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| -rw-r--r-- | lib/pleroma/safe_zip.ex | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/lib/pleroma/safe_zip.ex b/lib/pleroma/safe_zip.ex new file mode 100644 index 000000000..35fe2be19 --- /dev/null +++ b/lib/pleroma/safe_zip.ex @@ -0,0 +1,216 @@ +# Akkoma: Magically expressive social media +# Copyright © 2024 Akkoma Authors <https://akkoma.dev/> +# SPDX-License-Identifier: AGPL-3.0-only + +defmodule Pleroma.SafeZip do + @moduledoc """ + Wraps the subset of Erlang's zip module we’d like to use + but enforces path-traversal safety everywhere and other checks. + + For convenience almost all functions accept both elixir strings and charlists, + but output elixir strings themselves. However, this means the input parameter type + can no longer be used to distinguish archive file paths from archive binary data in memory, + thus where needed both a _data and _file variant are provided. + """ + + @type text() :: String.t() | [char()] + + defp is_safe_path?(path) do + # Path accepts elixir’s chardata() + case Path.safe_relative(path) do + {:ok, _} -> true + _ -> false + end + end + + defp is_safe_type?(file_type) do + if file_type in [:regular, :directory] do + true + else + false + end + end + + defp maybe_add_file(_type, _path_charlist, nil), do: nil + + defp maybe_add_file(:regular, path_charlist, file_list), + do: [to_string(path_charlist) | file_list] + + defp maybe_add_file(_type, _path_charlist, file_list), do: file_list + + @spec check_safe_archive_and_maybe_list_files(binary() | [char()], [term()], boolean()) :: + {:ok, [String.t()]} | {:error, reason :: term()} + defp check_safe_archive_and_maybe_list_files(archive, opts, list) do + acc = if list, do: [], else: nil + + with {:ok, table} <- :zip.table(archive, opts) do + Enum.reduce_while(table, {:ok, acc}, fn + # ZIP comment + {:zip_comment, _}, acc -> + {:cont, acc} + + # File entry + {:zip_file, path, info, _comment, _offset, _comp_size}, {:ok, fl} -> + with {_, type} <- {:get_type, elem(info, 2)}, + {_, true} <- {:type, is_safe_type?(type)}, + {_, true} <- {:safe_path, is_safe_path?(path)} do + {:cont, {:ok, maybe_add_file(type, path, fl)}} + else + {:get_type, e} -> + {:halt, + {:error, "Couldn't determine file type of ZIP entry at #{path} (#{inspect(e)})"}} + + {:type, _} -> + {:halt, {:error, "Potentially unsafe file type in ZIP at: #{path}"}} + + {:safe_path, _} -> + {:halt, {:error, "Unsafe path in ZIP: #{path}"}} + end + + # new OTP version? + _, _acc -> + {:halt, {:error, "Unknown ZIP record type"}} + end) + end + end + + @spec check_safe_archive_and_list_files(binary() | [char()], [term()]) :: + {:ok, [String.t()]} | {:error, reason :: term()} + defp check_safe_archive_and_list_files(archive, opts \\ []) do + check_safe_archive_and_maybe_list_files(archive, opts, true) + end + + @spec check_safe_archive(binary() | [char()], [term()]) :: :ok | {:error, reason :: term()} + defp check_safe_archive(archive, opts \\ []) do + case check_safe_archive_and_maybe_list_files(archive, opts, false) do + {:ok, _} -> :ok + error -> error + end + end + + @spec check_safe_file_list([text()], text()) :: :ok | {:error, term()} + defp check_safe_file_list([], _), do: :ok + + defp check_safe_file_list([path | tail], cwd) do + with {_, true} <- {:path, is_safe_path?(path)}, + {_, {:ok, fstat}} <- {:stat, File.stat(Path.expand(path, cwd))}, + {_, true} <- {:type, is_safe_type?(fstat.type)} do + check_safe_file_list(tail, cwd) + else + {:path, _} -> + {:error, "Unsafe path escaping cwd: #{path}"} + + {:stat, e} -> + {:error, "Unable to check file type of #{path}: #{inspect(e)}"} + + {:type, _} -> + {:error, "Unsafe type at #{path}"} + end + end + + defp check_safe_file_list(_, _), do: {:error, "Malformed file_list"} + + @doc """ + Checks whether the archive data contais file entries for all paths from fset + + Note this really only accepts entries corresponding to regular _files_, + if a path is contained as for example an directory, this does not count as a match. + """ + @spec contains_all_data?(binary(), MapSet.t()) :: true | false + def contains_all_data?(archive_data, fset) do + with {:ok, table} <- :zip.table(archive_data) do + remaining = + Enum.reduce(table, fset, fn + {:zip_file, path, info, _comment, _offset, _comp_size}, fset -> + if elem(info, 2) == :regular do + MapSet.delete(fset, path) + else + fset + end + + _, _ -> + fset + end) + |> MapSet.size() + + if remaining == 0, do: true, else: false + else + _ -> false + end + end + + @doc """ + List all file entries in ZIP, or error if invalid or unsafe. + + Note this really only lists regular files, no directories, ZIP comments or other types! + """ + @spec list_dir_file(text()) :: {:ok, [String.t()]} | {:error, reason :: term()} + def list_dir_file(archive) do + path = to_charlist(archive) + check_safe_archive_and_list_files(path) + end + + defp stringify_zip({:ok, {fname, data}}), do: {:ok, {to_string(fname), data}} + defp stringify_zip({:ok, fname}), do: {:ok, to_string(fname)} + defp stringify_zip(ret), do: ret + + @spec zip(text(), text(), [text()], boolean()) :: + {:ok, file_name :: String.t()} + | {:ok, {file_name :: String.t(), file_data :: binary()}} + | {:error, reason :: term()} + def zip(name, file_list, cwd, memory \\ false) do + opts = [{:cwd, to_charlist(cwd)}] + opts = if memory, do: [:memory | opts], else: opts + + with :ok <- check_safe_file_list(file_list, cwd) do + file_list = for f <- file_list, do: to_charlist(f) + name = to_charlist(name) + stringify_zip(:zip.zip(name, file_list, opts)) + end + end + + @spec unzip_file(text(), text(), [text()] | nil) :: + {:ok, [String.t()]} + | {:error, reason :: term()} + | {:error, {name :: text(), reason :: term()}} + def unzip_file(archive, target_dir, file_list \\ nil) do + do_unzip(to_charlist(archive), to_charlist(target_dir), file_list) + end + + @spec unzip_data(binary(), text(), [text()] | nil) :: + {:ok, [String.t()]} + | {:error, reason :: term()} + | {:error, {name :: text(), reason :: term()}} + def unzip_data(archive, target_dir, file_list \\ nil) do + do_unzip(archive, to_charlist(target_dir), file_list) + end + + defp stringify_unzip({:ok, [{_fname, _data} | _] = filebinlist}), + do: {:ok, Enum.map(filebinlist, fn {fname, data} -> {to_string(fname), data} end)} + + defp stringify_unzip({:ok, [_fname | _] = filelist}), + do: {:ok, Enum.map(filelist, fn fname -> to_string(fname) end)} + + defp stringify_unzip({:error, {fname, term}}), do: {:error, {to_string(fname), term}} + defp stringify_unzip(ret), do: ret + + @spec do_unzip(binary() | [char()], text(), [text()] | nil) :: + {:ok, [String.t()]} + | {:error, reason :: term()} + | {:error, {name :: text(), reason :: term()}} + defp do_unzip(archive, target_dir, file_list) do + opts = + if file_list != nil do + [ + file_list: for(f <- file_list, do: to_charlist(f)), + cwd: target_dir + ] + else + [cwd: target_dir] + end + + with :ok <- check_safe_archive(archive) do + stringify_unzip(:zip.unzip(archive, opts)) + end + end +end |