On egress side, xfrm lookup is called from __gre6_xmit() with the
fl6_gre_key field not initialized leading to policies selectors check
failure. Consequently, gre packets are sent without encryption.

On ingress side, INET6_PROTO_NOPOLICY was set, thus packets were not
checked against xfrm policies. Like for egress side, fl6_gre_key should be
correctly set, this is now done in decode_session6().

Fixes: c12b395a ("gre: Support GRE over IPv6")
Cc: stable@vger.kernel.org
Signed-off-by: NGhalem Boudour <ghalem.boudour@6wind.com>
Signed-off-by: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>