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SubjectRe: ext3 to include capabilities?
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weejock@ferret.lmh.ox.ac.uk said:
> On Fri, 2 Apr 1999, Pavel Machek wrote:
>
> > > > 1. Put capabilities information in the executable header.
> > > > 2. Mark the executable setuid root.
> > > > 3. Have the kernel check for #1 if #2, and prefer #1 if present.
>
> > Old security scripts program has root privileges. It is wrong, it has
> > only subset. But it is wrong _the right way_. Old scripts still see
> > the "bad scenario".
>
> > It is no-loose situation.
>
> It's a no-lose situation until you start using the new features to add
> privileges which weren't there in the first place.

That's not the common case, though - the first things that get converted to
use capabilities will surely be the existing suid stuff, won't they?

Are you suggesting that the whole system should break when you reboot to an old
kernel?

What wrong with sticking
if (geteuid() == 0 && getuid() != 0) exit(1);
in your new capability-aware utilities if it's so important to avoid suid
operation on old kernels?

A lot of people are going to want to remove the suid bit from existing
executables and add capabilities. If that then breaks when they reboot to an
old kernel, then we've done something blatantly wrong. Using the suid bit as a
marker to show the presence of a 'capability header' seems like an ideal
solution, because it provides backwards compatibility without any loss of
security in relation to the _existing_ situation. New capability-holding
utilities that were never suid and should never be suid can just include that
one-liner I gave above.



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Project Leader, Process Information Systems Mobile: (+44) 976 658355
Axiom (Cambridge) Ltd., Swaffham Bulbeck, Cambridge, CB5 0NA, UK.
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