From 64f1a5d0f5f25a755c88f581bd427c30b952bb3a Mon Sep 17 00:00:00 2001
From: Alfonso Acosta <fons@weave.works>
Date: Mon, 2 Jan 2017 08:37:05 +0000
Subject: [PATCH] Check that conntrack events are enabled in the kernel

---
 probe/endpoint/conntrack.go | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/probe/endpoint/conntrack.go b/probe/endpoint/conntrack.go
index ff5875e857..da55323ead 100644
--- a/probe/endpoint/conntrack.go
+++ b/probe/endpoint/conntrack.go
@@ -5,7 +5,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"os"
+	"io/ioutil"
 	"path/filepath"
 	"strconv"
 	"sync"
@@ -18,13 +18,13 @@ import (
 
 const (
 	// From https://www.kernel.org/doc/Documentation/networking/nf_conntrack-sysctl.txt
-	// Check a tcp-related file for existence since we need tcp tracking
-	procFileToCheck = "sys/net/netfilter/nf_conntrack_tcp_timeout_close"
-	timeWait        = "TIME_WAIT"
-	tcpProto        = "tcp"
-	newType         = "[NEW]"
-	updateType      = "[UPDATE]"
-	destroyType     = "[DESTROY]"
+	eventsPath = "sys/net/netfilter/nf_conntrack_events"
+
+	timeWait    = "TIME_WAIT"
+	tcpProto    = "tcp"
+	newType     = "[NEW]"
+	updateType  = "[UPDATE]"
+	destroyType = "[DESTROY]"
 )
 
 var (
@@ -104,9 +104,16 @@ func newConntrackFlowWalker(useConntrack bool, procRoot string, bufferSize int,
 
 // IsConntrackSupported returns true if conntrack is suppported by the kernel
 var IsConntrackSupported = func(procRoot string) error {
-	procFile := filepath.Join(procRoot, procFileToCheck)
-	_, err := os.Stat(procFile)
-	return err
+	// Make sure events are enabled, the conntrack CLI doesn't verify it
+	f := filepath.Join(procRoot, eventsPath)
+	contents, err := ioutil.ReadFile(f)
+	if err != nil {
+		return err
+	}
+	if string(contents) == "0" {
+		return fmt.Errorf("conntrack events (%s) are disabled", f)
+	}
+	return nil
 }
 
 func (c *conntrackWalker) loop() {