98 lines
3.5 KiB
Go
98 lines
3.5 KiB
Go
// Copyright 2019 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package cmd
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import (
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"fmt"
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"os"
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"path/filepath"
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"syscall"
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"gvisor.googlesource.com/gvisor/pkg/log"
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"gvisor.googlesource.com/gvisor/runsc/specutils"
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)
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// mountInChroot creates the destination mount point in the given chroot and
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// mounts the source.
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func mountInChroot(chroot, src, dst, typ string, flags uint32) error {
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chrootDst := filepath.Join(chroot, dst)
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log.Infof("Mounting %q at %q", src, chrootDst)
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if err := specutils.Mount(src, chrootDst, typ, flags); err != nil {
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return fmt.Errorf("error mounting %q at %q: %v", src, chrootDst, err)
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}
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return nil
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}
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func pivotRoot(root string) error {
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if err := os.Chdir(root); err != nil {
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return fmt.Errorf("error changing working directory: %v", err)
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}
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// pivot_root(new_root, put_old) moves the root filesystem (old_root)
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// of the calling process to the directory put_old and makes new_root
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// the new root filesystem of the calling process.
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//
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// pivot_root(".", ".") makes a mount of the working directory the new
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// root filesystem, so it will be moved in "/" and then the old_root
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// will be moved to "/" too. The parent mount of the old_root will be
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// new_root, so after umounting the old_root, we will see only
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// the new_root in "/".
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if err := syscall.PivotRoot(".", "."); err != nil {
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return fmt.Errorf("error changing root filesystem: %v", err)
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}
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if err := syscall.Unmount(".", syscall.MNT_DETACH); err != nil {
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return fmt.Errorf("error umounting the old root file system: %v", err)
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}
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return nil
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}
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// setUpChroot creates an empty directory with runsc mounted at /runsc and proc
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// mounted at /proc.
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func setUpChroot(pidns bool) error {
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// We are a new mount namespace, so we can use /tmp as a directory to
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// construct a new root.
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chroot := os.TempDir()
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log.Infof("Setting up sandbox chroot in %q", chroot)
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// Convert all shared mounts into slave to be sure that nothing will be
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// propagated outside of our namespace.
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if err := syscall.Mount("", "/", "", syscall.MS_SLAVE|syscall.MS_REC, ""); err != nil {
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return fmt.Errorf("error converting mounts: %v", err)
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}
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if err := syscall.Mount("runsc-root", chroot, "tmpfs", syscall.MS_NOSUID|syscall.MS_NODEV|syscall.MS_NOEXEC, ""); err != nil {
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return fmt.Errorf("error mounting tmpfs in choot: %v", err)
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}
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if pidns {
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flags := uint32(syscall.MS_NOSUID | syscall.MS_NODEV | syscall.MS_NOEXEC | syscall.MS_RDONLY)
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if err := mountInChroot(chroot, "proc", "/proc", "proc", flags); err != nil {
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return fmt.Errorf("error mounting proc in chroot: %v", err)
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}
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} else {
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if err := mountInChroot(chroot, "/proc", "/proc", "bind", syscall.MS_BIND|syscall.MS_RDONLY|syscall.MS_REC); err != nil {
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return fmt.Errorf("error mounting proc in chroot: %v", err)
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}
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}
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if err := syscall.Mount("", chroot, "", syscall.MS_REMOUNT|syscall.MS_RDONLY|syscall.MS_BIND, ""); err != nil {
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return fmt.Errorf("error remounting chroot in read-only: %v", err)
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}
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return pivotRoot(chroot)
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}
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