1 files changed, 120 insertions, 0 deletions
diff --git a/runsc/sandbox/chroot.go b/runsc/sandbox/chroot.go
new file mode 100644
index 000000000..a77a186c2
--- /dev/null
+++ b/runsc/sandbox/chroot.go
@@ -0,0 +1,120 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sandbox
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"gvisor.googlesource.com/gvisor/pkg/log"
+	"gvisor.googlesource.com/gvisor/runsc/boot"
+	"gvisor.googlesource.com/gvisor/runsc/specutils"
+)
+
+// chrootBinPath is the location inside the chroot where the runsc binary will
+// be mounted.
+const chrootBinPath = "/runsc"
+
+// mountInChroot creates the destination mount point in the given chroot and
+// mounts the source.
+func mountInChroot(chroot, src, dst, typ string, flags uint32) error {
+	chrootDst := filepath.Join(chroot, dst)
+	log.Infof("Mounting %q at %q", src, chrootDst)
+
+	return specutils.Mount(src, chrootDst, typ, flags)
+}
+
+// setUpChroot creates an empty directory with runsc mounted at /runsc, proc
+// mounted at /proc, and any dev files needed for the platform.
+func setUpChroot(platform boot.PlatformType) (string, error) {
+	// Create the chroot directory and make it accessible to all users.
+	chroot, err := ioutil.TempDir("", "runsc-sandbox-chroot-")
+	if err != nil {
+		return "", fmt.Errorf("TempDir() failed: %v", err)
+	}
+	if err := os.Chmod(chroot, 0777); err != nil {
+		return "", fmt.Errorf("Chmod(%q) failed: %v", chroot, err)
+	}
+	log.Infof("Setting up sandbox chroot in %q", chroot)
+
+	// Mount /proc.
+	if err := mountInChroot(chroot, "proc", "/proc", "proc", 0); err != nil {
+		return "", fmt.Errorf("error mounting proc in chroot: %v", err)
+	}
+
+	// Mount runsc at /runsc in the chroot.
+	binPath, err := specutils.BinPath()
+	if err != nil {
+		return "", err
+	}
+	if err := mountInChroot(chroot, binPath, chrootBinPath, "bind", syscall.MS_BIND|syscall.MS_RDONLY); err != nil {
+		return "", fmt.Errorf("error mounting runsc in chroot: %v", err)
+	}
+
+	// Mount dev files needed for platform.
+	var devMount string
+	switch platform {
+	case boot.PlatformKVM:
+		devMount = "/dev/kvm"
+	}
+	if devMount != "" {
+		if err := mountInChroot(chroot, devMount, devMount, "bind", syscall.MS_BIND); err != nil {
+			return "", fmt.Errorf("error mounting platform device in chroot: %v", err)
+		}
+	}
+
+	return chroot, nil
+}
+
+// tearDownChroot unmounts /proc and /runsc from the chroot before deleting the
+// directory.
+func tearDownChroot(chroot string) error {
+	// Unmount /proc.
+	proc := filepath.Join(chroot, "proc")
+	if err := syscall.Unmount(proc, 0); err != nil {
+		return fmt.Errorf("error unmounting %q: %v", proc, err)
+	}
+
+	// Unmount /runsc.
+	exe := filepath.Join(chroot, chrootBinPath)
+	if err := syscall.Unmount(exe, 0); err != nil {
+		return fmt.Errorf("error unmounting %q: %v", exe, err)
+	}
+
+	// Unmount platform dev files.
+	devFiles := []string{"dev/kvm"}
+	for _, f := range devFiles {
+		devPath := filepath.Join(chroot, f)
+		if _, err := os.Stat(devPath); err != nil {
+			if os.IsNotExist(err) {
+				continue
+			}
+			return fmt.Errorf("Stat(%q) failed: %v", devPath, err)
+		}
+		if err := syscall.Unmount(devPath, 0); err != nil {
+			return fmt.Errorf("error unmounting %q: %v", devPath, err)
+		}
+	}
+
+	// Remove chroot directory.
+	if err := os.RemoveAll(chroot); err != nil {
+		return fmt.Errorf("error removing %q: %v", chroot, err)
+	}
+
+	return nil
+}