bpo-36085: Enable better DLL resolution on Windows (GH-12302)

2 files changed, 74 insertions, 1 deletions

diff --git a/Lib/ctypes/__init__.py b/Lib/ctypes/__init__.py
index 5f78beda586..4107db3e397 100644
--- a/Lib/ctypes/__init__.py
+++ b/Lib/ctypes/__init__.py
@@ -326,7 +326,8 @@ class CDLL(object):
 
     def __init__(self, name, mode=DEFAULT_MODE, handle=None,
                  use_errno=False,
-                 use_last_error=False):
+                 use_last_error=False,
+                 winmode=None):
         self._name = name
         flags = self._func_flags_
         if use_errno:
@@ -341,6 +342,15 @@ class CDLL(object):
             """
             if name and name.endswith(")") and ".a(" in name:
                 mode |= ( _os.RTLD_MEMBER | _os.RTLD_NOW )
+        if _os.name == "nt":
+            if winmode is not None:
+                mode = winmode
+            else:
+                import nt
+                mode = nt._LOAD_LIBRARY_SEARCH_DEFAULT_DIRS
+                if '/' in name or '\\' in name:
+                    self._name = nt._getfullpathname(self._name)
+                    mode |= nt._LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR
 
         class _FuncPtr(_CFuncPtr):
             _flags_ = flags
diff --git a/Lib/ctypes/test/test_loading.py b/Lib/ctypes/test/test_loading.py
index f3b65b9d6e7..be367c6fa35 100644
--- a/Lib/ctypes/test/test_loading.py
+++ b/Lib/ctypes/test/test_loading.py
@@ -1,6 +1,9 @@
 from ctypes import *
 import os
+import shutil
+import subprocess
 import sys
+import sysconfig
 import unittest
 import test.support
 from ctypes.util import find_library
@@ -112,5 +115,65 @@ class LoaderTest(unittest.TestCase):
         # This is the real test: call the function via 'call_function'
         self.assertEqual(0, call_function(proc, (None,)))
 
+    @unittest.skipUnless(os.name == "nt",
+                         'test specific to Windows')
+    def test_load_dll_with_flags(self):
+        _sqlite3 = test.support.import_module("_sqlite3")
+        src = _sqlite3.__file__
+        if src.lower().endswith("_d.pyd"):
+            ext = "_d.dll"
+        else:
+            ext = ".dll"
+
+        with test.support.temp_dir() as tmp:
+            # We copy two files and load _sqlite3.dll (formerly .pyd),
+            # which has a dependency on sqlite3.dll. Then we test
+            # loading it in subprocesses to avoid it starting in memory
+            # for each test.
+            target = os.path.join(tmp, "_sqlite3.dll")
+            shutil.copy(src, target)
+            shutil.copy(os.path.join(os.path.dirname(src), "sqlite3" + ext),
+                        os.path.join(tmp, "sqlite3" + ext))
+
+            def should_pass(command):
+                with self.subTest(command):
+                    subprocess.check_output(
+                        [sys.executable, "-c",
+                         "from ctypes import *; import nt;" + command],
+                        cwd=tmp
+                    )
+
+            def should_fail(command):
+                with self.subTest(command):
+                    with self.assertRaises(subprocess.CalledProcessError):
+                        subprocess.check_output(
+                            [sys.executable, "-c",
+                             "from ctypes import *; import nt;" + command],
+                            cwd=tmp, stderr=subprocess.STDOUT,
+                        )
+
+            # Default load should not find this in CWD
+            should_fail("WinDLL('_sqlite3.dll')")
+
+            # Relative path (but not just filename) should succeed
+            should_pass("WinDLL('./_sqlite3.dll')")
+
+            # Insecure load flags should succeed
+            should_pass("WinDLL('_sqlite3.dll', winmode=0)")
+
+            # Full path load without DLL_LOAD_DIR shouldn't find dependency
+            should_fail("WinDLL(nt._getfullpathname('_sqlite3.dll'), " +
+                        "winmode=nt._LOAD_LIBRARY_SEARCH_SYSTEM32)")
+
+            # Full path load with DLL_LOAD_DIR should succeed
+            should_pass("WinDLL(nt._getfullpathname('_sqlite3.dll'), " +
+                        "winmode=nt._LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR)")
+
+            # User-specified directory should succeed
+            should_pass("import os; p = os.add_dll_directory(os.getcwd());" +
+                        "WinDLL('_sqlite3.dll'); p.close()")
+
+
+
 if __name__ == "__main__":
     unittest.main()