[v3.18] Fixes for ip_vti and ip6_vti

[v3.18] Fixes for ip_vti and ip6_vti

[Nicolas Dichtel]

Hi,

since commit ca7c7b9059e3 ("skbuff: Do not scrub skb mark within the same name
space", backport of upstream commit 213dd74aee76), the following three upstream
commits need also to be backported in the 3.18 branch:
  - cd5279c194f8 ("ip_vti/ip6_vti: Do not touch skb->mark on xmit")
  - 049f8e2e28d9 ("xfrm: Override skb->mark with tunnel->parm.i_key in
    xfrm_input")
  - d55c670cbc54 ("ip_vti/ip6_vti: Preserve skb->mark after rcv_cb call")

When the packet is handled by the ip_vti interface, it is temporarily marked
with the ip_vti interface key. Once the process is completed, the packet is
received via the ip_vti interface and its original mark should be restored
(typically to 0).
Before the backported patch, ip_vti counted on skb_scrub_packet to reset the
mark, but skb_scrub_packet nomore does.
Since the packet is still marked, it will match the outbound SP and so be
encrypted again.


Regards,
Nicolas