patch 0/11] lsm stacking: intro

[serue]

Hi,

The set of patches to follow introduces support for stacking LSMs.  I
am sending it out in the hopes of soliciting more widespread feedback
and testing.

The patches mainly do three things:

   1. Introduce the stacker LSM.
   2. Change the kernel object void * security fields to be hlists,
      and introduce an api for modules to share these.
   3. Modify SELinux to make use of stacker.

Motivation:

The purpose of these patches is to enable stacking multiple security
modules.  There are several cases where this would be very useful.  It
eases the testing of new modules with distro kernels, as it makes it
possible to stack new modules with selinux and capabilities -- for
instance if a user is running fedora.  Second, it enables running
selinux (or LIDS, etc) with integrity verification modules.  (Digsig is
an example of these, and within a few months hopefully the TPM-enabled
slim+evm modules, which verifies integrity of file contents and extended
attributes such as selinux contexts
(http://www.acsac.org/2004/workshop/David-Safford.pdf) will be released
for mainline inclusion).  Thirdly, there are systems where running
selinux is not practical for footprint reasons, and the security goals
are easily expressed as a very small module.  For instance, it might
be desirable to confine a web browser on a zaurus, or to implement a
site security policy on old hardware as per
http://mail.wirex.com/pipermail/linux-security-module/2005-May/6071.html

Performance impact of the actual stacker module is negligable.  The
security_{get,set,del,add}_value API does have a small performance
impact.  Please see
http://marc.theaimsgroup.com/?l=linux-security-module&m=111820455332752&w=2
and
http://marc.theaimsgroup.com/?l=linux-security-module&m=111824326500837&w=2
if interested in the performance results.  I am certainly interested in
ways to further speed up security_get_value.

thanks,
-serge
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