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Message-ID: <6pwskrbtmxjy2ti3xabfslmupjhat7dhrnbftinzhxgxnsveum@5jq5l6ws7hls>
Date: Mon, 10 Jun 2024 01:47:13 -0700
From: Jonathan Calmels <jcalmels@...0.net>
To: "Serge E. Hallyn" <serge@...lyn.com>
Cc: Andrew Morgan <morgan@...nel.org>, brauner@...nel.org,
 	ebiederm@...ssion.com, Jonathan Corbet <corbet@....net>,
 	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
 KP Singh <kpsingh@...nel.org>,
 	Matt Bobrowski <mattbobrowski@...gle.com>,
 Alexei Starovoitov <ast@...nel.org>,
 	Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>,
 	Martin KaFai Lau <martin.lau@...ux.dev>,
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 	Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>,
 	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, 	Luis Chamberlain <mcgrof@...nel.org>,
 Kees Cook <kees@...nel.org>, 	Joel Granados <j.granados@...sung.com>,
 John Johansen <john.johansen@...onical.com>,
 	David Howells <dhowells@...hat.com>,
 Jarkko Sakkinen <jarkko@...nel.org>,
 	Stephen Smalley <stephen.smalley.work@...il.com>,
 Ondrej Mosnacek <omosnace@...hat.com>, 	Mykola Lysenko <mykolal@...com>,
 Shuah Khan <shuah@...nel.org>, containers@...ts.linux.dev,
 	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-doc@...r.kernel.org, 	linux-security-module@...r.kernel.org,
 bpf@...r.kernel.org, apparmor@...ts.ubuntu.com,
 	keyrings@...r.kernel.org, selinux@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 1/4] capabilities: Add user namespace capabilities

On Sun, Jun 09, 2024 at 08:50:24PM GMT, Serge E. Hallyn wrote:
> On Sun, Jun 09, 2024 at 03:43:34AM -0700, Jonathan Calmels wrote:
> > Attackers often rely on user namespaces to get elevated (yet confined)
> > privileges in order to target specific subsystems (e.g. [1]). Distributions
> 
> I'd modify this to say "in order to target *bugs* in specific subsystems" :)

Ack

> > This effectively mimics the inheritable set rules and means that, by
> > default, only root in the user namespace can regain userns capabilities
> > previously dropped:
> 
> Something about this last sentence feels wrong, but I'm not sure what
> the best alternative would be.  As is, though, it makes it sound as though
> root in the userns can always regain previously dropped capabilities, but
> that's not true if dropped in ancestor ns, or if root also dropped the
> bits from its bounding set (right?).

Right, the wording is a little bit confusing here I admit.
What I meant to say is that if a cap is dropped in a *given* namespace,
then it can only be regained by root there. But yes, caps can never be
regained from ancestors ns. I'll try to rephrase it.

BTW, this is rather strict, but I think that's what we want right,
something simple? Alternative would be to have a new cap masked off by
default, but if granted to a userns, allows you to regain ancestors
caps.

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