runc run: refuse a frozen cgroup

Sometimes a container cgroup already exists but is frozen.
When this happens, runc init hangs, and it's not clear what is going on.

Refuse to run in a frozen cgroup; add a test case.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/factory_linux.go

@@ -4,6 +4,7 @@ package libcontainer
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -182,6 +183,16 @@ func (l *LinuxFactory) Create(id string, config *configs.Config) (Container, err
 		}
 	}
 
+	// Check that cgroup is not frozen. Do it even if Exists() above returned
+	// false, since in cgroup v1 it only checks "devices" controller.
+	st, err := cm.GetFreezerState()
+	if err != nil {
+		return nil, fmt.Errorf("unable to get cgroup freezer state: %w", err)
+	}
+	if st == configs.Frozen {
+		return nil, errors.New("container's cgroup unexpectedly frozen")
+	}
+
 	if err := os.MkdirAll(containerRoot, 0o711); err != nil {
 		return nil, err
 	}

tests/integration/cgroups.bats

@@ -322,3 +322,44 @@ function setup() {
 	[ "$status" -ne 0 ]
 	[[ "$output" == *"container's cgroup is not empty"* ]]
 }
+
+@test "runc run/create should refule pre-existing frozen cgroup" {
+	requires cgroups_freezer
+	if [[ "$ROOTLESS" -ne 0 ]]; then
+		requires rootless_cgroup
+	fi
+
+	set_cgroups_path
+
+	case $CGROUP_UNIFIED in
+	no)
+		FREEZER_DIR="${CGROUP_FREEZER_BASE_PATH}/${REL_CGROUPS_PATH}"
+		FREEZER="${FREEZER_DIR}/freezer.state"
+		STATE="FROZEN"
+		;;
+	yes)
+		FREEZER_DIR="${CGROUP_PATH}"
+		FREEZER="${FREEZER_DIR}/cgroup.freeze"
+		STATE="1"
+		;;
+	esac
+
+	# Create and freeze the cgroup.
+	mkdir "$FREEZER_DIR"
+	echo "$STATE" >"$FREEZER"
+
+	# Start a container.
+	runc run -d --console-socket "$CONSOLE_SOCKET" ct1
+	[ "$status" -eq 1 ]
+	# A warning should be printed.
+	[[ "$output" == *"container's cgroup unexpectedly frozen"* ]]
+
+	# Same check for runc create.
+	runc create --console-socket "$CONSOLE_SOCKET" ct2
+	[ "$status" -eq 1 ]
+	# A warning should be printed.
+	[[ "$output" == *"container's cgroup unexpectedly frozen"* ]]
+
+	# Cleanup.
+	rmdir "$FREEZER_DIR"
+}