hecate: preserve known_hosts ownership during key repair

internal/sshutil/sshutil.go

@@ -8,6 +8,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strings"
+	"syscall"
 	"time"
 )
 
@@ -134,11 +135,14 @@ func RepairKnownHosts(ctx context.Context, logger *log.Logger, knownHostsFiles [
 }
 
 func removeKnownHostEntry(ctx context.Context, logger *log.Logger, file string, entry string) {
+	uid, gid, mode := captureOwnership(file)
+
 	runCtx, cancel := context.WithTimeout(ctx, 8*time.Second)
 	defer cancel()
 
 	cmd := exec.CommandContext(runCtx, "ssh-keygen", "-R", entry, "-f", file)
 	out, err := cmd.CombinedOutput()
+	restoreOwnership(file, file+".old", uid, gid, mode)
 	if err == nil {
 		logf(logger, "known_hosts repaired: removed %s from %s", entry, file)
 		return
@@ -151,6 +155,36 @@ func removeKnownHostEntry(ctx context.Context, logger *log.Logger, file string,
 	logf(logger, "warning: known_hosts cleanup failed for %s in %s: %v: %s", entry, file, err, strings.TrimSpace(string(out)))
 }
 
+func captureOwnership(path string) (int, int, os.FileMode) {
+	info, err := os.Stat(path)
+	if err != nil {
+		return -1, -1, 0
+	}
+	st, ok := info.Sys().(*syscall.Stat_t)
+	if !ok {
+		return -1, -1, info.Mode().Perm()
+	}
+	return int(st.Uid), int(st.Gid), info.Mode().Perm()
+}
+
+func restoreOwnership(path string, backupPath string, uid int, gid int, mode os.FileMode) {
+	if uid < 0 || gid < 0 {
+		return
+	}
+	for _, candidate := range []string{path, backupPath} {
+		if candidate == "" {
+			continue
+		}
+		if _, err := os.Stat(candidate); err != nil {
+			continue
+		}
+		_ = os.Chown(candidate, uid, gid)
+		if mode != 0 {
+			_ = os.Chmod(candidate, mode)
+		}
+	}
+}
+
 func logf(logger *log.Logger, format string, args ...any) {
 	if logger != nil {
 		logger.Printf(format, args...)