Add box structure to handle containerized executions

pkg/box/rootfs.go

@@ -0,0 +1,91 @@
+// Copyright © 2020 Ettore Di Giacinto <mudler@gentoo.org>
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, see <http://www.gnu.org/licenses/>.
+
+package box
+
+import (
+	"os"
+	"path/filepath"
+	"syscall"
+)
+
+func PivotRoot(newroot string) error {
+	putold := filepath.Join(newroot, "/.pivot_root")
+
+	// bind mount newroot to itself - this is a slight hack needed to satisfy the
+	// pivot_root requirement that newroot and putold must not be on the same
+	// filesystem as the current root
+	if err := syscall.Mount(newroot, newroot, "", syscall.MS_BIND|syscall.MS_REC, ""); err != nil {
+		return err
+	}
+
+	// create putold directory
+	if err := os.MkdirAll(putold, 0700); err != nil {
+		return err
+	}
+
+	// call pivot_root
+	if err := syscall.PivotRoot(newroot, putold); err != nil {
+		return err
+	}
+
+	// ensure current working directory is set to new root
+	if err := os.Chdir("/"); err != nil {
+		return err
+	}
+
+	// umount putold, which now lives at /.pivot_root
+	putold = "/.pivot_root"
+	if err := syscall.Unmount(putold, syscall.MNT_DETACH); err != nil {
+		return err
+	}
+
+	// remove putold
+	if err := os.RemoveAll(putold); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func mountProc(newroot string) error {
+	source := "proc"
+	target := filepath.Join(newroot, "/proc")
+	fstype := "proc"
+	flags := 0
+	data := ""
+
+	os.MkdirAll(target, 0755)
+	if err := syscall.Mount(source, target, fstype, uintptr(flags), data); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func mountDev(newroot string) error {
+
+	source := "/dev"
+	target := filepath.Join(newroot, "/dev")
+	fstype := "bind"
+	data := ""
+
+	os.MkdirAll(target, 0755)
+	if err := syscall.Mount(source, target, fstype, syscall.MS_BIND|syscall.MS_REC, data); err != nil {
+		return err
+	}
+
+	return nil
+}