Comment 2 for bug 1659087

Iirc, as of 4.8 what you're seeing is upstream behavior, and yes it did get backported to xenial in the series you referenced.

Even if the inode is created with INVALID_UID/INVALID_GID you aren't going to be able to do anything with it. So I guess the question is why you need to be able to do that and whether or not you can accomplish that some other way. If not then the behavior would need to change upstream - even if we fix it in xenial 4.4 kernels you'll probably just hit it again later.

Note that you don't actually need to enter the user namespace to create the file, you just need fsuid/fsgid to be ids which have a mapping in the user ns.