[PATCH 4.9 22/32] lwtunnel: valid encap attr check should return 0 when lwtunnel is disabled

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Ahern <dsa@cumulusnetworks.com>


[ Upstream commit 2bd137de531367fb573d90150d1872cb2a2095f7 ]

An error was reported upgrading to 4.9.8:
    root@Typhoon:~# ip route add default table 210 nexthop dev eth0 via 10.68.64.1
    weight 1 nexthop dev eth0 via 10.68.64.2 weight 1
    RTNETLINK answers: Operation not supported

The problem occurs when CONFIG_LWTUNNEL is not enabled and a multipath
route is submitted.

The point of lwtunnel_valid_encap_type_attr is catch modules that
need to be loaded before any references are taken with rntl held. With
CONFIG_LWTUNNEL disabled, there will be no modules to load so the
lwtunnel_valid_encap_type_attr stub should just return 0.

Fixes: 9ed59592e3e3 ("lwtunnel: fix autoload of lwt modules")
Reported-by: pupilla@libero.it
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/net/lwtunnel.h |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/include/net/lwtunnel.h
+++ b/include/net/lwtunnel.h
@@ -176,7 +176,10 @@ static inline int lwtunnel_valid_encap_t
 }
 static inline int lwtunnel_valid_encap_type_attr(struct nlattr *attr, int len)
 {
-	return -EOPNOTSUPP;
+	/* return 0 since we are not walking attr looking for
+	 * RTA_ENCAP_TYPE attribute on nexthops.
+	 */
+	return 0;
 }
 
 static inline int lwtunnel_build_state(struct net_device *dev, u16 encap_type,