Fixes Issue #14992: os.makedirs(path, exist_ok=True) would raise an OSError

when the path existed and had the S_ISGID mode bit set when it was
not explicitly asked for.  This is no longer an exception as mkdir
cannot control if the OS sets that bit for it or not.

1 files changed, 14 insertions, 2 deletions

diff --git a/Lib/os.py b/Lib/os.py
index a1a35cd8e3..11e4d60d15 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -160,8 +160,20 @@ def makedirs(name, mode=0o777, exist_ok=False):
     try:
         mkdir(name, mode)
     except OSError as e:
-        if not (e.errno == errno.EEXIST and exist_ok and path.isdir(name) and
-                st.S_IMODE(lstat(name).st_mode) == _get_masked_mode(mode)):
+        dir_exists = path.isdir(name)
+        expected_mode = _get_masked_mode(mode)
+        if dir_exists:
+            # S_ISGID is automatically copied by the OS from parent to child
+            # directories on mkdir.  Don't consider it being set to be a mode
+            # mismatch as mkdir does not unset it when not specified in mode.
+            actual_mode = st.S_IMODE(lstat(name).st_mode) & ~st.S_ISGID
+        else:
+            actual_mode = -1
+        if not (e.errno == errno.EEXIST and exist_ok and dir_exists and
+                actual_mode == expected_mode):
+            if dir_exists and actual_mode != expected_mode:
+                e.strerror += ' (mode %o != expected mode %o)' % (
+                        actual_mode, expected_mode)
             raise
 
 def removedirs(name):