netdev - Re: [PATCH] tcp: Avoid infinite loop on recvmsg bug

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Date:	Wed, 07 Nov 2012 15:33:12 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Julius Werner <jwerner@...omium.org>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Patrick McHardy <kaber@...sh.net>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	James Morris <jmorris@...ei.org>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Dave Jones <davej@...hat.com>,
	Sameer Nanda <snanda@...omium.org>,
	Mandeep Singh Baines <msb@...omium.org>
Subject: Re: [PATCH] tcp: Avoid infinite loop on recvmsg bug

On Wed, 2012-11-07 at 13:14 -0800, Julius Werner wrote:
> > What I find very sad in all this is that you didnt mention the driver
> > that was triggering this bug.
> 
> Sorry, I was just trying to keep this thread focussed on one patch.
> The bug report that led me to this is publicly accessible at
> http://crosbug.com/35827. We have encountered the problem only once,
> on an Acer AC700 Chromebook that ran automated tests. The ethernet
> interface for the offending socket was provided by a USB-to-Ethernet
> dongle using the smsc95xx/usbnet module (v1.0.4).

This driver uses interesting skb_clone() games and skb->truesize lies :

skb->truesize = size + sizeof(struct sk_buff);

So you probably are fighting a bug we already fixed in upstream kernel.

(commit c8628155ece363 "tcp: reduce out_of_order memory use" did not
played well with cloned skbs.)

This issue was already discussed on netdev in the past.



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