Debian 10 - GnuDIP Dynamic DNS 
==============================

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## TCP Implementation with tinydns
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Public domain
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### Server: /opt/gnudip/gnudip-passwd.txt

    # To create hashed passwords : echo -n PASSWORD | md5sum
    #
    # Hashed-password                Domain      Name
    25f9e794323b453885f5181f1b624d0b example.com machine01
    6ebe76c9fb411be97b3b0d48b791a7c9 example.com ftp

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### Server: /opt/gnudip/gnudip-server.sh 

    #!/bin/bash
    PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
    CWD=$(dirname $(readlink -f $0))
    MYPID=$$
    
    ################################################################################
    # Configuration
    
    RECORDS="$CWD/records"
    LOGGER="logger -t gnudip-server[$MYPID]"
    HPASSFILE="$CWD/gnudip-passwd.txt"
    TTL=60
    
    # Message format USER:HPASS:DOMAIN:RCODE:IPADDR
    # USER+DOMAIN:128 HPASS:32 RCODE:1 IPADDR:15 Colons:4
    MAXMSGLEN=180
    READTMOUT=3
    
    ################################################################################
    # Read and sanitize client IP 
    
    # xinetd supplies client IP
    CLIENTIP=$(echo $REMOTE_HOST)
    
    IPSW=1
    if [[ $CLIENTIP =~ ^[0-9]{1,3}(\.[0-9]{1,3}){2}\.[0-9]{1,3}$ ]]; then
        IP=($(echo $CLIENTIP | sed -e 's,\., ,g'))
        [[
                ${IP[0]} -le 255 &&
                ${IP[1]} -le 255 &&
                ${IP[2]} -le 255 &&
                ${IP[3]} -le 255
        ]]
        IPSW=$?
    fi
    if [ "$IPSW" == "1" ]; then
        echo "Client IP address is not valid" | $LOGGER
        echo 1
        exit
    fi
    
    echo "Got new connection from $CLIENTIP" | $LOGGER
    
    ################################################################################
    # Generate and send salt 
    
    SALT=$(tr -dc A-Za-z0-9 </dev/urandom | head -c 10)
    echo "$SALT"
    
    ################################################################################
    # Read and sanitize request message 
    
    read -n $MAXMSGLEN -t $READTMOUT MSG
    MSG=$(echo $MSG | tr -dc A-Za-z0-9:.-)
    
    echo "Message: $MSG" | $LOGGER
    
    N=$(echo "$MSG" | grep -o ':' | wc -l)
    if [ "$N" != "3" ] && [ "$N" != "4" ]; then
        echo "Message should have 3-or-4 colons" | $LOGGER
        echo 1
        exit
    fi
    
    ################################################################################
    # Splitting and re-sanitizing request message
    
    USER="$(echo $MSG | cut -d: -f1)"
    USER=$(echo $USER | tr -dc A-Za-z0-9-)
    LEN=${#USER}
    if [ "$LEN" == "0" ]; then
        echo "Username length is zero" | $LOGGER
        echo 1
        exit
    fi
    
    HPASS="$(echo $MSG | cut -d: -f2)"
    HPASS=$(echo $HPASS | tr -dc A-Za-z0-9)
    LEN=${#HPASS}
    if [ "$LEN" != "32" ]; then
        echo "Hashed password length should be 32" | $LOGGER
        echo 1
        exit
    fi
    
    DOMAIN="$(echo $MSG | cut -d: -f3)"
    DOMAIN=$(echo $DOMAIN | tr -dc A-Za-z0-9.-)
    LEN=${#DOMAIN}
    if [ "$LEN" -lt "3" ]; then
        echo "Domain name length is less than 3" | $LOGGER
        echo 1
        exit
    fi
    
    # Request code 0 and 1 not implemented yet / TODO
    RCODE="$(echo $MSG | cut -d: -f4)"
    #if [ "$RCODE" != "0" ] && [ "$RCODE" != "1" ] && [ "$RCODE" != "2" ]; then
    if [ "$RCODE" != "2" ]; then
        echo "Unknown request code" | $LOGGER
        echo 1
        exit
    fi
    
    # Not used, because rcode 0 not implemented / Sanitize before use / IPv4
    #IPADDR="$(echo $MSG | cut -d: -f5)"
    
    ################################################################################
    # Fetch and sanitize credential
    
    CRED=$(egrep -v '^#|^ *$' "$HPASSFILE" | egrep " $USER$" | head -n1)
    if [ "$CRED" == "" ]; then
        echo "User not found: $USER" | $LOGGER
        echo 1
        exit
    fi
    
    REALHPASS=$(echo $CRED | cut -d' ' -f1)
    REALHPASS=$(echo $REALHPASS | tr -dc A-Za-z0-9)
    LEN=${#REALHPASS}
    if [ "$LEN" != "32" ]; then
            echo "Real hashed password length should be 32" | $LOGGER
            echo 1
            exit
    fi
    REALHPASS=$(echo -n "$REALHPASS.$SALT" | md5sum | sed 's, .*,,')
    
    REALDOMAIN=$(echo $CRED | cut -d' ' -f2)
    REALDOMAIN=$(echo $REALDOMAIN | tr -dc A-Za-z0-9.-)
    LEN=${#REALDOMAIN}
    if [ "$LEN" -lt "3" ]; then
            echo "Real domain name length is less than 3" | $LOGGER
            echo 1
            exit
    fi
    
    if [ "$HPASS" != "$REALHPASS" ] || [ "$DOMAIN" != "$REALDOMAIN" ]; then
        echo "Invalid login" | $LOGGER
        echo 1
        exit
    fi
    
    # for rcode 0 , client ip address should be changed / TODO
    # for rcode 1 , juest delete old record if exist / get ip from connection(??)
    # rcode 2 implementation :
    ################################################################################
    # Check if DNS record exist / TODO: DNS Abstraction
    
    TINYDNS="1.2.3.4"
    N=$(dnsq a $USER.$DOMAIN $TINYDNS | 
        egrep "^answer: $USER.$DOMAIN " | egrep -c " $CLIENTIP$")
    if [ "$N" != "0" ]; then
        echo "Record exist, nothing to do!" | $LOGGER
        echo 0
        exit
    fi
    
    ################################################################################
    # Create and send DNS record to add / TODO: DNS Abstraction
    
    RECORD="+$USER.$DOMAIN:$CLIENTIP:$TTL"
    echo "$RECORD" >> "$RECORDS/$DOMAIN-$MYPID"
    echo "Login OK: $RECORD" | $LOGGER
    echo 0
    exit

********************************************************************************
### Server: /opt/gnudip/gnudip-apply.sh 

    #!/bin/bash
    PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
    CWD=$(dirname $(readlink -f $0))
    RECORDS="$CWD/records"
    DOMAINSDIR="/opt/tinydns-scripts/domains"
    RESTART="/opt/tinydns-scripts/create-data-file.sh"
    TINYDNS="1.2.3.4"
    
    if [ ! -d "$RECORDS" ]; then
        mkdir -p $RECORDS
        chown nobody:nogroup $RECORDS
    fi
    
    N=$(ls $RECORDS | wc -l)
    if [ "$N" == "0" ] ;then
        exit
    fi
    
    RSTSW=0
    for F in $(find $RECORDS -type f); do
        RECORD=$(cat $F | head -n1)
        PREFIX=$(echo $RECORD | cut -d: -f1)
        NAME=${PREFIX:1}
        DOMAIN=$(echo $NAME | sed -e 's/^[^\.]*\.//g')
        IP=$(echo $RECORD | cut -d: -f2)
        echo $PREFIX
        echo $NAME
        echo $IP
        N=$(dnsq a $NAME $TINYDNS | egrep "^answer: $NAME " | egrep -c " $IP$")
        if [ "$N" != "0" ]; then
                continue
        fi
        RSTSW=1
        sed -i "/^$PREFIX:/d" "$DOMAINSDIR/$DOMAIN"
        echo $RECORD >> "$DOMAINSDIR/$DOMAIN"
        rm $F
    done
    
    [ "$RSTSW" == "1" ] && $RESTART
 

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### Server: /opt/gnudip/gnudip-apply-loop.sh 

    #!/bin/bash
    #
    # Start inside screen :
    # env SCREENDIR="/var/run/screen/S-root/" screen -dmS GNUDIP /opt/gnudip/gnudip-apply-loop.sh
    #
    PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
    CWD=$(dirname $(readlink -f $0))
    APPLY="$CWD/gnudip-apply.sh"
    SLEEP=5
    
    while :;do
        $APPLY
        sleep $SLEEP
    done

********************************************************************************
### Server: Add to /etc/services

    gnudip          3495/tcp

********************************************************************************
### Server: /etc/xinetd.d/gnudip 

    service gnudip
    {
        disable     = no
        flags       = IPv4
        socket_type = stream
        protocol    = tcp
        wait        = no
        user        = nobody
        server      = /opt/gnudip/gnudip-server.sh
        bind        = 0.0.0.0
    }

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### Server: /etc/rc.local

    env SCREENDIR="/var/run/screen/S-root/" screen -dmS GNUDIP /opt/gnudip/gnudip-apply-loop.sh


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### Client: /root/scripts/gnudip-client.sh

    #!/bin/bash
    #
    # Usage :
    # ncat ddns.topdns.ir 3495 -e gnudip-client.sh
    #
    
    PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
    MYPID=$$
    LOGGER="logger -t gnudip-client[$MYPID]"
    
    USER="machine01"
    PASS="123456789"
    DOMAIN="example.com"
    
    read SALT
    echo "Salt: $SALT" | $LOGGER 
    REQ="$USER:$(echo -n "$(echo -n "$PASS" | md5sum | sed 's, .*,,').$SALT" | md5sum | sed 's, .*,,'):$DOMAIN:2"
    echo "$REQ" | $LOGGER 
    echo "$REQ"
    read RESP
    echo "Response $RESP" | $LOGGER

********************************************************************************
### Client: /etc/crontab

    * * * * *   root    /usr/bin/ncat ddns.topdns.ir 3495 -e /root/scripts/gnudip-client.sh &> /dev/null

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### Links

    http://gnudip2.sourceforge.net/
    http://gnudip2.sourceforge.net/gnudip-www/
    http://gnudip2.sourceforge.net/gnudip-www/latest/gnudip/html/protocol.html
    http://gnudip2.sourceforge.net/gnudip-www/latest/gnudip/html/protocol_sample.txt
    http://gnudip2.sourceforge.net/gnudip-www/latest/gnudip/html/client/UNIX/
    http://gnudip2.sourceforge.net/gnudip-www/latest/maintenance_commands.html
    http://gnudip2.sourceforge.net/gnudip-www/latest/remote.html
    http://gnudip2.sourceforge.net/gnudip-www/latest/INSTALL.html
    http://gnudip2.sourceforge.net/gnudip-www/latest/BACKEND.html
    http://gnudip2.sourceforge.net/gnudip-www/latest/TODO.html
    http://gnudip2.sourceforge.net/gnudip-www/gnudip-2.3.5-www.tar.gz
    http://up.nl.eu.org/projects/gnudip.html
    https://github.com/rodajc/gnudiphttp/
    https://fossies.org/linux/misc/dns/old/gnudip-2.3.5.tar.gz/

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_BY: Pejman Moghadam_  
_TAG: gnudip, xinetd, ddns, dns, tinydns_  
_DATE: 2021-06-02 07:07:36_