Re: foreign fs security features (was Re: NCPFS overhaul)

David Woodhouse (Dave@imladris.demon.co.uk)
Mon, 06 Apr 1998 18:40:22 +0200

> > The "per-user hidden file" concept is very important.
> > The UFS filesystem is going to need it for Digital Unix
> > filesystems with multi-level secure directories enabled.
> > Novell Netware support needs it. I'd guess most "Trusted *"
> > systems have the concept.
>
> Its actually something thats quite hard to do right because of the
> discovery by creation problem. That requires two people have different
> files with the same name. Then a third person who can see both comes
> along - what do they see. And more interestingly what the hell goes in
> the dcache :)
>
> [the discovery by creation problem]
>
>
> A directory fred exists you cannot see
>
> You do
>
> mkdir fred
>
> do you
>
> a) return -EEXIST revealing the invisible space
> b) create another fred
>
> if b) what does a user with rights to see both now have to watch.
>
> Alan

[ The "paint it pink and put a 'Somebody Else's Problem' field around it"
solution. ]

As far as NCPFS cares, we ask the Netware server to make "fred" under the
connection ID of the calling user, and return whatever result it gives.
I'm not re-implementing the whole Netware security model under Linux, running
the mount as "SUPERVISOR" and managing security locally - I'm letting the
Netware box do as it sees fit. For network filesystems, this is hopefully a
non-issue.

My only problem along these lines is the caching, and that I'll handle by
declaring the local cache to only be valid for the user who cached it in the
first place. That won't cause too many problems, because I personally trashed
most of the NCPFS caching in November, to ensure consistency :)

---- ---- ----
David Woodhouse, Robinson College, CB3 9AN, England. (+44) 0976 658355
Dave@imladris.demon.co.uk http://www.imladris.demon.co.uk
finger pgp@dwmw2.robinson.cam.ac.uk for PGP key.

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