Make open O_CREATE mode 0 work

src/library_fs.js

@@ -1083,7 +1083,10 @@ FS.staticInit();
           }
         } else {
           // node doesn't exist, try to create it
-          node = FS.mknod(path, mode, 0);
+          // Ignore the permission bits here to ensure we can `open` this new
+          // file below. We use chmod below the apply the permissions once the
+          // file is open.
+          node = FS.mknod(path, mode | 0o777, 0);
           created = true;
         }
       }
@@ -1133,6 +1136,9 @@ FS.staticInit();
       if (stream.stream_ops.open) {
         stream.stream_ops.open(stream);
       }
+      if (created) {
+        FS.chmod(node, mode & 0o777);
+      }
 #if expectToReceiveOnModule('logReadFiles')
       if (Module['logReadFiles'] && !(flags & {{{ cDefs.O_WRONLY}}})) {
         if (!(path in FS.readFiles)) {

test/fs/test_fs_open_no_permissions.c

@@ -0,0 +1,19 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <assert.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <assert.h>
+#include <errno.h>
+#include <string.h>
+
+int main() {
+  int res = open("a", O_CREAT, 0);
+  printf("error: %s\n", strerror(errno));
+  assert(res >= 0);
+  struct stat st;
+  assert(stat("a", &st) == 0);
+  assert((st.st_mode & 0777) == 0);
+  printf("success\n");
+}

test/test_core.py

@@ -5858,6 +5858,10 @@ def test_fs_rename_on_existing(self):
       self.set_setting('FORCE_FILESYSTEM')
     self.do_runf('fs/test_fs_rename_on_existing.c', 'success')
 
+  @also_with_nodefs_both
+  def test_fs_open_no_permissions(self):
+    self.do_runf('fs/test_fs_open_no_permissions.c', 'success')
+
   @also_with_nodefs_both
   def test_fs_mkdir_dotdot(self):
     self.do_runf('fs/test_fs_mkdir_dotdot.c', 'success')