Re: Posix capabilities

From: Olaf Dietsche (
Date: Thu Oct 17 2002 - 05:37:30 EST

"Theodore Ts'o" <> writes:

> Personally, I'm not so convinced that capabilities are such a great
> idea. System administrators have a hard enough time keeping 12 bits
> of permissions correct on executable files; with capabilities they
> have to keep track of several hundred bits of capabilties flags, which

So you claim, system administrators are stupid people?

> must be set precisely correctly, or the programs will either (a) fail
> to function,

Which you will notice very fast.

> or (b) have a gaping huge security hole.

Which is not worse, but possibly a lot better, than setuid root.

> This probablem could be solved with some really scary, complex user
> tools (which no one has written yet). Alternatively you could just
> let programs continue to be setuid root, but modify the executable to
> explicitly drop all the capabilities except for the ones that are
> actually needed as one of the first things that executable does. It

Which isn't convincing, either. The benefit of capabilities is to
administer your system _without_ relying on someone else doing a
decent job.

> perhaps only gives you 90% of the benefits of the full-fledged
> capabilities model, but it's much more fool proof, and much easier to
> administer.

With capabilities you don't have to resort to programming, which _is_
already an easier way to administer. This also means, distribution
builders, who may not be coders, can contribute to enhance security.

Maybe this sounds like a plea for capabilities and maybe it is, but I
just want to put some things straight. Unless there's something
better, I stay with capabilities.

To be more constructive, I want to point to
<>. This is a modified
start-stop-daemon, which allows to change capabilities. With this
really scary, complex user tool (which to some extent it is, when you
look at the code), I was able to drop all the capabilities except for
the ones that are actually needed. ;-)

Regards, Olaf.
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