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Thread: Parse json and execute commands

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  1. #1
    Join Date
    Apr 2013
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    Parse json and execute commands

    Hi, I've a remote json, and I want fetch it and execute it every 6 hours, its a json with firewall settings (for iptables). Heres an example of the json

    Code:
    [
    "iptables --flush",
    "iptables -P INPUT DROP",
    "iptables -P FORWARD DROP",
    "iptables -P OUTPUT DROP",
    "iptables -A INPUT -i eth0 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT",
    "iptables -A OUTPUT -o eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT",
    "iptables -A OUTPUT -o eth0 -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT",
    "iptables -A INPUT -i eth0 -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT",
    "iptables -A OUTPUT -o eth0 -p tcp --dport 7171,7175 -m state --state NEW,ESTABLISHED -j ACCEPT",
    "iptables -A INPUT -i eth0 -p tcp --sport 7171,7175 -m state --state ESTABLISHED -j ACCEPT"
    ]
    The question is, how I can fetch it and execute with root permission with a bash script? I've searched something to parse the json, but I wasnt been sucessed. Thanks in advance.

  2. #2
    Join Date
    Jun 2009
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    Land of Paranoia and Guns
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    Distro
    Ubuntu 12.10 Quantal Quetzal

    Re: Parse json and execute commands

    First off, consider the security ramifications behind this sort of action. You're blindly depending on the security of this remote server- if it gets breached, an attacker could replace that file with whatever they want, and then your script would execute their commands with root permissions. So consider finding a way to do this without involving another server.

    For parsing the JSON, it would probably be easier to write your own program. For example, here is a simple python 3 program to do so.
    Don't actually use it as it blindly executes whatever it gets and is insecure in every way possible.
    Code:
    #!/usr/bin/env python3
    import json
    import subprocess
    import urllib.request
    commands = json.loads(urllib.request.urlopen("http://example.com/json/file").read().decode())
    for command in commands:
        program, *args = command.split()
        subprocess.call(program, *args)
    Last edited by epicoder; May 9th, 2013 at 01:02 AM.
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  3. #3
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    Re: Parse json and execute commands

    agreed, running the commands blindly would be a security nightmare. At the very least you need to whitelist commands eg only iptables is allowed, also you need to watch out for command terminating characters like ; and & (so doing something like iptables ...; malicious_cmd is not possible)
    if your question is answered, mark the thread as [SOLVED]. Thx.
    To post code or command output, use [code] tags.
    Check your bash script here // BashFAQ // BashPitfalls

  4. #4
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    Apr 2013
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    46

    Re: Parse json and execute commands

    I dont care about the security stuff right now, Im testing some ideias and I want to see how it works. Anyway, how make it always execute as root?

  5. #5
    Join Date
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    Re: Parse json and execute commands

    if your question is answered, mark the thread as [SOLVED]. Thx.
    To post code or command output, use [code] tags.
    Check your bash script here // BashFAQ // BashPitfalls

  6. #6
    Join Date
    Apr 2013
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    46

    Re: Parse json and execute commands

    Im trying to add the job with the following command, but is not working!

    Code:
    ubuntu@ip-10-252-16-247:~$ sudo crontab /etc/iptables.py 1 * * * * -u root
    "/etc/iptables.py":1: bad minute
    errors in crontab file, can't install.
    ubuntu@ip-10-252-16-247:~$

  7. #7
    Join Date
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    Land of Paranoia and Guns
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    Distro
    Ubuntu 12.10 Quantal Quetzal

    Re: Parse json and execute commands

    You are attempting to replace the crontab with /etc/iptables.py. Use
    Code:
    sudo crontab -e
    to edit the crontab.
    Last edited by epicoder; May 12th, 2013 at 01:18 PM.
    Don't use W3Schools as a resource! (Inconsequential foul language at the jump)
    Open Linux Forums (More foul language, but well worth it for the quality of support and good humor.)
    If you want to discuss W3Schools, please PM me instead of posting.

  8. #8
    Join Date
    Apr 2013
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    Re: Parse json and execute commands

    Heres mine crontab

    Code:
    # Edit this file to introduce tasks to be run by cron.
    #
    # Each task to run has to be defined through a single line
    # indicating with different fields when the task will be run
    # and what command to run for the task
    #
    # To define the time you can provide concrete values for
    # minute (m), hour (h), day of month (dom), month (mon),
    # and day of week (dow) or use '*' in these fields (for 'any').#
    # Notice that tasks will be started based on the cron's system
    # daemon's notion of time and timezones.
    #
    # Output of the crontab jobs (including errors) is sent through
    # email to the user the crontab file belongs to (unless redirected).
    #
    # For example, you can run a backup of all your user accounts
    # at 5 a.m every week with:
    # 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
    #
    # For more information see the manual pages of crontab(5) and cron(8)
    #
    # m h  dom mon dow   command
    
    
    0 * * * * /etc/iptables.py
    And its not working!

  9. #9
    Join Date
    Jun 2009
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    Land of Paranoia and Guns
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    Distro
    Ubuntu 12.10 Quantal Quetzal

    Re: Parse json and execute commands

    Make sure that:
    • You are editing root's crontab and not yours. (make sure crontab -e is run as root)
    • /etc/iptables.py is hashbanged. That is, this must be its first line: #!/usr/bin/env python
    • You are using the correct version of python. If this is a python 3 script, use #!/usr/bin/env python3
    • /etc/iptables.py is owned by root and is executable.


    Also, check root's mail spool (sudo mail) for mail from cron.
    Don't use W3Schools as a resource! (Inconsequential foul language at the jump)
    Open Linux Forums (More foul language, but well worth it for the quality of support and good humor.)
    If you want to discuss W3Schools, please PM me instead of posting.

  10. #10
    Join Date
    Apr 2013
    Beans
    46

    Re: Parse json and execute commands

    Is my fault, it was working, but in some boxes is not working, I dont know how!

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