[NPM] [Forward Port] fix: crash NPM if unable to locate kube chain

npm/pkg/dataplane/policies/chain-management_linux.go

@@ -89,6 +89,8 @@ var (
 
 	listHintChainArgs   = []string{"KUBE-IPTABLES-HINT", util.IptablesTableFlag, util.IptablesMangleTable, util.IptablesNumericFlag}
 	listCanaryChainArgs = []string{"KUBE-KUBELET-CANARY", util.IptablesTableFlag, util.IptablesMangleTable, util.IptablesNumericFlag}
+
+	errDetectingIptablesVersion = errors.New("unable to locate which iptables version kube proxy is using")
 )
 
 type exitErrorInfo struct {
@@ -187,7 +189,9 @@ func (pMgr *PolicyManager) bootup(_ []string) error {
 	klog.Infof("booting up iptables Azure chains")
 
 	// 0.1. Detect iptables version
-	pMgr.detectIptablesVersion()
+	if err := pMgr.detectIptablesVersion(); err != nil {
+		return npmerrors.SimpleErrorWrapper("failed to detect iptables version", err)
+	}
 
 	// Stop reconciling so we don't contend for iptables, and so we don't update the staleChains at the same time as reconcile()
 	// Reconciling would only be happening if this function were called to reset iptables well into the azure-npm pod lifecycle.
@@ -245,21 +249,20 @@ func (pMgr *PolicyManager) bootupAfterDetectAndCleanup() error {
 // NPM should use the same iptables version as kube-proxy.
 // kube-proxy creates an iptables chain as a hint for which version it uses.
 // For more details, see: https://kubernetes.io/blog/2022/09/07/iptables-chains-not-api/#use-case-iptables-mode
-func (pMgr *PolicyManager) detectIptablesVersion() {
+func (pMgr *PolicyManager) detectIptablesVersion() error {
 	klog.Info("first attempt detecting iptables version. looking for hint/canary chain in iptables-nft")
 	if pMgr.hintOrCanaryChainExist(util.IptablesNft) {
 		util.SetIptablesToNft()
-		return
+		return nil
 	}
 
 	klog.Info("second attempt detecting iptables version. looking for hint/canary chain in iptables-legacy")
 	if pMgr.hintOrCanaryChainExist(util.IptablesLegacy) {
 		util.SetIptablesToLegacy()
-		return
+		return nil
 	}
 
-	// default to nft if nothing is found
-	util.SetIptablesToNft()
+	return errDetectingIptablesVersion
 }
 
 func (pMgr *PolicyManager) hintOrCanaryChainExist(iptablesCmd string) bool {

npm/pkg/dataplane/policies/chain-management_linux_test.go

@@ -896,6 +896,7 @@ func TestDetectIptablesVersion(t *testing.T) {
 		name                    string
 		calls                   []testutils.TestCmd
 		expectedIptablesVersion string
+		expectedErr             bool
 	}
 
 	tests := []args{
@@ -942,7 +943,7 @@ func TestDetectIptablesVersion(t *testing.T) {
 			expectedIptablesVersion: util.IptablesLegacy,
 		},
 		{
-			name: "no kube chains: default nft",
+			name: "no kube chains: error",
 			calls: []testutils.TestCmd{
 				{
 					Cmd:      []string{"iptables-nft", "-w", "60", "-L", "KUBE-IPTABLES-HINT", "-t", "mangle", "-n"},
@@ -961,10 +962,10 @@ func TestDetectIptablesVersion(t *testing.T) {
 					ExitCode: 1,
 				},
 			},
-			expectedIptablesVersion: util.IptablesNft,
+			expectedErr: true,
 		},
 		{
-			name: "nft and legacy both fail: default nft",
+			name: "nft and legacy both fail: error",
 			calls: []testutils.TestCmd{
 				{
 					Cmd:      []string{"iptables-nft", "-w", "60", "-L", "KUBE-IPTABLES-HINT", "-t", "mangle", "-n"},
@@ -983,7 +984,7 @@ func TestDetectIptablesVersion(t *testing.T) {
 					ExitCode: 2,
 				},
 			},
-			expectedIptablesVersion: util.IptablesNft,
+			expectedErr: true,
 		},
 	}
 
@@ -1001,9 +1002,14 @@ func TestDetectIptablesVersion(t *testing.T) {
 				PlaceAzureChainFirst: util.PlaceAzureChainFirst,
 			}
 			pMgr := NewPolicyManager(ioshim, cfg)
-			pMgr.detectIptablesVersion()
 
-			require.Equal(t, tt.expectedIptablesVersion, util.Iptables)
+			err := pMgr.detectIptablesVersion()
+			if tt.expectedErr {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, tt.expectedIptablesVersion, util.Iptables)
+			}
 		})
 	}
 }