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bpo-40014: Fix os.getgrouplist() failure on macOS with many groups #19118

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Merged
vstinner merged 1 commit into from
Mar 23, 2020
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bpo-40014: Fix os.getgrouplist() failure on macOS with many groups #19118

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2020-03-23-17-52-00.bpo-40014.Ya70VG.rst
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Original file line number Diff line number Diff line change
@@ -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.
19 changes: 19 additions & 0 deletions Modules/posixmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6999,10 +6999,29 @@ 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) {

@corona10 corona10 Mar 23, 2020

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Just question:
I 've understood the situation.

Is there any reason not to try with INT_MAX for the last trying?

if (ngroups == INT_MAX) {
   return PyErr_NoMemory();
} else if (ngroups > INT_MAX / 2) {
    ngroups = INT_MAX;
} else {
    ngroups *= 2;
}

@vstinner vstinner Mar 23, 2020

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If (ngroups > INT_MAX / 2) is false, ngroups *= 2 would overflow: ngroups type is int.

} else if (ngroups > INT_MAX / 2) {
    ngroups = INT_MAX;

I don't think that it's worth it to bother with attempting that. I don't think that any user has more than 1073741823 groups. Such user is going to get larger issues than that.

@corona10 corona10 Mar 23, 2020

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Okay got it :) Sounds reasonable.

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. */
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