[3.15] gh-161389: Fix crash when passing invalid flags and traps to decimal.Context (GH-161393) (#161404)

gh-161389: Fix crash when passing invalid `flags` and `traps` to `decimal.Context` (GH-161393)
(cherry picked from commit 7054b71)

Co-authored-by: sobolevn <mail@sobolevn.me>

Author: miss-islington

Lib/test/test_decimal.py

@@ -3727,6 +3727,20 @@ def test_to_integral_value(self):
         self.assertRaises(TypeError, c.to_integral_value, '10')
         self.assertRaises(TypeError, c.to_integral_value, 10, 'x')
 
+    def test_crashing_signal_dict_traps(self):
+        # gh-161389
+        Context = self.decimal.Context
+        SignalDict = type(Context().traps)
+        with self.assertRaisesRegex((KeyError, ValueError), "signal dict"):
+            Context(traps=SignalDict())
+
+    def test_crashing_signal_dict_flags(self):
+        # gh-161389
+        Context = self.decimal.Context
+        SignalDict = type(Context().flags)
+        with self.assertRaisesRegex((KeyError, ValueError), "signal dict"):
+            Context(flags=SignalDict())
+
 @requires_cdecimal
 class CContextAPItests(ContextAPItests, unittest.TestCase):
     decimal = C

Misc/NEWS.d/next/Library/2026-11-05-11-56-50.gh-issue-161389.EIl2E6.rst

@@ -0,0 +1,2 @@
+Fixes a crash in :class:`decimal.Context` when passing invalid signaling
+dicts as *flags* and *traps*.

Modules/_decimal/_decimal.c

@@ -1168,6 +1168,9 @@ context_settraps_dict(PyObject *self, PyObject *value)
 
     decimal_state *state = get_module_state_from_ctx(self);
     if (PyDecSignalDict_Check(state, value)) {
+        if (SdFlagAddr(value) == NULL) {
+            return value_error_int(INVALID_SIGNALDICT_ERROR_MSG);
+        }
         flags = SdFlags(value);
     }
     else {
@@ -1234,6 +1237,9 @@ context_setstatus_dict(PyObject *self, PyObject *value)
 
     decimal_state *state = get_module_state_from_ctx(self);
     if (PyDecSignalDict_Check(state, value)) {
+        if (SdFlagAddr(value) == NULL) {
+            return value_error_int(INVALID_SIGNALDICT_ERROR_MSG);
+        }
         flags = SdFlags(value);
     }
     else {