bpo-34604: Fix possible mojibake in pwd.getpwnam() and grp.getgrnam() (GH-9098)

Pass the user/group name as Unicode to the formatting function,
instead of always decoding a bytes string from UTF-8.

Misc/NEWS.d/next/Library/2018-09-07-10-16-34.bpo-34604.xL7-kG.rst

+Fix possible mojibake in the error message of `pwd.getpwnam` and
+`grp.getgrnam`. Patch by William Grzybowski.

Modules/clinic/pwdmodule.c.h

@@ -14,7 +14,7 @@ PyDoc_STRVAR(pwd_getpwuid__doc__,
     {"getpwuid", (PyCFunction)pwd_getpwuid, METH_O, pwd_getpwuid__doc__},
 
 PyDoc_STRVAR(pwd_getpwnam__doc__,
-"getpwnam($module, arg, /)\n"
+"getpwnam($module, name, /)\n"
 "--\n"
 "\n"
 "Return the password database entry for the given user name.\n"
@@ -25,18 +25,18 @@ PyDoc_STRVAR(pwd_getpwnam__doc__,
     {"getpwnam", (PyCFunction)pwd_getpwnam, METH_O, pwd_getpwnam__doc__},
 
 static PyObject *
-pwd_getpwnam_impl(PyObject *module, PyObject *arg);
+pwd_getpwnam_impl(PyObject *module, PyObject *name);
 
 static PyObject *
-pwd_getpwnam(PyObject *module, PyObject *arg_)
+pwd_getpwnam(PyObject *module, PyObject *arg)
 {
     PyObject *return_value = NULL;
-    PyObject *arg;
+    PyObject *name;
 
-    if (!PyArg_Parse(arg_, "U:getpwnam", &arg)) {
+    if (!PyArg_Parse(arg, "U:getpwnam", &name)) {
         goto exit;
     }
-    return_value = pwd_getpwnam_impl(module, arg);
+    return_value = pwd_getpwnam_impl(module, name);
 
 exit:
     return return_value;
@@ -69,4 +69,4 @@ pwd_getpwall(PyObject *module, PyObject *Py_UNUSED(ignored))
 #ifndef PWD_GETPWALL_METHODDEF
     #define PWD_GETPWALL_METHODDEF
 #endif /* !defined(PWD_GETPWALL_METHODDEF) */
-/*[clinic end generated code: output=fc41d8d88ec206d8 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=3c93120d6dd86905 input=a9049054013a1b77]*/

Modules/grpmodule.c

@@ -245,7 +245,7 @@ grp_getgrnam_impl(PyObject *module, PyObject *name)
             PyErr_NoMemory();
         }
         else {
-            PyErr_Format(PyExc_KeyError, "getgrnam(): name not found: %s", name_chars);
+            PyErr_Format(PyExc_KeyError, "getgrnam(): name not found: %S", name);
         }
         goto out;
     }

Modules/pwdmodule.c

@@ -189,7 +189,7 @@ pwd_getpwuid(PyObject *module, PyObject *uidobj)
 /*[clinic input]
 pwd.getpwnam
 
-    arg: unicode
+    name: unicode
     /
 
 Return the password database entry for the given user name.
@@ -198,18 +198,18 @@ See `help(pwd)` for more on password database entries.
 [clinic start generated code]*/
 
 static PyObject *
-pwd_getpwnam_impl(PyObject *module, PyObject *arg)
-/*[clinic end generated code: output=6abeee92430e43d2 input=d5f7e700919b02d3]*/
+pwd_getpwnam_impl(PyObject *module, PyObject *name)
+/*[clinic end generated code: output=359ce1ddeb7a824f input=a6aeb5e3447fb9e0]*/
 {
-    char *buf = NULL, *buf2 = NULL, *name;
+    char *buf = NULL, *buf2 = NULL, *name_chars;
     int nomem = 0;
     struct passwd *p;
     PyObject *bytes, *retval = NULL;
 
-    if ((bytes = PyUnicode_EncodeFSDefault(arg)) == NULL)
+    if ((bytes = PyUnicode_EncodeFSDefault(name)) == NULL)
         return NULL;
     /* check for embedded null bytes */
-    if (PyBytes_AsStringAndSize(bytes, &name, NULL) == -1)
+    if (PyBytes_AsStringAndSize(bytes, &name_chars, NULL) == -1)
         goto out;
 #ifdef HAVE_GETPWNAM_R
     Py_BEGIN_ALLOW_THREADS
@@ -229,7 +229,7 @@ pwd_getpwnam_impl(PyObject *module, PyObject *arg)
             break;
         }
         buf = buf2;
-        status = getpwnam_r(name, &pwd, buf, bufsize, &p);
+        status = getpwnam_r(name_chars, &pwd, buf, bufsize, &p);
         if (status != 0) {
             p = NULL;
         }
@@ -245,7 +245,7 @@ pwd_getpwnam_impl(PyObject *module, PyObject *arg)
 
     Py_END_ALLOW_THREADS
 #else
-    p = getpwnam(name);
+    p = getpwnam(name_chars);
 #endif
     if (p == NULL) {
         if (nomem == 1) {
@@ -253,7 +253,7 @@ pwd_getpwnam_impl(PyObject *module, PyObject *arg)
         }
         else {
             PyErr_Format(PyExc_KeyError,
-                         "getpwnam(): name not found: %s", name);
+                         "getpwnam(): name not found: %S", name);
         }
         goto out;
     }