netdev - Re: [PATCH net-next] net/vxlan: Avoid unaligned access in vxlan_build

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Message-ID: <20160920154905.GN8920@oracle.com>
Date:   Tue, 20 Sep 2016 11:49:05 -0400
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Benc <jbenc@...hat.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Alexander Duyck <aduyck@...antis.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next] net/vxlan: Avoid unaligned access in
 vxlan_build_skb()

On (09/20/16 08:31), Tom Herbert wrote:
> 
> On Tue, Sep 20, 2016 at 7:27 AM, Sowmini Varadhan
> <sowmini.varadhan@...cle.com> wrote:
> > The vxlan header is at offset (14 + 20 + 8) into the packet,
> > so the vxh is not aligned in vxlan_build_skb. Use [get/put]_unaligned
> > functions to modify flags and vni field in the vxh.
> >
> I'm wondering if VXLAN is just the tip of the iceberg. Wouldn't this
> is also be a problem in GRE and Geneve when they encapsulate Ethernet?
> What about the outer IP header, wouldn't that potentially have
> unaligned accesses also when creating it?

Indeed. All of the above are true, and we have to conquer
each unaligned access, one at a time.

There's also the over-arching problem of arbitrary encapsulations
introducing intervening headers that throw off alignment. 
That would be a design discussion to be had with the ietf.

--Sowmini