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selinux: Re: [PATCH 00/15] RFC Source Policy Support

Re: [PATCH 00/15] RFC Source Policy Support

From: Stephen Smalley <sds_at_nospam>
Date: Wed Jan 27 2010 - 20:00:21 GMT
To: Caleb Case <ccase@tresys.com>


On Tue, 2010-01-26 at 17:08 -0500, Caleb Case wrote: <snip>
> Module Ordering - The current reference policy compilation
> infrastructure devotes substantial attention to dealing with ordering
> problems. Some of these problems are fundamental (such as the ordering
> of portcon statements) while others are an artifact of the current
> compiler and M4 (such as the need to separate out interface statements
> in .if files). Rather than devote substantial effort to creating
> mechanisms for specifying or dealing with ordering, it was felt that the
> long term solution to this problem is in the improvements that will come
> from the proposed common intermediate language [1]. Therefore, in the
> short term, several modules will be ordered specially based upon name
> and certain policy statements will only be supported in those specially
> ordered modules (e.g., a module for specifying defines such as
> DISTRO_REDHAT). These hacks can be removed at a later date.

These specially ordered modules and restrictions on policy statements usable by other modules sound just like the base module today. Did you just re-invent the base module under a different name?

> Base Module Removal - The decision to support a special base binary
> module was made to make bootstrapping a module store easier by including
> a module that was required to have a minimal but complete system policy
> and to deal with ordering by only allowing order dependent statements to
> appear in the base (such as object class or portcon). Over time it has
> become clear that the base module limitations outweigh any of the
> intended benefits. This is especially true as support for overriding
> policy modules is included. Therefore, the source semanage store will no
> longer support or require a special base module. Further, there will be
> no restrictions on the use of policy statements in modules. While this
> will allow some unintentional mistakes (e.g., including a broad portcon
> in a module that gets processed first) it will also allow additional
> freedom (e.g., the use of narrow portcon statements in modules).

I originally assumed you considered portcon statements to be one of the statements limited to the specially ordered modules above, but evidently not. So how then will you ensure proper ordering of them?

Why not just eliminate the ordering dependency altogether from portcons. Just mandate that more specific entries (e.g. portcon 80) always take precedence over less specific entries (e.g. portcon 1-1024), and sort them accordingly in the toolchain before generating the kernel policy.

> [User Experience Overview]
>
> The overall user experience will shift from using external tools to
> compile a policy package (.pp) to working directly with source modules.
>
> Source modules will be a single text file containing all of the policy
> for that module. For the current reference policy that will require
> combining the current interface, type enforcement, and file context
> files into a single text file. The user will then use that text file
> similarly to how the current binary modules are used. Insertion would be
> performed using semodule (the 'ref' extension is for the single file
> reference policy format):
>
> # semodule -i apache.ref
>
> Note that the language for the module will be inferred from the
> extension to avoid the general tools, such as semodule, needing an
> awareness of the format of all source policies. The name would be taken
> from the input filename.

I assume you mean that you don't want libsemanage to need to be aware of the format of all source policies, as semodule itself shouldn't ever peer inside of the module?

If I try to insert two modules with the same prefix but different suffixes, are they one module or two different ones?

> The first large change to user experience is the introduction of a
> command to retrieve a module:
>
> # semodule -g apache
> # ls
> apache.ref
>
> # semodule -g apache -o myapache.ref
> # ls
> myapache.ref
>
> Similarly, there is the addition of an edit command that is similar to
> sudoedit. This is purely a convenience; it will retrieve the module to a
> temporary location and install it after updates are made.
>
> # semodule --edit apache
>
> Finally, semodule now supports adding a user message when making
> changes:
>
> # semodule --edit apache -m "Allow apache to execute cowsay."

Do we really need/want to provide this functionality in semodule/libsemanage? Why not just have the user get the module, edit it as desired, and then insert it? By the way, this could also be referred to as checkout and checkin/commit. -- Stephen Smalley National Security Agency -- This message was distributed to subscribers of the selinux mailing list. If you no longer wish to subscribe, send mail to majordomo@tycho.nsa.gov with the words "unsubscribe selinux" without quotes as the message.