netdev - Re: [PATCH] phonet: Check input from user before allocating

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Message-ID: <1333417997.18626.1.camel@edumazet-glaptop>
Date:	Tue, 03 Apr 2012 03:53:17 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	remi@...lab.net, levinsasha928@...il.com,
	remi.denis-courmont@...ia.com, davej@...hat.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] phonet: Check input from user before allocating

On Mon, 2012-04-02 at 17:40 -0400, David Miller wrote:
> From: "Rémi Denis-Courmont" <remi@...lab.net>
> Date: Mon, 2 Apr 2012 22:01:40 +0300
> 
> > Le lundi 2 avril 2012 23:31:00 Sasha Levin, vous avez écrit :
> >> A phonet packet is limited to USHRT_MAX bytes, this is never checked during
> >> tx which means that the user can specify any size he wishes, and the kernel
> >> will attempt to allocate that size.
> > 
> > Does this really solve the problem?  I guess 128kb is still possible with 
> > USHRT_MAX plus skbuff overhead, which might still trigger OOM relatively 
> > easily once the memory gets sufficiently fragmented.
> > 
> > How does UDP deal with this?
> 
> UDP generates a fragment list of MTU sized SKBs.
> 
> Phonet could avoid the large allocations by building page based
> SKBs.

Not that AF_UNIX does nothing in this respect, it can use order-XX pages
for large datagrams.

(I beleve I sent a patch some time ago to address this point)



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