ch-image build inside a docker container

[MFTabriz]

I get
ch-run[1102]: error: can't init user+mount namespaces: Operation not permitted (ch_core.c:401 1)
while trying to run ch-image build --force (v0.27) inside an unprivileged docker container. Is there any workaround for this?

[reidpr]

My guess is that there is a workaround, because user namespaces can be nested, and I'd guess it has something to do with Docker's configuration.