Re: permissive vs. restrictive issue and solutions...

From: Crispin Cowan (crispinat_private)
Date: Sat Jun 02 2001 - 16:11:35 PDT

  • Next message: jmjonesat_private: "Re: permissive vs. restrictive issue and solutions..."

    jmjonesat_private wrote:
    
    > On Sat, 2 Jun 2001 Valdis.Kletnieksat_private wrote:
    > Whenever you introduce "options", you divide the audience into
    > subaudiences with differing objectives for evaluating the
    > implementation.  Since you have fewer people in "each camp", you
    > have fewer people looking at each solution.
    
    So following this argument, the security elements that are (likely) common to
    most security opions should be in the kernel, and those elements that are not
    common should be in a module.  This was the thought behind the original design,
    which leaves classic UNIX permissions in the kernel (because everyone uses them)
    and moving Capabilities to a module (because few people use them).
    
    The problem is that this separation has been found to be uncomfortable, because
    of the tension between the common desire for a restrictive-only LSM interface,
    and the occasional desire for permissive security controls.
    
    
    > The addition of chaining/stacking opens other opportunities for
    > a "commonly reviewable resource", in the same fashion that the
    > current "standard capability_plug" module needs to be reviewed
    
    Yep, that was the original design, too.
    
    So here's yet another idea:  split the LSM interface into two parts, permissive
    and restrictive.  Designers that want purely restrictive functionality use only
    the restrictive parts, and thus get easier/higher assurance. Those who want
    permissive functionality can turn it on if they need it.
    
    "Split" may be an over-statement.  Perhaps just a global switch that can disable
    the permissive interfaces would suffice?  Then a module designer could turn off
    permissiveness, and be assured that their module will "at least do no harm."
    
    Crispin
    
    --
    Crispin Cowan, Ph.D.
    Chief Scientist, WireX Communications, Inc. http://wirex.com
    Security Hardened Linux Distribution:       http://immunix.org
    Available for purchase: http://wirex.com//Products/Immunix/purchase.html
    
    
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