netdev - Re: Yet another bridge netfilter crash

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Message-ID: <20100723152609.GA7576@gondor.apana.org.au>
Date:	Fri, 23 Jul 2010 23:26:09 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Stephen Hemminger <shemminger@...tta.com>, netdev@...r.kernel.org
Subject: Re: Yet another bridge netfilter crash

On Fri, Jul 23, 2010 at 05:17:42PM +0200, Patrick McHardy wrote:
> 
> No concrete plans yet, but its something I'm definitely planning
> to try at some point.

Great!

> > There's also the matter of fragments jumping between bridges.
> 
> Conntrack zones can be used to avoid that, but that currently needs
> manual configuration.

I think this is something that we need to fix.  Because as it
stands, it can still crash if you get the wrong nf_bridge.

The reason is that skb->dev does not hold a ref count.  So the
reassembly code just throws it away and always uses the dev of
the last fragment.

This breaks when two bridges combine to reassemble a single
packet, as the nf_bridge attribute of the reassembled packet
may come from an skb whose device is now dead.  This is then
used to fill in the skb->dev (via nf_bridge->physindev).

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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