netdev - Re: [PATCH] net: Check skb->rxhash in gro

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Date:	Mon, 13 Jan 2014 13:37:41 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>, therbert@...gle.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH] net: Check skb->rxhash in gro_receive

On Mon, 2014-01-13 at 20:50 +0000, Ben Hutchings wrote:

> According to the original report of that vulnerability:
> 
> > skb_flow_dissect() were used by several places:                         
> > - packet scheduler that want classify flows                             
> > - skb_get_rxhash() that will be used by RPS, vxlan, multiqueue          
> > tap,macvtap packet fanout                                               
> > - skb_probe_transport_header() which was used for probing transport     
> > header for DODGY packets                                                
> > - __skb_get_poff() which will be used by socket filter             
> 
> So flow dissector is already part of the attack surface for both local
> and remote users in common configurations.

Take a debian or Android distro, and this bug is not hit on 'common
configurations'. Send them a 'packet of death', they will not hang,
unless some admin set up RPS/RFS on the incoming device.

Anyway, I see no point pushing this schem (flow dissect all incoming
packets). A router has no gain going to L4 header, but still might
need GRO.



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