netdev - Re: Possible networking regression in 3.6.0

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Date:	Tue, 02 Oct 2012 23:10:37 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	ja@....bg
Cc:	eric.dumazet@...il.com, chris2553@...glemail.com,
	netdev@...r.kernel.org, gpiez@....de, davej@...hat.com
Subject: Re: Possible networking regression in 3.6.0

From: Julian Anastasov <ja@....bg>
Date: Wed, 3 Oct 2012 02:24:53 +0300 (EEST)

> 	Can it be a problem related to fib_info reuse
> from different routes. For example, when local IP address
> is created for subnet we have:
> 
> broadcast 192.168.0.255 dev DEV  proto kernel  scope link  src 192.168.0.1
> 192.168.0.0/24 dev DEV  proto kernel  scope link  src 192.168.0.1
> local 192.168.0.1 dev DEV  proto kernel  scope host  src 192.168.0.1
> 
> 	The "dev DEV  proto kernel  scope link  src 192.168.0.1" is
> a reused fib_info structure where we put cached routes.
> The result can be same fib_info for 192.168.0.255 and
> 192.168.0.0/24. RTN_BROADCAST is cached only for input
> routes. Incoming broadcast to 192.168.0.255 can be cached
> and can cause problems for traffic forwarded to 192.168.0.0/24.
> So, this patch should solve the problem because it
> separates the broadcast from unicast traffic.

Now I understand the problem.

I think the way to fix this is to add cfg->fc_type as another
thing that fib_info objects are key'd by.

I think it also would fix your obscure output multicast case too.
 
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