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The most sophisticated Java security policy generator EVAR (TMSJSPGE)

The Java Virtual Machine (JVM) has very powerful security features, such as the security manager that allows writing policy files. The idea (how I use it) is to write a whitelist of files and network locations (and other things) the Java process is allowed to access. If something is accessed that is not on the whitelist, an Exception is thrown.

As already stated in 2004 "there's currently no tool available to automatically generate a policy file for specific code". So when you want a write a policy file for your code, you have to do it manually. Or maybe there is a tool and I simply didn't find it (please enlighten me!). Anyway, it's a shame I had to hack such an ugly ugly python-that-parses-Java-exceptions script and am too lazy to do it nicely in Java, but hey, better than nothing and you kind of only need it at "compile time". Afterwards you have a policy file and you can get rid of this tool again.

By floyd,, @floyd_ch, 2018

How it works

Long story short, I wrote a horrible python script that launches Java processes to wait for an exception, then add the permission stated in the exception to the policy and restart the process. It starts with an empty policy file only allowing read/write/delete to temporary file locations and will launche the Java process once per permission necessary. This is done until no more exceptions occure and the necessary policy file was created. Of course if your Java process is a daemon that doesn't exit when "all work is done", it might still throw permission exceptions during runtime, but at least it starts cleanly with that policy file.


Let's say you usually start your Java application with the following command line:

java -cp subfolder/:exampleDependency.jar org.example.package.SampleClass input_file.txt

The first thing you probably want to do, is manually add read access to "exampleDependency.jar" in the script by uncommenting the example in the policies variable and adjust the jar file name. Although this is not always necessary, you can end up with a nullpointer exception when the code tries to access ressources (eg. xml oder json configuration files) inside the jar file. Because that nullpointer exception does not state that it is a problem with the security manager/policy, this tool can not add that policy permission by itself. And you might get confused as well, so please do this step now.

Then you will need to execute the script like this (where policy.txt does not exist yet):

./ policy.txt -cp subfolder/:exampleDependency.jar org.example.package.SampleClass input_file.txt

The script will now fill policy.txt for you. It will start a subprocess with the following Java command line several times with different policy.txt files:

java -cp subfolder/:exampleDependency.jar org.example.package.SampleClass input_file.txt

After it ran through, you can now run your Java application with security manager turned on with the same command line:

java -cp subfolder/:exampleDependency.jar org.example.package.SampleClass input_file.txt

Of course you should now try all the functionalities of your application, to make sure it won't throw an exception and that it does not need any further permissions. For example you should try all different parsers that could touch the input_file.txt of our example application and therefore run with a lot of different input_file.txt.

That's it, you have a nice policy.txt file now.

Batch parsing corpus

You want to make sure that no permissions are missing for any of the input files and behavior of your Java program. The file is an example of how the script can be run over an entire folder of input files.


Java Security Policy Generator






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