rootless: harden slirp4netns with mount namespace and seccomp

When slirp4netns v0.4.0+ is used, now slirp4netns is hardened using
mount namespace ("sandbox") and seccomp to mitigate potential
vulnerabilities.

bump up rootlesskit: rootless-containers/rootlesskit@2fcff6c...791ac8c

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

contrib/dockerd-rootless.sh

@@ -39,6 +39,9 @@ fi
 
 : "${DOCKERD_ROOTLESS_ROOTLESSKIT_NET:=}"
 : "${DOCKERD_ROOTLESS_ROOTLESSKIT_MTU:=}"
+# if slirp4netns v0.4.0+ is installed, slirp4netns is hardened using sandbox (mount namespace) and seccomp
+: "${DOCKERD_ROOTLESS_ROOTLESSKIT_SLIRP4NETNS_SANDBOX:=auto}"
+: "${DOCKERD_ROOTLESS_ROOTLESSKIT_SLIRP4NETNS_SECCOMP:=auto}"
 net=$DOCKERD_ROOTLESS_ROOTLESSKIT_NET
 mtu=$DOCKERD_ROOTLESS_ROOTLESSKIT_MTU
 if [ -z $net ]; then
@@ -77,6 +80,8 @@ if [ -z $_DOCKERD_ROOTLESS_CHILD ]; then
 	# * /run: copy-up is required so that we can create /run/docker (hardcoded for plugins) in our namespace
 	exec $rootlesskit \
 		--net=$net --mtu=$mtu \
+		--slirp4netns-sandbox=$DOCKERD_ROOTLESS_ROOTLESSKIT_SLIRP4NETNS_SANDBOX \
+		--slirp4netns-seccomp=$DOCKERD_ROOTLESS_ROOTLESSKIT_SLIRP4NETNS_SECCOMP \
 		--disable-host-loopback --port-driver=builtin \
 		--copy-up=/etc --copy-up=/run \
 		$DOCKERD_ROOTLESS_ROOTLESSKIT_FLAGS \

hack/dockerfile/install/rootlesskit.installer

@@ -1,7 +1,7 @@
 #!/bin/sh
 
-# v0.6.0
-ROOTLESSKIT_COMMIT=2fcff6ceae968a1d895e6205e5154b107247356f
+# v0.7.0
+ROOTLESSKIT_COMMIT=791ac8cb209a107505cd1ca5ddf23a49913e176c
 
 install_rootlesskit() {
 	case "$1" in