slirp4netns: User-mode networking for unprivileged network namespaces

slirp4netns provides user-mode networking ("slirp") for unprivileged network namespaces.

Motivation

Starting with Linux 3.8, unprivileged users can create network_namespaces(7) along with user_namespaces(7). However, unprivileged network namespaces had not been very useful, because creating veth(4) pairs across the host and network namespaces still requires the root privileges. (i.e. No internet connection)

slirp4netns allows connecting a network namespace to the Internet in a completely unprivileged way, by connecting a TAP device in a network namespace to the usermode TCP/IP stack ("slirp").

Projects using slirp4netns

Kubernetes distributions:

• Usernetes (via RootlessKit)
• k3s (via RootlessKit)

Container engines:

• Podman
• Buildah
• ctnr (via slirp-cni-plugin)
• Docker & Moby (optionally, via RootlessKit)

Tools:

• RootlessKit
• become-root
• slirp-cni-plugin

Maintenance policy

Version	Status
v0.4.x	A ✅ (will be demoted to B after the release of v0.5.0)
v0.3.x	B ✅ (will be demoted to C after the release of v0.5.0)
v0.2.x	C ⚠️
Early versions prior to v0.2.x	D ⚠️

• A: Actively maintained. Patch releases for security fixes and other bug fixes are planned.
• B: Patch releases for security fixes are planned.
• C: No additional release is planned. However, anybody can still open PR for security fixes in the release/x.y branch.
• D: Not maintained. Distributors can continue to distribute this version, but they should apply security fixes by themselves.

See https://github.com/rootless-containers/slirp4netns/releases for the releases.

See https://github.com/rootless-containers/slirp4netns/security/advisories for the past security advisories.

Quick start

Install from source

Build dependencies:

• glib2-devel (libglib2.0-dev)
• libcap-devel (libcap-dev)
• libseccomp-devel (libseccomp-dev)

Install steps:

$ ./autogen.sh
$ ./configure --prefix=/usr
$ make
$ sudo make install

• To build slirp4netns as a static binary, please run ./configure with LDFLAGS=-static.
• If you set --prefix to $HOME, you don't need to run make install with sudo.

Install from binary

RHEL 8 & Fedora (28 or later):

$ sudo dnf install slirp4netns

RHEL/CentOS 7.7

$ sudo yum install slirp4netns

RHEL/CentOS 7.6

$ sudo curl -o /etc/yum.repos.d/vbatts-shadow-utils-newxidmap-epel-7.repo https://copr.fedorainfracloud.org/coprs/vbatts/shadow-utils-newxidmap/repo/epel-7/vbatts-shadow-utils-newxidmap-epel-7.repo
$ sudo yum install slirp4netns

You might need to enable user namespaces manually:

$ sudo sh -c 'echo "user.max_user_namespaces=28633" > /etc/sysctl.d/userns.conf'
$ sudo sysctl -p /etc/sysctl.d/userns.conf

Arch Linux:

$ sudo pacman -S slirp4netns

You might need to enable user namespaces manually:

$ sudo sh -c "echo 1 > /proc/sys/kernel/unprivileged_userns_clone"

openSUSE Tumbleweed

$ sudo zypper install slirp4netns

openSUSE Leap 15.0

$ sudo zypper addrepo --refresh http://download.opensuse.org/repositories/devel:/kubic/openSUSE_Leap_15.0/devel:kubic.repo
$ sudo zypper install slirp4netns

SUSE Linux Enterprise 15

$ sudo zypper addrepo --refresh http://download.opensuse.org/repositories/devel:/kubic/SLE_15/devel:kubic.repo
$ sudo zypper install slirp4netns

Debian GNU/Linux (10 or later) & Ubuntu (19.04 or later)

$ sudo apt install slirp4netns

NixOS

$ nix-env -i slirp4netns

Gentoo Linux

$ sudo emerge app-emulation/slirp4netns

Slackware

$ sudo sbopkg -i slirp4netns

Void Linux

$ sudo xbps-install slirp4netns

Usage

Terminal 1: Create user/network/mount namespaces

$ unshare --user --map-root-user --net --mount
unshared$ echo $$ > /tmp/pid

Terminal 2: Start slirp4netns

$ slirp4netns --configure --mtu=65520 --disable-host-loopback $(cat /tmp/pid) tap0
starting slirp, MTU=65520
...

Terminal 1: Make sure the tap0 is configured and connected to the Internet

unshared$ ip a
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
3: tap0: <BROADCAST,UP,LOWER_UP> mtu 65520 qdisc fq_codel state UNKNOWN group default qlen 1000
    link/ether c2:28:0c:0e:29:06 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.100/24 brd 10.0.2.255 scope global tap0
       valid_lft forever preferred_lft forever
    inet6 fe80::c028:cff:fe0e:2906/64 scope link 
       valid_lft forever preferred_lft forever
unshared$ echo "nameserver 10.0.2.3" > /tmp/resolv.conf
unshared$ mount --bind /tmp/resolv.conf /etc/resolv.conf
unshared$ curl https://example.com

See slirp4netns.1.md for further information.

Benchmarks

iperf3 (netns -> host)

Aug 28, 2018, on RootlessKit Travis: rootless-containers/rootlesskit#16

Implementation	MTU=1500	MTU=4000	MTU=16384	MTU=65520
vde_plug	763 Mbps	Unsupported	Unsupported	Unsupported
VPNKit	514 Mbps	526 Mbps	540 Mbps	Unsupported
slirp4netns	1.07 Gbps	2.78 Gbps	4.55 Gbps	9.21 Gbps

slirp4netns is faster than vde_plug and VPNKit because slirp4netns is optimized to avoid copying packets across the namespaces.

The latest revision of slirp4netns is regularly benchmarked (make benchmark) on Travis: https://travis-ci.org/rootless-containers/slirp4netns

Acknowledgement

See vendor/README.md.

License

GPL-2.0-or-later