Fix persistent symlink in project import

- Fix permissions after untar is done
- Refactor command line util

changelogs/unreleased/security-import-symlink.yml

+---
+title: Fix persistent symlink in project import
+merge_request:
+author:
+type: security

lib/gitlab/import_export/command_line_util.rb

@@ -3,7 +3,8 @@
 module Gitlab
   module ImportExport
     module CommandLineUtil
-      DEFAULT_MODE = 0700
+      UNTAR_MASK = 'u+rwX,go+rX,go-w'
+      DEFAULT_DIR_MODE = 0700
 
       def tar_czf(archive:, dir:)
         tar_with_options(archive: archive, dir: dir, options: 'czf')
@@ -14,8 +15,8 @@ module Gitlab
       end
 
       def mkdir_p(path)
-        FileUtils.mkdir_p(path, mode: DEFAULT_MODE)
-        FileUtils.chmod(DEFAULT_MODE, path)
+        FileUtils.mkdir_p(path, mode: DEFAULT_DIR_MODE)
+        FileUtils.chmod(DEFAULT_DIR_MODE, path)
       end
 
       private
@@ -41,6 +42,7 @@ module Gitlab
 
       def untar_with_options(archive:, dir:, options:)
         execute(%W(tar -#{options} #{archive} -C #{dir}))
+        execute(%W(chmod -R #{UNTAR_MASK} #{dir}))
       end
 
       def execute(cmd)

spec/lib/gitlab/import_export/command_line_util_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::ImportExport::CommandLineUtil do
+  include ExportFileHelper
+
+  let(:path) { "#{Dir.tmpdir}/symlink_test" }
+  let(:archive) { 'spec/fixtures/symlink_export.tar.gz' }
+  let(:shared) { Gitlab::ImportExport::Shared.new(nil) }
+
+  subject do
+    Class.new do
+      include Gitlab::ImportExport::CommandLineUtil
+
+      def initialize
+        @shared = Gitlab::ImportExport::Shared.new(nil)
+      end
+    end.new
+  end
+
+  before do
+    FileUtils.mkdir_p(path)
+    subject.untar_zxf(archive: archive, dir: path)
+  end
+
+  after do
+    FileUtils.rm_rf(path)
+  end
+
+  it 'has the right mask for project.json' do
+    expect(file_permissions("#{path}/project.json")).to eq(0755) # originally 777
+  end
+
+  it 'has the right mask for uploads' do
+    expect(file_permissions("#{path}/uploads")).to eq(0755) # originally 555
+  end
+end

spec/lib/gitlab/import_export/file_importer_spec.rb

 require 'spec_helper'
 
 describe Gitlab::ImportExport::FileImporter do
+  include ExportFileHelper
+
   let(:shared) { Gitlab::ImportExport::Shared.new(nil) }
   let(:storage_path) { "#{Dir.tmpdir}/file_importer_spec" }
   let(:valid_file) { "#{shared.export_path}/valid.json" }
@@ -8,6 +10,7 @@ describe Gitlab::ImportExport::FileImporter do
   let(:hidden_symlink_file) { "#{shared.export_path}/.hidden" }
   let(:subfolder_symlink_file) { "#{shared.export_path}/subfolder/invalid.json" }
   let(:evil_symlink_file) { "#{shared.export_path}/.\nevil" }
+  let(:custom_mode_symlink_file) { "#{shared.export_path}/symlink.mode" }
 
   before do
     stub_const('Gitlab::ImportExport::FileImporter::MAX_RETRIES', 0)
@@ -45,10 +48,18 @@ describe Gitlab::ImportExport::FileImporter do
       expect(File.exist?(subfolder_symlink_file)).to be false
     end
 
+    it 'removes symlinks without any file permissions' do
+      expect(File.exist?(custom_mode_symlink_file)).to be false
+    end
+
     it 'does not remove a valid file' do
       expect(File.exist?(valid_file)).to be true
     end
 
+    it 'does not change a valid file permissions' do
+      expect(file_permissions(valid_file)).not_to eq(0000)
+    end
+
     it 'creates the file in the right subfolder' do
       expect(shared.export_path).to include('test/abcd')
     end
@@ -84,5 +95,7 @@ describe Gitlab::ImportExport::FileImporter do
     FileUtils.ln_s(valid_file, subfolder_symlink_file)
     FileUtils.ln_s(valid_file, hidden_symlink_file)
     FileUtils.ln_s(valid_file, evil_symlink_file)
+    FileUtils.ln_s(valid_file, custom_mode_symlink_file)
+    FileUtils.chmod_R(0000, custom_mode_symlink_file)
   end
 end

spec/support/import_export/export_file_helper.rb

@@ -133,6 +133,6 @@ module ExportFileHelper
   end
 
   def file_permissions(file)
-    File.stat(file).mode & 0777
+    File.lstat(file).mode & 0777
   end
 end