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List:       selinux
Subject:    Re: What's a policy capability?
From:       dE <de.techno () gmail ! com>
Date:       2014-07-23 6:54:36
Message-ID: 53CF595C.7060209 () gmail ! com
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On 07/22/14 17:57, Christopher J. PeBenito wrote:
> On 7/22/2014 1:03 AM, dE wrote:
>> On 07/21/14 18:21, Stephen Smalley wrote:
>>> On 07/19/2014 04:03 AM, dE wrote:
>>>> I came cross this term and couldn't find much reference to it.
>>> A mechanism for telling the kernel that your policy supports some new
>>> feature/capability and therefore it is safe for the kernel to enable the
>>> corresponding check/logic.  Used as a way of supporting new
>>> checks/features in a backward-compatible manner:  old policies will not
>>> have defined the policy capability for the new feature and therefore
>>> will not enable the new check/logic by default, while new policies can
>>> opt into or out of the new check/logic at their discretion.
>>>
>> Ok, thanks for clarifying.
>>
>> But just curious -- these new checks may not be not be backwards
>> compatible? I mean if the kernel has enabled a policy feature, but the
>> loaded policy does not have any such capability, then can it cause any
>> problems?
> Yes.  One example is the open permission on file classes.  When that was
> added in the kernel, if you didn't have a policy that had open
> permissions in it, then your system wouldn't work at all; no domain
> would be allowed to open any file.  To fix that, we added the open_perms
> capability, so you could specify that your policy was updated for the
> open permission.
>
>> Also the policy has a version, using that it's capabilities can be known
>> to the kernel and it may enable disable the features based on that. So
>> in this case, why is policy capability required?
> That versions the policy database structure itself, not which object
> classes or permissions are included.  For example, when default_*
> statements were added, the policy structure had to be changed, so the
> policy version was incremented.
>

I've noticed, that there're only 2 policy capabilities in Fedora 19.


That must means this polcap feature is relatively new.
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