fix(params): reject non-finite values (inf, nan) in parameter files

float() silently accepts "inf", "-inf", "nan", and "infinity" as valid
values. When loading .param files, these non-finite values were stored
in the parameter dictionary without validation and could be uploaded to
the flight controller, causing undefined firmware behavior.

Added math.isfinite() check in _validate_parameter() to reject
non-finite values with a clear error message. Added BDD test covering
all non-finite value variants.

Signed-off-by: Yash Goel <yashhzd@users.noreply.github.com>
Signed-off-by: YASH GOEL <yashhzd@YASHs-Mac-Studio.local>

Author: yashhzd

ardupilot_methodic_configurator/data_model_par_dict.py

@@ -11,6 +11,7 @@
 
 import logging
 import re
+from math import isfinite as math_isfinite
 from os import path as os_path
 from os import popen as os_popen
 from sys import exc_info as sys_exc_info
@@ -197,9 +198,16 @@ def _validate_parameter(  # pylint: disable=too-many-arguments, too-many-positio
             raise SystemExit(msg)
         try:
             fvalue = float(value)
+            if not math_isfinite(fvalue):
+                msg = _(
+                    "Non-finite parameter value {value!r} (parsed as {fvalue}) for {parameter_name} in {param_file} line {i}"
+                ).format(value=value, fvalue=fvalue, parameter_name=parameter_name, param_file=param_file, i=i)
+                raise SystemExit(msg)
             parameter_dict[parameter_name] = Par(fvalue, comment)
         except ValueError as exc:
-            msg = _("Invalid parameter value {value} in {param_file} line {i}").format(value=value, param_file=param_file, i=i)
+            msg = _("Invalid parameter value {value!r} in {param_file} line {i}").format(
+                value=value, param_file=param_file, i=i
+            )
             raise SystemExit(msg) from exc
         except OSError as exc:
             _exc_type, exc_value, exc_traceback = sys_exc_info()

tests/test_data_model_par_dict.py

@@ -19,6 +19,7 @@
 import pytest
 
 import ardupilot_methodic_configurator.data_model_par_dict as par_dict_module
+from ardupilot_methodic_configurator import _
 from ardupilot_methodic_configurator.data_model_par_dict import Par, ParDict, is_within_tolerance, validate_param_name
 
 # pylint: disable=redefined-outer-name, too-many-lines
@@ -1495,3 +1496,27 @@ def test_parameter_validation_rejects_invalid_values(self) -> None:
                 ParDict.load_param_file_into_dict(f.name)
 
         os.unlink(f.name)
+
+    def test_parameter_validation_rejects_non_finite_values(self) -> None:
+        """
+        Parameter validation rejects infinite and NaN values.
+
+        GIVEN: A user has a parameter file containing non-finite values (inf, -inf, nan)
+        WHEN: They try to load the parameter file
+        THEN: A SystemExit should be raised indicating the value is non-finite
+        """
+        non_finite_values = ["inf", "-inf", "nan", "infinity", "-infinity"]
+
+        for bad_value in non_finite_values:
+            content = f"VALID_PARAM,{bad_value}"
+
+            with tempfile.NamedTemporaryFile(mode="w", suffix=".param", delete=False) as f:
+                f.write(content)
+                f.flush()
+                file_path = f.name
+
+            try:
+                with pytest.raises(SystemExit, match=_("Non-finite parameter value {value}").format(value=bad_value)):
+                    ParDict.load_param_file_into_dict(file_path)
+            finally:
+                os.unlink(file_path)