linux-kernel - Re: [PATCH v2 1/4] capabilities: Add user namespace capabilities

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Mon, 10 Jun 2024 07:48:55 -0500
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Jonathan Calmels <jcalmels@...0.net>
Cc: "Serge E. Hallyn" <serge@...lyn.com>, 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 Mon, Jun 10, 2024 at 01:47:13AM -0700, Jonathan Calmels wrote:
> 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,

Yes,

> 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.

we absolutely do not want to allow regaining caps dropped in an
ancestor namespace.

thanks,
-serge