gh-127691: add type checks when using `PyUnicodeError` objects (GH-127694)

3 files changed, 157 insertions, 68 deletions

diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
index 5ce398a..0959492 100644
--- a/Doc/whatsnew/3.14.rst
+++ b/Doc/whatsnew/3.14.rst
@@ -1045,6 +1045,12 @@ New features
 * Add :c:func:`PyUnstable_Object_EnableDeferredRefcount` for enabling
   deferred reference counting, as outlined in :pep:`703`.
 
+* The :ref:`Unicode Exception Objects <unicodeexceptions>` C API
+  now raises a :exc:`TypeError` if its exception argument is not
+  a :exc:`UnicodeError` object.
+  (Contributed by Bénédikt Tran in :gh:`127691`.)
+
+
 Porting to Python 3.14
 ----------------------
 
diff --git a/Misc/NEWS.d/next/C_API/2024-12-06-16-53-34.gh-issue-127691.k_Jitp.rst b/Misc/NEWS.d/next/C_API/2024-12-06-16-53-34.gh-issue-127691.k_Jitp.rst
new file mode 100644
index 0000000..c942ff3
--- /dev/null
+++ b/Misc/NEWS.d/next/C_API/2024-12-06-16-53-34.gh-issue-127691.k_Jitp.rst
@@ -0,0 +1,3 @@
+The :ref:`Unicode Exception Objects <unicodeexceptions>` C API
+now raises a :exc:`TypeError` if its exception argument is not
+a :exc:`UnicodeError` object. Patch by Bénédikt Tran.
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 287cbc2..6880c24 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -2668,7 +2668,7 @@ SimpleExtendsException(PyExc_ValueError, UnicodeError,
                        "Unicode related error.");
 
 static PyObject *
-get_string(PyObject *attr, const char *name)
+get_bytes(PyObject *attr, const char *name)
 {
     if (!attr) {
         PyErr_Format(PyExc_TypeError, "%.200s attribute not set", name);
@@ -2748,40 +2748,74 @@ unicode_error_adjust_end(Py_ssize_t end, Py_ssize_t objlen)
     return end;
 }
 
+#define _PyUnicodeError_CAST(PTR)   ((PyUnicodeErrorObject *)(PTR))
+#define PyUnicodeError_Check(PTR)   \
+    PyObject_TypeCheck((PTR), (PyTypeObject *)PyExc_UnicodeError)
+#define PyUnicodeError_CAST(PTR)    \
+    (assert(PyUnicodeError_Check(PTR)), _PyUnicodeError_CAST(PTR))
+
+
+static inline int
+check_unicode_error_type(PyObject *self, const char *expect_type)
+{
+    if (!PyUnicodeError_Check(self)) {
+        PyErr_Format(PyExc_TypeError,
+                     "expecting a %s object, got %T", expect_type, self);
+        return -1;
+    }
+    return 0;
+}
+
+
+static inline PyUnicodeErrorObject *
+as_unicode_error(PyObject *self, const char *expect_type)
+{
+    int rc = check_unicode_error_type(self, expect_type);
+    return rc < 0 ? NULL : _PyUnicodeError_CAST(self);
+}
+
 PyObject *
-PyUnicodeEncodeError_GetEncoding(PyObject *exc)
+PyUnicodeEncodeError_GetEncoding(PyObject *self)
 {
-    return get_unicode(((PyUnicodeErrorObject *)exc)->encoding, "encoding");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeEncodeError");
+    return exc == NULL ? NULL : get_unicode(exc->encoding, "encoding");
 }
 
 PyObject *
-PyUnicodeDecodeError_GetEncoding(PyObject *exc)
+PyUnicodeDecodeError_GetEncoding(PyObject *self)
 {
-    return get_unicode(((PyUnicodeErrorObject *)exc)->encoding, "encoding");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeDecodeError");
+    return exc == NULL ? NULL : get_unicode(exc->encoding, "encoding");
 }
 
 PyObject *
-PyUnicodeEncodeError_GetObject(PyObject *exc)
+PyUnicodeEncodeError_GetObject(PyObject *self)
 {
-    return get_unicode(((PyUnicodeErrorObject *)exc)->object, "object");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeEncodeError");
+    return exc == NULL ? NULL : get_unicode(exc->object, "object");
 }
 
 PyObject *
-PyUnicodeDecodeError_GetObject(PyObject *exc)
+PyUnicodeDecodeError_GetObject(PyObject *self)
 {
-    return get_string(((PyUnicodeErrorObject *)exc)->object, "object");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeDecodeError");
+    return exc == NULL ? NULL : get_bytes(exc->object, "object");
 }
 
 PyObject *
-PyUnicodeTranslateError_GetObject(PyObject *exc)
+PyUnicodeTranslateError_GetObject(PyObject *self)
 {
-    return get_unicode(((PyUnicodeErrorObject *)exc)->object, "object");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeTranslateError");
+    return exc == NULL ? NULL : get_unicode(exc->object, "object");
 }
 
 int
 PyUnicodeEncodeError_GetStart(PyObject *self, Py_ssize_t *start)
 {
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeEncodeError");
+    if (exc == NULL) {
+        return -1;
+    }
     PyObject *obj = get_unicode(exc->object, "object");
     if (obj == NULL) {
         return -1;
@@ -2796,8 +2830,11 @@ PyUnicodeEncodeError_GetStart(PyObject *self, Py_ssize_t *start)
 int
 PyUnicodeDecodeError_GetStart(PyObject *self, Py_ssize_t *start)
 {
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
-    PyObject *obj = get_string(exc->object, "object");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeDecodeError");
+    if (exc == NULL) {
+        return -1;
+    }
+    PyObject *obj = get_bytes(exc->object, "object");
     if (obj == NULL) {
         return -1;
     }
@@ -2809,45 +2846,63 @@ PyUnicodeDecodeError_GetStart(PyObject *self, Py_ssize_t *start)
 
 
 int
-PyUnicodeTranslateError_GetStart(PyObject *exc, Py_ssize_t *start)
+PyUnicodeTranslateError_GetStart(PyObject *self, Py_ssize_t *start)
 {
-    return PyUnicodeEncodeError_GetStart(exc, start);
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeTranslateError");
+    if (exc == NULL) {
+        return -1;
+    }
+    PyObject *obj = get_unicode(exc->object, "object");
+    if (obj == NULL) {
+        return -1;
+    }
+    Py_ssize_t size = PyUnicode_GET_LENGTH(obj);
+    Py_DECREF(obj);
+    *start = unicode_error_adjust_start(exc->start, size);
+    return 0;
 }
 
 
 static inline int
 unicode_error_set_start_impl(PyObject *self, Py_ssize_t start)
 {
-    ((PyUnicodeErrorObject *)self)->start = start;
+    PyUnicodeErrorObject *exc = _PyUnicodeError_CAST(self);
+    exc->start = start;
     return 0;
 }
 
 
 int
-PyUnicodeEncodeError_SetStart(PyObject *exc, Py_ssize_t start)
+PyUnicodeEncodeError_SetStart(PyObject *self, Py_ssize_t start)
 {
-    return unicode_error_set_start_impl(exc, start);
+    int rc = check_unicode_error_type(self, "UnicodeEncodeError");
+    return rc < 0 ? -1 : unicode_error_set_start_impl(self, start);
 }
 
 
 int
-PyUnicodeDecodeError_SetStart(PyObject *exc, Py_ssize_t start)
+PyUnicodeDecodeError_SetStart(PyObject *self, Py_ssize_t start)
 {
-    return unicode_error_set_start_impl(exc, start);
+    int rc = check_unicode_error_type(self, "UnicodeDecodeError");
+    return rc < 0 ? -1 : unicode_error_set_start_impl(self, start);
 }
 
 
 int
-PyUnicodeTranslateError_SetStart(PyObject *exc, Py_ssize_t start)
+PyUnicodeTranslateError_SetStart(PyObject *self, Py_ssize_t start)
 {
-    return unicode_error_set_start_impl(exc, start);
+    int rc = check_unicode_error_type(self, "UnicodeTranslateError");
+    return rc < 0 ? -1 : unicode_error_set_start_impl(self, start);
 }
 
 
 int
 PyUnicodeEncodeError_GetEnd(PyObject *self, Py_ssize_t *end)
 {
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeEncodeError");
+    if (exc == NULL) {
+        return -1;
+    }
     PyObject *obj = get_unicode(exc->object, "object");
     if (obj == NULL) {
         return -1;
@@ -2862,8 +2917,11 @@ PyUnicodeEncodeError_GetEnd(PyObject *self, Py_ssize_t *end)
 int
 PyUnicodeDecodeError_GetEnd(PyObject *self, Py_ssize_t *end)
 {
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
-    PyObject *obj = get_string(exc->object, "object");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeDecodeError");
+    if (exc == NULL) {
+        return -1;
+    }
+    PyObject *obj = get_bytes(exc->object, "object");
     if (obj == NULL) {
         return -1;
     }
@@ -2875,108 +2933,130 @@ PyUnicodeDecodeError_GetEnd(PyObject *self, Py_ssize_t *end)
 
 
 int
-PyUnicodeTranslateError_GetEnd(PyObject *exc, Py_ssize_t *end)
+PyUnicodeTranslateError_GetEnd(PyObject *self, Py_ssize_t *end)
 {
-    return PyUnicodeEncodeError_GetEnd(exc, end);
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeTranslateError");
+    if (exc == NULL) {
+        return -1;
+    }
+    PyObject *obj = get_unicode(exc->object, "object");
+    if (obj == NULL) {
+        return -1;
+    }
+    Py_ssize_t size = PyUnicode_GET_LENGTH(obj);
+    Py_DECREF(obj);
+    *end = unicode_error_adjust_end(exc->end, size);
+    return 0;
 }
 
 
 static inline int
-unicode_error_set_end_impl(PyObject *exc, Py_ssize_t end)
+unicode_error_set_end_impl(PyObject *self, Py_ssize_t end)
 {
-    ((PyUnicodeErrorObject *)exc)->end = end;
+    PyUnicodeErrorObject *exc = _PyUnicodeError_CAST(self);
+    exc->end = end;
     return 0;
 }
 
 
 int
-PyUnicodeEncodeError_SetEnd(PyObject *exc, Py_ssize_t end)
+PyUnicodeEncodeError_SetEnd(PyObject *self, Py_ssize_t end)
 {
-    return unicode_error_set_end_impl(exc, end);
+    int rc = check_unicode_error_type(self, "UnicodeEncodeError");
+    return rc < 0 ? -1 : unicode_error_set_end_impl(self, end);
 }
 
 
 int
-PyUnicodeDecodeError_SetEnd(PyObject *exc, Py_ssize_t end)
+PyUnicodeDecodeError_SetEnd(PyObject *self, Py_ssize_t end)
 {
-    return unicode_error_set_end_impl(exc, end);
+    int rc = check_unicode_error_type(self, "UnicodeDecodeError");
+    return rc < 0 ? -1 : unicode_error_set_end_impl(self, end);
 }
 
 
 int
-PyUnicodeTranslateError_SetEnd(PyObject *exc, Py_ssize_t end)
+PyUnicodeTranslateError_SetEnd(PyObject *self, Py_ssize_t end)
 {
-    return unicode_error_set_end_impl(exc, end);
+    int rc = check_unicode_error_type(self, "UnicodeTranslateError");
+    return rc < 0 ? -1 : unicode_error_set_end_impl(self, end);
 }
 
+
 PyObject *
-PyUnicodeEncodeError_GetReason(PyObject *exc)
+PyUnicodeEncodeError_GetReason(PyObject *self)
 {
-    return get_unicode(((PyUnicodeErrorObject *)exc)->reason, "reason");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeEncodeError");
+    return exc == NULL ? NULL : get_unicode(exc->reason, "reason");
 }
 
 
 PyObject *
-PyUnicodeDecodeError_GetReason(PyObject *exc)
+PyUnicodeDecodeError_GetReason(PyObject *self)
 {
-    return get_unicode(((PyUnicodeErrorObject *)exc)->reason, "reason");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeDecodeError");
+    return exc == NULL ? NULL : get_unicode(exc->reason, "reason");
 }
 
 
 PyObject *
-PyUnicodeTranslateError_GetReason(PyObject *exc)
+PyUnicodeTranslateError_GetReason(PyObject *self)
 {
-    return get_unicode(((PyUnicodeErrorObject *)exc)->reason, "reason");
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeTranslateError");
+    return exc == NULL ? NULL : get_unicode(exc->reason, "reason");
 }
 
 
 int
-PyUnicodeEncodeError_SetReason(PyObject *exc, const char *reason)
+PyUnicodeEncodeError_SetReason(PyObject *self, const char *reason)
 {
-    return set_unicodefromstring(&((PyUnicodeErrorObject *)exc)->reason,
-                                 reason);
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeEncodeError");
+    return exc == NULL ? -1 : set_unicodefromstring(&exc->reason, reason);
 }
 
 
 int
-PyUnicodeDecodeError_SetReason(PyObject *exc, const char *reason)
+PyUnicodeDecodeError_SetReason(PyObject *self, const char *reason)
 {
-    return set_unicodefromstring(&((PyUnicodeErrorObject *)exc)->reason,
-                                 reason);
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeDecodeError");
+    return exc == NULL ? -1 : set_unicodefromstring(&exc->reason, reason);
 }
 
 
 int
-PyUnicodeTranslateError_SetReason(PyObject *exc, const char *reason)
+PyUnicodeTranslateError_SetReason(PyObject *self, const char *reason)
 {
-    return set_unicodefromstring(&((PyUnicodeErrorObject *)exc)->reason,
-                                 reason);
+    PyUnicodeErrorObject *exc = as_unicode_error(self, "UnicodeTranslateError");
+    return exc == NULL ? -1 : set_unicodefromstring(&exc->reason, reason);
 }
 
 
 static int
-UnicodeError_clear(PyUnicodeErrorObject *self)
+UnicodeError_clear(PyObject *self)
 {
-    Py_CLEAR(self->encoding);
-    Py_CLEAR(self->object);
-    Py_CLEAR(self->reason);
+    PyUnicodeErrorObject *exc = PyUnicodeError_CAST(self);
+    Py_CLEAR(exc->encoding);
+    Py_CLEAR(exc->object);
+    Py_CLEAR(exc->reason);
     return BaseException_clear((PyBaseExceptionObject *)self);
 }
 
 static void
-UnicodeError_dealloc(PyUnicodeErrorObject *self)
+UnicodeError_dealloc(PyObject *self)
 {
+    PyTypeObject *type = Py_TYPE(self);
     _PyObject_GC_UNTRACK(self);
-    UnicodeError_clear(self);
-    Py_TYPE(self)->tp_free((PyObject *)self);
+    (void)UnicodeError_clear(self);
+    type->tp_free(self);
 }
 
 static int
-UnicodeError_traverse(PyUnicodeErrorObject *self, visitproc visit, void *arg)
+UnicodeError_traverse(PyObject *self, visitproc visit, void *arg)
 {
-    Py_VISIT(self->encoding);
-    Py_VISIT(self->object);
-    Py_VISIT(self->reason);
+    PyUnicodeErrorObject *exc = PyUnicodeError_CAST(self);
+    Py_VISIT(exc->encoding);
+    Py_VISIT(exc->object);
+    Py_VISIT(exc->reason);
     return BaseException_traverse((PyBaseExceptionObject *)self, visit, arg);
 }
 
@@ -3015,7 +3095,7 @@ UnicodeEncodeError_init(PyObject *self, PyObject *args, PyObject *kwds)
         return -1;
     }
 
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
+    PyUnicodeErrorObject *exc = PyUnicodeError_CAST(self);
     Py_XSETREF(exc->encoding, Py_NewRef(encoding));
     Py_XSETREF(exc->object, Py_NewRef(object));
     exc->start = start;
@@ -3027,7 +3107,7 @@ UnicodeEncodeError_init(PyObject *self, PyObject *args, PyObject *kwds)
 static PyObject *
 UnicodeEncodeError_str(PyObject *self)
 {
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
+    PyUnicodeErrorObject *exc = PyUnicodeError_CAST(self);
     PyObject *result = NULL;
     PyObject *reason_str = NULL;
     PyObject *encoding_str = NULL;
@@ -3135,7 +3215,7 @@ UnicodeDecodeError_init(PyObject *self, PyObject *args, PyObject *kwds)
         }
     }
 
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
+    PyUnicodeErrorObject *exc = PyUnicodeError_CAST(self);
     Py_XSETREF(exc->encoding, Py_NewRef(encoding));
     Py_XSETREF(exc->object, object /* already a strong reference */);
     exc->start = start;
@@ -3147,7 +3227,7 @@ UnicodeDecodeError_init(PyObject *self, PyObject *args, PyObject *kwds)
 static PyObject *
 UnicodeDecodeError_str(PyObject *self)
 {
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
+    PyUnicodeErrorObject *exc = PyUnicodeError_CAST(self);
     PyObject *result = NULL;
     PyObject *reason_str = NULL;
     PyObject *encoding_str = NULL;
@@ -3236,7 +3316,7 @@ UnicodeTranslateError_init(PyObject *self, PyObject *args, PyObject *kwds)
         return -1;
     }
 
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
+    PyUnicodeErrorObject *exc = PyUnicodeError_CAST(self);
     Py_XSETREF(exc->object, Py_NewRef(object));
     exc->start = start;
     exc->end = end;
@@ -3248,7 +3328,7 @@ UnicodeTranslateError_init(PyObject *self, PyObject *args, PyObject *kwds)
 static PyObject *
 UnicodeTranslateError_str(PyObject *self)
 {
-    PyUnicodeErrorObject *exc = (PyUnicodeErrorObject *)self;
+    PyUnicodeErrorObject *exc = PyUnicodeError_CAST(self);
     PyObject *result = NULL;
     PyObject *reason_str = NULL;