net: openvswitch: add explicit drop action

From: Eric Garver <eric@garver.life>

This adds an explicit drop action. This is used by OVS to drop packets
for which it cannot determine what to do. An explicit action in the
kernel allows passing the reason _why_ the packet is being dropped or
zero to indicate no particular error happened (i.e: OVS intentionally
dropped the packet).

Since the error codes coming from userspace mean nothing for the kernel,
we squash all of them into only two drop reasons:
- OVS_DROP_EXPLICIT_WITH_ERROR to indicate a non-zero value was passed
- OVS_DROP_EXPLICIT to indicate a zero value was passed (no error)

e.g. trace all OVS dropped skbs

 # perf trace -e skb:kfree_skb --filter="reason >= 0x30000"
 [..]
 106.023 ping/2465 skb:kfree_skb(skbaddr: 0xffffa0e8765f2000, \
  location:0xffffffffc0d9b462, protocol: 2048, reason: 196611)

reason: 196611 --> 0x30003 (OVS_DROP_EXPLICIT)

Also, this patch allows ovs-dpctl.py to add explicit drop actions as:
  "drop"     -> implicit empty-action drop
  "drop(0)"  -> explicit non-error action drop
  "drop(42)" -> explicit error action drop

Signed-off-by: Eric Garver <eric@garver.life>
Co-developed-by: Adrian Moreno <amorenoz@redhat.com>
Signed-off-by: Adrian Moreno <amorenoz@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index bb7aa181da30..e188f32ea96f 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -1485,6 +1485,15 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 				return dec_ttl_exception_handler(dp, skb,
 								 key, a);
 			break;
+
+		case OVS_ACTION_ATTR_DROP: {
+			enum ovs_drop_reason reason = nla_get_u32(a)
+				? OVS_DROP_EXPLICIT_WITH_ERROR
+				: OVS_DROP_EXPLICIT;
+
+			ovs_kfree_skb_reason(skb, reason);
+			return 0;
+		}
 		}
 
 		if (unlikely(err)) {