Re: [PATCH] libselinux: add "poly_property" type to X contexts backend

[Eamon Walsh <ewalsh@tycho.nsa.gov>]

Glenn Faden wrote:
> Eamon Walsh wrote:
>   
>> Xavier Toth wrote:
>>     
>>> I'm curious as to why you chose the route of specifying which
>>> properties are polyinstantiated instead of which are not bearing in
>>> mind what Glenn said in a previous post?
>>>   
>>>       
>> The server will check the "property" lines first and if it doesn't 
>> find a match it will check the "poly_property" lines.  So, as long as 
>> the wildcard entry in the x_contexts file is changed from property to 
>> poly_property, the default will be to polyinstantiate.
>>
>> However I wasn't planning on treating the root window any differently 
>> from other windows, so this behavior would apply to all windows.
>>     
> I've never seen a requirement for polyinstantiation of properties on 
> per-client windows. I've seen requirements for relabeling properties, 
> however. For example, the trusted selection manager needs to create 
> properties that are readable by the client who requests a 
> ConvertSelection. We do this by calling a new X protocol extension.

SELinux protocol extension allows clients to create windows and 
properties with different security contexts.

>  How 
> do you plan to have trusted clients act on behalf of other clients with 
> different security contexts?

I haven't done the polyinstantiation for selections yet, but my current 
plan is to implement a trusted clipboard manager that will display the 
various clipboard contents and allow users to upgrade or downgrade, 
which means that the clipboard manager will take ownership of the 
selection at the target level and just pipe the data through.  This 
scheme shouldn't require tweaking properties on the fly.  However this 
would not be point-to-point but would make the selection available to 
all applications at the target level.

> Similarly, how can a trusted client 
> read/write a polyinstantiated property with a different security context?
>   

By launching a helper process at the appropriate level.


-- 
Eamon Walsh <ewalsh@tycho.nsa.gov>
National Security Agency


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