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From Mark Thomas <ma...@apache.org>
Subject Re: [OT] SecurityManager and Java Policy Files
Date Wed, 10 Nov 2010 21:29:59 GMT
On 10/11/2010 21:15, Christopher Schultz wrote:
> I'm looking for references that explain the interaction between the
> SecurityManager itself, the policy, signed code, and the use of
> AccessController/PrivilegedAction.
> 
> Online resources and articles as well as dead trees would be fine. My
> Google-fu just isn't turning up anything relevant. I get either horribly
> technical specifications of things or trifles that just say "run under a
> SecurityManager and everything will be secure!".
> 
> Any help would be greatly appreciated.

I don't recall ever finding anything that useful. What I can do is
condense my limited knowledge into a few lines that may help.

For code to perform some actions (e.g. reading a file, exiting the JVM
etc) it needs the associated permission when running under a security
manager.

The policy file handles mapping code to permissions.

When code tries to perform a protected function then:
- if no privileged block is present in the call stack then every class
in the call stack must have the necessary permission
- if a privileged block is present in the call stack then every class in
the call stack from the class performing the action to the privileged
block must have the necessary permission


To take a specific example, consider the PersistentManager. It needs to
read/write sessions from the file system, create objects, manipulate
class loaders and a bunch of other stuff that requires permissions.
Session loading/unloading can be triggered by a web application so it is
possible for web app code to be in the call stack for a call to load().

Web apps have minimal permissions that do not include the permissions
needed by the load() method. The PersistentManager class does have the
necessary permissions.

The load() method uses a privileged block so web apps can call the
load() method without having the necessary permissions. To be secure the
load() method has to make sure web apps can't trick it into doing
something it shouldn't.

Does that help?

Mark

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