Forward KeyboardInterrupt from privilege-dropped child to parent

Register a KeyboardInterrupt codec in the IPC serializer and catch it
alongside Exception in _drop_and_execute so a Ctrl+C delivered to the
child is serialized over the pipe instead of escaping as an uncaught
BaseException. The parent's drop_privileges wrapper now re-raises any
BaseException it receives, letting ref_util_exception_hook format the
interrupt as a single "[-] Keyboard Interrupt" line.

Author: Nils Bars

ref_utils/process.py

@@ -92,8 +92,10 @@ def _drop_and_execute(
         exception_str = traceback.format_exc()
         print_err(f"[!] Unexpected error:\n{exception_str}")
         exit(1)
-    except Exception as e:
-        # Forward exception to our parent
+    except (Exception, KeyboardInterrupt) as e:
+        # Forward exception to our parent. KeyboardInterrupt is included so a
+        # Ctrl+C delivered to this child does not escape as an uncaught
+        # BaseException and produce a duplicate traceback from multiprocessing.
         serialized_e = safe_dumps(e)
         conn.send_bytes(serialized_e)
     finally:
@@ -127,7 +129,7 @@ def wrapper(*args: Any, **kwargs: Any) -> Any:
         # Deserialize using JSON-based serialization (secure alternative to pickle)
         ret = safe_loads(serialized_ret)
         p.join()
-        if isinstance(ret, Exception):
+        if isinstance(ret, BaseException):
             raise ret
         return ret
 

ref_utils/serialization.py

@@ -259,6 +259,19 @@ def _register_standard_exceptions(serializer: IPCSerializer) -> None:
             )
         )
 
+    # KeyboardInterrupt is a BaseException, not an Exception, so the generic
+    # Exception fallback below does not cover it. Register it explicitly so
+    # privilege-dropping child processes can forward a Ctrl+C back to the
+    # parent instead of producing a duplicate traceback.
+    serializer.register(
+        TypeCodec(
+            type_tag="builtin.KeyboardInterrupt",
+            target_type=KeyboardInterrupt,
+            to_dict=lambda e: {"args": list(e.args)},
+            from_dict=lambda d: KeyboardInterrupt(*d.get("args", [])),
+        )
+    )
+
     # Generic Exception fallback - handles any Exception subclass
     # This must be registered LAST as it matches any Exception
     serializer.register(