linux-kernel - Re: [PATCH] Security: Add __init to register_security to disable load a security module on runtime

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Message-Id: <201002271530.JCB31845.FOLJMFVFOHtQSO@I-love.SAKURA.ne.jp>
Date:	Sat, 27 Feb 2010 15:30:01 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	wzt.wzt@...il.com
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, sds@...ho.nsa.gov,
	jmorris@...ei.org
Subject: Re: [PATCH] Security: Add __init to register_security to disable load a security module on runtime

Zhitong Wang wrote:
> LSM original intention is not allowed to load security modules on runtime, right?

My understanding is that the reason register_security() became no longer
exported to loadable kernel modules is the difficulty of cleanly
initializing/finalizing security modules since security modules usually
allocate/release memory on various structures. When that change happened
(i.e. as of 2.6.24), SELinux was the only in-tree LSM user.

Those security modules which needn't to allocate/release memory on various
structures can be loaded on runtime, if register_security() is exported to
loadable kernel modules.

If a distribution user adds a loadable kernel module (which is not a security
module) which distributor didn't select, the user can get distributor's support
except problems caused by that module.

However, due to limitation that security modules cannot be added as loadable
kernel modules, when a distribution user wants to select security modules which
distributor didn't select, distributor's support is no longer provided
(i.e. not only problems caused by the security modules selected by the user
but also problems caused by the rest of kernel and userland).

What's the difference between a kernel module which uses LSM and a kernel
module which does not use LSM? Any kernel modules can cause severe problems.

My understanding is that LSM's original intention is to allow Linux users to
select security modules. Why LSM places security modules under adverse condition?
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