[DNM] tests/int: add "runc exec [init changes cgroup]"

tests/integration/exec.bats

@@ -321,6 +321,41 @@ function check_exec_debug() {
 	[ "$status" -eq 0 ]
 }
 
+# https://github.com/opencontainers/runc/issues/5089
+@test "runc exec [init changes cgroup]" {
+	requires root cgroups_v2
+
+	NEW_CGROUP_REL=/runc-tst-$$
+	NEW_CGROUP=/sys/fs/cgroup$NEW_CGROUP_REL
+	mkdir $NEW_CGROUP
+
+	# The container is placed into a $CGROUP_V2_PATH cgroup.
+	set_cgroups_path
+	# And upon the start it moves itself into $NEW_CGROUP.
+	set_cgroup_mount_writable
+	update_config '	  .linux.namespaces -= [{"type": "cgroup"}]
+			| .process.args = ["sh", "-c", "echo 1 > '$NEW_CGROUP'/cgroup.procs && exec sleep 1h"]'
+
+	runc run -d --console-socket "$CONSOLE_SOCKET" test_busybox
+	[ $status -eq 0 ]
+	testcontainer test_busybox running
+	sleep 1
+	# Remove the original container cgroup. If systemd cgroup manager is used by runc,
+	# the cgroup might have already be deleted by systemd, so we ignore rmdir errors.
+	rmdir "$CGROUP_V2_PATH" || true
+	test -d "$CGROUP_V2_PATH" && false
+
+	# Test that runc exec is able to fallback to container's init cgroup
+	# even if the original cgroup is gone.
+	runc exec test_busybox cat /proc/self/cgroup
+	[ $status -eq 0 ]
+	[ "$output" = "0::$NEW_CGROUP_REL" ]
+
+	# Cleanup.
+	runc delete -f test_busybox
+	rmdir "$NEW_CGROUP"
+}
+
 @test "runc exec [execve error]" {
 	cat <<EOF >rootfs/run.sh
 #!/mmnnttbb foo bar