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Re: 4th set of permission bits?


From: Ivan Jager
Subject: Re: 4th set of permission bits?
Date: Fri, 01 Dec 2000 13:14:47 -0300

IMHO, the best solution would be to drop the last set of permissions and
port the ACL patch for Linux from http://acl.bestbits.at/ :) How hard
would that be?

Marcus Brinkmann wrote:
> 
> On Fri, Dec 01, 2000 at 08:05:38PM +0800, Robert Marlow wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > Hmm... I keep reading over and over and I don't see how my idea doesn't
> > work... maybe an example and you can show me where it is flawed.
> >
> > say a file begins with the permissions following:
> >
> > rwxr-xr-xr-x
> >
> > ie, the last 3 bits for the non logged-in user is defaulted to
> > the same as that of worlds (the 2nd set of 3 bits).
> 
> Explain to me how this "is defaulted to" should work in your opinion.
> Defaulted to by whom? At which time?
> 
> > Then a user, who doesn't care about setting the non logged-in user's
> > permissions any differently to worlds simply executes chmod as if
> > the non logged-in user wasn't an issue:
> >
> > chmod 700
> >
> > The outcome would be the following because the non logged-in user
> > defaults to the same permissions as world's by design
> >
> > rwx---------
> >
> > Otherwise, if a user wanted the non logged-in user to have different
> > permissions they could specify them. Something like this (though
> > it would have to be modified to avoid confusion with things like
> > sticky bits) could be used
> >
> > chmod 7550
> >
> > giving permissions of
> >
> > rwxr-xr-x---
> >
> > So basically what I'm getting at is there's no need for the extra
> > bit that I can see - the last 3 set of permissions is ALWAYS used
> > by the non logged-in user.
> 
> That would be okay so far.
> 
> > But if specifying permissions for that
> > user isn't necessary, they just default to being the same as that
> > of world's.
> 
> This is exactly what the extra bit is for. It determines if "specifying
> permissions for that user" is necessary or not. Otherwise the default would
> have to be ---.
> 
> > This way the permissions for the non logged-in user
> > is always independant of that of world's. The decision just lies
> > in whether or not to specify permissions for that user separately
> > or not. If there is something I'm still missing, please show
> > me the counterexample of why what I'm thinking wouldn't work.
> 
> The problem is that you can't say use the world's bit as a default if
> nothing else is specified, as for every chmod() you have to specify all
> permission flags, as well as for every open() with O_CREAT. The "default"
> would be ---, which is probably not what you want if you don't want the
> not-logged in user to be anything special.
> 
> Is that more clear? The way you see it it would work, but there would be no
> way to say that the default should be the same as world. That's why we have
> the extra bit, to say "independant" or "default to world".
> 
> Marcus

-- 
Ivan Jager



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