path: root/epan/dissectors/packet-ax25-kiss.c

/* packet-ax25-kiss.c
 *
 * Routines for AX.25 KISS protocol dissection
 * Copyright 2010,2012 R.W. Stearn <richard@rns-stearn.demon.co.uk>
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

/*
 * This dissector handles the "KISS" protocol as implemented by the
 * Linux kernel.
 *
 * The original definition of the KISS protocol can be found here:
 *   http://www.ka9q.net/papers/kiss.html
 * and here:
 *   http://www.ax25.net/kiss.aspx
 *
 * The Linux implementation does not appear to attempt to implement that
 * protocol in full. It does provide the ability to send a KISS command via
 * ax25_kiss_cmd() and internally will send FULLDUPLEX KISS commands if
 * DAMA is enabled/disabled.
 * i.e.:
 *      ax25_dev_dama_on  sends FullDuplex ON
 *      ax25_dev_dama_off sends FullDuplex OFF
 *
 * Data frames are prefixed with a "Data Frame" command but the port appears to
 * be always 0.
 *
 * Abstract from http://www.ka9q.net/papers/kiss.html
 * --------------------------------------------------
 * For reference the first byte of a KISS frame is the frame type and the TNC
 * port number,
 *   LSB 4 bits = frame type,
 *   MSB 4 bits = port number.
 *
 * The frame types are:
 * Command        Function         Comments
 *    0           Data frame       The  rest  of the frame is data to
 *                                 be sent on the HDLC channel.
 *
 *    1           TXDELAY          The next  byte  is  the  transmitter
 *                                 keyup  delay  in  10 ms units.
 *                                 The default start-up value is 50
 *                                 (i.e., 500 ms).
 *
 *    2           P                The next byte  is  the  persistence
 *                                 parameter,  p, scaled to the range
 *                                 0 - 255 with the following
 *                                 formula:
 *
 *                                          P = p * 256 - 1
 *
 *                                 The  default  value  is  P  =  63
 *                                 (i.e.,  p  =  0.25).
 *
 *    3           SlotTime         The next byte is the slot interval
 *                                 in 10 ms units.
 *                                 The default is 10 (i.e., 100ms).
 *
 *    4           TXtail           The next byte is the time to hold
 *                                 up the TX after the FCS has been
 *                                 sent, in 10 ms units.  This command
 *                                 is obsolete, and is included  here
 *                                 only for  compatibility  with  some
 *                                 existing  implementations.
 *
 *    5          FullDuplex        The next byte is 0 for half duplex,
 *                                 nonzero  for full  duplex.
 *                                 The  default  is  0
 *                                 (i.e.,  half  duplex).
 *
 *    6          SetHardware       Specific for each TNC.  In the
 *                                 TNC-1, this command  sets  the
 *                                 modem speed.  Other implementations
 *                                 may use this function  for   other
 *                                 hardware-specific   functions.
 *
 *    FF         Return            Exit KISS and return control to a
 *                                 higher-level program. This is useful
 *                                 only when KISS is  incorporated
 *                                 into the TNC along with other
 *                                 applications.
 *
 *
 * G8BPQ extensions:
 *
 *    12          Data frame       Data with acknowledge request
 *
 *    14          Poll mode        Set poll mode
 *
 *   Checksum mode
 *
*/

#include "config.h"

#include <epan/packet.h>
#include <epan/capture_dissectors.h>
#include <epan/prefs.h>

#define STRLEN	80

#define KISS_HEADER_SIZE	 1 /* length of the KISS type header */

/* KISS frame types */
#define KISS_DATA_FRAME		 0
#define KISS_TXDELAY		 1
#define KISS_PERSISTENCE	 2
#define KISS_SLOT_TIME		 3
#define KISS_TXTAIL		 4
#define KISS_FULLDUPLEX		 5
#define KISS_SETHARDWARE	 6
#define KISS_DATA_FRAME_ACK	12
#define KISS_POLL_MODE		14
#define KISS_RETURN		15

#define KISS_CMD_MASK           0x0f
#define KISS_PORT_MASK          0xf0

/* Global preferences */
static bool gPREF_CKSUM_MODE;

void proto_register_ax25_kiss(void);
void proto_reg_handoff_ax25_kiss(void);

/* Initialize the protocol and registered fields */
static int proto_ax25_kiss;

static int hf_ax25_kiss_cmd;
static int hf_ax25_kiss_port;
static int hf_ax25_kiss_txdelay;
static int hf_ax25_kiss_persistence;
static int hf_ax25_kiss_slottime;
static int hf_ax25_kiss_txtail;
static int hf_ax25_kiss_fullduplex;
static int hf_ax25_kiss_sethardware;
static int hf_ax25_kiss_data_ack;
static int hf_ax25_kiss_cksum;


/* Initialize the subtree pointers */
static int ett_ax25_kiss;

static dissector_handle_t kiss_handle;

static capture_dissector_handle_t ax25_cap_handle;

/* Dissector handles - all the possibles are listed */
static dissector_handle_t ax25_handle;

static const value_string kiss_frame_types[] = {
	{ KISS_DATA_FRAME, 	"Data frame" },
	{ KISS_TXDELAY,    	"Tx delay" },
	{ KISS_PERSISTENCE,	"Persistence" },
	{ KISS_SLOT_TIME,  	"Slot time" },
	{ KISS_TXTAIL,     	"Tx tail" },
	{ KISS_FULLDUPLEX, 	"Full duplex" },
	{ KISS_SETHARDWARE,	"Set hardware" },
	{ KISS_DATA_FRAME_ACK,	"Data frame ack" },
	{ KISS_POLL_MODE,	"Poll mode" },
	{ KISS_RETURN,     	"Return" },
	{ 0, NULL }
};

static bool
capture_ax25_kiss( const unsigned char *pd, int offset, int len, capture_packet_info_t *cpinfo, const union wtap_pseudo_header *pseudo_header)
{
	int    l_offset;
	uint8_t kiss_cmd;

	if ( ! BYTES_ARE_IN_FRAME( offset, len, KISS_HEADER_SIZE ) )
		return false;

	l_offset  = offset;
	kiss_cmd  = pd[ l_offset ];
	l_offset += KISS_HEADER_SIZE; /* step over kiss header */
	switch ( kiss_cmd & KISS_CMD_MASK )
	{
		case KISS_DATA_FRAME	:
			return call_capture_dissector( ax25_cap_handle, pd, l_offset, len, cpinfo, pseudo_header );
		case KISS_TXDELAY	: break;
		case KISS_PERSISTENCE	: break;
		case KISS_SLOT_TIME	: break;
		case KISS_TXTAIL	: break;
		case KISS_FULLDUPLEX	: break;
		case KISS_SETHARDWARE	: break;
		case KISS_DATA_FRAME_ACK:
			l_offset += 2;
			return call_capture_dissector( ax25_cap_handle, pd, l_offset, len, cpinfo, pseudo_header );
		case KISS_POLL_MODE	: break;
		case KISS_RETURN	: break;
		default			: break;
	}
	return false;
}

/* Code to actually dissect the packets */
static int
dissect_ax25_kiss( tvbuff_t *tvb, packet_info *pinfo, proto_tree *parent_tree, void* data _U_ )
{
	proto_item *ti;
	proto_tree *kiss_tree;
	int         offset;
	int         kiss_cmd;
	int         kiss_type;
	int         kiss_port;
	int         kiss_param;
	int         kiss_param_len;
	int         kiss_cksum;
	int         kiss_cksum_index;
	int         kiss_tvb_length;
	const char *frame_type_text;
	char       *info_buffer;
	tvbuff_t   *next_tvb = NULL;

	info_buffer    = (char *)wmem_alloc( pinfo->pool, STRLEN );
	info_buffer[0] = '\0';

	col_set_str( pinfo->cinfo, COL_PROTOCOL, "AX.25 KISS" );
	col_clear( pinfo->cinfo, COL_INFO );

	/* protocol offset for the KISS header */
	offset = 0;

	kiss_cmd   = tvb_get_uint8( tvb, offset ) & 0xff;
	kiss_type  = kiss_cmd & KISS_CMD_MASK;
	kiss_port  = (kiss_cmd & KISS_PORT_MASK) >> 4;
	offset    += KISS_HEADER_SIZE;

	kiss_param      = 0;
	kiss_param_len  = 0;
	switch ( kiss_type )
		{
		case KISS_TXDELAY	: kiss_param_len = 1; kiss_param = tvb_get_uint8( tvb, offset ) & 0xff; break;
		case KISS_PERSISTENCE	: kiss_param_len = 1; kiss_param = tvb_get_uint8( tvb, offset ) & 0xff; break;
		case KISS_SLOT_TIME	: kiss_param_len = 1; kiss_param = tvb_get_uint8( tvb, offset ) & 0xff; break;
		case KISS_TXTAIL	: kiss_param_len = 1; kiss_param = tvb_get_uint8( tvb, offset ) & 0xff; break;
		case KISS_FULLDUPLEX	: kiss_param_len = 1; kiss_param = tvb_get_uint8( tvb, offset ) & 0xff; break;
		case KISS_SETHARDWARE	:
					kiss_param_len = tvb_captured_length_remaining( tvb, offset );
					if ( kiss_param_len < 0 )
						kiss_param_len = 0;
					if ( (kiss_param_len > 0) && gPREF_CKSUM_MODE )
						kiss_param_len--;
					break;
		case KISS_DATA_FRAME_ACK: kiss_param_len = 2; kiss_param = tvb_get_uint8( tvb, offset ) & 0xff; break;
		default			: break;
		}
	frame_type_text = val_to_str(kiss_type, kiss_frame_types, "Unknown (%u)");
	snprintf( info_buffer, STRLEN, "%s, Port %u", frame_type_text, kiss_port );
	if ( kiss_param_len > 0 )
		snprintf( info_buffer, STRLEN, "%s %u, Port %u", frame_type_text, kiss_param, kiss_port );

	offset += kiss_param_len;

	col_add_str( pinfo->cinfo, COL_INFO, info_buffer );

	if ( parent_tree )
		{
		/* protocol offset for the KISS header */
		offset = 0;

		/* create display subtree for the protocol */
		ti = proto_tree_add_protocol_format( parent_tree, proto_ax25_kiss, tvb, offset,
			tvb_captured_length_remaining( tvb, offset ),
			"KISS: %s",
			info_buffer
			);

		kiss_tree = proto_item_add_subtree( ti, ett_ax25_kiss );

		proto_tree_add_uint( kiss_tree, hf_ax25_kiss_cmd,  tvb, offset, KISS_HEADER_SIZE,
					kiss_cmd );
		proto_tree_add_uint( kiss_tree, hf_ax25_kiss_port, tvb, offset, KISS_HEADER_SIZE,
					kiss_port );
		offset += KISS_HEADER_SIZE;

		switch ( kiss_type  )
			{
			case KISS_DATA_FRAME	: break;
			case KISS_TXDELAY	:
						proto_tree_add_uint( kiss_tree, hf_ax25_kiss_txdelay,
							tvb, offset, kiss_param_len, kiss_param );
						offset += kiss_param_len;
						break;
			case KISS_PERSISTENCE	:
						proto_tree_add_uint( kiss_tree, hf_ax25_kiss_persistence,
							tvb, offset, kiss_param_len, kiss_param );
						offset += kiss_param_len;
						break;
			case KISS_SLOT_TIME	:
						proto_tree_add_uint( kiss_tree, hf_ax25_kiss_slottime,
							tvb, offset, kiss_param_len, kiss_param );
						offset += kiss_param_len;
						break;
			case KISS_TXTAIL	:
						proto_tree_add_uint( kiss_tree, hf_ax25_kiss_txtail,
							tvb, offset, kiss_param_len, kiss_param );
						offset += kiss_param_len;
						break;
			case KISS_FULLDUPLEX	:
						proto_tree_add_uint( kiss_tree, hf_ax25_kiss_fullduplex,
							tvb, offset, kiss_param_len, kiss_param );
						offset += kiss_param_len;
						break;
			case KISS_SETHARDWARE	:
						proto_tree_add_item( kiss_tree, hf_ax25_kiss_sethardware,
							tvb, offset, kiss_param_len, ENC_NA );
						offset += kiss_param_len;
						break;
			case KISS_DATA_FRAME_ACK:
						proto_tree_add_uint( kiss_tree, hf_ax25_kiss_data_ack,
							tvb, offset, kiss_param_len, kiss_param );
						offset += kiss_param_len;
						break;
			case KISS_POLL_MODE	: break;
			case KISS_RETURN	: break;
			default			: break;
			}

		if ( gPREF_CKSUM_MODE )
		{
			kiss_cksum = 0;
			kiss_tvb_length = tvb_captured_length(tvb) - 1;
			if ( kiss_tvb_length > 0 )
			{
				for ( kiss_cksum_index = 0; kiss_cksum_index < kiss_tvb_length; kiss_cksum_index++ )
					kiss_cksum ^= (tvb_get_uint8( tvb, kiss_cksum_index ) & 0xff);

				proto_tree_add_checksum(kiss_tree, tvb, 0, hf_ax25_kiss_cksum, -1, NULL, pinfo, kiss_cksum, ENC_NA, PROTO_CHECKSUM_GENERATED);
			}
		}
	}

	/* Call sub-dissectors here */

	if ( ( kiss_type == KISS_DATA_FRAME ) || ( kiss_type == KISS_DATA_FRAME_ACK ) )
		{
		next_tvb = tvb_new_subset_remaining( tvb, offset );
		call_dissector( ax25_handle, next_tvb, pinfo, parent_tree );
		}

	return tvb_captured_length(tvb);
}

void
proto_register_ax25_kiss(void)
{
	module_t *ax25_kiss_module;

	/* Setup list of header fields */
	static hf_register_info hf[] = {
		{ &hf_ax25_kiss_cmd,
			{ "Cmd",			"ax25_kiss.cmd",
			FT_UINT8, BASE_DEC, VALS(kiss_frame_types), KISS_CMD_MASK,
			NULL, HFILL }
		},
		{ &hf_ax25_kiss_port,
			{ "Port",			"ax25_kiss.port",
			FT_UINT8, BASE_DEC, NULL, KISS_PORT_MASK,
			NULL, HFILL }
		},
		{ &hf_ax25_kiss_txdelay,
			{ "Tx delay",			"ax25_kiss.txdelay",
			FT_UINT8, BASE_DEC, NULL, 0x0,
			NULL, HFILL }
		},
		{ &hf_ax25_kiss_persistence,
			{ "Persistence",		"ax25_kiss.persistence",
			FT_UINT8, BASE_DEC, NULL, 0x0,
			NULL, HFILL }
		},
		{ &hf_ax25_kiss_slottime,
			{ "Slot time",			"ax25_kiss.slottime",
			FT_UINT8, BASE_DEC, NULL, 0x0,
			NULL, HFILL }
		},
		{ &hf_ax25_kiss_txtail,
			{ "Tx tail",			"ax25_kiss.txtail",
			FT_UINT8, BASE_DEC, NULL, 0x0,
			NULL, HFILL }
		},
		{ &hf_ax25_kiss_fullduplex,
			{ "Full duplex",		"ax25_kiss.fullduplex",
			FT_UINT8, BASE_DEC, NULL, 0x0,
			NULL, HFILL }
		},
		{ &hf_ax25_kiss_sethardware,
			{ "Set hardware",		"ax25_kiss.sethardware",
			FT_BYTES, BASE_NONE, NULL, 0x0,
			NULL, HFILL }
		},
		{ &hf_ax25_kiss_data_ack,
			{ "Data ack",		"ax25_kiss.data_ack",
			FT_UINT16, BASE_DEC, NULL, 0x0,
			NULL, HFILL }
		},
		{ &hf_ax25_kiss_cksum,
			{ "Checksum",		"ax25_kiss.cksum",
			FT_UINT16, BASE_HEX, NULL, 0x0,
			NULL, HFILL }
		},
	};

	/* Setup protocol subtree array */
	static int *ett[] = {
		&ett_ax25_kiss,
	};

	/* Register the protocol name and description */
	proto_ax25_kiss = proto_register_protocol( "AX.25 KISS", "AX.25 KISS", "ax25_kiss" );

	/* Register the dissector */
	kiss_handle = register_dissector( "ax25_kiss", dissect_ax25_kiss, proto_ax25_kiss );

	/* Required function calls to register the header fields and subtrees used */
	proto_register_field_array( proto_ax25_kiss, hf, array_length( hf ) );
	proto_register_subtree_array( ett, array_length( ett ) );

	/* Register preferences module */
	ax25_kiss_module = prefs_register_protocol( proto_ax25_kiss, NULL);

	prefs_register_bool_preference(ax25_kiss_module, "showcksum",
	     "Set checksum mode",
	     "Enable checksum calculation.",
	     &gPREF_CKSUM_MODE );

}

void
proto_reg_handoff_ax25_kiss(void)
{
	capture_dissector_handle_t ax25_kiss_cap_handle;

	dissector_add_uint( "wtap_encap", WTAP_ENCAP_AX25_KISS, kiss_handle );
	ax25_kiss_cap_handle = create_capture_dissector_handle(capture_ax25_kiss, proto_ax25_kiss);
	capture_dissector_add_uint("wtap_encap", WTAP_ENCAP_AX25_KISS, ax25_kiss_cap_handle);

	/* only currently implemented for AX.25 */
	ax25_handle = find_dissector_add_dependency( "ax25", proto_ax25_kiss );

	ax25_cap_handle = find_capture_dissector("ax25");
}

/*
 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 *
 * Local variables:
 * c-basic-offset: 8
 * tab-width: 8
 * indent-tabs-mode: t
 * End:
 *
 * vi: set shiftwidth=8 tabstop=8 noexpandtab:
 * :indentSize=8:tabSize=8:noTabs=false:
 */