netdev - Re: [Patch v2] ipv6: mld: Prevent skb_over

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Message-Id: <20140101.233022.923203259739709098.davem@davemloft.net>
Date:	Wed, 01 Jan 2014 23:30:22 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	travisb@...stanetworks.com
Cc:	netdev@...r.kernel.org, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net
Subject: Re: [Patch v2] ipv6: mld: Prevent skb_over_panic with large MTUs

From: Travis Brown <travisb@...stanetworks.com>
Date: Mon, 23 Dec 2013 15:16:21 -0800

> MLD limits the maximum skb size to fit within a single page. Later
> code uses the device MTU, if available, to determine whether the skb
> has sufficient room for another field. On interfaces with MTUs larger
> than the page size, less the skb overhead, this can result in the skb
> being overrun and a skb_over_panic being generated.
> 
> Use skb_availroom() instead of MTU check.
> 
> Signed-off-by: Travis Brown <travisb@...stanetworks.com>
> Fixes: 72e09ad107e78 ("ipv6: avoid high order allocations")

I would rather that you, for consistency, mimick what the ipv4
multicast code does, which is:

1) Try the requested size, no matter how large, then progressively
   try smaller sizes.

2) Store the obtained size in the SKB control block.

Thanks.
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