linux-kernel - Re: fs: sandboxed process brings host down

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Message-ID: <20160122212157.GG17997@ZenIV.linux.org.uk>
Date:	Fri, 22 Jan 2016 21:21:57 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	David Howells <dhowells@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Robert Swiecki <swiecki@...gle.com>,
	Kees Cook <keescook@...gle.com>
Subject: Re: fs: sandboxed process brings host down

On Fri, Jan 22, 2016 at 10:06:14PM +0100, Dmitry Vyukov wrote:
> Hello,
> 
> While running syzkaller fuzzer I hit the following problem. Supervisor
> process sandboxes worker processes that do random activities with
> CLONE_NEWUSER | CLONE_NEWNS | CLONE_NEWPID | CLONE_NEWUTS |
> CLONE_NEWNET | CLONE_NEWIPC | CLONE_IO, setrlimit, chroot, etc.
> Because of that worker process gains ability to bring whole machine
> down (does not happen without the sandbox).

AFAICS, what you are doing is essentially mount --rbind / / in infinite
loop in luserns.  Which ends up eating all memory.  There's any number
of ways to do the same.  We can play whack-a-mole with them until the
kernel is completely ossified with accounting code of different sorts.
Or one can disable userns and be done with that.