utils/file: Create files as running user instead of effective user

utils/file.go

@@ -24,6 +24,7 @@ import (
 	"strings"
 
 	"github.com/steiler/acls"
+	"golang.org/x/sys/unix"
 
 	log "github.com/sirupsen/logrus"
 )
@@ -196,6 +197,16 @@ func CreateFile(file, content string) (err error) {
 		return err
 	}
 
+	// Change file ownership to user running Containerlab instead of effective UID
+	realUID, effUID, _ := unix.Getresuid()
+	if realUID != effUID {
+		realGID, _, _ := unix.Getresgid()
+		err = os.Chown(file, realUID, realGID)
+		if err != nil {
+			return err
+		}
+	}
+
 	return f.Close()
 }