Merge pull request #12318 from aarondav/best-effort-iptables-lock

Do our best not to invoke iptables concurrently if --wait is unsupported

iptables/iptables.go

@@ -8,6 +8,7 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"sync"
 
 	"github.com/Sirupsen/logrus"
 )
@@ -25,8 +26,10 @@ const (
 )
 
 var (
-	iptablesPath        string
-	supportsXlock       = false
+	iptablesPath  string
+	supportsXlock = false
+	// used to lock iptables commands if xtables lock is not supported
+	bestEffortLock      sync.Mutex
 	ErrIptablesNotFound = errors.New("Iptables not found")
 )
 
@@ -289,6 +292,9 @@ func Raw(args ...string) ([]byte, error) {
 	}
 	if supportsXlock {
 		args = append([]string{"--wait"}, args...)
+	} else {
+		bestEffortLock.Lock()
+		defer bestEffortLock.Unlock()
 	}
 
 	logrus.Debugf("%s, %v", iptablesPath, args)

iptables/iptables_test.go

@@ -5,6 +5,7 @@ import (
 	"os/exec"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 )
 
@@ -168,6 +169,45 @@ func TestOutput(t *testing.T) {
 	}
 }
 
+func TestConcurrencyWithWait(t *testing.T) {
+	RunConcurrencyTest(t, true)
+}
+
+func TestConcurrencyNoWait(t *testing.T) {
+	RunConcurrencyTest(t, false)
+}
+
+// Runs 10 concurrent rule additions. This will fail if iptables
+// is actually invoked simultaneously without --wait.
+// Note that if iptables does not support the xtable lock on this
+// system, then allowXlock has no effect -- it will always be off.
+func RunConcurrencyTest(t *testing.T, allowXlock bool) {
+	var wg sync.WaitGroup
+
+	if !allowXlock && supportsXlock {
+		supportsXlock = false
+		defer func() { supportsXlock = true }()
+	}
+
+	ip := net.ParseIP("192.168.1.1")
+	port := 1234
+	dstAddr := "172.17.0.1"
+	dstPort := 4321
+	proto := "tcp"
+
+	for i := 0; i < 10; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			err := natChain.Forward(Append, ip, port, proto, dstAddr, dstPort)
+			if err != nil {
+				t.Fatal(err)
+			}
+		}()
+	}
+	wg.Wait()
+}
+
 func TestCleanup(t *testing.T) {
 	var err error
 	var rules []byte