len, cpinfo, pseudo_header);
} else {
/*
* Treat it as a normal DLT_NULL header.
*/
if (!BYTES_ARE_IN_FRAME(0, len, (int)sizeof(null_header)))
return FALSE;
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 = GUINT32_SWAP_LE_BE(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 = GUINT16_SWAP_LE_BE(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 "capture_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)
return try_capture_dissector("ethertype", null_header, pd, 4, len, cpinfo, pseudo_header);
else
return try_capture_dissector("null.bsd", null_header, pd, 4, len, cpinfo, pseudo_header);
}
return FALSE;
}
static int
dissect_null(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
{
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 */
col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "N/A");
col_set_str(pinfo->cinfo, COL_RES_DL_DST, "N/A");
col_set_str(pinfo->cinfo, COL_PROTOCOL, "N/A");
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 = GUINT32_SWAP_LE_BE(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 = GUINT16_SWAP_LE_BE(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, dissect it
* as one, 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, ENC_NA);
fh_tree = proto_item_add_subtree(ti, ett_null);
proto_tree_add_uint(fh_tree, hf_null_etype, tvb, 0, 4,
(guint16) null_header);
}
next_tvb = tvb_new_subset_remaining(tvb, 4);
if (!dissector_try_uint(ethertype_dissector_table,
(guint16) null_header, next_tvb, pinfo, tree))
call_data_dissector(next_tvb, pinfo, tree);
} 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, ENC_NA);
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_remaining(tvb, 4);
if (!dissector_try_uint(null_dissector_table, null_header,
next_tvb, pinfo, tree)) {
/* No sub-dissector found. Label rest of packet as "Data" */
call_data_dissector(next_tvb, pinfo, tree);
}
}
}
return tvb_captured_length(tvb);
}
/*
* OpenBSD DLT_LOOP; like DLT_NULL, but with the first 4 byte *always*
* being a *big-endian* type.
*/
static int
dissect_loop(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
{
guint32 loop_family;
proto_tree *fh_tree;
proto_item *ti;
tvbuff_t *next_tvb;
/* load the top pane info. This should be overwritten by
the next protocol in the stack */
col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "N/A");
col_set_str(pinfo->cinfo, COL_RES_DL_DST, "N/A");
col_set_str(pinfo->cinfo, COL_PROTOCOL, "N/A");
col_set_str(pinfo->cinfo, COL_INFO, "Null/Loopback");
/* populate a tree in the second pane with the status of the link
layer (ie none) */
loop_family = tvb_get_ntohl(tvb, 0);
if (tree) {
ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, ENC_NA);
fh_tree = proto_item_add_subtree(ti, ett_null);
proto_tree_add_uint(fh_tree, hf_null_family, tvb, 0, 4, loop_family);
}
next_tvb = tvb_new_subset_remaining(tvb, 4);
if (!dissector_try_uint(null_dissector_table, loop_family,
next_tvb, pinfo, tree)) {
/* No sub-dissector found. Label rest of packet as "Data" */
call_data_dissector(next_tvb, pinfo, tree);
}
return tvb_captured_length(tvb);
}
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,
NULL, HFILL }},
{ &hf_null_family,
{ "Family", "null.family", FT_UINT32, BASE_DEC, VALS(family_vals), 0x0,
NULL, 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",
"Null type", proto_null, FT_UINT32, BASE_DEC);
register_capture_dissector_table("null.bsd", "Null/Loopback BSD AF");
}
void
proto_reg_handoff_null(void)
{
dissector_handle_t null_handle, loop_handle;
capture_dissector_handle_t null_cap_handle;
/*
* Get a handle for the PPP-in-HDLC-like-framing dissector and
* the "I don't know what this is" dissector.
*/
ppp_hdlc_handle = find_dissector_add_dependency("ppp_hdlc", proto_null);
ethertype_dissector_table = find_dissector_table("ethertype");
null_handle = create_dissector_handle(dissect_null, proto_null);
dissector_add_uint("wtap_encap", WTAP_ENCAP_NULL, null_handle);
loop_handle = create_dissector_handle(dissect_loop, proto_null);
dissector_add_uint("wtap_encap", WTAP_ENCAP_LOOP, loop_handle);
null_cap_handle = create_capture_dissector_handle(capture_null, proto_null);
capture_dissector_add_uint("wtap_encap", WTAP_ENCAP_NULL, null_cap_handle);
capture_dissector_add_uint("wtap_encap", WTAP_ENCAP_LOOP, null_cap_handle);
ppp_hdlc_cap_handle = find_capture_dissector("ppp_hdlc");
}
/*
* Editor modelines
*
* Local Variables:
* c-basic-offset: 2
* tab-width: 8
* indent-tabs-mode: nil
* End:
*
* ex: set shiftwidth=2 tabstop=8 expandtab:
* :indentSize=2:tabSize=8:noTabs=true:
*/
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