Cap the amount of data util.Unzip extracts

internal/config/plugin_installer.go

@@ -420,7 +420,7 @@ func (pv *PluginVersion) DownloadAndInstall(out io.Writer) error {
 		return err
 	}
 	targetDir := filepath.Join(ConfigDir, "plug", pv.pack.Name)
-	dirPerm := os.FileMode(0755)
+	dirPerm := util.DirMode
 	if err = os.MkdirAll(targetDir, dirPerm); err != nil {
 		return err
 	}

internal/util/util.go

@@ -51,6 +51,9 @@ var (
 // To be used for file writes before umask is applied
 const FileMode os.FileMode = 0666
 
+// To be used for directory creation before umask is applied
+const DirMode os.FileMode = 0755
+
 const BackupSuffix = ".micro-backup"
 
 const OverwriteFailMsg = `An error occurred while writing to the file:
@@ -629,6 +632,9 @@ func String(s []byte) string {
 	return string(s)
 }
 
+// maxUnzipSize is the most Unzip will extract from a single archive
+const maxUnzipSize = 1 << 30
+
 // Unzip unzips a file to given folder
 func Unzip(src, dest string) error {
 	r, err := zip.OpenReader(src)
@@ -637,7 +643,9 @@ func Unzip(src, dest string) error {
 	}
 	defer r.Close()
 
-	os.MkdirAll(dest, 0755)
+	os.MkdirAll(dest, DirMode)
+
+	var remaining int64 = maxUnzipSize
 
 	// Closure to address file descriptors issue with all the deferred .Close() methods
 	extractAndWriteFile := func(f *zip.File) error {
@@ -654,20 +662,28 @@ func Unzip(src, dest string) error {
 			return fmt.Errorf("illegal file path: %s", path)
 		}
 
+		// Check for zip bombs (output far larger than the archive). archive/zip
+		// refuses to read past the size declared in an entry's header, so the
+		// declared size is what gets checked against the budget.
+		if f.UncompressedSize64 > uint64(remaining) {
+			return fmt.Errorf("file too large: %s", path)
+		}
+
 		if f.FileInfo().IsDir() {
 			os.MkdirAll(path, f.Mode())
 		} else {
-			os.MkdirAll(filepath.Dir(path), f.Mode())
+			os.MkdirAll(filepath.Dir(path), DirMode)
 			f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, f.Mode())
 			if err != nil {
 				return err
 			}
 			defer f.Close()
 
-			_, err = io.Copy(f, rc)
+			n, err := io.Copy(f, rc)
 			if err != nil {
 				return err
 			}
+			remaining -= n
 		}
 		return nil
 	}

internal/util/util_test.go

@@ -1,6 +1,10 @@
 package util
 
 import (
+	"archive/zip"
+	"bytes"
+	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -31,3 +35,63 @@ func TestSliceVisualEnd(t *testing.T) {
 	assert.Equal(t, []byte("ello"), slc)
 	assert.Equal(t, 0, n)
 }
+
+func writeZip(t *testing.T, add func(w *zip.Writer)) string {
+	path := filepath.Join(t.TempDir(), "test.zip")
+	f, err := os.Create(path)
+	assert.NoError(t, err)
+	w := zip.NewWriter(f)
+	add(w)
+	assert.NoError(t, w.Close())
+	assert.NoError(t, f.Close())
+	return path
+}
+
+func TestUnzip(t *testing.T) {
+	src := writeZip(t, func(w *zip.Writer) {
+		fw, _ := w.Create("dir/hello.txt")
+		fw.Write([]byte("hello"))
+	})
+	dest := t.TempDir()
+
+	assert.NoError(t, Unzip(src, dest))
+	data, err := os.ReadFile(filepath.Join(dest, "dir", "hello.txt"))
+	assert.NoError(t, err)
+	assert.Equal(t, "hello", string(data))
+}
+
+func TestUnzipTooLarge(t *testing.T) {
+	// A header that claims more than the limit, backed by only a few real bytes
+	src := writeZip(t, func(w *zip.Writer) {
+		fw, _ := w.CreateRaw(&zip.FileHeader{
+			Name:               "bomb.txt",
+			Method:             zip.Store,
+			CompressedSize64:   5,
+			UncompressedSize64: maxUnzipSize + 1,
+		})
+		fw.Write([]byte("hello"))
+	})
+	dest := t.TempDir()
+
+	err := Unzip(src, dest)
+	assert.EqualError(t, err, "file too large: "+filepath.Join(dest, "bomb.txt"))
+	_, err = os.Stat(filepath.Join(dest, "bomb.txt"))
+	assert.True(t, os.IsNotExist(err))
+}
+
+func TestUnzipUnderstatedSize(t *testing.T) {
+	// A header that declares 10 bytes in front of 300 real ones. Unzip trusts
+	// the declared size because archive/zip refuses to read past it.
+	payload := bytes.Repeat([]byte("micro "), 50)
+	src := writeZip(t, func(w *zip.Writer) {
+		fw, _ := w.CreateRaw(&zip.FileHeader{
+			Name:               "bomb.txt",
+			Method:             zip.Store,
+			CompressedSize64:   uint64(len(payload)),
+			UncompressedSize64: 10,
+		})
+		fw.Write(payload)
+	})
+
+	assert.Equal(t, zip.ErrFormat, Unzip(src, t.TempDir()))
+}