Wireshark-dev: Re: [Wireshark-dev] Packet Size limited during capture message
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From: Brian Oleksa <oleksab@xxxxxxxxxxxxxxxxxxxxxx>
Date: Wed, 24 Mar 2010 09:59:36 -0400
Guy / Bill / Chris / Jakub / Mike

So I did some more troubleshooting only to find the following:
The dissector crashes in WinXP but not on my Fedora Core 9 box. This is weird.
Using editcap... I was able to find the frame on windows to which wireshark crashed on (which was frame 17641). I opened the same .pcap file on my FC-9 box (it did not crash)...but I went to frame 17641 only to find out that it is a Malformed Packet.
How I determine if it is a Helen packet or not....is that all helen packets start with 0xbead which is the "magic number". I have never had this problem before as I found thousands of Helen packets this way. But this malformed packet has a magic number of 0x293e .... which then through the rest of the packet info off and crashed wireshark (on Windows). 

Any thoughts..??
Do I need to make sure that the hf_helen_magic is equal to 0xBEAD.....and if not I discard this packet..??
Why did it find this packet and assume that it was a Helen Packet..?? Was it because 0x293e is equal to 0xBEAD in length so it just assumed it was a helen packet..?? 

Attached is the code.

Thanks for your help,
Brian


/* ***** BEGIN LICENSE BLOCK *****
    This program will dissect Dark Corner Software's Helen Packets.
    Copyright (C) 2010  Kenneth Flynn  flynnk@xxxxxxxxxxxxxxxxxxxxxx

    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 3 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, see <http://www.gnu.org/licenses/>.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>
#include <glib.h>
#include <epan/packet.h>
#include <time.h>
#include <string.h>

#define PROTO_TAG_HELEN    "HELEN"

static int proto_helen = -1;

static dissector_handle_t helen_handle;

void dissect_helen(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);

/*The following port is registered with IANA*/
static int helen_port = 5136;

static const char *mon_names[12] = {"Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"};

static const value_string helen_gps_status[] = {
	{ 0, "Good" },
	{ 1, "No Fix" },
	{ 2, "Bad GPS Read" },
	{ 0, NULL }
};

/*not used*/
static const range_string helen_code[] = {
    {0x8000, 0xfffe, "Experimental"},
    {0xffff, 0xffff, "Encryption Extension"},
    {0, 0, "Tail"},
    {1, 1, "GPS Extension"},
    {2, 2, "Flow Extension"},
    {3, 3, "Host Extension"},
    {4, 4, "File Extension"},
    {5, 999, "Reserved"},
    {1000, 1000, "Minotaur SA Extension"},
    {16000, 32767, "Unassigned"},
    {0, 0, NULL}
};

static gint hf_helen_magic = -1;
static gint hf_helen_checksum = -1;
static gint hf_helen_txTime = -1;

static gint hf_helen = -1;
static gint hf_helen_time = -1;
static gint hf_helen_ipv4 = -1;
static gint hf_helen_ipv6 = -1;
static gint hf_helen_nos = -1;
static gint hf_helen_flowname = -1;
static gint hf_helen_longitude = -1;
static gint hf_helen_latitude = -1;
static gint hf_helen_altitude = -1;
static gint hf_helen_bearing = -1;
static gint hf_helen_speed = -1;
static gint hf_helen_sequence_num = -1;
static gint hf_helen_gpsstatus = -1;
static gint hf_helen_source = -1;

/*not used*/
static gint hf_helen_code = -1;

static gint ett_helen = -1;

void dissect_helen(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree) {

    proto_item *helen_item = NULL;
    proto_item *helen_sub_item = NULL;
    proto_tree *helen_tree = NULL;
    proto_tree *helen_header_tree = NULL;

	col_set_str(pinfo->cinfo, COL_PROTOCOL, PROTO_TAG_HELEN);
    col_clear(pinfo->cinfo, COL_INFO);

    if (tree) {
        guint32 offset = 0;
        guint32 orig_offset = 18;
        nstime_t t;
		guint64 msecs_since_the_epoch;
		struct tm *tmp;
        helen_item = proto_tree_add_item(tree, proto_helen, tvb, 0, -1, FALSE);
        helen_tree = proto_item_add_subtree(helen_item, ett_helen);
        helen_header_tree = proto_item_add_subtree(helen_item, ett_helen);
        helen_sub_item = proto_tree_add_item(helen_tree, hf_helen_magic, tvb, offset, 2, FALSE);
        offset += 2;
		helen_sub_item = proto_tree_add_item(helen_tree, hf_helen_checksum, tvb, offset, 8, FALSE);
		offset += 8;

		msecs_since_the_epoch = tvb_get_ntoh64(tvb, offset);
		t.secs = msecs_since_the_epoch/1000;
		t.nsecs = (msecs_since_the_epoch%1000)*1000000;	/* milliseconds to nanoseconds */
		tmp = gmtime(&t.secs);

        proto_tree_add_time_format(helen_tree, hf_helen_txTime, tvb, offset, 8, &t,
            "Date: %s %2d, %d %02d:%02d:%02d UTC",mon_names[tmp->tm_mon],tmp->tm_mday,
			tmp->tm_year + 1900,tmp->tm_hour,tmp->tm_min,tmp->tm_sec);

	/*not used*/
		//proto_tree_add_uint_format(helen_tree, hf_helen_txTime, tvb, offset, 8, msecs_since_the_epoch,
		//	"Date: %s %2d, %d %02d:%02d:%02d UTC",mon_names[tmp->tm_mon],tmp->tm_mday,
		//	tmp->tm_year + 1900,tmp->tm_hour,tmp->tm_min,tmp->tm_sec, msecs_since_the_epoch%1000);

        helen_header_tree = proto_item_add_subtree(helen_sub_item, ett_helen);
        {
            #define MAX_BUFFER 100
			char *buf = (char*)ep_alloc(MAX_BUFFER);
            char * packet_name = "";
            proto_tree *helen_sub_tree = NULL;
            offset = 18;

            for (;;) {
                guint16 code;
                guint16 numBytes = 0;
                guint unknownPacket = 0;
                guint codeOffset;
                offset = orig_offset;
		    	code = tvb_get_ntohs(tvb, offset);
                codeOffset = offset;
                offset += 2;

                switch (code) {
                    case 0: packet_name = "End of Packet";
                        break;
                    case 1: packet_name = "GPS Extension";
                        break;
                    case 2: packet_name = "Flow Extension";
                        break;
                    case 3: packet_name = "Host Extension";
                        break;
                    default: packet_name = "Unknown code";
                        unknownPacket = 1;
                        break;
                }

			/*not used*/
				//proto_tree_add_item(tree, hf_helen_code, tvb, offset, 2, FALSE);

                g_snprintf(buf, MAX_BUFFER, "%s", packet_name);

                if (unknownPacket) {
                    g_snprintf(buf, MAX_BUFFER, "Unknown packet: %d", code);
                }

                helen_item = proto_tree_add_text(tree, tvb, codeOffset, 2, "%s", buf);
                helen_sub_tree = proto_item_add_subtree(helen_item, ett_helen);

                if (code == 0) {
                    break;
                }

                numBytes = tvb_get_ntohs(tvb, offset);
                offset += 2;

                /* GPS: */
                if (code == 1) {
                    guint8 fieldsAvail;
                    fieldsAvail = tvb_get_guint8(tvb, offset);
                    offset += 1;

                    /* Status: */
                    if ((fieldsAvail & 1) != 0) {
                 		proto_tree_add_item(helen_sub_tree, hf_helen_gpsstatus ,tvb , offset, 1, FALSE);
                        offset += 1;
                    }

                    /* Time: */
                    if ((fieldsAvail & 2) != 0) {
						nstime_t t;
						guint64 msecs_since_the_epoch;
						struct tm *tmp;
					    msecs_since_the_epoch = tvb_get_ntoh64(tvb, offset);
						t.secs = msecs_since_the_epoch/1000;
						t.nsecs = (msecs_since_the_epoch%1000)*1000000;	/* milliseconds to nanoseconds */
						tmp = gmtime(&t.secs);
                        proto_tree_add_time_format(helen_sub_tree, hf_helen_time, tvb, offset, 8, &t,
                                "Date: %s %2d, %d %02d:%02d:%02d UTC",mon_names[tmp->tm_mon],tmp->tm_mday,
								tmp->tm_year + 1900,tmp->tm_hour,tmp->tm_min,tmp->tm_sec);
                        offset += 8;
                    }

                    /* Longitude: */
                    if ((fieldsAvail & 4) != 0) {
                        proto_tree_add_item(helen_sub_tree, hf_helen_longitude, tvb, offset, 4, FALSE);
                        offset += 4;
                    }

                    /* Latitude: */
                    if ((fieldsAvail & 8) != 0) {
                        proto_tree_add_item(helen_sub_tree, hf_helen_latitude, tvb, offset, 4, FALSE);
                        offset += 4;
                    }

                    /* Altitude: */
                    if ((fieldsAvail & 16) != 0) {
                        proto_tree_add_item(helen_sub_tree, hf_helen_altitude, tvb, offset, 4, FALSE);
                        offset += 4;
                    }

                    /* Bearing: */
                    if ((fieldsAvail & 32) != 0) {
                        proto_tree_add_item(helen_sub_tree, hf_helen_bearing, tvb, offset, 4, FALSE);
                        offset += 4;
                    }

                    /* Speed: */
                    if ((fieldsAvail & 64) != 0) {
                        gfloat speed;
                        speed = tvb_get_ntohieee_float(tvb,offset);;
                        if (speed != 0.0) {
							proto_tree_add_item(helen_sub_tree, hf_helen_speed, tvb, offset, 4, FALSE);
                        }
                        offset += 4;
                    }

                    /* Number of Satellites: */
                    if ((fieldsAvail & 128) != 0) {
                        proto_tree_add_item(helen_sub_tree, hf_helen_nos, tvb, offset, 1, FALSE);
                        offset += 1;
                    }
                }

                /* FLOW: */
                if (code == 2) {
                    proto_tree_add_item(helen_sub_tree, hf_helen_flowname, tvb, offset, 8, FALSE);
                    offset += 8;

                    /* Sequence number: */
        			proto_tree_add_item(helen_sub_tree, hf_helen_sequence_num, tvb, offset, 4, FALSE);
                    offset += 4;

                    if (numBytes == 16) {
					   /* Source: */
					   proto_tree_add_item(helen_sub_tree, hf_helen_source, tvb, offset, 4, FALSE);
					   offset += 4;
                    }
                }

                /* HOST: */
                if (code == 3) {
                    /* Size: */
                    guint8 size;
                    size = tvb_get_guint8(tvb, offset);
                    offset += 1;

                    if (size == 4) {
                        proto_tree_add_item(helen_sub_tree, hf_helen_ipv4, tvb, offset, 4, FALSE);
                        offset += 4;
                    } else
                    {
						proto_tree_add_item(helen_sub_tree, hf_helen_ipv6, tvb, offset, 16, FALSE);
						offset += 16;
					}
			    }
                orig_offset += numBytes + 4;
            }
        }
    }
}

void proto_reg_handoff_helen(void) {
    static gboolean initialized = FALSE;

        if (!initialized) {
            helen_handle = create_dissector_handle(dissect_helen, proto_helen);
            dissector_add("udp.port", helen_port, helen_handle);
        }
    initialized = TRUE;
}

void proto_register_helen(void) {
    static hf_register_info hf[] = {
        { &hf_helen,
            { "Data", "helen.data", FT_NONE, BASE_NONE, NULL, 0x0,
                "HELEN PDU", HFILL}},
        { &hf_helen_magic,
            { "Magic Number", "helen.magicNumber", FT_UINT8, BASE_HEX, NULL, 0x0,
                NULL, HFILL}},
        { &hf_helen_checksum,
           { "Checksum", "helen.checksum", FT_UINT64, BASE_DEC, NULL, 0x0,
                NULL, HFILL}},
        { &hf_helen_txTime,
            { "System Tx Time", "helen.SystemTxTime", FT_ABSOLUTE_TIME, BASE_NONE, NULL, 0x0,
                NULL, HFILL}},
        { &hf_helen_time,
	        { "Time", "helen.time", FT_ABSOLUTE_TIME, BASE_NONE, NULL, 0x0,
	            NULL, HFILL}},
	    { &hf_helen_ipv4,
			{ "IPv4", "helen.ipv4address", FT_IPv4, BASE_NONE, NULL, 0x0,
	            NULL, HFILL}},
	    { &hf_helen_ipv6,
			{ "IPv6", "helen.ipv6address", FT_IPv6, BASE_NONE, NULL, 0x0,
	            NULL, HFILL}},
        { &hf_helen_sequence_num,
			{ "Sequence Number", "helen.sequenceNumber", FT_UINT32, BASE_DEC, NULL, 0x0,
                NULL, HFILL}},
        { &hf_helen_source,
			{ "Source", "helen.source", FT_UINT32, BASE_DEC, NULL, 0x0,
                NULL, HFILL}},
        { &hf_helen_nos,
			{ "Number of Satellites", "helen.numberOfSatellites", FT_UINT8, BASE_DEC, NULL, 0x0,
			NULL, HFILL}},
		{ &hf_helen_flowname,
			{ "Flowname", "helen.flowname", FT_STRING, BASE_NONE, NULL, 0x0,
			NULL, HFILL}},
		{ &hf_helen_gpsstatus,
			{ "GPS Status", "helen.gpsStatus", FT_UINT8, BASE_DEC, VALS(helen_gps_status), 0x0,
			NULL, HFILL}},
	/*not used*/
		{ &hf_helen_code,
			{ "Packet COde", "helen.packetCode", FT_UINT8, BASE_DEC, VALS(helen_code), 0x0,
			NULL, HFILL}},
	/**/
		{ &hf_helen_longitude,
			{ "Longitude", "helen.longitude", FT_FLOAT, BASE_DEC, NULL, 0x0,
			NULL, HFILL}},
		{ &hf_helen_latitude,
			{ "Latitude", "helen.latitude", FT_FLOAT, BASE_DEC, NULL, 0x0,
			NULL, HFILL}},
		{ &hf_helen_altitude,
			{ "Altitude", "helen.altitude", FT_FLOAT, BASE_DEC, NULL, 0x0,
			NULL, HFILL}},
		{ &hf_helen_bearing,
			{ "Bearing", "helen.bearing", FT_FLOAT, BASE_DEC, NULL, 0x0,
			NULL, HFILL}},
		{ &hf_helen_speed,
			{ "Speed", "helen.speed", FT_FLOAT, BASE_DEC, NULL, 0x0,
			NULL, HFILL}},
    };

    static gint * ett[] = {&ett_helen};

    proto_helen = proto_register_protocol("HELEN", "HELEN", "helen");
    proto_register_field_array(proto_helen, hf, array_length(hf));
    proto_register_subtree_array(ett, array_length(ett));
    register_dissector("helen", dissect_helen, proto_helen);
}