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Update unzip.go to fix path traversal bug #41

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Update unzip.go to fix path traversal bug #41

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40 changes: 38 additions & 2 deletions unzip/unzip.go
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,8 @@ import (

"github.com/klauspost/compress/zstd"
"github.com/xi2/xz"
"path/filepath"
securejoin "github.com/cyphar/filepath-securejoin"
)

// concurrency controls the maximum level of concurrency we'll allow.
Expand Down Expand Up @@ -47,6 +49,9 @@ type extractor struct {
}

func (e *extractor) Extract() error {
if err := e.normalizeOut(); err != nil {
return err
}
if r, err := zip.OpenReader(e.In); err == nil {
defer r.Close()
return e.extractZip(r)
Expand Down Expand Up @@ -88,6 +93,17 @@ func isStructuralError(err error) bool {
_, ok := err.(bzip2.StructuralError)
return ok
}
func (e *extractor) normalizeOut() error {
if e.Out == "" {
e.Out = "." // default: current dir
}
abs, err := filepath.Abs(e.Out)
if err != nil {
return err
}
e.Out = abs
return nil
}

func (e *extractor) extractTar(f io.Reader) error {
r := tar.NewReader(f)
Expand All @@ -99,7 +115,11 @@ func (e *extractor) extractTar(f io.Reader) error {
}
return err
}
out := path.Join(e.Out, strings.TrimLeft(strings.TrimPrefix(hdr.Name, e.Prefix), "/"))
name := strings.TrimLeft(strings.TrimPrefix(hdr.Name, e.Prefix), "/")
out, err := securejoin.SecureJoin(e.Out, name)
if err != nil {
return err
}
if err := e.makeParentDir(out); err != nil {
return err
}
Expand All @@ -117,6 +137,18 @@ func (e *extractor) extractTar(f io.Reader) error {
return err
}
case tar.TypeSymlink:
// Require relative symlink targets.
if filepath.IsAbs(hdr.Linkname) {
return fmt.Errorf("reject symlink absolute target: %q", hdr.Linkname)
}

// Ensure the symlink target doesn't escape when interpreted relative to the link's directory.
linkDir := filepath.Dir(out)
_, err := securejoin.SecureJoin(linkDir, hdr.Linkname)
if err != nil {
return fmt.Errorf("reject symlink traversal target %q: %w", hdr.Linkname, err)
}

if err := os.Symlink(hdr.Linkname, out); err != nil {
return err
}
Expand Down Expand Up @@ -167,7 +199,11 @@ func (e *extractor) extractFile(f *zip.File) error {
return err
}
defer r.Close()
out := path.Join(e.Out, f.Name)
out, err := securejoin.SecureJoin(e.Out, f.Name)
if err != nil {
return err
}

if e.File != "" {
out = e.Out
}
Expand Down