From: Shmulik Ladkani <redacted>
Date: Fri, 28 Oct 2016 19:07:57 +0300

On Fri, 28 Oct 2016 13:13:45 +0800 Eli Cooper [off-list ref] wrote:

quoted

Maybe we
should clear IP6CB in ip6tunnel_xmit(), rather than in every tunnel's codes?

This seems reasonable.

A potential issue might be whether it needs to be done earlier, although
I've reviewed current versions of both 'ip6_tnl_xmit' and
'udp_tunnel6_xmit_skb' and it looks okay. But please verify.

quoted

By the way, I don't see any point in setting IPCB(skb)->flags in
udp_tunnel6_xmit_skb(). It will not be interpreted as IPCB any further
past ip6tunnel_xmit(), even if it were not cleared. Plus, nothing seems
to use these flags anyway.

This seems right.

It was introduced in 6a93cc9052 "udp-tunnel: Add a few more UDP tunnel APIs".

If you checkout that tree, you'll notice same treatment to
IPCB(skb)->opt and IPCB(skb)->flags in l2tp_xmit_skb... maybe it was
just copied ;-)

I think for now, we should clear IP6CB in ip6tunnel_xmit()
unconditionally, and remove the IPCB() stuff from the UDP tunneling
code.

If we need some kind of preservation of some of the IP6CB(skb)->flag
bits for whatever reason, we can add that later.  Right now that
code was producing essentially garbage.