flowprobe: fix accumulation of tcp flags in flow entries

Currently, TCP flags of a flow entry don't get reset once the flow is
exported (unlike other meta information about a flow - packet delta
count and octet delta count). So TCP flags are accumulated as long as
the flow is active. When the flow expires, it is exported the last time,
and its pool entry is freed for further reuse. The next flow that gets
this pool entry will already have non-zero TCP flags. If it's a TCP
flow, the flags will keep being accumulated. This might look fine when
exported. If it's a non-TCP flow, that will definitely look erroneous.

With this fix, reset TCP flags once the flow is exported. Also, cover
the reuse case with tests.

Type: fix
Change-Id: I5f8560afffcfe107909117d3d063e8a69793437e
Signed-off-by: Alexander Chernavin <achernavin@netgate.com>

2 files changed, 75 insertions, 0 deletions

diff --git a/src/plugins/flowprobe/node.c b/src/plugins/flowprobe/node.c
index 8466eda3792..274ea388ccd 100644
--- a/src/plugins/flowprobe/node.c
+++ b/src/plugins/flowprobe/node.c
@@ -740,6 +740,7 @@ flowprobe_export_entry (vlib_main_t * vm, flowprobe_entry_t * e)
   e->packetcount = 0;
   e->octetcount = 0;
   e->last_exported = vlib_time_now (vm);
+  e->prot.tcp.flags = 0;
 
   b0->current_length = offset;
 
diff --git a/test/test_flowprobe.py b/test/test_flowprobe.py
index 5da0f74944b..234cb3b55c7 100644
--- a/test/test_flowprobe.py
+++ b/test/test_flowprobe.py
@@ -33,6 +33,19 @@ TMPL_L2_FIELD_COUNT = 3
 TMPL_L3_FIELD_COUNT = 4
 TMPL_L4_FIELD_COUNT = 3
 
+IPFIX_TCP_FLAGS_ID = 6
+IPFIX_SRC_TRANS_PORT_ID = 7
+IPFIX_DST_TRANS_PORT_ID = 11
+
+TCP_F_FIN = 0x01
+TCP_F_SYN = 0x02
+TCP_F_RST = 0x04
+TCP_F_PSH = 0x08
+TCP_F_ACK = 0x10
+TCP_F_URG = 0x20
+TCP_F_ECE = 0x40
+TCP_F_CWR = 0x80
+
 
 class VppCFLOW(VppObject):
     """CFLOW object for IPFIX exporter and Flowprobe feature"""
@@ -509,6 +522,67 @@ class Flowprobe(MethodHolder):
         ipfix.remove_vpp_config()
         self.logger.info("FFP_TEST_FINISH_0000")
 
+    def test_flow_entry_reuse(self):
+        """Verify flow entry reuse doesn't accumulate meta info"""
+        self.pg_enable_capture(self.pg_interfaces)
+        self.pkts = []
+
+        # enable ip4 datapath for an interface
+        # set active and passive timers
+        ipfix = VppCFLOW(
+            test=self,
+            active=2,
+            passive=3,
+            intf="pg3",
+            layer="l3 l4",
+            datapath="ip4",
+            direction="rx",
+            mtu=100,
+        )
+        ipfix.add_vpp_config()
+
+        # template packet should arrive immediately
+        ipfix_decoder = IPFIXDecoder()
+        templates = ipfix.verify_templates(ipfix_decoder, count=1)
+
+        # make a tcp packet
+        self.pkts = [
+            (
+                Ether(src=self.pg3.remote_mac, dst=self.pg4.local_mac)
+                / IP(src=self.pg3.remote_ip4, dst=self.pg4.remote_ip4)
+                / TCP(sport=1234, dport=4321)
+                / Raw(b"\xa5" * 50)
+            )
+        ]
+
+        # send the tcp packet two times, each time with new set of flags
+        tcp_flags = (
+            TCP_F_SYN | TCP_F_ACK,
+            TCP_F_RST | TCP_F_PSH,
+        )
+        for f in tcp_flags:
+            self.pkts[0][TCP].flags = f
+            capture = self.send_packets(src_if=self.pg3, dst_if=self.pg4)
+
+            # verify meta info - packet/octet delta and tcp flags
+            cflow = self.wait_for_cflow_packet(self.collector, templates[0], timeout=6)
+            self.verify_cflow_data(ipfix_decoder, capture, cflow)
+            self.verify_cflow_data_detail(
+                ipfix_decoder,
+                capture,
+                cflow,
+                {
+                    IPFIX_TCP_FLAGS_ID: f,
+                    IPFIX_SRC_TRANS_PORT_ID: 1234,
+                    IPFIX_DST_TRANS_PORT_ID: 4321,
+                },
+            )
+
+        self.collector.get_capture(3)
+
+        # cleanup
+        ipfix.remove_vpp_config()
+
     def test_interface_dump(self):
         """Dump interfaces with IPFIX flow record generation enabled"""
         self.logger.info("FFP_TEST_START_0003")