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rootfs: umount all procfs and sysfs with --no-pivot #1962

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Jan 15, 2019
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rootfs: umount all procfs and sysfs with --no-pivot #1962

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35 changes: 35 additions & 0 deletions libcontainer/rootfs_linux.go
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Original file line number Diff line number Diff line change
Expand Up @@ -748,6 +748,41 @@ func pivotRoot(rootfs string) error {
}

func msMoveRoot(rootfs string) error {
mountinfos, err := mount.GetMounts()
if err != nil {
return err
}

absRootfs, err := filepath.Abs(rootfs)
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AFAICS this is not needed since rootfs is already validated by (*ConfigValidator).rootfs()

if err != nil {
return err
}

for _, info := range mountinfos {
p, err := filepath.Abs(info.Mountpoint)
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not needed either as paths returned from the kernel are absolute and clean (unless I'm missing something).

I have addressed this in #2255 (a separate commit to keep things simple), PTAL @giuseppe

if err != nil {
return err
}
// Umount every syfs and proc file systems, except those under the container rootfs
if (info.Fstype != "proc" && info.Fstype != "sysfs") || filepath.HasPrefix(p, absRootfs) {
continue
}
// Be sure umount events are not propagated to the host.
if err := unix.Mount("", p, "", unix.MS_SLAVE|unix.MS_REC, ""); err != nil {
return err
}
if err := unix.Unmount(p, unix.MNT_DETACH); err != nil {
if err != unix.EINVAL && err != unix.EPERM {
return err
} else {
// If we have not privileges for umounting (e.g. rootless), then
// cover the path.
if err := unix.Mount("tmpfs", p, "tmpfs", 0, ""); err != nil {
return err
}
}
}
}
if err := unix.Mount(rootfs, "/", "", unix.MS_MOVE, ""); err != nil {
return err
}
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