netdev - Re: Linux kernel patch: elide fib_validate_source() completely when possible

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Message-ID: <20140123142058.GK7269@order.stressinduktion.org>
Date:	Thu, 23 Jan 2014 15:20:58 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Julian Anastasov <ja@....bg>
Cc:	David Miller <davem@...emloft.net>,
	gregory.hoggarth@...iedtelesis.co.nz, netdev@...r.kernel.org
Subject: Re: Linux kernel patch: elide fib_validate_source() completely when possible - bad side effect?

Hi Julian,

On Thu, Jan 23, 2014 at 11:47:33AM +0200, Julian Anastasov wrote:
> On Thu, 23 Jan 2014, Hannes Frederic Sowa wrote:
> 
> > E.g. we register all local registered broadcast addresses in a structure
> > like inet_addr_lst so we only need to check if the packet would leave
> > this host with a broadcast hardware address. If the packet is forwarded
> > the router must do the same check as only it knows the local broadcast
> > addresses. I hope this is correct. ;)
> 
> 	Now when we can override the local table with ip
> rules or to prepend route in local table, we can not be
> sure that the broadcast routes are returned in all cases,
> users can add unicast routes for such addresses.
> 
> 	I don't remember for useful case where one may need to
> override broadcast routes but adding such exceptions looks
> risky.

The check I envisioned would only actually block the ifa_broadcast of only the
incoming interface as source address. So we wouldn't depend on the view of the
routing tables at all.

But I have no strong opinion on that.

Greetings,

  Hannes

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