linux-kernel - Re: [RFC PATCH 1/2] devices cgroup: allow can_attach() if ns

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]

Message-ID: <20130723190426.GA9577@tp>
Date:	Tue, 23 Jul 2013 14:04:26 -0500
From:	Serge Hallyn <serge.hallyn@...ntu.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Containers <containers@...ts.linux-foundation.org>
Subject: Re: [RFC PATCH 1/2] devices cgroup: allow can_attach() if ns_capable

Quoting Tejun Heo (tj@...nel.org):
> On Tue, Jul 23, 2013 at 2:38 PM, Serge Hallyn <serge.hallyn@...ntu.com> wrote:
> > This doesn't delegate it into the container.  It allows me, on the host,
> > to set the cgroup for a container.
> 
> Hmmm? I'm a bit confused. Isn't the description saying that the patch
> allows pseudo-root in userns to change cgroup membership even if it
> isn't actually root?

If task A is uid 1000 on the host, and creates task B as uid X in a new
user namespace, then task A, still being uid 1000 on the host, is
privileged with respect to B and his namespace - i.e.
ns_capable(B->userns, CAP_SYS_ADMIN) is true.

> Besides, I find the whole check rather bogus and would actually much
> prefer just nuking the check and just follow the standard permission
> checks.

I'd be ok with that - but there's one case I'm not sure about:  If PAM
sets me up with /sys/fs/cgroup/devices/serge owned by me, then if I'm
thinking right, removing can_attach would mean I could move init into
/sys/fs/cgroup/devices/serge...

Is there something else stopping that from happening?

-serge
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/