bpo-42146: Fix memory leak in subprocess.Popen() in case of uid/gid overflow (GH-22966)

Fix memory leak in subprocess.Popen() in case of uid/gid overflow

Also add a test that would catch this leak with `--huntrleaks`.

Alas, the test for `extra_groups` also exposes an inconsistency
in our error reporting: we use a custom ValueError for `extra_groups`,
but propagate OverflowError for `user` and `group`.

Author: Alexey Izbyshev

Lib/test/test_subprocess.py

@@ -1895,6 +1895,10 @@ def test_user(self):
         with self.assertRaises(ValueError):
             subprocess.check_call(ZERO_RETURN_CMD, user=-1)
 
+        with self.assertRaises(OverflowError):
+            subprocess.check_call(ZERO_RETURN_CMD,
+                                  cwd=os.curdir, env=os.environ, user=2**64)
+
         if pwd is None and name_uid is not None:
             with self.assertRaises(ValueError):
                 subprocess.check_call(ZERO_RETURN_CMD, user=name_uid)
@@ -1938,6 +1942,10 @@ def test_group(self):
         with self.assertRaises(ValueError):
             subprocess.check_call(ZERO_RETURN_CMD, group=-1)
 
+        with self.assertRaises(OverflowError):
+            subprocess.check_call(ZERO_RETURN_CMD,
+                                  cwd=os.curdir, env=os.environ, group=2**64)
+
         if grp is None:
             with self.assertRaises(ValueError):
                 subprocess.check_call(ZERO_RETURN_CMD, group=name_group)
@@ -1986,6 +1994,11 @@ def test_extra_groups(self):
         with self.assertRaises(ValueError):
             subprocess.check_call(ZERO_RETURN_CMD, extra_groups=[-1])
 
+        with self.assertRaises(ValueError):
+            subprocess.check_call(ZERO_RETURN_CMD,
+                                  cwd=os.curdir, env=os.environ,
+                                  extra_groups=[2**64])
+
         if grp is None:
             with self.assertRaises(ValueError):
                 subprocess.check_call(ZERO_RETURN_CMD,

Misc/NEWS.d/next/Library/2020-10-25-19-25-02.bpo-42146.6A8uvS.rst

@@ -0,0 +1,2 @@
+Fix memory leak in :func:`subprocess.Popen` in case an uid (gid) specified in
+`user` (`group`, `extra_groups`) overflows `uid_t` (`gid_t`).

Modules/_posixsubprocess.c

@@ -772,7 +772,7 @@ subprocess_fork_exec(PyObject* self, PyObject *args)
     uid_t uid;
     gid_t gid, *groups = NULL;
     int child_umask;
-    PyObject *cwd_obj, *cwd_obj2;
+    PyObject *cwd_obj, *cwd_obj2 = NULL;
     const char *cwd;
     pid_t pid;
     int need_to_reenable_gc = 0;
@@ -894,7 +894,6 @@ subprocess_fork_exec(PyObject* self, PyObject *args)
         cwd = PyBytes_AsString(cwd_obj2);
     } else {
         cwd = NULL;
-        cwd_obj2 = NULL;
     }
 
     if (groups_list != Py_None) {
@@ -1080,6 +1079,7 @@ subprocess_fork_exec(PyObject* self, PyObject *args)
     return PyLong_FromPid(pid);
 
 cleanup:
+    Py_XDECREF(cwd_obj2);
     if (envp)
         _Py_FreeCharPArray(envp);
     if (argv)