gh-105375: Improve error handling in the builtins extension module (#105585)

Author: erlend-aasland

Misc/NEWS.d/next/Core and Builtins/2023-06-08-10-10-07.gh-issue-105375.35VGDd.rst

@@ -0,0 +1,2 @@
+Fix bugs in the :mod:`builtins` module where exceptions could end up being
+overwritten.

Python/bltinmodule.c

@@ -2162,17 +2162,29 @@ builtin_input_impl(PyObject *module, PyObject *prompt)
 
         /* stdin is a text stream, so it must have an encoding. */
         stdin_encoding = PyObject_GetAttr(fin, &_Py_ID(encoding));
+        if (stdin_encoding == NULL) {
+            tty = 0;
+            goto _readline_errors;
+        }
         stdin_errors = PyObject_GetAttr(fin, &_Py_ID(errors));
-        if (!stdin_encoding || !stdin_errors ||
-                !PyUnicode_Check(stdin_encoding) ||
-                !PyUnicode_Check(stdin_errors)) {
+        if (stdin_errors == NULL) {
+            tty = 0;
+            goto _readline_errors;
+        }
+        if (!PyUnicode_Check(stdin_encoding) ||
+            !PyUnicode_Check(stdin_errors))
+        {
             tty = 0;
             goto _readline_errors;
         }
         stdin_encoding_str = PyUnicode_AsUTF8(stdin_encoding);
+        if (stdin_encoding_str == NULL) {
+            goto _readline_errors;
+        }
         stdin_errors_str = PyUnicode_AsUTF8(stdin_errors);
-        if (!stdin_encoding_str || !stdin_errors_str)
+        if (stdin_errors_str == NULL) {
             goto _readline_errors;
+        }
         tmp = PyObject_CallMethodNoArgs(fout, &_Py_ID(flush));
         if (tmp == NULL)
             PyErr_Clear();
@@ -2183,17 +2195,29 @@ builtin_input_impl(PyObject *module, PyObject *prompt)
             const char *stdout_encoding_str, *stdout_errors_str;
             PyObject *stringpo;
             stdout_encoding = PyObject_GetAttr(fout, &_Py_ID(encoding));
+            if (stdout_encoding == NULL) {
+                tty = 0;
+                goto _readline_errors;
+            }
             stdout_errors = PyObject_GetAttr(fout, &_Py_ID(errors));
-            if (!stdout_encoding || !stdout_errors ||
-                    !PyUnicode_Check(stdout_encoding) ||
-                    !PyUnicode_Check(stdout_errors)) {
+            if (stdout_errors == NULL) {
+                tty = 0;
+                goto _readline_errors;
+            }
+            if (!PyUnicode_Check(stdout_encoding) ||
+                !PyUnicode_Check(stdout_errors))
+            {
                 tty = 0;
                 goto _readline_errors;
             }
             stdout_encoding_str = PyUnicode_AsUTF8(stdout_encoding);
+            if (stdout_encoding_str == NULL) {
+                goto _readline_errors;
+            }
             stdout_errors_str = PyUnicode_AsUTF8(stdout_errors);
-            if (!stdout_encoding_str || !stdout_errors_str)
+            if (stdout_errors_str == NULL) {
                 goto _readline_errors;
+            }
             stringpo = PyObject_Str(prompt);
             if (stringpo == NULL)
                 goto _readline_errors;