Subject: Re: [PATCH net-next 7/8] net/mlx5e: XDP TX forwarding support

From: Jesper Dangaard Brouer <[email-masked]>
Date: Tue, 20 Sep 2016 23:04:30 +0200

On Tue, 20 Sep 2016 09:45:28 -0700
Alexei Starovoitov <[email-masked]> wrote:

> To your other question:
> > Please explain why a eBPF program error (div by zero) must be a silent drop?  
> 
> because 'div by zero' is an abnormal situation that shouldn't be exploited.
> Meaning if xdp program is doing DoS prevention and it has a bug that
> attacker can now exploit by sending a crafted packet that causes
> 'div by zero' and kernel will warn then attack got successful.
> Therefore it has to be silent drop.

Understood and documented:
 https://github.com/netoptimizer/prototype-kernel/commit/a4e60e2d7a894

Our current solution is not very optimal, it only result in onetime
WARN_ONCE() see bpf_warn_invalid_xdp_action().  But is should not be
affected by the DoS attack scenario you described.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer