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Re: Vnode scope implementation
On Sun, Jul 19, 2009 at 03:58:40PM +0300, Elad Efrat 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
That's not MAC!
Supporting euid 0 is a reason that kauth needs to be able to switch
"not allowed" to "allowed", but without additional information (that
might be fs-specific) it is likely to turn into a too-blunt hammer.
E.g. even root isn't allowed to exec /etc/passwd, because it's not
executable. I think this requires subdividing the fs check further...
David A. Holland
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