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