Security of fuse-overlayfs with LXC (unprivileged)

LXC
1

To support Docker in my unprivileged LXC container and avoid using the very inefficient “VFS” storage driver, I decided to use “fuse-overlayfs”.

To accomplish that I added the following config to my container:

#Required for Docker overlayfs
#fuse-overlayfs package installed both on host and inside container
lxc.mount.entry = /dev/fuse dev/fuse none bind,create=file 0 0

This setup works flawlessly, but how secure is it?

Is it any better than using overlay with “modprobe overlay permit_mounts_in_userns=1” on the host, which would allow an attacker in the container to gain host root privileges ? (https://lwn.net/Articles/671641/)

1 Like
2

FUSE should be slightly safer by running the filesystem in userspace, it will be significantly slower than unprivileged overlay though.

There’s no security concerns that I’m aware of with exposing /dev/fuse to the container, FUSE has been properly namespaced or a while now and we expose it by default to all LXD containers.

3

Thanks a lot for clarifying. For my setup security is more important than performance so I accept the performance decrease fuse causes.