Fix allow netbird traffic for nftables and userspace (#1446)

Add default allow rules for input and output chains as part of the allownetbird call for userspace mode

client/firewall/nftables/acl_linux.go

@@ -58,6 +58,7 @@ type AclManager struct {
 type iFaceMapper interface {
 	Name() string
 	Address() iface.WGAddress
+	IsUserspaceBind() bool
 }
 
 func newAclManager(table *nftables.Table, wgIface iFaceMapper, routeingFwChainName string) (*AclManager, error) {
@@ -198,6 +199,81 @@ func (m *AclManager) DeleteRule(rule firewall.Rule) error {
 	return nil
 }
 
+// createDefaultAllowRules In case if the USP firewall manager can use the native firewall manager we must to create allow rules for
+// input and output chains
+func (m *AclManager) createDefaultAllowRules() error {
+	expIn := []expr.Any{
+		&expr.Payload{
+			DestRegister: 1,
+			Base:         expr.PayloadBaseNetworkHeader,
+			Offset:       12,
+			Len:          4,
+		},
+		// mask
+		&expr.Bitwise{
+			SourceRegister: 1,
+			DestRegister:   1,
+			Len:            4,
+			Mask:           []byte{0x00, 0x00, 0x00, 0x00},
+			Xor:            zeroXor,
+		},
+		// net address
+		&expr.Cmp{
+			Register: 1,
+			Data:     []byte{0x00, 0x00, 0x00, 0x00},
+		},
+		&expr.Verdict{
+			Kind: expr.VerdictAccept,
+		},
+	}
+
+	_ = m.rConn.InsertRule(&nftables.Rule{
+		Table:    m.workTable,
+		Chain:    m.chainInputRules,
+		Position: 0,
+		Exprs:    expIn,
+	})
+
+	expOut := []expr.Any{
+		&expr.Payload{
+			DestRegister: 1,
+			Base:         expr.PayloadBaseNetworkHeader,
+			Offset:       16,
+			Len:          4,
+		},
+		// mask
+		&expr.Bitwise{
+			SourceRegister: 1,
+			DestRegister:   1,
+			Len:            4,
+			Mask:           []byte{0x00, 0x00, 0x00, 0x00},
+			Xor:            zeroXor,
+		},
+		// net address
+		&expr.Cmp{
+			Register: 1,
+			Data:     []byte{0x00, 0x00, 0x00, 0x00},
+		},
+		&expr.Verdict{
+			Kind: expr.VerdictAccept,
+		},
+	}
+
+	_ = m.rConn.InsertRule(&nftables.Rule{
+		Table:    m.workTable,
+		Chain:    m.chainOutputRules,
+		Position: 0,
+		Exprs:    expOut,
+	})
+
+	err := m.rConn.Flush()
+	if err != nil {
+		log.Debugf("failed to create default allow rules: %s", err)
+		return err
+	}
+	return nil
+}
+
 // Flush rule/chain/set operations from the buffer
 //
 // Method also get all rules after flush and refreshes handle values in the rulesets