# HG changeset patch
# Parent 5754f069b12342acb69dff739782416092522748

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -14372,32 +14372,43 @@ os_confstr_impl(PyModuleDef *module, int
 {
     PyObject *result = NULL;
     char buffer[255];
+    char *recvbuf = buffer;
+    char *allocated = NULL;
+    size_t buflen = sizeof(buffer);
     size_t len;
-
-    errno = 0;
-    len = confstr(name, buffer, sizeof(buffer));
+    const int max_attempts = 20;
+    int attempts_remaining = max_attempts;
+
+    /* Reset errno before each call as we may need to check it afterwards */
+    while (errno = 0, (len = confstr(name, recvbuf, buflen)) > buflen) {
+        if (--attempts_remaining <= 0) {
+            PyErr_Format(PyExc_RuntimeError,
+                         "confstr() made %d consecutive requests for a larger "
+                         "buffer; giving up", max_attempts);
+            goto finally;
+        }
+        recvbuf = PyMem_Realloc(allocated, len);
+        if (recvbuf == NULL) {
+            PyErr_NoMemory();
+            goto finally;
+        }
+        allocated = recvbuf;
+        buflen = len;
+    }
+
     if (len == 0) {
         if (errno) {
             posix_error();
-            return NULL;
         }
         else {
-            Py_RETURN_NONE;
-        }
-    }
-
-    if (len >= sizeof(buffer)) {
-        size_t len2;
-        char *buf = PyMem_Malloc(len);
-        if (buf == NULL)
-            return PyErr_NoMemory();
-        len2 = confstr(name, buf, len);
-        assert(len == len2);
-        result = PyUnicode_DecodeFSDefaultAndSize(buf, len-1);
-        PyMem_Free(buf);
-    }
-    else
-        result = PyUnicode_DecodeFSDefaultAndSize(buffer, len-1);
+            result = Py_None;
+            Py_INCREF(Py_None);
+        }
+    }
+    else
+        result = PyUnicode_DecodeFSDefaultAndSize(recvbuf, len-1);
+finally:
+    PyMem_Free(allocated);
     return result;
 }
 #endif /* HAVE_CONFSTR */