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`bin/entrypoint.sh` now runs `netwatch-server prepare-data-dir`, which refuses a `DATA_DIR` that is not `/data` or a path below it written in full, then creates `DATA_DIR`, gives `/data` and everything in it to `netwatch` and sets mode 750 on `/data` and `DATA_DIR`. Every step goes through a Go `os.Root` opened on `/data`, which follows a symbolic link only when it is relative and stays inside `/data`, so neither a link already there nor one a host process swaps in while the container starts can make root create or change anything outside `/data`. The README says which `DATA_DIR` values are accepted. Model: opus-5-5
83 lines
2.3 KiB
Go
83 lines
2.3 KiB
Go
package reportbuf
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import (
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"errors"
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"io/fs"
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"os"
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"os/user"
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"path/filepath"
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"strconv"
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)
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// ErrDataDirOutsideVolume is returned by PrepareDataDir for a DATA_DIR
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// that is not the volume or a path below it, written in full.
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var ErrDataDirOutsideVolume = errors.New(
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"must be /data or a path below it, with no '.', '..' or extra '/'")
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// PrepareDataDir gets dir, the server's DATA_DIR, ready for owner, the
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// user the server runs as, so that a host directory mounted at volume,
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// /data in the image, needs no preparing: it creates dir, gives volume
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// and everything in it to owner, and gives volume and dir the mode the
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// server gives a directory it creates. dir must be volume or a path
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// below it, with no '.', '..', empty part or '/' at the end.
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//
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// bin/entrypoint.sh runs this as root, which would follow a symbolic
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// link anywhere, so every step goes through an os.Root opened on
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// volume: it follows a link only when it is written as a relative
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// path that stays inside volume, and refuses any other. A process on
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// the host can swap a link onto a path in volume at any moment while
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// this runs, but the os.Root checks each link as it reaches it, so the
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// most that can do is make a step fail or act on something else
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// inside volume.
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func PrepareDataDir(volume, dir string, owner *user.User) error {
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// rel is dir as a path from volume; IsLocal is false for one that
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// leads out of it.
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rel, err := filepath.Rel(volume, dir)
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if err != nil || dir != filepath.Clean(dir) || !filepath.IsLocal(rel) {
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return ErrDataDirOutsideVolume
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}
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uid, err := strconv.Atoi(owner.Uid)
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if err != nil {
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return err
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}
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gid, err := strconv.Atoi(owner.Gid)
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if err != nil {
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return err
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}
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root, err := os.OpenRoot(volume)
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if err != nil {
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return err
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}
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defer func() { _ = root.Close() }()
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err = root.MkdirAll(rel, dirPerms)
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if err != nil {
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return err
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}
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// WalkDir does not follow a symbolic link, and Lchown gives the
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// link itself to owner, not what it points to.
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err = fs.WalkDir(root.FS(), ".",
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func(name string, _ fs.DirEntry, err error) error {
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if err != nil {
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return err
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}
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return root.Lchown(name, uid, gid)
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})
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if err != nil {
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return err
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}
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err = root.Chmod(".", dirPerms)
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if err != nil {
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return err
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}
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return root.Chmod(rel, dirPerms)
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}
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