%%%-------------------------------------------------------------------
%%% File : mod_block_strangers.erl
%%% Author : Alexey Shchepin <alexey@process-one.net>
%%% Purpose : Block packets from non-subscribers
%%% Created : 25 Dec 2016 by Alexey Shchepin <alexey@process-one.net>
%%%
%%%
%%% ejabberd, Copyright (C) 2002-2022 ProcessOne
%%%
%%% This program is free software; you can redistribute it and/or
%%% modify it under the terms of the GNU General Public License as
%%% published by the Free Software Foundation; either version 2 of the
%%% License, or (at your option) any later version.
%%%
%%% This program is distributed in the hope that it will be useful,
%%% but WITHOUT ANY WARRANTY; without even the implied warranty of
%%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
%%% General Public License for more details.
%%%
%%% You should have received a copy of the GNU General Public License along
%%% with this program; if not, write to the Free Software Foundation, Inc.,
%%% 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
%%%
%%%-------------------------------------------------------------------
-module(mod_block_strangers).
-author('alexey@process-one.net').
-behaviour(gen_mod).
%% API
-export([start/2, stop/1, reload/3, mod_doc/0,
depends/2, mod_opt_type/1, mod_options/1]).
-export([filter_packet/1, filter_offline_msg/1, filter_subscription/2]).
-include_lib("xmpp/include/xmpp.hrl").
-include("logger.hrl").
-include("translate.hrl").
-define(SETS, gb_sets).
-type c2s_state() :: ejabberd_c2s:state().
%%%===================================================================
%%% Callbacks and hooks
%%%===================================================================
start(Host, _Opts) ->
ejabberd_hooks:add(user_receive_packet, Host,
?MODULE, filter_packet, 25),
ejabberd_hooks:add(roster_in_subscription, Host,
?MODULE, filter_subscription, 25),
ejabberd_hooks:add(offline_message_hook, Host,
?MODULE, filter_offline_msg, 25).
stop(Host) ->
ejabberd_hooks:delete(user_receive_packet, Host,
?MODULE, filter_packet, 25),
ejabberd_hooks:delete(roster_in_subscription, Host,
?MODULE, filter_subscription, 25),
ejabberd_hooks:delete(offline_message_hook, Host,
?MODULE, filter_offline_msg, 25).
reload(_Host, _NewOpts, _OldOpts) ->
ok.
-spec filter_packet({stanza(), c2s_state()}) -> {stanza(), c2s_state()} |
{stop, {drop, c2s_state()}}.
filter_packet({#message{from = From} = Msg, State} = Acc) ->
LFrom = jid:tolower(From),
LBFrom = jid:remove_resource(LFrom),
#{pres_a := PresA} = State,
case (?SETS):is_element(LFrom, PresA)
orelse (?SETS):is_element(LBFrom, PresA)
orelse sets_bare_member(LBFrom, PresA) of
false ->
case check_message(Msg) of
allow -> Acc;
deny -> {stop, {drop, State}}
end;
true ->
Acc
end;
filter_packet(Acc) ->
Acc.
-spec filter_offline_msg({_, message()}) -> {_, message()} | {stop, {drop, message()}}.
filter_offline_msg({_Action, #message{} = Msg} = Acc) ->
case check_message(Msg) of
allow -> Acc;
deny -> {stop, {drop, Msg}}
end.
-spec filter_subscription(boolean(), presence()) -> boolean() | {stop, false}.
filter_subscription(Acc, #presence{meta = #{captcha := passed}}) ->
Acc;
filter_subscription(Acc, #presence{from = From, to = To, lang = Lang,
id = SID, type = subscribe} = Pres) ->
LServer = To#jid.lserver,
case mod_block_strangers_opt:drop(LServer) andalso
mod_block_strangers_opt:captcha(LServer) andalso
need_check(Pres) of
true ->
case check_subscription(From, To) of
false ->
BFrom = jid:remove_resource(From),
BTo = jid:remove_resource(To),
Limiter = jid:tolower(BFrom),
case ejabberd_captcha:create_captcha(
SID, BTo, BFrom, Lang, Limiter,
fun(Res) -> handle_captcha_result(Res, Pres) end) of
{ok, ID, Body, CaptchaEls} ->
Msg = #message{from = BTo, to = From,
id = ID, body = Body,
sub_els = CaptchaEls},
case mod_block_strangers_opt:log(LServer) of
true ->
?INFO_MSG("Challenge subscription request "
"from stranger ~ts to ~ts with "
"CAPTCHA",
[jid:encode(From), jid:encode(To)]);
false ->
ok
end,
ejabberd_router:route(Msg);
{error, limit} ->
ErrText = ?T("Too many CAPTCHA requests"),
Err = xmpp:err_resource_constraint(ErrText, Lang),
ejabberd_router:route_error(Pres, Err);
_ ->
ErrText = ?T("Unable to generate a CAPTCHA"),
Err = xmpp:err_internal_server_error(ErrText, Lang),
ejabberd_router:route_error(Pres, Err)
end,
{stop, false};
true ->
Acc
end;
false ->
Acc
end;
filter_subscription(Acc, _) ->
Acc.
-spec handle_captcha_result(captcha_succeed | captcha_failed, presence()) -> ok.
handle_captcha_result(captcha_succeed, Pres) ->
Pres1 = xmpp:put_meta(Pres, captcha, passed),
ejabberd_router:route(Pres1);
handle_captcha_result(captcha_failed, #presence{lang = Lang} = Pres) ->
Txt = ?T("The CAPTCHA verification has failed"),
ejabberd_router:route_error(Pres, xmpp:err_not_allowed(Txt, Lang)).
%%%===================================================================
%%% Internal functions
%%%===================================================================
-spec check_message(message()) -> allow | deny.
check_message(#message{from = From, to = To, lang = Lang} = Msg) ->
LServer = To#jid.lserver,
case need_check(Msg) of
true ->
case check_subscription(From, To) of
false ->
Drop = mod_block_strangers_opt:drop(LServer),
Log = mod_block_strangers_opt:log(LServer),
if
Log ->
?INFO_MSG("~ts message from stranger ~ts to ~ts",
[if Drop -> "Rejecting";
true -> "Allow"
end,
jid:encode(From), jid:encode(To)]);
true ->
ok
end,
if
Drop ->
Txt = ?T("Messages from strangers are rejected"),
Err = xmpp:err_policy_violation(Txt, Lang),
Msg1 = maybe_adjust_from(Msg),
ejabberd_router:route_error(Msg1, Err),
deny;
true ->
allow
end;
true ->
allow
end;
false ->
allow
end.
-spec maybe_adjust_from(message()) -> message().
maybe_adjust_from(#message{type = groupchat, from = From} = Msg) ->
Msg#message{from = jid:remove_resource(From)};
maybe_adjust_from(#message{} = Msg) ->
Msg.
-spec need_check(presence() | message()) -> boolean().
need_check(Pkt) ->
To = xmpp:get_to(Pkt),
From = xmpp:get_from(Pkt),
IsSelf = To#jid.luser == From#jid.luser andalso
To#jid.lserver == From#jid.lserver,
LServer = To#jid.lserver,
IsEmpty = case Pkt of
#message{body = [], subject = []} ->
true;
_ ->
false
end,
IsError = (error == xmpp:get_type(Pkt)),
AllowLocalUsers = mod_block_strangers_opt:allow_local_users(LServer),
Access = mod_block_strangers_opt:access(LServer),
not (IsSelf orelse IsEmpty orelse IsError
orelse acl:match_rule(LServer, Access, From) == allow
orelse ((AllowLocalUsers orelse From#jid.luser == <<"">>)
andalso ejabberd_router:is_my_host(From#jid.lserver))).
-spec check_subscription(jid(), jid()) -> boolean().
check_subscription(From, To) ->
LocalServer = To#jid.lserver,
{RemoteUser, RemoteServer, _} = jid:tolower(From),
case mod_roster:is_subscribed(From, To) of
false when RemoteUser == <<"">> ->
false;
false ->
%% Check if the contact's server is in the roster
mod_block_strangers_opt:allow_transports(LocalServer)
andalso mod_roster:is_subscribed(jid:make(RemoteServer), To);
true ->
true
end.
-spec sets_bare_member(ljid(), ?SETS:set()) -> boolean().
sets_bare_member({U, S, <<"">>} = LBJID, Set) ->
case ?SETS:next(?SETS:iterator_from(LBJID, Set)) of
{{U, S, _}, _} -> true;
_ -> false
end.
depends(_Host, _Opts) ->
[].
mod_opt_type(access) ->
econf:acl();
mod_opt_type(drop) ->
econf:bool();
mod_opt_type(log) ->
econf:bool();
mod_opt_type(captcha) ->
econf:bool();
mod_opt_type(allow_local_users) ->
econf:bool();
mod_opt_type(allow_transports) ->
econf:bool().
mod_options(_) ->
[{access, none},
{drop, true},
{log, false},
{captcha, false},
{allow_local_users, true},
{allow_transports, true}].
mod_doc() ->
#{desc =>
?T("This module allows to block/log messages coming from an "
"unknown entity. If a writing entity is not in your roster, "
"you can let this module drop and/or log the message. "
"By default you'll just not receive message from that entity. "
"Enable this module if you want to drop SPAM messages."),
opts =>
[{access,
#{value => ?T("AccessName"),
desc =>
?T("The option is supposed to be used when 'allow_local_users' "
"and 'allow_transports' are not enough. It's an ACL where "
"'deny' means the message will be rejected (or a CAPTCHA "
"would be generated for a presence, if configured), and "
"'allow' means the sender is whitelisted and the stanza "
"will pass through. The default value is 'none', which "
"means nothing is whitelisted.")}},
{drop,
#{value => "true | false",
desc =>
?T("This option specifies if strangers messages should "
"be dropped or not. The default value is 'true'.")}},
{log,
#{value => "true | false",
desc =>
?T("This option specifies if strangers' messages should "
"be logged (as info message) in ejabberd.log. "
"The default value is 'false'.")}},
{allow_local_users,
#{value => "true | false",
desc =>
?T("This option specifies if strangers from the same "
"local host should be accepted or not. "
"The default value is 'true'.")}},
{allow_transports,
#{value => "true | false",
desc =>
?T("If set to 'true' and some server's JID is in user's "
"roster, then messages from any user of this server "
"are accepted even if no subscription present. "
"The default value is 'true'.")}},
{captcha,
#{value => "true | false",
desc =>
?T("Whether to generate CAPTCHA or not in response to "
"messages from strangers. See also section "
"https://docs.ejabberd.im/admin/configuration/#captcha"
"[CAPTCHA] of the Configuration Guide. "
"The default value is 'false'.")}}]}.
