netdev - Re: [RFC PATCH] xfrm: Add option to reset oif in xfrm lookup

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Message-ID: <20160728050828.GJ5710@gauss.secunet.com>
Date:	Thu, 28 Jul 2016 07:08:28 +0200
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
CC:	<dsa@...ulusnetworks.com>, <netdev@...r.kernel.org>,
	<herbert@...dor.apana.org.au>
Subject: Re: [RFC PATCH] xfrm: Add option to reset oif in xfrm lookup

On Mon, Jul 25, 2016 at 06:34:32PM -0600, Subash Abhinov Kasiviswanathan wrote:
> We are seeing incorrect routing when tunneling packets over an
> interface and sending it over another interface. This scenario
> worked on 3.18 (and earlier) and failed on 4.4 kernel. The rules
> / routes / policies were the same across kernels.
> 
> Commit 42a7b32b73d6 ("xfrm: Add oif to dst lookups") allowed
> preservation of the oif from a raw packet to a transformed packet.
> This causes issues with forwarding scenarios where the
> existing oif causes an incorrect route lookup.
> 
> Create a new sysctl which resets oif in xfrm policy. Default value
> is 0 which means that oif is preserved on transform.

Please don't try to workaround a bug with a sysctl.
If we have a bug here, we should fix it. Choosing
between bug A and bug B with a sysctl is not what
we are doing ;)