Extract GitLab Pages using RubyZip

RubyZip allows us to perform strong validation of
expanded paths where we do extract file.

We introduce the following additional checks
to extract routines:

1. None of path components can be symlinked,
2. We drop privileges support for directories,
3. Symlink source needs to point within the target directory,
   like `public/`,
4. The symlink source needs to exist ahead of time.

1 files changed, 36 insertions, 0 deletions

diff --git a/lib/safe_zip/extract_params.rb b/lib/safe_zip/extract_params.rb
new file mode 100644
index 00000000000..bd3b788bac9
--- /dev/null
+++ b/lib/safe_zip/extract_params.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+module SafeZip
+  class ExtractParams
+    include Gitlab::Utils::StrongMemoize
+
+    attr_reader :directories, :extract_path
+
+    def initialize(directories:, to:)
+      @directories = directories
+      @extract_path = ::File.realpath(to)
+    end
+
+    def matching_target_directory(path)
+      target_directories.find do |directory|
+        path.start_with?(directory)
+      end
+    end
+
+    def target_directories
+      strong_memoize(:target_directories) do
+        directories.map do |directory|
+          ::File.join(::File.expand_path(directory, extract_path), '')
+        end
+      end
+    end
+
+    def directories_wildcard
+      strong_memoize(:directories_wildcard) do
+        directories.map do |directory|
+          ::File.join(directory, '*')
+        end
+      end
+    end
+  end
+end