When importing an extension on Windows, the code reads the PE 'import

Thomas Heller · Thomas Heller · commit 1df04617b7e8 · 2004-07-02T08:53:57.000Z
table' of the dll, to make sure that the dll really was build for the
correct Python version.  It does this by looking for an entry
'pythonXY.dll' (X.Y is the Python version number).

The code now checks the size of the dll's import table before reading
entries from it.  Before this patch, the code crashed trying to read
the import table when the size was zero (as in Win2k's wmi.dll, for
example).

Look for imports of 'pythonXY_d.dll' in a debug build instead of
'pythonXY.dll'.

Fixes SF 951851: Crash when reading "import table" of certain windows dlls.

Already backported to the 2.3 branch.
diff --git a/Python/dynload_win.c b/Python/dynload_win.c
@@ -116,6 +116,10 @@ static char *GetPythonImport (HINSTANCE hModule)
 	   string constant holding the import name is located. */
 
 	if (DWORD_AT(dllbase + opt_offset + num_dict_off) >= 2) {
+		/* We have at least 2 tables - the import table is the second
+		   one.  But still it may be that the table size is zero */
+		if (0 == DWORD_AT(dllbase + opt_offset + import_off + sizeof(DWORD)))
+			return NULL;
 		import_data = dllbase + DWORD_AT(dllbase +
 						 opt_offset +
 						 import_off);
@@ -128,7 +132,11 @@ static char *GetPythonImport (HINSTANCE hModule)
 				/* Ensure python prefix is followed only
 				   by numbers to the end of the basename */
 				pch = import_name + 6;
+#ifdef _DEBUG
+				while (*pch && pch[0] != '_' && pch[1] != 'd' && pch[2] != '.') {
+#else
 				while (*pch && *pch != '.') {
+#endif
 					if (*pch >= '0' && *pch <= '9') {
 						pch++;
 					} else {
@@ -221,7 +229,11 @@ dl_funcptr _PyImport_GetDynLoadFunc(const char *fqname, const char *shortname,
 		} else {
 			char buffer[256];
 
+#ifdef _DEBUG
+			PyOS_snprintf(buffer, sizeof(buffer), "python%d%d_d.dll",
+#else
 			PyOS_snprintf(buffer, sizeof(buffer), "python%d%d.dll",
+#endif
 				      PY_MAJOR_VERSION,PY_MINOR_VERSION);
 			import_python = GetPythonImport(hDLL);
 
