bpo-33625: Release GIL for grp.getgr{nam,gid} and pwd.getpw{nam,uid} (GH-7081)

Release GIL on grp.getgrnam(), grp.getgrgid(), pwd.getpwnam() and
pwd.getpwuid() if reentrant variants of these functions are available.

Patch by William Grzybowski.

1 files changed, 98 insertions, 6 deletions

diff --git a/Modules/pwdmodule.c b/Modules/pwdmodule.c
index bbef2de9c52..36192a57043 100644
--- a/Modules/pwdmodule.c
+++ b/Modules/pwdmodule.c
@@ -50,6 +50,8 @@ exception is raised if the entry asked for cannot be found.");
 static int initialized;
 static PyTypeObject StructPwdType;
 
+#define DEFAULT_BUFFER_SIZE 1024
+
 static void
 sets(PyObject *v, int i, const char* val)
 {
@@ -116,8 +118,11 @@ static PyObject *
 pwd_getpwuid(PyObject *module, PyObject *uidobj)
 /*[clinic end generated code: output=c4ee1d4d429b86c4 input=ae64d507a1c6d3e8]*/
 {
+    PyObject *retval = NULL;
     uid_t uid;
+    int nomem = 0;
     struct passwd *p;
+    char *buf = NULL, *buf2 = NULL;
 
     if (!_Py_Uid_Converter(uidobj, &uid)) {
         if (PyErr_ExceptionMatches(PyExc_OverflowError))
@@ -125,7 +130,47 @@ pwd_getpwuid(PyObject *module, PyObject *uidobj)
                          "getpwuid(): uid not found");
         return NULL;
     }
-    if ((p = getpwuid(uid)) == NULL) {
+#ifdef HAVE_GETPWUID_R
+    Py_BEGIN_ALLOW_THREADS
+    int status;
+    Py_ssize_t bufsize;
+    struct passwd pwd;
+
+    bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
+    if (bufsize == -1) {
+        bufsize = DEFAULT_BUFFER_SIZE;
+    }
+
+    while(1) {
+        buf2 = PyMem_RawRealloc(buf, bufsize);
+        if (buf2 == NULL) {
+            nomem = 1;
+            break;
+        }
+        buf = buf2;
+        status = getpwuid_r(uid, &pwd, buf, bufsize, &p);
+        if (status != 0) {
+            p = NULL;
+        }
+        if (p != NULL || status != ERANGE) {
+            break;
+        }
+        if (bufsize > (PY_SSIZE_T_MAX >> 1)) {
+            nomem = 1;
+            break;
+        }
+        bufsize <<= 1;
+    }
+
+    Py_END_ALLOW_THREADS
+#else
+    p = getpwuid(uid);
+#endif
+    if (p == NULL) {
+        PyMem_RawFree(buf);
+        if (nomem == 1) {
+            return PyErr_NoMemory();
+        }
         PyObject *uid_obj = _PyLong_FromUid(uid);
         if (uid_obj == NULL)
             return NULL;
@@ -134,7 +179,11 @@ pwd_getpwuid(PyObject *module, PyObject *uidobj)
         Py_DECREF(uid_obj);
         return NULL;
     }
-    return mkpwent(p);
+    retval = mkpwent(p);
+#ifdef HAVE_GETPWUID_R
+    PyMem_RawFree(buf);
+#endif
+    return retval;
 }
 
 /*[clinic input]
@@ -152,7 +201,8 @@ static PyObject *
 pwd_getpwnam_impl(PyObject *module, PyObject *arg)
 /*[clinic end generated code: output=6abeee92430e43d2 input=d5f7e700919b02d3]*/
 {
-    char *name;
+    char *buf = NULL, *buf2 = NULL, *name;
+    int nomem = 0;
     struct passwd *p;
     PyObject *bytes, *retval = NULL;
 
@@ -161,13 +211,55 @@ pwd_getpwnam_impl(PyObject *module, PyObject *arg)
     /* check for embedded null bytes */
     if (PyBytes_AsStringAndSize(bytes, &name, NULL) == -1)
         goto out;
-    if ((p = getpwnam(name)) == NULL) {
-        PyErr_Format(PyExc_KeyError,
-                     "getpwnam(): name not found: %s", name);
+#ifdef HAVE_GETPWNAM_R
+    Py_BEGIN_ALLOW_THREADS
+    int status;
+    Py_ssize_t bufsize;
+    struct passwd pwd;
+
+    bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
+    if (bufsize == -1) {
+        bufsize = DEFAULT_BUFFER_SIZE;
+    }
+
+    while(1) {
+        buf2 = PyMem_RawRealloc(buf, bufsize);
+        if (buf2 == NULL) {
+            nomem = 1;
+            break;
+        }
+        buf = buf2;
+        status = getpwnam_r(name, &pwd, buf, bufsize, &p);
+        if (status != 0) {
+            p = NULL;
+        }
+        if (p != NULL || status != ERANGE) {
+            break;
+        }
+        if (bufsize > (PY_SSIZE_T_MAX >> 1)) {
+            nomem = 1;
+            break;
+        }
+        bufsize <<= 1;
+    }
+
+    Py_END_ALLOW_THREADS
+#else
+    p = getpwnam(name);
+#endif
+    if (p == NULL) {
+        if (nomem == 1) {
+            PyErr_NoMemory();
+        }
+        else {
+            PyErr_Format(PyExc_KeyError,
+                         "getpwnam(): name not found: %s", name);
+        }
         goto out;
     }
     retval = mkpwent(p);
 out:
+    PyMem_RawFree(buf);
     Py_DECREF(bytes);
     return retval;
 }