Can't run fuse inside podman: fusermount: mount failed: Operation not permitted

Question

I'm trying to design a podmod container that can run fuse inside, for example to use sshfs or run some appimages.

However I get errors:

fusermount: mount failed: Operation not permitted

Any idea what's wrong? I tried to use --device fuse and the host is running a recent kernel 5.4.77 (running NixOs)

My Dockerfile:

FROM ubuntu:latest
# podman3 has docker-compose
# But this may be more efficient: https://podman.io/blogs/2018/12/03/podman-runlabel.html
# Nope, can't find how to use $HOME
RUN apt update -y && apt install -y mesa-utils clinfo intel-opencl-icd ocl-icd-opencl-dev inetutils-ping sshfs
RUN apt install -y libglu1-mesa libgomp1 wget curl libsm6 libxrender1 libxext6
RUN apt install -y libxi6 libxrender1 libxrandr2 libxcursor1 libxinerama1
RUN apt-get install -y -qq --no-install-recommends \
    libglvnd0 \
    libgl1 \
    libglx0 \
    libegl1 \
    libxext6 \
    libx11-6\
    bash-completion\
    fuse-overlayfs\
    libfuse2\
    libglib2.0-0

Commands to run:

podman build -t myimage:latest -f Dockerfile
# TODO: check better solution than allowing everybody. +local?
xhost +
podman run -P -v /tmp/.X11-unix:/tmp/.X11-unix\
    -v $HOME/.Xauthority:/root/.Xauthority\
    --security-opt=label=disable\
    -e DISPLAY=$DISPLAY\
    --security-opt=seccomp=unconfined\
    --device /dev/snd\
    --device /dev/input\
    --device /dev/dri\
    --device /dev/fuse\
    -v /dev/shm:/dev/shm\
    --ipc=host\
    --volume /etc/localtime:/etc/localtime:ro\
    -v /home:/home\
    -v /mnt:/mnt\
    -v /nix:/nix\
    -h $HOSTNAME\
    --workdir=$PWD\
    --rm -it  myimage:latest

Commands that fail and that are expected to work:

$ sshfs -v me@myhost:~/ /tmp/host
fusermount: mount failed: Operation not permitted

Second example:

$ cd /tmp
$ wget https://github.com/littleweeb/Desktop/releases/download/v0.4.0_linux/LittleWeeb-0.4.0.303.AppImage
$ chmod +x LittleWeeb-0.4.0.303.AppImage
$ ./LittleWeeb-0.4.0.303.AppImage
fusermount: mount failed: Operation not permitted

Some sanity checks inside the container:

$ ls -al /dev/fuse
crw-rw-rw- 1 nobody nogroup 10, 229 Dec 18 10:28 /dev/fuse

I tried to strace the sshfs and the first error I can see is on:

mount("me@myhost:~/", "/tmp/host", "fuse.sshfs", MS_NOSUID|MS_NODEV, "fd=3,rootmode=40000,user_id=0,gr"...) = -1 EPERM (Operation not permitted)

Answer 1

To use fuse, the user needs to be privileged. There a couple of options for granting the privilege: using setuid or using capabilities. I tried only the setuid way: the fusermount binary must be setuid root:

chown root:root $(which fusermount3)
sudo chmod u+s $(which fusermount3)
ls -l $(which fusermount3)
-rws--x--x 1 root root 39416 Apr 24 11:50 /home/acolin/gpref/usr/bin/fusermount3

The same issue arises with fuse installed inside Gentoo Prefix.