From baa8f229f7ac6c5ae5e389083d9bf4757f9aef8d Mon Sep 17 00:00:00 2001
From: Martynas Pumputis <martynasp@gmail.com>
Date: Fri, 25 Nov 2016 18:05:38 +0000
Subject: [PATCH] Detect enabling of hairpin mode on vethwe-bridge

Enabled hairpin mode on vethwe-bridge was one of the root causes
for installing looping flows in the fastdp mode.

Also, it confused the weave custom L2 bridge, as the bridge treats
a bounced back packet, e.g. ARP brodcast request, as a local one
(the case for "Captured a packet associated with remote host").
---
 net/bridge.go                   | 35 +++++++++++++++++++++++++++++++++
 prog/weaver/main.go             |  6 ++++++
 test/705_detect_hairpin_test.sh | 12 +++++++++++
 3 files changed, 53 insertions(+)
 create mode 100755 test/705_detect_hairpin_test.sh

diff --git a/net/bridge.go b/net/bridge.go
index 07d1f6cb..da0bd40a 100644
--- a/net/bridge.go
+++ b/net/bridge.go
@@ -1,6 +1,9 @@
 package net
 
 import (
+	"fmt"
+
+	"github.com/Sirupsen/logrus"
 	"github.com/vishvananda/netlink"
 )
 
@@ -51,3 +54,35 @@ func isDatapath(link netlink.Link) bool {
 		return false
 	}
 }
+
+func DetectHairpin(portIfName string, log *logrus.Logger) error {
+	link, err := netlink.LinkByName(portIfName)
+	if err != nil {
+		return fmt.Errorf("Unable to find link %q: %s", portIfName, err)
+	}
+
+	ch := make(chan netlink.LinkUpdate)
+	// See EnsureInterface for why done channel is not passed
+	if err := netlink.LinkSubscribe(ch, nil); err != nil {
+		return fmt.Errorf("Unable to subscribe to netlink updates: %s", err)
+	}
+
+	pi, err := netlink.LinkGetProtinfo(link)
+	if err != nil {
+		return fmt.Errorf("Unable to get link protinfo %q: %s", portIfName, err)
+	}
+	if pi.Hairpin {
+		return fmt.Errorf("Hairpin mode enabled on %q", portIfName)
+	}
+
+	go func() {
+		for up := range ch {
+			if up.Attrs().Name == portIfName && up.Attrs().Protinfo != nil &&
+				up.Attrs().Protinfo.Hairpin {
+				log.Errorf("Hairpin mode enabled on %q", portIfName)
+			}
+		}
+	}()
+
+	return nil
+}
diff --git a/prog/weaver/main.go b/prog/weaver/main.go
index 92cb5bba..2050f49e 100644
--- a/prog/weaver/main.go
+++ b/prog/weaver/main.go
@@ -226,6 +226,12 @@ func main() {
 	overlay, bridge := createOverlay(datapathName, ifaceName, isAWSVPC, config.Host, config.Port, bufSzMB)
 	networkConfig.Bridge = bridge
 
+	if bridge != nil {
+		if err := weavenet.DetectHairpin("vethwe-bridge", Log); err != nil {
+			Log.Errorf("DetectHairpin failed: %s", err)
+		}
+	}
+
 	name := peerName(routerName, bridge.Interface())
 
 	if nickName == "" {
diff --git a/test/705_detect_hairpin_test.sh b/test/705_detect_hairpin_test.sh
new file mode 100755
index 00000000..4ba915ed
--- /dev/null
+++ b/test/705_detect_hairpin_test.sh
@@ -0,0 +1,12 @@
+#! /bin/bash
+
+. ./config.sh
+
+start_suite "Detect hairpin mode"
+
+weave_on $HOST1 launch
+
+assert_raises "run_on $HOST1 sudo ip link set vethwe-bridge type bridge_slave hairpin on"
+assert_raises "docker_on $HOST1 logs weave 2>&1 | grep -q 'Hairpin mode enabled on \"vethwe-bridge\"'"
+
+end_suite