Date: Sun, 30 Dec 2012 15:00:40 +0400 From: Vasily Kulikov <segoon@...nwall.com> To: "Eric W. Biederman" <ebiederm@...ssion.com> Cc: Containers <containers@...ts.linux-foundation.org>, "Serge E. Hallyn" <serge.hallyn@...ntu.com>, linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH/RFC] user_ns: fix missing limiting of user_ns counts On Fri, Dec 28, 2012 at 20:05 -0800, Eric W. Biederman wrote: > > A related issue which is NOT FIXED HERE is limits for all resources > > available for containerized pseudo roots. E.g. I succeeded creating > > thousands of veth network devices without problems by a non-root user, > > there seems no limit in number of network devices. I suspect it is > > possible to setup routing and net_ns'es the way it will be very > > time-consuming for kernel to handle IP packets inside of ksoftirq, which > > is not counted as this user scheduler time. I suppose the issue is not > > veth-specific, almost all newly available for unprivileged users code > > pathes are vulnerable to DoS attacks. > > veth at least should process packets synchronously so I don't see how > you will get softirq action. What do you mean -- synchronously? From my limited understanding of veth job, it is handled like every network packet in system, via: veth_xmit() -> dev_forward_skb() -> netif_rx() -> enqueue_to_backlog() enqueue_to_backlog() adds the packet to softnet_data->input_pkt_queue. Then inside of softirq process_backlog() moves ->input_pkt_queue to ->process_queue and calls __netif_receive_skb(), which does all networking stack magic. AFAICS, one could create user_ns, net_ns inside of it, and setup routing tables and netfilter to infinitely pass few network packets from and to veth, abusing ksoftirq. -- Vasily Kulikov http://www.openwall.com - bringing security into open computing environments
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