map: Fix TCP MSS clamping for MAP-E traffic.

Original MSS clamp patch by Vladimir Ratnikov.
Modified to apply only to TCP packets.

Type: fix
Test: Wrote new unit test to ensure MAP-E TCP MSS clamping.
Change-Id: I77c69714a2e3cc3b7473aa12b645243bb595c2a2
Signed-off-by: Vladimir Ratnikov <vratnikov@netgate.com>
Signed-off-by: Jon Loeliger <jdl@netgate.com>

2 files changed, 84 insertions, 2 deletions

diff --git a/src/plugins/map/ip4_map.c b/src/plugins/map/ip4_map.c
index f2a00907a57..68c3d73094c 100644
--- a/src/plugins/map/ip4_map.c
+++ b/src/plugins/map/ip4_map.c
@@ -209,6 +209,20 @@ ip4_map (vlib_main_t * vm, vlib_node_runtime_t * node, vlib_frame_t * frame)
 	   */
 	  port0 = ip4_map_port_and_security_check (d0, p0, &error0);
 
+	  /*
+	   * Clamp TCP MSS value.
+	   */
+	  if (ip40->protocol == IP_PROTOCOL_TCP)
+	    {
+	      tcp_header_t *tcp = ip4_next_header (ip40);
+	      if (mm->tcp_mss > 0 && tcp_syn (tcp))
+		{
+		  ip_csum_t csum = tcp->checksum;
+		  map_mss_clamping (tcp, &csum, mm->tcp_mss);
+		  tcp->checksum = ip_csum_fold (csum);
+		}
+	    }
+
 	  /* Decrement IPv4 TTL */
 	  ip4_map_decrement_ttl (ip40, &error0);
 	  bool df0 =
diff --git a/src/plugins/map/test/test_map.py b/src/plugins/map/test/test_map.py
index 0bb7a859f8b..94cb6d7865d 100644
--- a/src/plugins/map/test/test_map.py
+++ b/src/plugins/map/test/test_map.py
@@ -96,8 +96,8 @@ class TestMAP(VppTestCase):
         self.assertEqual(rv[0].tag, tag,
                          "output produced incorrect tag value.")
 
-    def test_map_e(self):
-        """ MAP-E """
+    def test_map_e_udp(self):
+        """ MAP-E UDP"""
 
         #
         # Add a route to the MAP-BR
@@ -363,6 +363,74 @@ class TestMAP(VppTestCase):
         self.validate(rx[0][1], v6_reply1)
         self.validate(rx[1][1], v6_reply2)
 
+    def test_map_e_tcp_mss(self):
+        """ MAP-E TCP MSS"""
+
+        #
+        # Add a route to the MAP-BR
+        #
+        map_br_pfx = "2001::"
+        map_br_pfx_len = 32
+        map_route = VppIpRoute(self,
+                               map_br_pfx,
+                               map_br_pfx_len,
+                               [VppRoutePath(self.pg1.remote_ip6,
+                                             self.pg1.sw_if_index)])
+        map_route.add_vpp_config()
+
+        #
+        # Add a domain that maps from pg0 to pg1
+        #
+        map_dst = '2001::/32'
+        map_src = '3000::1/128'
+        client_pfx = '192.168.0.0/16'
+        map_translated_addr = '2001:0:101:5000:0:c0a8:101:5'
+        tag = 'MAP-E TCP tag.'
+        self.vapi.map_add_domain(ip4_prefix=client_pfx,
+                                 ip6_prefix=map_dst,
+                                 ip6_src=map_src,
+                                 ea_bits_len=20,
+                                 psid_offset=4,
+                                 psid_length=4,
+                                 tag=tag)
+
+        # Enable MAP on pg0 interface.
+        self.vapi.map_if_enable_disable(is_enable=1,
+                                        sw_if_index=self.pg0.sw_if_index,
+                                        is_translation=0)
+
+        # Enable MAP on pg1 interface.
+        self.vapi.map_if_enable_disable(is_enable=1,
+                                        sw_if_index=self.pg1.sw_if_index,
+                                        is_translation=0)
+
+        # TCP MSS clamping
+        mss_clamp = 1300
+        self.vapi.map_param_set_tcp(mss_clamp)
+
+        #
+        # Send a v4 packet that will be encapped.
+        #
+        p_ether = Ether(dst=self.pg0.local_mac, src=self.pg0.remote_mac)
+        p_ip4 = IP(src=self.pg0.remote_ip4, dst='192.168.1.1')
+        p_tcp = TCP(sport=20000, dport=30000, flags="S",
+                    options=[("MSS", 1455)])
+        p4 = p_ether / p_ip4 / p_tcp
+
+        self.pg1.add_stream(p4)
+        self.pg_enable_capture(self.pg_interfaces)
+        self.pg_start()
+
+        rx = self.pg1.get_capture(1)
+        rx = rx[0]
+
+        self.assertTrue(rx.haslayer(IPv6))
+        self.assertEqual(rx[IP].src, p4[IP].src)
+        self.assertEqual(rx[IP].dst, p4[IP].dst)
+        self.assertEqual(rx[IPv6].src, "3000::1")
+        self.assertEqual(rx[TCP].options,
+                         TCP(options=[('MSS', mss_clamp)]).options)
+
     def validate(self, rx, expected):
         self.assertEqual(rx, expected.__class__(scapy.compat.raw(expected)))