netdev - Re: [PATCH] net:ppp: replace too strict capability restriction on opening /dev/ppp

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Message-ID: <87wplkihbp.fsf@tassilo.jf.intel.com>
Date:	Sun, 19 Jun 2016 22:02:02 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Shanker Wang <shanker@...a.tsinghua.edu.cn>
Cc:	netdev@...r.kernel.org,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Guillaume Nault <g.nault@...halink.fr>,
	Miao Wang <shankerwangmiao@...il.com>
Subject: Re: [PATCH] net:ppp: replace too strict capability restriction on opening  /dev/ppp

Shanker Wang <shanker@...a.tsinghua.edu.cn> writes:

> This patch removes the check for CAP_NET_ADMIN in the initial namespace
> when opening /dev/open. Instead, CAP_NET_ADMIN is checked in the user
> namespace the net namespace was created so that /dev/ppp cat get opened
> in a unprivileged container.

Seems dangerous. From a quick look at the PPP ioctl there is no limit
how many PPP devices this can create. So a container having access to
this would be able to fill all kernel memory. Probably needs more
auditing and hardening first.

In general there seems to be a lot of attack surface for root
in PPP.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only