Tema na diplomku

[Vladimir Mencl, MK, susSED]

On Fri, 1 Oct 1999, HORČIČKA Martin wrote:

> Zdravim vsechny,
> 
> nevite nekdo o nejakem zajimavem tematu na diplomku (kolem FreeBSD)? Myslim
> neco jako spojit nutne s uzitecnym.

Myslim si, ze stale zhave tema (uz nekolik let) jsou ACL.

(Uz na jare 1997, kdyz jsem mel podobne umysly, chtel jsem tenkrat delat
pro FreeBSD "masquerading", a natd me jaksi predbehl) mi nekdo ve
freebsd-hackers doporucoval ACL...

  Ted zrovna to nekdo znovu vytahl na svetlo ve freebsd-security.
(Pripojuji na konec mail, co se toho tykal....)


   Nevim, z jake skoly a fakulty jsi, a co by se u vas dalo jako
diplomka pouzit. ACL by asi urcite byly uzitecne, a asi by se tam dost
teorie na vymysleni taky dalo pripadne najit....

> 
> Odpovidejte, prosim, primo na me.

  Ja si myslim, ze tuto odpoved ma smysl poslat do konference....



					Vlada


---------- Forwarded message ----------
From: Robert Watson <robert at cyrus.watson.org>
To: Lev Serebryakov <lev at imc.macro.ru>
Cc: freebsd-security at FreeBSD.ORG
Date: Thu, 30 Sep 1999 15:21:47 -0400 (EDT)
Reply-To: Robert Watson <robert+freebsd at cyrus.watson.org>
Subject: Re: Filesystem with ACLs

On Wed, 29 Sep 1999, Lev Serebryakov wrote:

> Hi, All!
> 
>   Is here some FS with ACLs (NT or Novell Netware-like) for FreeBSD or
>   some project to add ACLs to FFS?

Over the past couple of years, a number of people have expressed interest
in an ACLfs, but the big sticking point has been the way to implement it.
The easiest way to implement would be via a file system layer--i.e.,
rather than modifying FFS itself, have a layer that you slap on top that
adds ACLs to an existing FFS file system.  However, the layering code is
at present broken in FreeBSD, so before a layer like that could be
developed, we'd have to wait for layering to be fixed :-).

The other alternatives considered include modifying FFS at a disk block
level to add space for ACLs, bind them to directories and/or files.  This
means modifying the FFS code, the file system checker, etc, and that would
be fairly painful, and probably less likely to be integrated into the base
OS because of the changes.

Another alternative is to follow the model of the Quota people--store ACL
informatino in t a file in the root directory of the FS, and dump changes
out to that file as required.

None of these is ideal--the quota and layer mechanisms due to the lack of
underlying support, and also because of the consistency issue--ACLs are
important when it comes to maintaining consistent versions of meta-data on
disk for a file.  The modification of FFS introduces significant
complications also.

If I had to implement ACLfs today, I'd probably do it the quota approach,
even though I think that's an ugly solution, as it would be easiest to
implement.  Anyone who lives in FS-land have ay news about when/whether
layering will work again someday? :-)  I saw a sequence of posts on
freebsd-fs a while back discussing fixes to the infrastructure for locking
and aliasing, but I'm really not up on that stuff.

As to the semantics of ACLs--Posix.1e defines a set of semantics and
utilities for managing ACLs.  My personal feeling is that they are overly
complex and not all that intuitive (they are the same, for reference, as
Solaris ACLs).  I prefer the Coda/AFS model of having ACLs on directories,
and having only limited permissions on files.  While this would be messy
for a lot of existing UNIX utitilies/directories, and messes up hard
links, it provides a really simple and intuitive approach to ACL
management.  At first I found it constraining, but in the end it
encouraged me to manage my directory structure better :-).  And it was
certainly easier to manage 90 sets of directory permissions that over
4000 sets of file permissions.

  Robert N M Watson 

robert at fledge.watson.org              http://www.watson.org/~robert/
PGP key fingerprint: AF B5 5F FF A6 4A 79 37  ED 5F 55 E9 58 04 6A B1
TIS Labs at Network Associates, Safeport Network Services



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