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rootfs: do not permit /proc mounts to non-directories #2207

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Jan 22, 2020
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rootfs: do not permit /proc mounts to non-directories #2207

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12 changes: 12 additions & 0 deletions libcontainer/rootfs_linux.go
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Original file line number Diff line number Diff line change
Expand Up @@ -299,6 +299,18 @@ func mountToRootfs(m *configs.Mount, rootfs, mountLabel string, enableCgroupns b

switch m.Device {
case "proc", "sysfs":
// If the destination already exists and is not a directory, we bail
// out This is to avoid mounting through a symlink or similar -- which
// has been a "fun" attack scenario in the past.
// TODO: This won't be necessary once we switch to libpathrs and we can
// stop all of these symlink-exchange attacks.
if fi, err := os.Lstat(dest); err != nil {
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if !os.IsNotExist(err) {
return err
}
} else if fi.Mode()&os.ModeDir == 0 {
return fmt.Errorf("filesystem %q must be mounted on ordinary directory", m.Device)
}
if err := os.MkdirAll(dest, 0755); err != nil {
return err
}
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