1 files changed, 144 insertions, 0 deletions
diff --git a/cli/internal/cacheitem/restore_directory.go b/cli/internal/cacheitem/restore_directory.go
new file mode 100644
index 0000000..4704d66
--- /dev/null
+++ b/cli/internal/cacheitem/restore_directory.go
@@ -0,0 +1,144 @@
+package cacheitem
+
+import (
+	"archive/tar"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/vercel/turbo/cli/internal/turbopath"
+)
+
+// restoreDirectory restores a directory.
+func restoreDirectory(dirCache *cachedDirTree, anchor turbopath.AbsoluteSystemPath, header *tar.Header) (turbopath.AnchoredSystemPath, error) {
+	processedName, err := canonicalizeName(header.Name)
+	if err != nil {
+		return "", err
+	}
+
+	// We need to traverse `processedName` from base to root split at
+	// `os.Separator` to make sure we don't end up following a symlink
+	// outside of the restore path.
+
+	// Create the directory.
+	if err := safeMkdirAll(dirCache, anchor, processedName, header.Mode); err != nil {
+		return "", err
+	}
+
+	return processedName, nil
+}
+
+type cachedDirTree struct {
+	anchorAtDepth []turbopath.AbsoluteSystemPath
+	prefix        []turbopath.RelativeSystemPath
+}
+
+func (cr *cachedDirTree) getStartingPoint(path turbopath.AnchoredSystemPath) (turbopath.AbsoluteSystemPath, []turbopath.RelativeSystemPath) {
+	pathSegmentStrings := strings.Split(path.ToString(), string(os.PathSeparator))
+	pathSegments := make([]turbopath.RelativeSystemPath, len(pathSegmentStrings))
+	for index, pathSegmentString := range pathSegmentStrings {
+		pathSegments[index] = turbopath.RelativeSystemPathFromUpstream(pathSegmentString)
+	}
+
+	i := 0
+	for i = 0; i < len(cr.prefix) && i < len(pathSegments); i++ {
+		if pathSegments[i] != cr.prefix[i] {
+			break
+		}
+	}
+
+	// 0: root anchor, can't remove it.
+	cr.anchorAtDepth = cr.anchorAtDepth[:i+1]
+
+	// 0: first prefix.
+	cr.prefix = cr.prefix[:i]
+
+	return cr.anchorAtDepth[i], pathSegments[i:]
+}
+
+func (cr *cachedDirTree) Update(anchor turbopath.AbsoluteSystemPath, newSegment turbopath.RelativeSystemPath) {
+	cr.anchorAtDepth = append(cr.anchorAtDepth, anchor)
+	cr.prefix = append(cr.prefix, newSegment)
+}
+
+// safeMkdirAll creates all directories, assuming that the leaf node is a directory.
+// FIXME: Recheck the symlink cache before creating a directory.
+func safeMkdirAll(dirCache *cachedDirTree, anchor turbopath.AbsoluteSystemPath, processedName turbopath.AnchoredSystemPath, mode int64) error {
+	// Iterate through path segments by os.Separator, appending them onto the anchor.
+	// Check to see if that path segment is a symlink with a target outside of anchor.
+
+	// Pull the iteration starting point from thie directory cache.
+	calculatedAnchor, pathSegments := dirCache.getStartingPoint(processedName)
+	for _, segment := range pathSegments {
+		calculatedAnchor, checkPathErr := checkPath(anchor, calculatedAnchor, segment)
+		// We hit an existing directory or absolute path that was invalid.
+		if checkPathErr != nil {
+			return checkPathErr
+		}
+
+		// Otherwise we continue and check the next segment.
+		dirCache.Update(calculatedAnchor, segment)
+	}
+
+	// If we have made it here we know that it is safe to call os.MkdirAll
+	// on the Join of anchor and processedName.
+	//
+	// This could _still_ error, but we don't care.
+	return processedName.RestoreAnchor(anchor).MkdirAll(os.FileMode(mode))
+}
+
+// checkPath ensures that the resolved path (if restoring symlinks).
+// It makes sure to never traverse outside of the anchor.
+func checkPath(originalAnchor turbopath.AbsoluteSystemPath, accumulatedAnchor turbopath.AbsoluteSystemPath, segment turbopath.RelativeSystemPath) (turbopath.AbsoluteSystemPath, error) {
+	// Check if the segment itself is sneakily an absolute path...
+	// (looking at you, Windows. CON, AUX...)
+	if filepath.IsAbs(segment.ToString()) {
+		return "", errTraversal
+	}
+
+	// Find out if this portion of the path is a symlink.
+	combinedPath := accumulatedAnchor.Join(segment)
+	fileInfo, err := combinedPath.Lstat()
+
+	// Getting an error here means we failed to stat the path.
+	// Assume that means we're safe and continue.
+	if err != nil {
+		return combinedPath, nil
+	}
+
+	// Find out if we have a symlink.
+	isSymlink := fileInfo.Mode()&os.ModeSymlink != 0
+
+	// If we don't have a symlink it's safe.
+	if !isSymlink {
+		return combinedPath, nil
+	}
+
+	// Check to see if the symlink targets outside of the originalAnchor.
+	// We don't do eval symlinks because we could find ourself in a totally
+	// different place.
+
+	// 1. Get the target.
+	linkTarget, readLinkErr := combinedPath.Readlink()
+	if readLinkErr != nil {
+		return "", readLinkErr
+	}
+
+	// 2. See if the target is absolute.
+	if filepath.IsAbs(linkTarget) {
+		absoluteLinkTarget := turbopath.AbsoluteSystemPathFromUpstream(linkTarget)
+		if originalAnchor.HasPrefix(absoluteLinkTarget) {
+			return absoluteLinkTarget, nil
+		}
+		return "", errTraversal
+	}
+
+	// 3. Target is relative (or absolute Windows on a Unix device)
+	relativeLinkTarget := turbopath.RelativeSystemPathFromUpstream(linkTarget)
+	computedTarget := accumulatedAnchor.UntypedJoin(linkTarget)
+	if computedTarget.HasPrefix(originalAnchor) {
+		// Need to recurse and make sure the target doesn't link out.
+		return checkPath(originalAnchor, accumulatedAnchor, relativeLinkTarget)
+	}
+	return "", errTraversal
+}