Re: [PATCH] Smack: Simplified Mandatory Access Control Kernel

[Keith Owens <kaos@ocs.com.au>]

Casey Schaufler (on Sat, 11 Aug 2007 10:57:31 -0700) wrote:
>Smack is the Simplified Mandatory Access Control Kernel.
>
> [snip]
>
>Smack defines and uses these labels:
>
>    "*" - pronounced "star"
>    "_" - pronounced "floor"
>    "^" - pronounced "hat"
>    "?" - pronounced "huh"
>
>The access rules enforced by Smack are, in order:
>
>1. Any access requested by a task labeled "*" is denied.
>2. A read or execute access requested by a task labeled "^"
>   is permitted.
>3. A read or execute access requested on an object labeled "_"
>   is permitted.
>4. Any access requested on an object labeled "*" is permitted.
>5. Any access requested by a task on an object with the same
>   label is permitted.
>6. Any access requested that is explicitly defined in the loaded
>   rule set is permitted.
>7. Any other access is denied.

Some security systems that have the concept of "no default access"
(task labeled "*") also allow access by those tasks but only if there
is an explicit rule giving access to the task.  IOW, rule 6 is applied
before rule 1.  In my experience this simplifies special cases where a
task should only have access to a very small set of resources.  I'm
curious why smack goes the other way?