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>

2 files changed, 219 insertions, 0 deletions

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index e47ebbbe71b8..2c151bb322c1 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -169,6 +169,10 @@ static int clone_execute(struct datapath *dp, struct sk_buff *skb,
 			 const struct nlattr *actions, int len,
 			 bool last, bool clone_flow_key);
 
+static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
+			      struct sw_flow_key *key,
+			      const struct nlattr *attr, int len);
+
 static void update_ethertype(struct sk_buff *skb, struct ethhdr *hdr,
 			     __be16 ethertype)
 {
@@ -1213,6 +1217,40 @@ static int execute_recirc(struct datapath *dp, struct sk_buff *skb,
 	return clone_execute(dp, skb, key, recirc_id, NULL, 0, last, true);
 }
 
+static int execute_check_pkt_len(struct datapath *dp, struct sk_buff *skb,
+				 struct sw_flow_key *key,
+				 const struct nlattr *attr, bool last)
+{
+	const struct nlattr *actions, *cpl_arg;
+	const struct check_pkt_len_arg *arg;
+	int rem = nla_len(attr);
+	bool clone_flow_key;
+
+	/* The first netlink attribute in 'attr' is always
+	 * 'OVS_CHECK_PKT_LEN_ATTR_ARG'.
+	 */
+	cpl_arg = nla_data(attr);
+	arg = nla_data(cpl_arg);
+
+	if (skb->len <= arg->pkt_len) {
+		/* Second netlink attribute in 'attr' is always
+		 * 'OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL'.
+		 */
+		actions = nla_next(cpl_arg, &rem);
+		clone_flow_key = !arg->exec_for_lesser_equal;
+	} else {
+		/* Third netlink attribute in 'attr' is always
+		 * 'OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER'.
+		 */
+		actions = nla_next(cpl_arg, &rem);
+		actions = nla_next(actions, &rem);
+		clone_flow_key = !arg->exec_for_greater;
+	}
+
+	return clone_execute(dp, skb, key, 0, nla_data(actions),
+			     nla_len(actions), last, clone_flow_key);
+}
+
 /* Execute a list of actions against 'skb'. */
 static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 			      struct sw_flow_key *key,
@@ -1374,6 +1412,16 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 
 			break;
 		}
+
+		case OVS_ACTION_ATTR_CHECK_PKT_LEN: {
+			bool last = nla_is_last(a, rem);
+
+			err = execute_check_pkt_len(dp, skb, key, a, last);
+			if (last)
+				return err;
+
+			break;
+		}
 		}
 
 		if (unlikely(err)) {
diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
index 691da853bef5..b7543700db87 100644
--- a/net/openvswitch/flow_netlink.c
+++ b/net/openvswitch/flow_netlink.c
@@ -91,6 +91,7 @@ static bool actions_may_change_flow(const struct nlattr *actions)
 		case OVS_ACTION_ATTR_SET:
 		case OVS_ACTION_ATTR_SET_MASKED:
 		case OVS_ACTION_ATTR_METER:
+		case OVS_ACTION_ATTR_CHECK_PKT_LEN:
 		default:
 			return true;
 		}
@@ -2838,6 +2839,87 @@ static int validate_userspace(const struct nlattr *attr)
 	return 0;
 }
 
+static const struct nla_policy cpl_policy[OVS_CHECK_PKT_LEN_ATTR_MAX + 1] = {
+	[OVS_CHECK_PKT_LEN_ATTR_PKT_LEN] = {.type = NLA_U16 },
+	[OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER] = {.type = NLA_NESTED },
+	[OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL] = {.type = NLA_NESTED },
+};
+
+static int validate_and_copy_check_pkt_len(struct net *net,
+					   const struct nlattr *attr,
+					   const struct sw_flow_key *key,
+					   struct sw_flow_actions **sfa,
+					   __be16 eth_type, __be16 vlan_tci,
+					   bool log, bool last)
+{
+	const struct nlattr *acts_if_greater, *acts_if_lesser_eq;
+	struct nlattr *a[OVS_CHECK_PKT_LEN_ATTR_MAX + 1];
+	struct check_pkt_len_arg arg;
+	int nested_acts_start;
+	int start, err;
+
+	err = nla_parse_strict(a, OVS_CHECK_PKT_LEN_ATTR_MAX, nla_data(attr),
+			       nla_len(attr), cpl_policy, NULL);
+	if (err)
+		return err;
+
+	if (!a[OVS_CHECK_PKT_LEN_ATTR_PKT_LEN] ||
+	    !nla_get_u16(a[OVS_CHECK_PKT_LEN_ATTR_PKT_LEN]))
+		return -EINVAL;
+
+	acts_if_lesser_eq = a[OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL];
+	acts_if_greater = a[OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER];
+
+	/* Both the nested action should be present. */
+	if (!acts_if_greater || !acts_if_lesser_eq)
+		return -EINVAL;
+
+	/* validation done, copy the nested actions. */
+	start = add_nested_action_start(sfa, OVS_ACTION_ATTR_CHECK_PKT_LEN,
+					log);
+	if (start < 0)
+		return start;
+
+	arg.pkt_len = nla_get_u16(a[OVS_CHECK_PKT_LEN_ATTR_PKT_LEN]);
+	arg.exec_for_lesser_equal =
+		last || !actions_may_change_flow(acts_if_lesser_eq);
+	arg.exec_for_greater =
+		last || !actions_may_change_flow(acts_if_greater);
+
+	err = ovs_nla_add_action(sfa, OVS_CHECK_PKT_LEN_ATTR_ARG, &arg,
+				 sizeof(arg), log);
+	if (err)
+		return err;
+
+	nested_acts_start = add_nested_action_start(sfa,
+		OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL, log);
+	if (nested_acts_start < 0)
+		return nested_acts_start;
+
+	err = __ovs_nla_copy_actions(net, acts_if_lesser_eq, key, sfa,
+				     eth_type, vlan_tci, log);
+
+	if (err)
+		return err;
+
+	add_nested_action_end(*sfa, nested_acts_start);
+
+	nested_acts_start = add_nested_action_start(sfa,
+		OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER, log);
+	if (nested_acts_start < 0)
+		return nested_acts_start;
+
+	err = __ovs_nla_copy_actions(net, acts_if_greater, key, sfa,
+				     eth_type, vlan_tci, log);
+
+	if (err)
+		return err;
+
+	add_nested_action_end(*sfa, nested_acts_start);
+	add_nested_action_end(*sfa, start);
+	return 0;
+}
+
 static int copy_action(const struct nlattr *from,
 		       struct sw_flow_actions **sfa, bool log)
 {
@@ -2884,6 +2966,7 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
 			[OVS_ACTION_ATTR_POP_NSH] = 0,
 			[OVS_ACTION_ATTR_METER] = sizeof(u32),
 			[OVS_ACTION_ATTR_CLONE] = (u32)-1,
+			[OVS_ACTION_ATTR_CHECK_PKT_LEN] = (u32)-1,
 		};
 		const struct ovs_action_push_vlan *vlan;
 		int type = nla_type(a);
@@ -3085,6 +3168,19 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
 			break;
 		}
 
+		case OVS_ACTION_ATTR_CHECK_PKT_LEN: {
+			bool last = nla_is_last(a, rem);
+
+			err = validate_and_copy_check_pkt_len(net, a, key, sfa,
+							      eth_type,
+							      vlan_tci, log,
+							      last);
+			if (err)
+				return err;
+			skip_copy = true;
+			break;
+		}
+
 		default:
 			OVS_NLERR(log, "Unknown Action type %d", type);
 			return -EINVAL;
@@ -3183,6 +3279,75 @@ static int clone_action_to_attr(const struct nlattr *attr,
 	return err;
 }
 
+static int check_pkt_len_action_to_attr(const struct nlattr *attr,
+					struct sk_buff *skb)
+{
+	struct nlattr *start, *ac_start = NULL;
+	const struct check_pkt_len_arg *arg;
+	const struct nlattr *a, *cpl_arg;
+	int err = 0, rem = nla_len(attr);
+
+	start = nla_nest_start(skb, OVS_ACTION_ATTR_CHECK_PKT_LEN);
+	if (!start)
+		return -EMSGSIZE;
+
+	/* The first nested attribute in 'attr' is always
+	 * 'OVS_CHECK_PKT_LEN_ATTR_ARG'.
+	 */
+	cpl_arg = nla_data(attr);
+	arg = nla_data(cpl_arg);
+
+	if (nla_put_u16(skb, OVS_CHECK_PKT_LEN_ATTR_PKT_LEN, arg->pkt_len)) {
+		err = -EMSGSIZE;
+		goto out;
+	}
+
+	/* Second nested attribute in 'attr' is always
+	 * 'OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL'.
+	 */
+	a = nla_next(cpl_arg, &rem);
+	ac_start =  nla_nest_start(skb,
+		OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL);
+	if (!ac_start) {
+		err = -EMSGSIZE;
+		goto out;
+	}
+
+	err = ovs_nla_put_actions(nla_data(a), nla_len(a), skb);
+	if (err) {
+		nla_nest_cancel(skb, ac_start);
+		goto out;
+	} else {
+		nla_nest_end(skb, ac_start);
+	}
+
+	/* Third nested attribute in 'attr' is always
+	 * OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER.
+	 */
+	a = nla_next(a, &rem);
+	ac_start =  nla_nest_start(skb,
+				   OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER);
+	if (!ac_start) {
+		err = -EMSGSIZE;
+		goto out;
+	}
+
+	err = ovs_nla_put_actions(nla_data(a), nla_len(a), skb);
+	if (err) {
+		nla_nest_cancel(skb, ac_start);
+		goto out;
+	} else {
+		nla_nest_end(skb, ac_start);
+	}
+
+	nla_nest_end(skb, start);
+	return 0;
+
+out:
+	nla_nest_cancel(skb, start);
+	return err;
+}
+
 static int set_action_to_attr(const struct nlattr *a, struct sk_buff *skb)
 {
 	const struct nlattr *ovs_key = nla_data(a);
@@ -3277,6 +3442,12 @@ int ovs_nla_put_actions(const struct nlattr *attr, int len, struct sk_buff *skb)
 				return err;
 			break;
 
+		case OVS_ACTION_ATTR_CHECK_PKT_LEN:
+			err = check_pkt_len_action_to_attr(a, skb);
+			if (err)
+				return err;
+			break;
+
 		default:
 			if (nla_put(skb, type, nla_len(a), nla_data(a)))
 				return -EMSGSIZE;