linux-kernel - Re: [PATCH v4 4/7] fs: Limit file caps to the user namespace of the super block

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Message-ID: <87k2reidqf.fsf@x220.int.ebiederm.org>
Date:	Fri, 25 Sep 2015 12:57:12 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Seth Forshee <seth.forshee@...onical.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	James Morris <james.l.morris@...cle.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Andy Lutomirski <luto@...capital.net>,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org
Subject: Re: [PATCH v4 4/7] fs: Limit file caps to the user namespace of the super block

Seth Forshee <seth.forshee@...onical.com> writes:

> On Thu, Sep 24, 2015 at 04:59:35PM -0500, Eric W. Biederman wrote:
>> Seth Forshee <seth.forshee@...onical.com> writes:
>> 
>> > Capability sets attached to files must be ignored except in the
>> > user namespaces where the mounter is privileged, i.e. s_user_ns
>> > and its descendants. Otherwise a vector exists for gaining
>> > privileges in namespaces where a user is not already privileged.
>> >
>> > Add a new helper function, in_user_ns(), to test whether a user
>> > namespace is the same as or a descendant of another namespace.
>> > Use this helper to determine whether a file's capability set
>> > should be applied to the caps constructed during exec.
>> 
>> No issues with this but given that we always pass current_user_ns()
>> we may want to simplify the users of in_user_ns by renaming it
>> current_in_user_ns() and hard codeing current_user_ns().
>
> Sure, if that's what you prefer then I'll change it.

I took your patch as is.  This is a suggestion for a possible
incremental improvement.

Eric
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