Account for platform path restrictions (Windows)

extractor.go

@@ -13,9 +13,28 @@ import (
 type Extractor struct {
 	Path     string
 	Progress func(int64) int64
+
+	// SanitizePathFunc can be provided if you wish to inspect and/or modify the source path
+	// returning an error from this function will abort extraction
+	SanitizePathFunc func(path string) (saferPath string, userDefined error)
+
+	// LinkFunc can be provided for user specified handling of filesystem links
+	// returning an error from this function aborts extraction
+	LinkFunc func(Link) error
+}
+
+// Link represents a filesystem link where Name is the link's destination path,
+// Target is what the link actually points to,
+// and Root is the extraction root
+type Link struct {
+	Root, Name, Target string
 }
 
 func (te *Extractor) Extract(reader io.Reader) error {
+	if isNullDevice(te.Path) {
+		return nil
+	}
+
 	tarReader := tar.NewReader(reader)
 
 	// Check if the output path already exists, so we know whether we should
@@ -61,35 +80,77 @@ func (te *Extractor) Extract(reader io.Reader) error {
 	return nil
 }
 
-// outputPath returns the path at whicht o place tarPath
-func (te *Extractor) outputPath(tarPath string) string {
-	elems := strings.Split(tarPath, "/") // break into elems
-	elems = elems[1:]                    // remove original root
+// Sanitize sets up the extractor to use built in sanitation functions
+// (Modify paths to be platform legal, symlinks may not escape extraction root)
+// or unsets any previously set sanitation functions on the extractor
+// (no special rules are applied when extracting)
+func (te *Extractor) Sanitize(toggle bool) {
+	if toggle {
+		te.SanitizePathFunc = sanitizePath
+		te.LinkFunc = func(inLink Link) error {
+			if err := childrenOnly(inLink); err != nil {
+				return err
+			}
+			if err := platformLink(inLink); err != nil {
+				return err
+			}
+			return os.Symlink(inLink.Target, inLink.Name)
+		}
+	} else {
+		te.SanitizePathFunc = nil
+		te.LinkFunc = nil
+	}
+}
 
-	path := fp.Join(elems...)     // join elems
-	path = fp.Join(te.Path, path) // rebase on extractor root
-	return path
+// outputPath returns the path at which to place tarPath
+func (te *Extractor) outputPath(tarPath string) (outPath string, err error) {
+	elems := strings.Split(tarPath, "/")    // break into elems
+	elems = elems[1:]                       // remove original root
+	outPath = strings.Join(elems, "/")      // join elems
+	outPath = gopath.Join(te.Path, outPath) // rebase on to extraction target root
+	// sanitize path to be platform legal
+	if te.SanitizePathFunc != nil {
+		outPath, err = te.SanitizePathFunc(outPath)
+	} else {
+		outPath = fp.FromSlash(outPath)
+	}
+	return
 }
 
 func (te *Extractor) extractDir(h *tar.Header, depth int) error {
-	path := te.outputPath(h.Name)
+	path, err := te.outputPath(h.Name)
+	if err != nil {
+		return err
+	}
 
 	if depth == 0 {
-		// if this is the root root directory, use it as the output path for remaining files
+		// if this is the root directory, use it as the output path for remaining files
 		te.Path = path
 	}
 
 	return os.MkdirAll(path, 0755)
 }
 
 func (te *Extractor) extractSymlink(h *tar.Header) error {
-	return os.Symlink(h.Linkname, te.outputPath(h.Name))
+	path, err := te.outputPath(h.Name)
+	if err != nil {
+		return err
+	}
+
+	if te.LinkFunc != nil {
+		return te.LinkFunc(Link{Root: te.Path, Name: h.Name, Target: h.Linkname})
+	}
+
+	return os.Symlink(h.Linkname, path)
 }
 
 func (te *Extractor) extractFile(h *tar.Header, r *tar.Reader, depth int, rootExists bool, rootIsDir bool) error {
-	path := te.outputPath(h.Name)
+	path, err := te.outputPath(h.Name)
+	if err != nil {
+		return err
+	}
 
-	if depth == 0 { // if depth is 0, this is the only file (we aren't 'ipfs get'ing a directory)
+	if depth == 0 { // if depth is 0, this is the only file (we aren't extracting a directory)
 		if rootExists && rootIsDir {
 			// putting file inside of a root dir.
 			fnameo := gopath.Base(h.Name)
@@ -130,5 +191,27 @@ func copyWithProgress(to io.Writer, from io.Reader, cb func(int64) int64) error
 			return err
 		}
 	}
+}
+
+// childrenOnly will return an error if link targets escape their root
+func childrenOnly(inLink Link) error {
+	if fp.IsAbs(inLink.Target) {
+		return fmt.Errorf("Link target %q is an absolute path (forbidden)", inLink.Target)
+	}
 
+	resolvedTarget := fp.Join(inLink.Name, inLink.Target)
+	rel, err := fp.Rel(inLink.Root, resolvedTarget)
+	if err != nil {
+		return err
+	}
+	//disallow symlinks from climbing out of the target root
+	if strings.HasPrefix(rel, "..") {
+		return fmt.Errorf("Symlink target %q escapes root %q", inLink.Target, inLink.Root)
+	}
+	//disallow pointing to your own root from above as well
+	if strings.HasPrefix(resolvedTarget, inLink.Root) {
+		return fmt.Errorf("Symlink target %q escapes and re-enters its own root %q (forbidden)", inLink.Target, inLink.Root)
+	}
+
+	return nil
 }

sanitize.go

@@ -0,0 +1,19 @@
+// +build !windows
+
+package tar
+
+import (
+	"os"
+)
+
+func isNullDevice(path string) bool {
+	return path == os.DevNull
+}
+
+func sanitizePath(path string) (string, error) {
+	return path, nil
+}
+
+func platformLink(inLink Link) error {
+	return nil
+}

sanitize_windows.go

@@ -0,0 +1,83 @@
+package tar
+
+import (
+	"fmt"
+	"net/url"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+)
+
+//https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
+var reservedNames = [...]string{"CON", "PRN", "AUX", "NUL", "COM1", "COM2", "COM3", "COM4", "COM5", "COM6", "COM7", "COM8", "COM9", "LPT1", "LPT2", "LPT3", "LPT4", "LPT5", "LPT6", "LPT7", "LPT8", "LPT9"}
+var reservedCharsRegex *regexp.Regexp
+
+const reservedCharsStr = `[<>:"\\|?*]`                    //NOTE: `/` is not included as it is our standard path separator
+const reservedNamesRegexFmt = `(?i)^(%s)(?: *%s*)?[^\w ]` // $reservedName, $reservedCharsStr
+
+func init() {
+	reservedCharsRegex = regexp.MustCompile(reservedCharsStr)
+}
+
+func isNullDevice(path string) bool {
+	if len(path) != 3 {
+		return false
+	}
+	if path[0]|0x20 != 'n' {
+		return false
+	}
+	if path[1]|0x20 != 'u' {
+		return false
+	}
+	if path[2]|0x20 != 'l' {
+		return false
+	}
+	return true
+}
+
+func sanitizePath(path string) (string, error) {
+	pathElements := strings.Split(path, "/")
+
+	//first pass: strip illegal tail & prefix reserved names `CON .` -> `_CON`
+	for pi := range pathElements {
+		pathElements[pi] = strings.TrimRight(pathElements[pi], ". ") //MSDN: Do not end a file or directory name with a space or a period
+
+		for _, rn := range reservedNames {
+			re, _ := regexp.Compile(fmt.Sprintf(reservedNamesRegexFmt, rn, reservedCharsStr)) //no err, regex is a constant with guaranteed constant arguments
+			if matched := re.MatchString(pathElements[pi]); matched {
+				pathElements[pi] = "_" + pathElements[pi]
+				break
+			}
+		}
+	}
+
+	//second pass: scan and encode reserved characters ? -> %3F
+	res := strings.Join(pathElements, `/`) //intentionally avoiding [file]path.Clean() being called with Join(); we do our own filtering first
+	illegalIndices := reservedCharsRegex.FindAllStringIndex(res, -1)
+
+	if illegalIndices != nil {
+		var lastIndex int
+		var builder strings.Builder
+		allocAssist := (len(res) - len(illegalIndices)) + (len(illegalIndices) * 3) //3 = encoded length
+		builder.Grow(allocAssist)
+
+		for _, si := range illegalIndices {
+			builder.WriteString(res[lastIndex:si[0]])              //append up to problem char
+			builder.WriteString(url.QueryEscape(res[si[0]:si[1]])) //escape and append problem char
+			lastIndex = si[1]
+		}
+		builder.WriteString(res[lastIndex:]) //append remainder
+		res = builder.String()
+	}
+
+	return filepath.FromSlash(res), nil
+}
+
+func platformLink(inLink Link) error {
+	if strings.HasPrefix(inLink.Target, string(os.PathSeparator)) || strings.HasPrefix(inLink.Target, "/") {
+		return fmt.Errorf("Link target %q is relative to drive root (forbidden)", inLink.Target)
+	}
+
+	return nil
+}