linux-kernel - Re: [LSF TOPIC] beyond uidmapping, & towards a better security model

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Date: Sat, 17 Feb 2024 22:31:29 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	lsf-pc@...ts.linux-foundation.org
Subject: Re: [LSF TOPIC] beyond uidmapping, & towards a better security model

On Sat, Feb 17, 2024 at 03:56:40PM -0500, Kent Overstreet wrote:
> AKA - integer identifiers considered harmful

Sure, but how far are you willing to take this?  You've recently been
complaining about inode numbers:
https://lore.kernel.org/linux-fsdevel/20231211233231.oiazgkqs7yahruuw@moria.home.lan/

> The solution (originally from plan9, of course) is - UIDs shouldn't be
> numbers, they should be strings; and additionally, the strings should be
> paths.
> 
> Then, if 'alice' is a user, 'alice.foo' and 'alice.bar' would be
> subusers, created by alice without any privileged operations or mucking
> with outside system state, and 'alice' would be superuser w.r.t.
> 'alice.foo' and 'alice.bar'.

Waitwaitwait.  You start out saying "they are paths" and then you use
'.' as the path separator.  I mean, I come from a tradition that *does*
use '.' as the path separator (RISC OS, from Acorn DFS, which I believe
was influenced by the Phoenix command interpreter), but Unix tends to
use / as the separator.

One of the critical things about plan9 that means you have to think
hard before transposing its ideas to Linux is that it doesn't have suid
programs.  So if I create willy/root, it's essential that a program
which is suid only becomes suid with respect to other programs inside
willy's domain.  And it doesn't just apply to filesystem things, but
"can I send signals" and dozens of other things.  So there's a lot
to be fleshed out here.