openvswitch: Avoid memory corruption in queue_userspace_packet()

In queue_userspace_packet(), the ovs_nla_put_flow return value is
not checked. This is fine as long as key_attr_size() returns the
correct value. In case it does not, the current code may corrupt buffer
memory. Add a run time assertion catch this case to avoid silent
failure.
Reported-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: Andy Zhou <azhou@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>

net/openvswitch/datapath.c

@@ -464,7 +464,8 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb,
 	upcall->dp_ifindex = dp_ifindex;
 
 	nla = nla_nest_start(user_skb, OVS_PACKET_ATTR_KEY);
-	ovs_nla_put_flow(upcall_info->key, upcall_info->key, user_skb);
+	err = ovs_nla_put_flow(upcall_info->key, upcall_info->key, user_skb);
+	BUG_ON(err);
 	nla_nest_end(user_skb, nla);
 
 	if (upcall_info->userdata)