[PATCH v2] openvswitch: Fix condition check in do_execute_actions() by using nla_ok()

[Jiasheng Jiang <jiasheng@iscas.ac.cn>]

Just using 'rem > 0' might be unsafe, so it's better
to use the nla_ok() instead.
Because we can see from the nla_next() that
'*remaining' might be smaller than 'totlen'. And nla_ok()
will avoid it happening.
For example, ovs_dp_process_packet() -> ovs_execute_actions()
-> do_execute_actions(), and attr comes from OVS_CB(skb)->input_vport,
which restores the received packet from the user space.

Fixes: ccb1352e76cff0524e7ccb2074826a092dd13016
('net: Add Open vSwitch kernel components.')
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
---
 net/openvswitch/actions.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index 77d924a..c23537f 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -1238,8 +1238,7 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 	const struct nlattr *a;
 	int rem;
 
-	for (a = attr, rem = len; rem > 0;
-	     a = nla_next(a, &rem)) {
+	nla_for_each_attr(a, attr, len, rem) {
 		int err = 0;
 
 		switch (nla_type(a)) {
-- 
2.7.4