Re: Vnode scope implementation

[Elad Efrat <elad%NetBSD.org@localhost>]

On Sun, Jul 19, 2009 at 3:49 PM, YAMAMOTO 
Takashi<yamt%mwd.biglobe.ne.jp@localhost> wrote:
> hi,
>
>> On Sun, Jul 19, 2009 at 10:34 AM, YAMAMOTO
>> Takashi<yamt%mwd.biglobe.ne.jp@localhost> wrote:
>>
>>> can you explain what's the point to call kauth when fs_decision is
>>> already non-0?
>>> i don't think it's a good idea to let kauth allow operations which
>>> have already been rejected by the filesystem itself.
>>
>> I think it's a very good idea, because then kauth(9) can implement MACs.
>
> can you explain how it's required for MAC?  it isn't clear to me.

Consider a file owned by yamt:yamt (say, 1000:1000) with permissions
0600. Let's say root is trying to access that file. Because root has
euid 0, and the file has uid 1000, the file-system will deny access
due to uid mismatch. However, once kauth(9) gets a chance to flip the
decision, it can say, "but really, euid 0 should have access to this
file".

Consider also someone trying to create an "isolating" secmodel, where
once a uid is in the list, it can't do anything. If you can't flip
decisions, the file-system will allow it to access its own files, no?

-e.