containerd: add /etc/containerd/config-rootless.toml

`/etc/containerd/config-rootless.toml` is the config for running kind in rootless Docker/Podman.

* `ociwrapper` script is used to remove `.linux.resources.devices` from `config.json`,
  because `.linux.resources.devices` is meaningless on rootless and yet produces errors.
  Workaround until we get proper fixes in containerd and runc.

* restrict_oom_score_adj is set to true to ignore oom_score_adj errors

The entrypoint overrides `/etc/containerd/config.toml` with `config-rootless.toml` when running in rootless Docker/Podman.
The rootless-ness is detected by comparing `/proc/1/uid_map` with `0 0 4294967295`.

Note that Kubernetes needs to be patched as well (see the PR description text)

Signed-off-by: Akihiro Suda <[email protected]>

images/base/Dockerfile

@@ -70,6 +70,7 @@ RUN echo "Ensuring scripts are executable ..." \
       libseccomp2 pigz \
       bash ca-certificates curl rsync \
       nfs-common \
+      jq \
     && find /lib/systemd/system/sysinit.target.wants/ -name "systemd-tmpfiles-setup.service" -delete \
     && rm -f /lib/systemd/system/multi-user.target.wants/* \
     && rm -f /etc/systemd/system/*.wants/* \

images/base/files/usr/local/bin/entrypoint

@@ -236,6 +236,13 @@ enable_network_magic(){
   fi
 }
 
+select_containerd_config_toml() {
+  if ! egrep -q "0[[:space:]]+0[[:space:]]+4294967295" /proc/1/uid_map; then
+    echo "INFO: Detected rootless provider. Overriding /etc/containerd/config.toml with /etc/containerd/config-rootless.toml" >&2
+    cp -f /etc/containerd/config-rootless.toml /etc/containerd/config.toml
+  fi
+}
+
 # run pre-init fixups
 fix_kmsg
 fix_mount
@@ -246,6 +253,7 @@ fix_product_uuid
 configure_proxy
 select_iptables
 enable_network_magic
+select_containerd_config_toml
 
 # we want the command (expected to be systemd) to be PID1, so exec to it
 exec "$@"

images/base/files/usr/local/bin/ociwrapper

@@ -0,0 +1,40 @@
+#!/bin/bash
+#
+# A wrapper script to remove .linux.resources.devices, which are meaningless in userns.
+# Needs jq.
+#
+# Workaround until we get proper fixes in containerd and runc
+set -eu -o pipefail
+RUNTIME="runc"
+
+if egrep -q "0[[:space:]]+0[[:space:]]+4294967295" /proc/self/uid_map; then
+	# we are not in userns, no need to patch the config
+	exec $RUNTIME "$@"
+	exit $?
+fi
+
+bundle="."
+bundle_flag=""
+# FIXME: support `--bundle=STRING` as well
+for f in $@; do
+	if [[ -n $bundle_flag ]]; then
+		bundle=$f
+		break
+	else
+		case $f in
+		-b | --bundle)
+			bundle_flag=$f
+			;;
+		esac
+	fi
+done
+
+if [ -f $bundle/config.json ]; then
+    q="del(.linux.resources.devices) | del(.linux.devices)"
+	tmp=$(mktemp -d ociwrapper.XXXXXXXX)
+	jq "$q" <$bundle/config.json >$tmp/config.json
+	mv $tmp/config.json $bundle/config.json
+	rm -rf $tmp
+fi
+
+exec $RUNTIME "$@"

pkg/build/nodeimage/build_impl.go

@@ -187,7 +187,8 @@ func (c *buildContext) buildImage(dir string) error {
 		return errors.New("failed to find imported pause image")
 	}
 	containerdConfig, err := getContainerdConfig(containerdConfigTemplateData{
-		SandboxImage: pauseImage,
+		SandboxImage:       pauseImage,
+		DefaultRuntimeName: "runc",
 	})
 	if err != nil {
 		return err
@@ -196,6 +197,18 @@ func (c *buildContext) buildImage(dir string) error {
 	if err := createFile(cmder, containerdConfigPath, containerdConfig); err != nil {
 		return err
 	}
+	containerdRootlessConfig, err := getContainerdConfig(containerdConfigTemplateData{
+		SandboxImage:        pauseImage,
+		DefaultRuntimeName:  "ociwrapper",
+		RestrictOOMScoreAdj: true,
+	})
+	if err != nil {
+		return err
+	}
+	const containerdRootlessConfigPath = "/etc/containerd/config-rootless.toml"
+	if err := createFile(cmder, containerdRootlessConfigPath, containerdRootlessConfig); err != nil {
+		return err
+	}
 
 	// Save the image changes to a new image
 	cmd := exec.Command(

pkg/build/nodeimage/containerd_config.go

@@ -24,18 +24,25 @@ import (
 )
 
 type containerdConfigTemplateData struct {
-	SandboxImage string
+	SandboxImage        string
+	DefaultRuntimeName  string
+	RestrictOOMScoreAdj bool
 }
 
 const containerdConfigTemplate = `# explicitly use v2 config format
 version = 2
 
 # set default runtime handler to v2, which has a per-pod shim
 [plugins."io.containerd.grpc.v1.cri".containerd]
-  default_runtime_name = "runc"
+  default_runtime_name = "{{.DefaultRuntimeName}}"
 [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc]
   runtime_type = "io.containerd.runc.v2"
 
+[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.ociwrapper]
+  runtime_type = "io.containerd.runc.v2"
+[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.ociwrapper.options]
+  BinaryName = "ociwrapper"
+
 # Setup a runtime with the magic name ("test-handler") used for Kubernetes
 # runtime class tests ...
 [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.test-handler]
@@ -49,6 +56,8 @@ version = 2
   # allow hugepages controller to be missing
   # see https://github.com/containerd/cri/pull/1501
   tolerate_missing_hugepages_controller = true
+  # restrict_oom_score_adj is required if we are running in UserNS (i.e. Rootless Docker/Podman),
+  restrict_oom_score_adj = {{.RestrictOOMScoreAdj}}
 `
 
 func getContainerdConfig(data containerdConfigTemplateData) (string, error) {