bpo-32890, os: Use errno instead of GetLastError() in execve() and truncate() (GH-5784)

path_error() uses GetLastError() on Windows, but some os functions
are implemented via CRT APIs which report errors via errno.
This may result in raising OSError with invalid error code (such
as zero).

Introduce posix_path_error() function and use it where appropriate.

3 files changed, 27 insertions, 3 deletions

diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 6dbc255612..3f6e48f0c8 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -1589,6 +1589,16 @@ class ExecTests(unittest.TestCase):
         with self.assertRaises(ValueError):
             os.execve(args[0], args, newenv)
 
+    @unittest.skipUnless(sys.platform == "win32", "Win32-specific test")
+    def test_execve_with_empty_path(self):
+        # bpo-32890: Check GetLastError() misuse
+        try:
+            os.execve('', ['arg'], {})
+        except OSError as e:
+            self.assertTrue(e.winerror is None or e.winerror != 0)
+        else:
+            self.fail('No OSError raised')
+
 
 @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
 class Win32ErrorTests(unittest.TestCase):
diff --git a/Misc/NEWS.d/next/Windows/2018-03-08-20-02-38.bpo-32890.3jzFzY.rst b/Misc/NEWS.d/next/Windows/2018-03-08-20-02-38.bpo-32890.3jzFzY.rst
new file mode 100644
index 0000000000..e8a63b3341
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2018-03-08-20-02-38.bpo-32890.3jzFzY.rst
@@ -0,0 +1,2 @@
+Fix usage of GetLastError() instead of errno in os.execve() and
+os.truncate().
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 23552bea4c..9ccdc8eff1 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -1456,13 +1456,19 @@ win32_error_object(const char* function, PyObject* filename)
 #endif /* MS_WINDOWS */
 
 static PyObject *
+posix_path_object_error(PyObject *path)
+{
+    return PyErr_SetFromErrnoWithFilenameObject(PyExc_OSError, path);
+}
+
+static PyObject *
 path_object_error(PyObject *path)
 {
 #ifdef MS_WINDOWS
     return PyErr_SetExcFromWindowsErrWithFilenameObject(
                 PyExc_OSError, 0, path);
 #else
-    return PyErr_SetFromErrnoWithFilenameObject(PyExc_OSError, path);
+    return posix_path_object_error(path);
 #endif
 }
 
@@ -1484,6 +1490,12 @@ path_error(path_t *path)
 }
 
 static PyObject *
+posix_path_error(path_t *path)
+{
+    return posix_path_object_error(path->object);
+}
+
+static PyObject *
 path_error2(path_t *path, path_t *path2)
 {
     return path_object_error2(path->object, path2->object);
@@ -5141,7 +5153,7 @@ os_execve_impl(PyObject *module, path_t *path, PyObject *argv, PyObject *env)
 
     /* If we get here it's definitely an error */
 
-    path_error(path);
+    posix_path_error(path);
 
     free_string_array(envlist, envc);
   fail:
@@ -9477,7 +9489,7 @@ os_truncate_impl(PyObject *module, path_t *path, Py_off_t length)
     _Py_END_SUPPRESS_IPH
     Py_END_ALLOW_THREADS
     if (result < 0)
-        return path_error(path);
+        return posix_path_error(path);
 
     Py_RETURN_NONE;
 }