Hi. I have a question regarding the security implications of host directory pass-through. My question probably applies to both lxd and incus, but I decided to ask my question here as I plan on migrating my live systems to incus soon and thus that’s my primary interest going forward.
TL;DR - is it “less secure” for the host server to pass through a regular host directory to a vm using ‘lxc config device add…’ vs using the default lxd/incus storage?
I created a directory (‘/home/andrew/vmdir’) on the host. I then created a test file (‘host-creation’) in the host under vmdir (as a normal user). And then I created a virtual machine (‘vm’) on the same host using:
lxc init ubuntu:22.04 vm --vm
I then passed through the directory as a disk (‘demo’) to the vm to mount it under /root/vmdir:
lxc config device add vm demo disk source=/home/andrew/vmdir path=root/vmdir.
I started the vm, exec into it and I can see the directory, and create/delete files in it. Including any created by the host. I can, as a non-root user in the host create/delete files created in the vm in that passed through directory as normal (albeit it asks me if I want to remove the write-protection.
My question is: are there any specific security weaknesses/issues/vulnerabilities to the host for passing a directory through to the vm vs say using the default storage and creating native directories inside the vm without passing through a disk device? How different is this (or not) to passing a directory through to a vm using e.g. virt-manager?
A screenshot showing my actual experience is shown below for completeness. I was surprised (pleasantly) that this worked as easily as it did. I am just wondering if I am creating security issues for the bare-metal server if I use this to pass through some storage?