# RootlessKit: the gate to the rootless world RootlessKit is a kind of Linux-native "fake root" utility, made for mainly running [Docker and Kubernetes as an unprivileged user](https://github.com/rootless-containers/usernetes), so as to protect the real root on the host from potential container-breakout attacks. - [What it actually does](#what-it-actually-does) - [Projects using RootlessKit](#projects-using-rootlesskit) - [Setup](#setup) - [Requirements](#requirements) - [Distribution-specific hints](#distribution-specific-hints) - [Usage](#usage) - [State directory](#state-directory) - [Environment variables](#environment-variables) - [Network Drivers](#network-drivers) - [`--net=host` (default)](#--nethost-default) - [`--net=slirp4netns` (recommended)](#--netslirp4netns-recommended) - [`--net=vpnkit`](#--netvpnkit) - [`--net=lxc-user-nic` (experimental)](#--netlxc-user-nic-experimental) - [Port Drivers](#port-drivers) ## What it actually does RootlessKit creates [`user_namespaces(7)`](http://man7.org/linux/man-pages/man7/user_namespaces.7.html) and [`mount_namespaces(7)`](http://man7.org/linux/man-pages/man7/mount_namespaces.7.html), and executes [`newuidmap(1)`](http://man7.org/linux/man-pages/man1/newuidmap.1.html)/[`newgidmap(1)`](http://man7.org/linux/man-pages/man1/newgidmap.1.html) along with [`subuid(5)`](http://man7.org/linux/man-pages/man5/subuid.5.html) and [`subgid(5)`](http://man7.org/linux/man-pages/man5/subgid.5.html). RootlessKit also supports isolating [`network_namespaces(7)`](http://man7.org/linux/man-pages/man7/network_namespaces.7.html) with userspace NAT using ["slirp"](#network-drivers). Kernel NAT using SUID-enabled [`lxc-user-nic(1)`](https://linuxcontainers.org/lxc/manpages/man1/lxc-user-nic.1.html) is also experimentally supported. ## Projects using RootlessKit * [Docker/Moby](https://get.docker.com/rootless) * [Usernetes](https://github.com/rootless-containers/usernetes): Docker & Kubernetes, installable under a non-root user's `$HOME`. * [k3s](https://k3s.io/): Lightweight Kubernetes * [BuildKit](https://github.com/moby/buildkit): Next-generation `docker build` backend ## Setup ```console $ go get github.com/rootless-containers/rootlesskit/cmd/rootlesskit $ go get github.com/rootless-containers/rootlesskit/cmd/rootlessctl ``` or just run `make` to make binaries under `./bin` directory. ### Requirements * `newuidmap` and `newgidmap` need to be installed on the host. These commands are provided by the `uidmap` package on most distributions. * `/etc/subuid` and `/etc/subgid` should contain more than 65536 sub-IDs. e.g. `penguin:231072:65536`. These files are automatically configured on most distributions. ```console $ id -u 1001 $ whoami penguin $ grep "^$(whoami):" /etc/subuid penguin:231072:65536 $ grep "^$(whoami):" /etc/subgid penguin:231072:65536 ``` #### Distribution-specific hints Debian (excluding Ubuntu): * `sudo sh -c "echo 1 > /proc/sys/kernel/unprivileged_userns_clone"` is required Arch Linux: * `sudo sh -c "echo 1 > /proc/sys/kernel/unprivileged_userns_clone"` is required RHEL/CentOS 7: * `sudo sh -c "echo 28633 > /proc/sys/user/max_user_namespaces"` is required * [COPR package `vbatts/shadow-utils-newxidmap`](https://copr.fedorainfracloud.org/coprs/vbatts/shadow-utils-newxidmap/) needs to be installed ## Usage Inside `rootlesskit`, your UID is mapped to 0 but it is not the real root: ```console $ rootlesskit bash rootlesskit$ id uid=0(root) gid=0(root) groups=0(root),65534(nogroup) rootlesskit$ ls -l /etc/shadow -rw-r----- 1 nobody nogroup 1050 Aug 21 19:02 /etc/shadow rootlesskit$ $ cat /etc/shadow cat: /etc/shadow: Permission denied ``` Environment variables are kept untouched: ```console $ rootlesskit bash rootlesskit$ echo $USER penguin rootlesskit$ echo $HOME /home/penguin rootlesskit$ echo $XDG_RUNTIME_DIR /run/user/1001 ``` Filesystems can be isolated from the host with `--copy-up`: ```console $ rootlesskit --copy-up=/etc bash rootlesskit$ rm /etc/resolv.conf rootlesskit$ vi /etc/resolv.conf ``` You can even create network namespaces with [Slirp](#network-drivers): ```console $ rootlesskit --copy-up=/etc --copy-up=/run --net=slirp4netns --disable-host-loopback bash rootlesskit$ ip netns add foo ... ``` Proc filesystem view: ```console $ rootlesskit bash rootlesskit$ cat /proc/self/uid_map 0 1001 1 1 231072 65536 rootlesskit$ cat /proc/self/gid_map 0 1001 1 1 231072 65536 rootlesskit$ cat /proc/self/setgroups allow ``` Full CLI options: ```console NAME: rootlesskit - the gate to the rootless world USAGE: rootlesskit [global options] command [command options] [arguments...] VERSION: 0.3.0+dev COMMANDS: help, h Shows a list of commands or help for one command GLOBAL OPTIONS: --debug debug mode --state-dir value state directory --net value network driver [host, slirp4netns, vpnkit, lxc-user-nic(experimental), vdeplug_slirp(deprecated)] (default: "host") --slirp4netns-binary value path of slirp4netns binary for --net=slirp4netns (default: "slirp4netns") --vpnkit-binary value path of VPNKit binary for --net=vpnkit (default: "vpnkit") --lxc-user-nic-binary value path of lxc-user-nic binary for --net=lxc-user-nic (default: "/usr/lib/x86_64-linux-gnu/lxc/lxc-user-nic") --lxc-user-nic-bridge value lxc-user-nic bridge name (default: "lxcbr0") --mtu value MTU for non-host network (default: 65520 for slirp4netns, 1500 for others) (default: 0) --cidr value CIDR for slirp4netns network (default: 10.0.2.0/24, requires slirp4netns v0.3.0+ for custom CIDR) --disable-host-loopback prohibit connecting to 127.0.0.1:* on the host namespace --copy-up value mount a filesystem and copy-up the contents. e.g. "--copy-up=/etc" (typically required for non-host network) --copy-up-mode value copy-up mode [tmpfs+symlink] (default: "tmpfs+symlink") --port-driver value port driver for non-host network. [none, socat, slirp4netns, builtin(experimental)] (default: "none") --help, -h show help --version, -v print the version ``` ## State directory The following files will be created in the state directory, which can be specified with `--state-dir`: * `lock`: lock file * `child_pid`: decimal PID text that can be used for `nsenter(1)`. * `api.sock`: REST API socket for `rootlessctl`. See [Port Drivers](#port-drivers) section. If `--state-dir` is not specified, RootlessKit creates a temporary state directory on `/tmp` and removes it on exit. Undocumented files are subject to change. ## Environment variables The following environment variables will be set for the child process: * `ROOTLESSKIT_STATE_DIR` (since v0.3.0): absolute path to the state dir Undocumented environment variables are subject to change. ## Network Drivers RootlessKit provides several drivers for providing network connectivity: * `--net=host`: use host network namespace (default) * `--net=slirp4netns`: use [slirp4netns](https://github.com/rootless-containers/slirp4netns) (recommended) * `--net=vpnkit`: use [VPNKit](https://github.com/moby/vpnkit) * `--net=lxc-user-nic`: use `lxc-user-nic` (experimental) * `--net=vdeplug_slirp`: use [vdeplug_slirp](https://github.com/rd235/vdeplug_slirp) (deprecated) [Benchmark (Aug 28, 2018)](https://github.com/rootless-containers/rootlesskit/pull/16): | Implementation | MTU=1500 | MTU=4000 | MTU=16384 | MTU=65520 |---------------------------------|------------|-------------|-------------|------------ |(rootful veth) |(52.1 Gbps) | (45.4 Gbps) | (43.6 Gbps )| (51.5 Gbps) |`rootlesskit --net=slirp4netns` | 1.07 Gbps | 2.78 Gbps | 4.55 Gbps | 9.21 Gbps |`rootlesskit --net=vpnKit` | 514 Mbps | 526 Mbps | 540 Mbps |(Unsupported) |`rootlesskit --net=vdeplug_slirp`| 763 Mbps |(Unsupported)|(Unsupported)|(Unsupported) | `--net=lxc-user-nic` is as fast as rootful veth. ### `--net=host` (default) `--net=host` does not isolate the network namespace from the host. Pros: * No performance overhead * Supports ICMP Echo (`ping`) when `/proc/sys/net/ipv4/ping_group_range` is configured Cons: * No permission for network-namespaced operations, e.g. creating iptables rules, running `tcpdump` To route ICMP Echo packets (`ping`), you need to write the range of GIDs to [`net.ipv4.ping_group_range`](http://man7.org/linux/man-pages/man7/icmp.7.html). ```console $ sudo sh -c "echo 0 2147483647 > /proc/sys/net/ipv4/ping_group_range" ``` ### `--net=slirp4netns` (recommended) `--net=slirp4netns` isolates the network namespace from the host and launch [slirp4netns](https://github.com/rootless-containers/slirp4netns) for providing usermode networking. Pros: * Possible to perform network-namespaced operations, e.g. creating iptables rules, running `tcpdump` * Supports ICMP Echo (`ping`) when `/proc/sys/net/ipv4/ping_group_range` is configured Cons: * Extra performance overhead (but still faster than `--net=vpnkit`) * Supports only TCP, UDP, and ICMP Echo packets To use `--net=slirp4netns`, you need to install slirp4netns. v0.3.0 or later is recommended. ```console $ sudo dnf install slirp4netns ``` or ```console $ sudo apt-get install slirp4netns ``` If binary package is not available for your distribution, install from the source: ```console $ git clone https://github.com/rootless-containers/slirp4netns $ cd slirp4netns $ ./autogen.sh && ./configure && make $ cp slirp4netns ~/bin ``` The network is configured as follows by default: * IP: 10.0.2.100/24 * Gateway: 10.0.2.2 * DNS: 10.0.2.3 The network configuration can be changed by specifying custom CIDR, e.g. `--cidr=10.0.3.0/24` (requires slirp4netns v0.3.0+). Specifying `--copy-up=/etc` is highly recommended unless `/etc/resolv.conf` on the host is statically configured. Otherwise `/etc/resolv.conf` in the RootlessKit's mount namespace will be unmounted when `/etc/resolv.conf` on the host is recreated, typically by NetworkManager or systemd-resolved. It is also highly recommended to specyfy`--disable-host-loopback`. Otherwise ports listening on 127.0.0.1 in the host are accessible as 10.0.2.2 in the RootlessKit's network namespace. Example session: ```console $ rootlesskit --net=slirp4netns --copy-up=/etc --disable-host-loopback bash rootlesskit$ ip a 1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: tap0: mtu 65520 qdisc fq_codel state UP group default qlen 1000 link/ether 46:dc:8d:09:fd:f2 brd ff:ff:ff:ff:ff:ff inet 10.0.2.100/24 scope global tap0 valid_lft forever preferred_lft forever inet6 fe80::44dc:8dff:fe09:fdf2/64 scope link valid_lft forever preferred_lft forever ootlesskit$ ip r default via 10.0.2.2 dev tap0 10.0.2.0/24 dev tap0 proto kernel scope link src 10.0.2.100 rootlesskit$ cat /etc/resolv.conf nameserver 10.0.2.3 rootlesskit$ curl https://www.google.com ... ``` ### `--net=vpnkit` `--net=vpnkit` isolates the network namespace from the host and launch [VPNKit](https://github.com/moby/vpnkit) for providing usermode networking. Pros: * Possible to perform network-namespaced operations, e.g. creating iptables rules, running `tcpdump` Cons: * Extra performance overhead * Supports only TCP and UDP packets. No support for ICMP Echo (`ping`) unlike `--net=slirp4netns`, even if `/proc/sys/net/ipv4/ping_group_range` is configured. To use `--net=vpnkit`, you need to install VPNkit. ```console $ git clone https://github.com/moby/vpnkit.git $ cd vpnkit $ make $ cp vpnkit.exe ~/bin/vpnkit ``` The network is configured as follows by default: * IP: 192.168.65.3/24 * Gateway: 192.168.65.1 * DNS: 192.168.65.1 As in `--net=slirp4netns`, specifying `--copy-up=/etc` and `--disable-host-loopback` is highly recommended. If `--disable-host-loopback` is not specified, ports listening on 127.0.0.1 in the host are accessible as 192.168.65.2 in the RootlessKit's network namespace. ### `--net=lxc-user-nic` (experimental) `--net=lxc-user-nic` isolates the network namespace from the host and launch [`lxc-user-nic(1)`](https://linuxcontainers.org/lxc/manpages/man1/lxc-user-nic.1.html) SUID binary for providing kernel-mode NAT. Pros: * No performance overhead * Possible to perform network-namespaced operations, e.g. creating iptables rules, running `tcpdump` * Supports ICMP Echo (`ping`) without `/proc/sys/net/ipv4/ping_group_range` configuration Cons: * Less secure * Needs `/etc/lxc/lxc-usernet` configuration To use `lxc-user-nic`, you need to install `liblxc-common` package: ```console $ sudo apt-get install liblxc-common ``` You also need to set up [`/etc/lxc/lxc-usernet`](https://linuxcontainers.org/lxc/manpages/man5/lxc-usernet.5.html): ``` # USERNAME TYPE BRIDGE COUNT penguin veth lxcbr0 1 ``` The `COUNT` value needs to be increased to run multiple RootlessKit instances with `--net=lxc-user-nic` simultaneously. It may take a few seconds to configure the interface using DHCP. If you start and stop RootlessKit too frequently, you might use up all available DHCP addresses. You might need to reset `/var/lib/misc/dnsmasq.lxcbr0.leases` and restart the `lxc-net` service. Currently, the MAC address is always set to a random address. ## Port Drivers `rootlessctl` can be used for exposing the ports in the network namespace to the host network namespace. You also need to launch `rootlesskit` with `--port-driver=(socat|slirp4netns|builtin)`. `builtin` is the fastest but currently experimental. For example, to expose 80 in the child as 8080 in the parent: ```console $ rootlesskit --state-dir=/run/user/1001/rootlesskit/foo --net=slirp4netns --disable-host-loopback --copy-up=/etc --port-driver=builtin bash rootlesskit$ rootlessctl --socket=/run/user/1001/rootlesskit/foo/api.sock add-ports 0.0.0.0:8080:80/tcp 1 rootlesskit$ rootlessctl --socket=/run/user/1001/rootlesskit/foo/api.sock list-ports ID PROTO PARENTIP PARENTPORT CHILDPORT 1 tcp 0.0.0.0 8080 80 rootlesskit$ rootlessctl --socket=/run/user/1001/rootlesskit/foo/api.sock remove-ports 1 1 ``` You can also expose ports using `socat` and `nsenter` instead of RootlessKit's port drivers. ```console $ pid=$(cat /run/user/1001/rootlesskit/foo/child_pid) $ socat -t -- TCP-LISTEN:8080,reuseaddr,fork EXEC:"nsenter -U -n -t $pid socat -t -- STDIN TCP4\:127.0.0.1\:80" ```