linux-kernel - Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces

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Date:	Mon, 25 Jul 2016 10:17:15 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	"Michael Kerrisk \(man-pages\)" <mtk.manpages@...il.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andrew Vagin <avagin@...tuozzo.com>,
	Linux API <linux-api@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"criu\@openvz.org" <criu@...nvz.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Andrey Vagin <avagin@...nvz.org>
Subject: Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces

"Serge E. Hallyn" <serge@...lyn.com> writes:

> Quoting Michael Kerrisk (man-pages) (mtk.manpages@...il.com):
>> Hi Eric,
>> 
>> On 07/25/2016 03:18 PM, Eric W. Biederman wrote:
>> >"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> writes:
>> >
>> >>Hi Andrey,
>> >>
>> >>On 07/22/2016 08:25 PM, Andrey Vagin wrote:
>> >>Perhaps add "and the caller does not have CAP_SYS_ADMIN" in the initial
>> >>user namespace"?
>> >
>> >Having looked at that bit of code I don't think capabilities really
>> >have a role to play.
>> 
>> Yes, I caught up with that now. I await to see how this plays out
>> in the next patch version.
>
> Thanks - that had caught my eye but I hadn't had time to look into the
> justification for this.  Hiding this kind of thing indeed seems wrong to
> me, unless there is a really good justification for it, i.e. a way
> to use that info in an exploit.

To avoid breaking checkpoint/restart we need to limit information to the
namespaces the caller is a member of for the user and pid namespaces.

This roughly duplicates the parentage checks in ns_capable.

Conceptually this is the same as limiting .. in a chroot environment.

Eric