Secure and user friendly mounts for unprivileged

[techtonik (anatoly techtonik)]

Thanks. I could make the volume writable after enabling shiftfs with LXD and using shift=true for adding disk devices:

lxc config device add $NAME $NAME-shared disk source=$PWD \
  path=/root/$NAME shift=true

But I am still not sure it is secure after reading this thread on setuid:

Trying out `shiftfs`

Yeah, if setuid is possible on a path that’s visible to an unprivileged user on the host, root in the container could say copy /bin/sh to that path, chown 0:0 and chmod u+s it, making it setuid root for anyone on the host who’s allowed to run it.

I am not sure that getting into details of what setuid is and how it works is user friendly approach to security. Maybe there is no concern in this case? Is there a code I can run on guest/host to check if my mount is exploitable to this setuid attack?