fix: fix reverse routing for KubeSpan

This allows it to not come down when rp_filter is enabled.
Fixes #9814

Signed-off-by: Dmitry Sharshakov <[email protected]>

Author: dsseng

internal/app/machined/pkg/controllers/kubespan/manager.go

@@ -378,6 +378,7 @@ func (ctrl *ManagerController) Run(ctx context.Context, r controller.Runtime, lo
 						},
 						Verdict: pointer.To(nethelpers.VerdictAccept),
 					},
+					// Mark packets to be sent over the KubeSpan link.
 					{
 						MatchDestinationAddress: &network.NfTablesAddressMatch{
 							IncludeSubnets: allowedIPsSet.Prefixes(),
@@ -388,6 +389,18 @@ func (ctrl *ManagerController) Run(ctx context.Context, r controller.Runtime, lo
 						},
 						Verdict: pointer.To(nethelpers.VerdictAccept),
 					},
+					// Mark incoming packets from the KubeSpan link for rp_filter to find the correct routing table.
+					{
+						MatchIIfName: &network.NfTablesIfNameMatch{
+							InterfaceNames: []string{constants.KubeSpanLinkName},
+							Operator:       nethelpers.OperatorEqual,
+						},
+						SetMark: &network.NfTablesMark{
+							Mask: ^uint32(constants.KubeSpanDefaultFirewallMask),
+							Xor:  constants.KubeSpanDefaultForceFirewallMark,
+						},
+						Verdict: pointer.To(nethelpers.VerdictAccept),
+					},
 				}
 
 				return nil

internal/app/machined/pkg/controllers/kubespan/manager_test.go

@@ -244,9 +244,9 @@ func (suite *ManagerSuite) TestReconcile() {
 			asrt.Equal(nethelpers.ChainPriorityFilter, spec.Priority)
 			asrt.Equal(nethelpers.VerdictAccept, spec.Policy)
 
-			asrt.Len(spec.Rules, 2)
+			asrt.Len(spec.Rules, 3)
 
-			if len(spec.Rules) != 2 {
+			if len(spec.Rules) != 3 {
 				return
 			}
 
@@ -277,6 +277,21 @@ func (suite *ManagerSuite) TestReconcile() {
 				},
 				spec.Rules[1],
 			)
+
+			asrt.Equal(
+				network.NfTablesRule{
+					MatchIIfName: &network.NfTablesIfNameMatch{
+						InterfaceNames: []string{constants.KubeSpanLinkName},
+						Operator:       nethelpers.OperatorEqual,
+					},
+					SetMark: &network.NfTablesMark{
+						Mask: ^uint32(constants.KubeSpanDefaultFirewallMask),
+						Xor:  constants.KubeSpanDefaultForceFirewallMark,
+					},
+					Verdict: pointer.To(nethelpers.VerdictAccept),
+				},
+				spec.Rules[2],
+			)
 		},
 	)
 

internal/app/machined/pkg/controllers/runtime/kernel_param_defaults.go

@@ -120,6 +120,11 @@ func (ctrl *KernelParamDefaultsController) getKernelParams() []*kernel.Param {
 			Key:   "proc.sys.net.ipv4.tcp_keepalive_intvl",
 			Value: "60",
 		},
+		// Consider fwmark for rp_filter routing table lookup.
+		{
+			Key:   "proc.sys.net.ipv4.conf.kubespan.src_valid_mark",
+			Value: "1",
+		},
 		{
 			Key:   "proc.sys.kernel.panic",
 			Value: "10",