Re: [PATCH net-next] net/vxlan: Avoid unaligned access in vxlan_build_skb()

On Tue, Sep 20, 2016 at 10:09 AM, Jiri Benc [off-list ref] wrote:

On Tue, 20 Sep 2016 18:43:33 +0200, Jiri Benc wrote:

quoted

On Tue, 20 Sep 2016 12:31:08 -0400, Sowmini Varadhan wrote:

quoted

The vxlan header is after the ethernet header (14 bytes),
IP header (20 bytes, assuming no options) and udp header (8 bytes).

If the VXLAN header is not aligned to 4 bytes, then IP header is not
aligned to 4 bytes, too, and you have greater problems than just VXLAN.

...which is indeed the case. Sorry, I guess I'm too much focused on
VXLAN-GPE nowadays and I missed that we're building this before the
inner Ethernet header.

But the point stands, we have much greater problems here than VXLAN.
And I don't think that wrapping all IP address accesses into
get/put_unaligned all around the stack is the solution.

RIght, this is problem with the encapsulations themselves. IP
protocols are supposed to be four-byte aligned and Ethernet
encapsulation is obviously breaking that. We can't address this in
existing standards like GRE-TEB, but for new encapsulations we should
make sure this avoided. I've posted on nvo3 list about this issue.

Tom

 Jiri