[PATCH 2/2] openvswitch: Fix condition check in output_userspace() by using nla_ok()

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() -> output_userspace(), 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 <redacted>
---
 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 c23537f..e8236dd 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c

@@ -915,8 +915,7 @@ static int output_userspace(struct datapath *dp, struct sk_buff *skb,
 	upcall.cmd = OVS_PACKET_CMD_ACTION;
 	upcall.mru = OVS_CB(skb)->mru;
 
-	for (a = nla_data(attr), rem = nla_len(attr); rem > 0;
-	     a = nla_next(a, &rem)) {
+	nla_for_each_nested(a, attr, rem) {
 		switch (nla_type(a)) {
 		case OVS_USERSPACE_ATTR_USERDATA:
 			upcall.userdata = a;

-- 
2.7.4

On Fri, Sep 17, 2021 at 1:25 AM Jiasheng Jiang [off-list ref] wrote:

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() -> output_userspace(), 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 <redacted>

These nl-attributes are built and verified at time of OVS flow
install, so the rest of checks in nla_ok, is not required.