archive/zip: error if using io/fs on zip with duplicate entries

Fixes #50390

Change-Id: I92787cdb3fa198ff88dcaadeccfcb49a3a6a88cf
Reviewed-on: https://go-review.googlesource.com/c/go/+/374954
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/archive/zip/reader.go

@@ -662,6 +662,7 @@ type fileListEntry struct {
 	name  string
 	file  *File
 	isDir bool
+	isDup bool
 }
 
 type fileInfoDirEntry interface {
@@ -669,11 +670,14 @@ type fileInfoDirEntry interface {
 	fs.DirEntry
 }
 
-func (e *fileListEntry) stat() fileInfoDirEntry {
+func (e *fileListEntry) stat() (fileInfoDirEntry, error) {
-	if !e.isDir {
+	if e.isDup {
-		return headerFileInfo{&e.file.FileHeader}
+		return nil, errors.New(e.name + ": duplicate entries in zip file")
 	}
-	return e
+	if !e.isDir {
+		return headerFileInfo{&e.file.FileHeader}, nil
+	}
+	return e, nil
 }
 
 // Only used for directories.
@@ -708,17 +712,37 @@ func toValidName(name string) string {
 
 func (r *Reader) initFileList() {
 	r.fileListOnce.Do(func() {
+		// files and knownDirs map from a file/directory name
+		// to an index into the r.fileList entry that we are
+		// building. They are used to mark duplicate entries.
+		files := make(map[string]int)
+		knownDirs := make(map[string]int)
+
+		// dirs[name] is true if name is known to be a directory,
+		// because it appears as a prefix in a path.
 		dirs := make(map[string]bool)
-		knownDirs := make(map[string]bool)
+
 		for _, file := range r.File {
 			isDir := len(file.Name) > 0 && file.Name[len(file.Name)-1] == '/'
 			name := toValidName(file.Name)
 			if name == "" {
 				continue
 			}
+
+			if idx, ok := files[name]; ok {
+				r.fileList[idx].isDup = true
+				continue
+			}
+			if idx, ok := knownDirs[name]; ok {
+				r.fileList[idx].isDup = true
+				continue
+			}
+
 			for dir := path.Dir(name); dir != "."; dir = path.Dir(dir) {
 				dirs[dir] = true
 			}
+
+			idx := len(r.fileList)
 			entry := fileListEntry{
 				name:  name,
 				file:  file,
@@ -726,11 +750,16 @@ func (r *Reader) initFileList() {
 			}
 			r.fileList = append(r.fileList, entry)
 			if isDir {
-				knownDirs[name] = true
+				knownDirs[name] = idx
+			} else {
+				files[name] = idx
 			}
 		}
 		for dir := range dirs {
-			if !knownDirs[dir] {
+			if _, ok := knownDirs[dir]; !ok {
+				if idx, ok := files[dir]; ok {
+					r.fileList[idx].isDup = true
+				} else {
 					entry := fileListEntry{
 						name:  dir,
 						file:  nil,
@@ -739,6 +768,7 @@ func (r *Reader) initFileList() {
 					r.fileList = append(r.fileList, entry)
 				}
 			}
+		}
 
 		sort.Slice(r.fileList, func(i, j int) bool { return fileEntryLess(r.fileList[i].name, r.fileList[j].name) })
 	})
@@ -831,7 +861,7 @@ type openDir struct {
 }
 
 func (d *openDir) Close() error               { return nil }
-func (d *openDir) Stat() (fs.FileInfo, error) { return d.e.stat(), nil }
+func (d *openDir) Stat() (fs.FileInfo, error) { return d.e.stat() }
 
 func (d *openDir) Read([]byte) (int, error) {
 	return 0, &fs.PathError{Op: "read", Path: d.e.name, Err: errors.New("is a directory")}
@@ -850,7 +880,11 @@ func (d *openDir) ReadDir(count int) ([]fs.DirEntry, error) {
 	}
 	list := make([]fs.DirEntry, n)
 	for i := range list {
-		list[i] = d.files[d.offset+i].stat()
+		s, err := d.files[d.offset+i].stat()
+		if err != nil {
+			return nil, err
+		}
+		list[i] = s
 	}
 	d.offset += n
 	return list, nil

src/archive/zip/reader_test.go

@@ -505,6 +505,35 @@ var tests = []ZipTest{
 			},
 		},
 	},
+	{
+		Name: "dupdir.zip",
+		File: []ZipTestFile{
+			{
+				Name:     "a/",
+				Content:  []byte{},
+				Mode:     fs.ModeDir | 0666,
+				Modified: time.Date(2021, 12, 29, 0, 0, 0, 0, timeZone(0)),
+			},
+			{
+				Name:     "a/b",
+				Content:  []byte{},
+				Mode:     0666,
+				Modified: time.Date(2021, 12, 29, 0, 0, 0, 0, timeZone(0)),
+			},
+			{
+				Name:     "a/b/",
+				Content:  []byte{},
+				Mode:     fs.ModeDir | 0666,
+				Modified: time.Date(2021, 12, 29, 0, 0, 0, 0, timeZone(0)),
+			},
+			{
+				Name:     "a/b/c",
+				Content:  []byte{},
+				Mode:     0666,
+				Modified: time.Date(2021, 12, 29, 0, 0, 0, 0, timeZone(0)),
+			},
+		},
+	},
 }
 
 func TestReader(t *testing.T) {
@@ -1141,6 +1170,7 @@ func TestFS(t *testing.T) {
 			[]string{"a/b/c"},
 		},
 	} {
+		test := test
 		t.Run(test.file, func(t *testing.T) {
 			t.Parallel()
 			z, err := OpenReader(test.file)
@@ -1155,6 +1185,60 @@ func TestFS(t *testing.T) {
 	}
 }
 
+func TestFSWalk(t *testing.T) {
+	for _, test := range []struct {
+		file    string
+		want    []string
+		wantErr bool
+	}{
+		{
+			file: "testdata/unix.zip",
+			want: []string{".", "dir", "dir/bar", "dir/empty", "hello", "readonly"},
+		},
+		{
+			file: "testdata/subdir.zip",
+			want: []string{".", "a", "a/b", "a/b/c"},
+		},
+		{
+			file:    "testdata/dupdir.zip",
+			wantErr: true,
+		},
+	} {
+		test := test
+		t.Run(test.file, func(t *testing.T) {
+			t.Parallel()
+			z, err := OpenReader(test.file)
+			if err != nil {
+				t.Fatal(err)
+			}
+			var files []string
+			sawErr := false
+			err = fs.WalkDir(z, ".", func(path string, d fs.DirEntry, err error) error {
+				if err != nil {
+					if !test.wantErr {
+						t.Errorf("%s: %v", path, err)
+					}
+					sawErr = true
+					return nil
+				}
+				files = append(files, path)
+				return nil
+			})
+			if err != nil {
+				t.Errorf("fs.WalkDir error: %v", err)
+			}
+			if test.wantErr && !sawErr {
+				t.Error("succeeded but want error")
+			} else if !test.wantErr && sawErr {
+				t.Error("unexpected error")
+			}
+			if test.want != nil && !reflect.DeepEqual(files, test.want) {
+				t.Errorf("got %v want %v", files, test.want)
+			}
+		})
+	}
+}
+
 func TestFSModTime(t *testing.T) {
 	t.Parallel()
 	z, err := OpenReader("testdata/subdir.zip")