net: openvswitch: Add a new action check_pkt_len

This patch adds a new action - 'check_pkt_len' which checks the
packet length and executes a set of actions if the packet
length is greater than the specified length or executes
another set of actions if the packet length is lesser or equal to.

This action takes below nlattrs
  * OVS_CHECK_PKT_LEN_ATTR_PKT_LEN - 'pkt_len' to check for

  * OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER - Nested actions
    to apply if the packet length is greater than the specified 'pkt_len'

  * OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL - Nested
    actions to apply if the packet length is lesser or equal to the
    specified 'pkt_len'.

The main use case for adding this action is to solve the packet
drops because of MTU mismatch in OVN virtual networking solution.
When a VM (which belongs to a logical switch of OVN) sends a packet
destined to go via the gateway router and if the nic which provides
external connectivity, has a lesser MTU, OVS drops the packet
if the packet length is greater than this MTU.

With the help of this action, OVN will check the packet length
and if it is greater than the MTU size, it will generate an
ICMP packet (type 3, code 4) and includes the next hop mtu in it
so that the sender can fragment the packets.

Reported-at:
https://mail.openvswitch.org/pipermail/ovs-discuss/2018-July/047039.html
Suggested-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Numan Siddique <nusiddiq@redhat.com>
CC: Gregory Rose <gvrose8192@gmail.com>
CC: Pravin B Shelar <pshelar@ovn.org>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Tested-by: Greg Rose <gvrose8192@gmail.com>
Reviewed-by: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 42 insertions, 0 deletions

diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
index dbe0cbe4f1b7..dfabacee6903 100644
--- a/include/uapi/linux/openvswitch.h
+++ b/include/uapi/linux/openvswitch.h
@@ -798,6 +798,44 @@ struct ovs_action_push_eth {
         struct ovs_key_ethernet addresses;
 };
 
+/*
+ * enum ovs_check_pkt_len_attr - Attributes for %OVS_ACTION_ATTR_CHECK_PKT_LEN.
+ *
+ * @OVS_CHECK_PKT_LEN_ATTR_PKT_LEN: u16 Packet length to check for.
+ * @OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER: Nested OVS_ACTION_ATTR_*
+ * actions to apply if the packer length is greater than the specified
+ * length in the attr - OVS_CHECK_PKT_LEN_ATTR_PKT_LEN.
+ * @OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL - Nested OVS_ACTION_ATTR_*
+ * actions to apply if the packer length is lesser or equal to the specified
+ * length in the attr - OVS_CHECK_PKT_LEN_ATTR_PKT_LEN.
+ */
+enum ovs_check_pkt_len_attr {
+        OVS_CHECK_PKT_LEN_ATTR_UNSPEC,
+        OVS_CHECK_PKT_LEN_ATTR_PKT_LEN,
+        OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER,
+        OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL,
+        __OVS_CHECK_PKT_LEN_ATTR_MAX,
+
+#ifdef __KERNEL__
+        OVS_CHECK_PKT_LEN_ATTR_ARG          /* struct check_pkt_len_arg  */
+#endif
+};
+
+#define OVS_CHECK_PKT_LEN_ATTR_MAX (__OVS_CHECK_PKT_LEN_ATTR_MAX - 1)
+
+#ifdef __KERNEL__
+struct check_pkt_len_arg {
+        u16 pkt_len;    /* Same value as OVS_CHECK_PKT_LEN_ATTR_PKT_LEN'. */
+        bool exec_for_greater;  /* When true, actions in IF_GREATER will
+                                 * not change flow keys. False otherwise.
+                                 */
+        bool exec_for_lesser_equal; /* When true, actions in IF_LESS_EQUAL
+                                     * will not change flow keys. False
+                                     * otherwise.
+                                     */
+};
+#endif
+
 /**
  * enum ovs_action_attr - Action types.
  *
@@ -842,6 +880,9 @@ struct ovs_action_push_eth {
  * packet, or modify the packet (e.g., change the DSCP field).
  * @OVS_ACTION_ATTR_CLONE: make a copy of the packet and execute a list of
  * actions without affecting the original packet and key.
+ * @OVS_ACTION_ATTR_CHECK_PKT_LEN: Check the packet length and execute a set
+ * of actions if greater than the specified packet length, else execute
+ * another set of actions.
  *
  * Only a single header can be set with a single %OVS_ACTION_ATTR_SET.  Not all
  * fields within a header are modifiable, e.g. the IPv4 protocol and fragment
@@ -876,6 +917,7 @@ enum ovs_action_attr {
         OVS_ACTION_ATTR_POP_NSH,      /* No argument. */
         OVS_ACTION_ATTR_METER,        /* u32 meter ID. */
         OVS_ACTION_ATTR_CLONE,        /* Nested OVS_CLONE_ATTR_*.  */
+        OVS_ACTION_ATTR_CHECK_PKT_LEN, /* Nested OVS_CHECK_PKT_LEN_ATTR_*. */
 
         __OVS_ACTION_ATTR_MAX,        /* Nothing past this will be accepted
                                        * from userspace. */