From 1cdc61c7673f71f2cef57715e482c84efda6d9e0 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Mon, 23 Mar 2020 12:21:07 -0700
Subject: [PATCH] bpo-40014: Fix os.getgrouplist() on macOS (GH-19118)

On macOS, getgrouplist() returns a non-zero value without setting
errno if the group list is too small. Double the list size and call
it again in this case.
(cherry picked from commit 8ec7370c89aa522602eb9604086ce9f09770953d)

Co-authored-by: Victor Stinner <vstinner@python.org>
---
 .../2020-03-23-17-52-00.bpo-40014.Ya70VG.rst  |  3 +++
 Modules/posixmodule.c                         | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2020-03-23-17-52-00.bpo-40014.Ya70VG.rst

diff --git a/Misc/NEWS.d/next/Library/2020-03-23-17-52-00.bpo-40014.Ya70VG.rst b/Misc/NEWS.d/next/Library/2020-03-23-17-52-00.bpo-40014.Ya70VG.rst
new file mode 100644
index 00000000000000..58f14fa9a72d07
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-03-23-17-52-00.bpo-40014.Ya70VG.rst
@@ -0,0 +1,3 @@
+Fix ``os.getgrouplist()``: on macOS, the ``getgrouplist()`` function returns a
+non-zero value without setting ``errno`` if the group list is too small. Double
+the list size and call it again in this case.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 58cb9b0d468d2f..8d456730a38272 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -6178,10 +6178,29 @@ posix_getgrouplist(PyObject *self, PyObject *args)
     if (groups == NULL)
         return PyErr_NoMemory();
 
+#ifdef __APPLE__
+    while (getgrouplist(user, basegid, groups, &ngroups)) {
+        /* On macOS, getgrouplist() returns a non-zero value without setting
+           errno if the group list is too small. Double the list size and call
+           it again in this case. */
+        PyMem_Free(groups);
+
+        if (ngroups > INT_MAX / 2) {
+            return PyErr_NoMemory();
+        }
+        ngroups *= 2;
+
+        groups = PyMem_New(int, ngroups);
+        if (groups == NULL) {
+            return PyErr_NoMemory();
+        }
+    }
+#else
     if (getgrouplist(user, basegid, groups, &ngroups) == -1) {
         PyMem_Del(groups);
         return posix_error();
     }
+#endif
 
 #ifdef _Py_MEMORY_SANITIZER
     /* Clang memory sanitizer libc intercepts don't know getgrouplist. */