[ovs-dev] [PATCH ovn] ovn-northd: Drop IP packets destined to router owned IPs (after NAT).

Dumitru Ceara dceara at redhat.com
Mon Sep 7 16:03:38 UTC 2020


OVN was dropping IP packets destined to IPs owned by logical routers but
only if those IPs are not used for SNAT rules. However, if a packet
doesn't match an existing NAT session and its destination is still a
router owned IP, it can be safely dropped. Otherwise it will trigger an
unnecessary packet-in in stage lr_in_arp_request.

To achieve that we add flows that drop traffic to router owned IPs in
table lr_in_arp_resolve.

Reported-by: Tim Rozet <trozet at redhat.com>
Reported-at: https://bugzilla.redhat.com/1876174
Signed-off-by: Dumitru Ceara <dceara at redhat.com>
---
 northd/ovn-northd.8.xml | 24 ++++++++++++
 northd/ovn-northd.c     | 48 ++++++++++++++++++++++++
 tests/ovn.at            | 99 ++++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 169 insertions(+), 2 deletions(-)

diff --git a/northd/ovn-northd.8.xml b/northd/ovn-northd.8.xml
index 989e364..b9170fc 100644
--- a/northd/ovn-northd.8.xml
+++ b/northd/ovn-northd.8.xml
@@ -2943,6 +2943,30 @@ outport = <var>P</var>;
 
       <li>
         <p>
+          Traffic with IP destination an address owned by the router should be
+          dropped. Such traffic is normally dropped in ingress table
+          <code>IP Input</code> except for IPs that are also shared with SNAT
+          rules. However, if there was no unSNAT operation that happened
+          successfully until this point in the pipeline and the destination IP
+          of the packet is still a router owned IP, the packets can be safely
+          dropped.
+        </p>
+
+        <p>
+          A priority-1 logical flow with match <code>ip4.dst = {..}</code>
+          matches on traffic destined to router owned IPv4 addresses and
+          has action <code>drop;</code>.
+        </p>
+
+        <p>
+          A priority-1 logical flow with match <code>ip6.dst = {..}</code>
+          matches on traffic destined to router owned IPv4 addresses and
+          has action <code>drop;</code>.
+        </p>
+      </li>
+
+      <li>
+        <p>
           Dynamic MAC bindings.  These flows resolve MAC-to-IP bindings
           that have become known dynamically through ARP or neighbor
           discovery.  (The ingress table <code>ARP Request</code> will
diff --git a/northd/ovn-northd.c b/northd/ovn-northd.c
index 3de7161..dcce846 100644
--- a/northd/ovn-northd.c
+++ b/northd/ovn-northd.c
@@ -10587,6 +10587,54 @@ build_lrouter_flows(struct hmap *datapaths, struct hmap *ports,
         }
     }
 
+    /* Drop IP traffic destined to router owned IPs. Part of it is dropped
+     * in stage "lr_in_ip_input" but traffic that could have been unSNATed
+     * but didn't match any existing session might still end up here.
+     */
+    HMAP_FOR_EACH (op, key_node, ports) {
+        if (!op->nbrp) {
+            continue;
+        }
+
+        if (op->lrp_networks.n_ipv4_addrs > 0) {
+            ds_clear(&match);
+            ds_put_cstr(&match, "ip4.dst == {");
+
+            for (size_t i = 0; i < op->lrp_networks.n_ipv4_addrs; i++) {
+                ds_put_format(&match, "%s, ",
+                              op->lrp_networks.ipv4_addrs[i].addr_s);
+            }
+
+            ds_chomp(&match, ' ');
+            ds_chomp(&match, ',');
+            ds_put_char(&match, '}');
+
+            /* Drop traffic with IP.dest == router-ip. */
+            ovn_lflow_add_with_hint(lflows, op->od, S_ROUTER_IN_ARP_RESOLVE, 1,
+                                    ds_cstr(&match), "drop;",
+                                    &op->nbrp->header_);
+        }
+
+        if (op->lrp_networks.n_ipv6_addrs > 0) {
+            ds_clear(&match);
+            ds_put_cstr(&match, "ip6.dst == {");
+
+            for (size_t i = 0; i < op->lrp_networks.n_ipv6_addrs; i++) {
+                ds_put_format(&match, "%s, ",
+                              op->lrp_networks.ipv6_addrs[i].addr_s);
+            }
+
+            ds_chomp(&match, ' ');
+            ds_chomp(&match, ',');
+            ds_put_char(&match, '}');
+
+            /* Drop traffic with IP.dest == router-ip. */
+            ovn_lflow_add_with_hint(lflows, op->od, S_ROUTER_IN_ARP_RESOLVE, 1,
+                                    ds_cstr(&match), "drop;",
+                                    &op->nbrp->header_);
+        }
+    }
+
     HMAP_FOR_EACH (od, key_node, datapaths) {
         if (!od->nbr) {
             continue;
diff --git a/tests/ovn.at b/tests/ovn.at
index 2ee3862..d946c1d 100644
--- a/tests/ovn.at
+++ b/tests/ovn.at
@@ -21377,8 +21377,12 @@ OVN_POPULATE_ARP
 
 ovn-nbctl --wait=hv sync
 
-AT_CHECK([ovn-sbctl lflow-list | grep lr_in_arp_resolve | grep 10.0.0.1], [1], [])
-AT_CHECK([ovn-sbctl lflow-list | grep lr_in_arp_resolve | grep 10.0.0.2], [1], [])
+AT_CHECK([ovn-sbctl lflow-list | grep lr_in_arp_resolve | grep 10.0.0.1], [0], [dnl
+  table=13(lr_in_arp_resolve  ), priority=1    , match=(ip4.dst == {10.0.0.1}), action=(drop;)
+])
+AT_CHECK([ovn-sbctl lflow-list | grep lr_in_arp_resolve | grep 10.0.0.2], [0], [dnl
+  table=13(lr_in_arp_resolve  ), priority=1    , match=(ip4.dst == {10.0.0.2}), action=(drop;)
+])
 
 ip_to_hex() {
     printf "%02x%02x%02x%02x" "$@"
@@ -21446,3 +21450,94 @@ OVS_WAIT_UNTIL([test x$(as hv1 ovn-appctl -t ovn-controller debug/status) = "xru
 
 OVN_CLEANUP([hv1])
 AT_CLEANUP
+
+# Test dropping traffic destined to router owned IPs.
+AT_SETUP([ovn -- gateway router drop traffic for own IPs])
+ovn_start
+
+ovn-nbctl lr-add r1 -- set logical_router r1 options:chassis=hv1
+ovn-nbctl ls-add s1
+
+# Connnect r1 to s1.
+ovn-nbctl lrp-add r1 lrp-r1-s1 00:00:00:00:01:01 10.0.1.1/24
+ovn-nbctl lsp-add s1 lsp-s1-r1 -- set Logical_Switch_Port lsp-s1-r1 type=router \
+    options:router-port=lrp-r1-s1 addresses=router
+
+# Create logical port p1 in s1
+ovn-nbctl lsp-add s1 p1 \
+-- lsp-set-addresses p1 "f0:00:00:00:01:02 10.0.1.2"
+
+# Create two hypervisor and create OVS ports corresponding to logical ports.
+net_add n1
+
+sim_add hv1
+as hv1
+ovs-vsctl add-br br-phys
+ovn_attach n1 br-phys 192.168.0.1
+ovs-vsctl -- add-port br-int hv1-vif1 -- \
+    set interface hv1-vif1 external-ids:iface-id=p1 \
+    options:tx_pcap=hv1/vif1-tx.pcap \
+    options:rxq_pcap=hv1/vif1-rx.pcap \
+    ofport-request=1
+
+# Pre-populate the hypervisors' ARP tables so that we don't lose any
+# packets for ARP resolution (native tunneling doesn't queue packets
+# for ARP resolution).
+OVN_POPULATE_ARP
+
+ovn-nbctl --wait=hv sync
+
+sw_key=$(ovn-sbctl --bare --columns tunnel_key list datapath_binding r1)
+
+AT_CHECK([ovn-sbctl lflow-list | grep lr_in_arp_resolve | grep 10.0.1.1], [0], [dnl
+  table=13(lr_in_arp_resolve  ), priority=1    , match=(ip4.dst == {10.0.1.1}), action=(drop;)
+])
+
+ip_to_hex() {
+    printf "%02x%02x%02x%02x" "$@"
+}
+
+# Send ip packets from p1 to lrp-r1-s1
+src_mac="f00000000102"
+dst_mac="000000000101"
+src_ip=`ip_to_hex 10 0 1 2`
+dst_ip=`ip_to_hex 10 0 1 1`
+packet=${dst_mac}${src_mac}08004500001c0000000040110000${src_ip}${dst_ip}0035111100080000
+as hv1 ovs-appctl netdev-dummy/receive hv1-vif1 $packet
+
+# No packet-ins should reach ovn-controller.
+AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep "actions=controller" | grep -v n_packets=0 -c], [1], [dnl
+0
+])
+
+# The packet should have been dropped in the lr_in_ip_input stage.
+AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep -E "table=11, n_packets=1,.* priority=60,ip,metadata=0x${sw_key},nw_dst=10.0.1.1 actions=drop" -c], [0], [dnl
+1
+])
+
+# Use the router IP as SNAT IP.
+ovn-nbctl set logical_router r1 options:lb_force_snat_ip=10.0.1.1
+ovn-nbctl --wait=hv sync
+
+# Send ip packets from p1 to lrp-r1-s1
+src_mac="f00000000102"
+dst_mac="000000000101"
+src_ip=`ip_to_hex 10 0 1 2`
+dst_ip=`ip_to_hex 10 0 1 1`
+packet=${dst_mac}${src_mac}08004500001c0000000040110000${src_ip}${dst_ip}0035111100080000
+as hv1 ovs-appctl netdev-dummy/receive hv1-vif1 $packet
+
+# Even after configuring a router owned IP for SNAT, no packet-ins should
+# reach ovn-controller.
+AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep "actions=controller" | grep -v n_packets=0 -c], [1], [dnl
+0
+])
+
+# The packet should've been dropped in the lr_in_arp_resolve stage.
+AT_CHECK([as hv1 ovs-ofctl dump-flows br-int | grep -E "table=21, n_packets=1,.* priority=1,ip,metadata=0x${sw_key},nw_dst=10.0.1.1 actions=drop" -c], [0], [dnl
+1
+])
+
+OVN_CLEANUP([hv1])
+
+AT_CLEANUP
\ No newline at end of file
-- 
1.8.3.1



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