ipsec: Improve the handling of NAT-T keepalive messages

Type: improvement

Ethernet frames on the wire are a minimum of 64 bytes, so use the length in the UDP header to determine if the ESP payload is one bytes of the special SPI, rather than the buffer's size (which will include the ethernet header's padding).
In the case of drop advance the packet back to the IP header so the ipx-drop node sees a sane packet.

Signed-off-by: Neale Ranns <neale@graphiant.com>
Change-Id: Ic3b75487919f0c77507d6f725bd11202bc5afee8

diff --git a/src/vnet/ipsec/ipsec_tun_in.c b/src/vnet/ipsec/ipsec_tun_in.c
index 4f8af00..c414be0 100644 (file)
--- a/src/vnet/ipsec/ipsec_tun_in.c
+++ b/src/vnet/ipsec/ipsec_tun_in.c
@@ -186,18 +186,35 @@ ipsec_tun_protect_input_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
        {
          ip60 = (ip6_header_t *) ip40;
          esp0 = (esp_header_t *) (ip60 + 1);
-         hdr_sz0 = sizeof (ip6_header_t);
+         buf_rewind0 = hdr_sz0 = sizeof (ip6_header_t);
        }
       else
        {
-         /* NAT UDP port 4500 case, don't advance any more */
          if (ip40->protocol == IP_PROTOCOL_UDP)
            {
+             /* NAT UDP port 4500 case, don't advance any more */
              esp0 =
                (esp_header_t *) ((u8 *) ip40 + ip4_header_bytes (ip40) +
                                  sizeof (udp_header_t));
              hdr_sz0 = 0;
              buf_rewind0 = ip4_header_bytes (ip40) + sizeof (udp_header_t);
+
+             const udp_header_t *udp0 =
+               (udp_header_t *) ((u8 *) ip40 + ip4_header_bytes (ip40));
+
+             /* length 9 = sizeof(udp_header) + 1 byte of special SPI */
+             if (clib_net_to_host_u16 (udp0->length) == 9 &&
+                 esp0->spi_bytes[0] == 0xff)
+               {
+                 b[0]->error =
+                   node->errors[IPSEC_TUN_PROTECT_INPUT_ERROR_NAT_KEEPALIVE];
+
+                 next[0] = VNET_DEVICE_INPUT_NEXT_IP4_DROP;
+                 len0 = 0;
+
+                 vlib_buffer_advance (b[0], -buf_rewind0);
+                 goto trace00;
+               }
            }
          else
            {
@@ -213,15 +230,11 @@ ipsec_tun_protect_input_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
 
       if (len0 < sizeof (esp_header_t))
        {
-         if (esp0->spi_bytes[0] == 0xff)
-           b[0]->error =
-             node->errors[IPSEC_TUN_PROTECT_INPUT_ERROR_NAT_KEEPALIVE];
-         else
-           b[0]->error =
-             node->errors[IPSEC_TUN_PROTECT_INPUT_ERROR_TOO_SHORT];
+         b[0]->error = node->errors[IPSEC_TUN_PROTECT_INPUT_ERROR_TOO_SHORT];
 
          next[0] = is_ip6 ? VNET_DEVICE_INPUT_NEXT_IP6_DROP :
                             VNET_DEVICE_INPUT_NEXT_IP4_DROP;
+         vlib_buffer_advance (b[0], -buf_rewind0);
          goto trace00;
        }
 

diff --git a/test/template_ipsec.py b/test/template_ipsec.py
index bbfe776..725cec5 100644 (file)
--- a/test/template_ipsec.py
+++ b/test/template_ipsec.py
@@ -1293,10 +1293,13 @@ class IpsecTun4(object):
         self.verify_counters4(p, count)
 
     def verify_keepalive(self, p):
+        # the sizeof Raw is calculated to pad to the minimum ehternet
+        # frame size of 64 btyes
         pkt = (Ether(src=self.tun_if.remote_mac, dst=self.tun_if.local_mac) /
                IP(src=p.remote_tun_if_host, dst=self.tun_if.local_ip4) /
                UDP(sport=333, dport=4500) /
-               Raw(b'\xff'))
+               Raw(b'\xff') /
+               Padding(0 * 21))
         self.send_and_assert_no_replies(self.tun_if, pkt*31)
         self.assert_error_counter_equal(
             '/err/%s/NAT Keepalive' % self.tun4_input_node, 31)
@@ -1309,6 +1312,15 @@ class IpsecTun4(object):
         self.assert_error_counter_equal(
             '/err/%s/Too Short' % self.tun4_input_node, 31)
 
+        pkt = (Ether(src=self.tun_if.remote_mac, dst=self.tun_if.local_mac) /
+               IP(src=p.remote_tun_if_host, dst=self.tun_if.local_ip4) /
+               UDP(sport=333, dport=4500) /
+               Raw(b'\xfe') /
+               Padding(0 * 21))
+        self.send_and_assert_no_replies(self.tun_if, pkt*31)
+        self.assert_error_counter_equal(
+            '/err/%s/Too Short' % self.tun4_input_node, 62)
+
 
 class IpsecTun4Tests(IpsecTun4):
     """ UT test methods for Tunnel v4 """