rootless: enable IPv6 in RootlessKit network namespace

cmd/nerdctl/container/container_run_network_linux_test.go

@@ -838,8 +838,8 @@ func TestHostsFileMounts(t *testing.T) {
 }
 
 func TestRunContainerWithStaticIP6(t *testing.T) {
-	if rootlessutil.IsRootless() {
-		t.Skip("Static IP6 assignment is not supported rootless mode yet.")
+	if rootlessutil.IsRootless() && !rootlessutil.RootlessKitIPv6Enabled() {
+		t.Skip("Rootless IPv6 requires CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6=true; see docs/rootless.md")
 	}
 	networkName := "test-network"
 	networkSubnet := "2001:db8:5::/64"

docs/rootless.md

@@ -165,6 +165,11 @@ Rootless containerd recognizes the following environment variables to configure
   the host loopback IP address (127.0.0.1) and abstract sockets are exposed to Dockerfile's "RUN" instructions during `nerdctl build` (not `nerdctl run`).
   The drawback is fixed in BuildKit v0.13. Upgrading from a prior version of BuildKit needs removing the old systemd unit:
   `containerd-rootless-setuptool.sh uninstall-buildkit && rm -f ~/.config/buildkit/buildkitd.toml`
+* `CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6=(true|false)`: whether to enable IPv6 inside the RootlessKit network namespace.
+  Defaults to "false". After enabling this, create IPv6-capable CNI networks with
+  `nerdctl network create --ipv6 --subnet <v6-subnet>` as usual. Published ports over IPv6 are
+  supported with `--port-driver=builtin` (the default). `--port-driver=slirp4netns` does not yet
+  support IPv6 port forwarding upstream.
 
 To set these variables, create `~/.config/systemd/user/containerd.service.d/override.conf` as follows:
 ```ini

extras/rootless/containerd-rootless.sh

@@ -44,6 +44,11 @@
 #   the host loopback IP address (127.0.0.1) and abstract sockets are exposed to Dockerfile's "RUN" instructions during `nerdctl build` (not `nerdctl run`).
 #   The drawback is fixed in BuildKit v0.13. Upgrading from a prior version of BuildKit needs removing the old systemd unit:
 #   `containerd-rootless-setuptool.sh uninstall-buildkit && rm -f ~/.config/buildkit/buildkitd.toml`
+# * CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6=(true|false): whether to enable IPv6 inside the RootlessKit network namespace.
+#   Defaults to "false". Requires a RootlessKit network driver that supports IPv6 (slirp4netns >= v0.4.0 with an
+#   IPv6-capable build). When using `--port-driver=slirp4netns`, published ports over IPv6 additionally require
+#   IPv6 support in slirp4netns's port driver, which is not yet available upstream
+#   (see https://github.com/rootless-containers/slirp4netns/pull/276).
 
 # See also: https://github.com/containerd/nerdctl/blob/main/docs/rootless.md#configuring-rootlesskit
 
@@ -78,6 +83,7 @@ if [ -z "$_CONTAINERD_ROOTLESS_CHILD" ]; then
 	: "${CONTAINERD_ROOTLESS_ROOTLESSKIT_SLIRP4NETNS_SANDBOX:=auto}"
 	: "${CONTAINERD_ROOTLESS_ROOTLESSKIT_SLIRP4NETNS_SECCOMP:=auto}"
 	: "${CONTAINERD_ROOTLESS_ROOTLESSKIT_DETACH_NETNS:=auto}"
+	: "${CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6:=false}"
 	net=$CONTAINERD_ROOTLESS_ROOTLESSKIT_NET
 	mtu=$CONTAINERD_ROOTLESS_ROOTLESSKIT_MTU
 	if [ -z "$net" ]; then
@@ -137,6 +143,23 @@ if [ -z "$_CONTAINERD_ROOTLESS_CHILD" ]; then
 		;;
 	esac
 
+	case "$CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6" in
+	1 | true)
+		if ! rootlesskit --help | grep -qw -- "--ipv6"; then
+			echo "CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6=true requires a RootlessKit build that supports --ipv6"
+			exit 1
+		fi
+		CONTAINERD_ROOTLESS_ROOTLESSKIT_FLAGS="--ipv6 $CONTAINERD_ROOTLESS_ROOTLESSKIT_FLAGS"
+		;;
+	0 | false)
+		# NOP
+		;;
+	*)
+		echo "Unknown CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6 value: $CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6"
+		exit 1
+		;;
+	esac
+
 	# Re-exec the script via RootlessKit, so as to create unprivileged {user,mount,network} namespaces.
 	#
 	# --copy-up allows removing/creating files in the directories by creating tmpfs and symlinks

hack/test-integration-rootless.sh

@@ -82,6 +82,15 @@ if [ ! -e "$HOME/.config/nerdctl-test-setup-done" ]; then
 		systemctl --user daemon-reload
 	fi
 
+	if [ "${CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6:-false}" = "true" ]; then
+		mkdir -p "$HOME/.config/systemd/user/containerd.service.d"
+		cat <<-EOF >"$HOME/.config/systemd/user/containerd.service.d/ipv6.conf"
+		[Service]
+		Environment="CONTAINERD_ROOTLESS_ROOTLESSKIT_IPV6=true"
+		EOF
+		systemctl --user daemon-reload
+	fi
+
 	containerd-rootless-setuptool.sh install
 	if grep -q "options use-vc" /etc/resolv.conf; then
 		containerd-rootless-setuptool.sh nsenter -- sh -euc 'echo "options use-vc" >>/etc/resolv.conf'

pkg/rootlessutil/rootlessutil_linux.go

@@ -17,6 +17,7 @@
 package rootlessutil
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"os"
@@ -119,3 +120,25 @@ func WithDetachedNetNSIfAny(fn func() error) error {
 	}
 	return ns.WithNetNSPath(netns, func(_ ns.NetNS) error { return fn() })
 }
+
+// RootlessKitIPv6Enabled reports whether the running RootlessKit parent process was launched with --ipv6.
+func RootlessKitIPv6Enabled() bool {
+	stateDir, err := RootlessKitStateDir()
+	if err != nil {
+		return false
+	}
+	pid, err := RootlessKitChildPid(stateDir)
+	if err != nil {
+		return false
+	}
+	cmdline, err := os.ReadFile(filepath.Join("/proc", strconv.Itoa(pid), "cmdline"))
+	if err != nil {
+		return false
+	}
+	for _, arg := range bytes.Split(cmdline, []byte{0}) {
+		if string(arg) == "--ipv6" {
+			return true
+		}
+	}
+	return false
+}