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// Copyright 2018 Google LLC
//
// 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/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)
if err := specutils.Mount(src, chrootDst, typ, flags); err != nil {
return fmt.Errorf("error mounting %q at %q: %v", src, chrootDst, err)
}
return nil
}
// setUpChroot creates an empty directory with runsc mounted at /runsc and proc
// mounted at /proc.
func setUpChroot() (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", syscall.MS_NOSUID|syscall.MS_NODEV|syscall.MS_NOEXEC); 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)
}
return chroot, nil
}
// tearDownChroot unmounts /proc and /runsc from the chroot before deleting the
// directory.
func tearDownChroot(chroot string) error {
log.Debugf("Removing chroot mounts %q", chroot)
// 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)
}
// Remove chroot directory.
if err := os.RemoveAll(chroot); err != nil {
return fmt.Errorf("error removing %q: %v", chroot, err)
}
return nil
}
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