Category: Linux

July 5th, 2017 | Garland Joseph

This script is part of a series of scripts that perform packet capture between two endpoints.  In this case, the endpoints are a Unix machine and a windows machine. This script was tested with the “source endpoint” as a Redhat Linux and the “target endpoint” a Windows 2016 Server machine.  

The circular traces are started on each machine and stopped whenever an event is detected on the Unix side.  In this case the event is to monitor a file (i.e., log) for a particular string.

Requirements: Wireshark installed on Windows. OpenSSH installed on Windows. 

Scenario

Script

#Author: Garland R. Joseph, garland.joseph@gmail.com
# Date: May 2017
# u2wcap: See usage below. "Unix to Windows Capture"
#
# This script is offered as is. It is designed to
# run a circular trace using tcpdump on UNIX system
# and wireshark on Windows systems.
#
# You will either have to manually enter the password
# for the root account on the remote system or setup
# ssh keys from promptless access.
#
# The traces will stop once a key string SEARCH_STRING is
# found in LOG_FILE.
#
# Note: Some UNIX systems like LINUX Fedora will
# result in permsission denied when using
# tcpdump -W and -C options and writing to / or /root.
#
# Modify the REM_INTERFACE parameter below to fix the interface number
# on the windows system. Do a tshark -D to determine the interface number.
#
#
# -----

#
# Defaults
#

USAGE="u2wcap [-v] [ -c capture_file ] [ -w secs ] -h remote_host -l log_file -s search_string"
DEBUG=false
SLEEP_TIME="5" #seconds
LOCAL_CAPTURE_FILE="/tmp/capture"
TCPDUMPCMD="tcpdump -C 1 -W 2 -w ${LOCAL_CAPTURE_FILE}"

#
# Options for remote tracing
#

REM_CAP_FILE="capture.windows"
REM_USER="wireshark"
REM_INTERFACE="4"
FILESIZE=1000 #units or kB, so this means 1 Meg
#FILESIZE=500000 #512 Meg
#$FILESIZE=1000000 #units or kB, so this means 1 Gig
FILECOUNT="2" #creates a count of FILECOUNT of trace files at most of size FILESIZE
TSHARK_LOCATION="c:\progra~1\wireshark\tshark"
#TRACECMD="$TSHARK_LOCATION -b filesize:$FILESIZE -b files:$FILECOUNT -w ${REM_CAP_FILE}"
TRACECMD="$TSHARK_LOCATION -b filesize:$FILESIZE -b files:$FILECOUNT -w ${REM_CAP_FILE} -i ${REM_INTERFACE}"


#
# Process command line arguments
#

while getopts ":vc:w:l:s:h:" opts
do
case ${opts} in
v) DEBUG=true ;;
c) CAPTURE_FILE=${OPTARG} ;;
w) SLEEP_TIME=${OPTARG} ;;
s) SEARCH_STRING=${OPTARG} ;;
l) LOG_FILE=${OPTARG} ;;
h) REMOTE_HOST=${OPTARG} ;;
":") echo "Please specify a value for ${OPTARG}" ; exit ;;
\?) echo "${OPTARG} is not a valid switch" ; echo "${USAGE}" ; exit;;
esac
done

#
# Insure required values have been specified, check for existence of
# log file, getops should handle case of no values for -l and -s.
# A sanity check in the event getopts varies per unix
#

if [[ -z ${SEARCH_STRING} || -z ${LOG_FILE} || -z ${REMOTE_HOST} ]]
then
echo ${USAGE}
exit
fi
if ! [[ -f ${LOG_FILE} ]]
then
echo "File ${LOG_FILE} does not exist"
exit
fi

#
# Start trace on remote host
#
$(ssh ${REM_USER}@${REMOTE_HOST} ${TRACECMD})& 2>&1 > /dev/null

#
# Start trace on this host
#

${TCPDUMPCMD} 2>/dev/null 1>/dev/null & LOCAL_PID=$!
${DEBUG} && echo "${0}-I-LOCAL_PID, local pid is ${LOCAL_PID}."

#
# Monitor log file
#

old_count=`grep -c ${SEARCH_STRING} ${LOG_FILE}`
(( new_count=old_count ))
(( i = 0 ))
while (( old_count == new_count ))
do
(( i++ ))
${DEBUG} && echo "${0}-F-SLEEP, sleeping ${SLEEP_TIME}, iternation ${i}."
sleep ${SLEEP_TIME}
new_count=`grep -c ${SEARCH_STRING} ${LOG_FILE}`
done

#
# At this point, search string has been found, stop traces
#

kill ${LOCAL_PID}
ssh ${REM_USER}@${REMOTE_HOST} taskkill /f /fi \"imagename eq tshark*\"

#
# Reminders
#

echo "Consult files ${REM_CAP_FILE} on remote host ${REMOTE_HOST} and ${LOC_CAP_FILE} on local host."

exit