Restore dns on unclean shutdown (#1494)

client/internal/dns/unclean_shutdown_linux.go

@@ -0,0 +1,96 @@
+//go:build !android
+
+package dns
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"net/netip"
+	"os"
+	"path/filepath"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	fileUncleanShutdownResolvConfLocation  = "/var/lib/netbird/resolv.conf"
+	fileUncleanShutdownManagerTypeLocation = "/var/lib/netbird/manager"
+)
+
+func CheckUncleanShutdown(wgIface string) error {
+	if _, err := os.Stat(fileUncleanShutdownResolvConfLocation); err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			// no file -> clean shutdown
+			return nil
+		} else {
+			return fmt.Errorf("state: %w", err)
+		}
+	}
+
+	log.Warnf("detected unclean shutdown, file %s exists", fileUncleanShutdownResolvConfLocation)
+
+	managerData, err := os.ReadFile(fileUncleanShutdownManagerTypeLocation)
+	if err != nil {
+		return fmt.Errorf("read %s: %w", fileUncleanShutdownManagerTypeLocation, err)
+	}
+
+	managerFields := strings.Split(string(managerData), ",")
+	if len(managerFields) < 2 {
+		return errors.New("split manager data: insufficient number of fields")
+	}
+	osManagerTypeStr, dnsAddressStr := managerFields[0], managerFields[1]
+
+	dnsAddress, err := netip.ParseAddr(dnsAddressStr)
+	if err != nil {
+		return fmt.Errorf("parse dns address %s failed: %w", dnsAddressStr, err)
+	}
+
+	log.Warnf("restoring unclean shutdown dns settings via previously detected manager: %s", osManagerTypeStr)
+
+	// determine os manager type, so we can invoke the respective restore action
+	osManagerType, err := newOsManagerType(osManagerTypeStr)
+	if err != nil {
+		return fmt.Errorf("detect previous host manager: %w", err)
+	}
+
+	manager, err := newHostManagerFromType(wgIface, osManagerType)
+	if err != nil {
+		return fmt.Errorf("create previous host manager: %w", err)
+	}
+
+	if err := manager.restoreUncleanShutdownDNS(&dnsAddress); err != nil {
+		return fmt.Errorf("restore unclean shutdown backup: %w", err)
+	}
+
+	return nil
+}
+
+func createUncleanShutdownIndicator(sourcePath string, managerType osManagerType, dnsAddress string) error {
+	dir := filepath.Dir(fileUncleanShutdownResolvConfLocation)
+	if err := os.MkdirAll(dir, os.FileMode(0755)); err != nil {
+		return fmt.Errorf("create dir %s: %w", dir, err)
+	}
+
+	if err := copyFile(sourcePath, fileUncleanShutdownResolvConfLocation); err != nil {
+		return fmt.Errorf("create %s: %w", sourcePath, err)
+	}
+
+	managerData := fmt.Sprintf("%s,%s", managerType, dnsAddress)
+
+	if err := os.WriteFile(fileUncleanShutdownManagerTypeLocation, []byte(managerData), 0644); err != nil { //nolint:gosec
+		return fmt.Errorf("create %s: %w", fileUncleanShutdownManagerTypeLocation, err)
+	}
+	return nil
+}
+
+func removeUncleanShutdownIndicator() error {
+	if err := os.Remove(fileUncleanShutdownResolvConfLocation); err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return fmt.Errorf("remove %s: %w", fileUncleanShutdownResolvConfLocation, err)
+	}
+	if err := os.Remove(fileUncleanShutdownManagerTypeLocation); err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return fmt.Errorf("remove %s: %w", fileUncleanShutdownManagerTypeLocation, err)
+	}
+	return nil
+}