kernelbase: Fix string size variable overflow in GetModuleFileNameW().

dlls/kernel32/tests/module.c

@@ -190,6 +190,11 @@ static void testGetModuleFileName(const char* name)
 
     ok(len1A / 2 == len2A,
        "Correct length in GetModuleFilenameA with buffer too small (%d/%d)\n", len1A / 2, len2A);
+
+    len1A = GetModuleFileNameA(hMod, bufA, 0x10000);
+    ok(len1A > 0, "Getting module filename for handle %p\n", hMod);
+    len1W = GetModuleFileNameW(hMod, bufW, 0x10000);
+    ok(len1W > 0, "Getting module filename for handle %p\n", hMod);
 }
 
 static void testGetModuleFileName_Wrong(void)

dlls/kernelbase/loader.c

@@ -311,7 +311,7 @@ DWORD WINAPI DECLSPEC_HOTPATCH GetModuleFileNameW( HMODULE module, LPWSTR filena
     }
 
     name.Buffer = filename;
-    name.MaximumLength = size * sizeof(WCHAR);
+    name.MaximumLength = min( size, UNICODE_STRING_MAX_CHARS ) * sizeof(WCHAR);
     status = LdrGetDllFullName( module, &name );
     if (!status || status == STATUS_BUFFER_TOO_SMALL) len = name.Length / sizeof(WCHAR);
     SetLastError( RtlNtStatusToDosError( status ));