Re: Where Are We?

From: Stephen Smalley (sdsat_private)
Date: Wed Jun 06 2001 - 10:14:16 PDT

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

    On Wed, 6 Jun 2001 jmjonesat_private wrote:
    
    > Stephen Smalley: The minimal invasive hook is to let the kernel
    >           have its way, then potentially override it with the module,
    >           but capabilities have to stay for political reasons.
    
    Keeping capabilities is not just political - it is also practical,
    allowing us to leverage the work already done by Linux-Privs.
    I'll try to briefly summarize my proposal, adjusting it to
    reflect some of the follow-on discussion.  But I'm not
    worrying about word counts.  Here is my proposal:
    
    1) We keep the capabilities module, but we revert the calls to capable()
    in the kernel.  The capable() function remains as a stub that calls the
    LSM capable() hook.  We also replace the capabilities system calls with 
    stubs that call LSM hooks, and move their functionality into the 
    capabilities module.  We partition the ptrace and execve/compute_creds
    logic to separate out the logic that should be private to the
    capabilities module from the base kernel DAC logic.
    
    2) All LSM hooks other than capable() should be used authoritatively.
    If kernel logic exists that corresponds to a LSM hook and if
    the hook can be colocated with the kernel logic, then the
    kernel decision is computed and passed to the hook as an
    additional parameter, and the hook returns the final decision.
    
    3) In some cases, we may add other LSM hooks to operations that are
    already authoritatively controlled by capable() in order to 
    provide finer-grained distinctions than are possible with the
    capable() calls.  But we try to leverage the existing capable() calls 
    to the greatest extent possible, only introducing these finer-grained
    hooks where we have a clear argument that the capable() call is
    inadequate.
    
    --
    Stephen D. Smalley, NAI Labs
    ssmalleyat_private
    
    
    
    
    
    
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