File

mod_cloud_notify_encrypted/mod_cloud_notify_encrypted.lua @ 4651:8231774f5bfd

mod_cloud_notify_encrypted: Ensure body substring remains valid UTF-8 The `body:sub()` call risks splitting the string in the middle of a multi-byte UTF-8 sequence. This should have been caught by util.stanza validation, but that would have caused some havoc, at the very least causing the notification to not be sent. There have been no reports of this happening. Likely because this module isn't widely deployed among users with languages that use many longer UTF-8 sequences. The util.encodings.utf8.valid() function is O(n) where only the last sequence really needs to be checked, but it's in C and expected to be fast.
author Kim Alvefur <zash@zash.se>
date Sun, 22 Aug 2021 13:22:59 +0200
parent 4650:44af84178cea
child 5054:62480053c87b
line wrap: on
line source

local array = require "util.array";
local base64 = require "util.encodings".base64;
local valid_utf8 = require "util.encodings".utf8.valid;
local ciphers = require "openssl.cipher";
local jid = require "util.jid";
local json = require "util.json";
local random = require "util.random";
local set = require "util.set";
local st = require "util.stanza";

local xmlns_jmi = "urn:xmpp:jingle-message:0";
local xmlns_jingle_apps_rtp = "urn:xmpp:jingle:apps:rtp:1";
local xmlns_push = "urn:xmpp:push:0";
local xmlns_push_encrypt = "tigase:push:encrypt:0";
local xmlns_push_encrypt_aes_128_gcm = "tigase:push:encrypt:aes-128-gcm";
local xmlns_push_jingle = "tigase:push:jingle:0";

local function detect_stanza_encryption(stanza)
	local eme = stanza:get_child("encryption", "urn:xmpp:eme:0");
	if eme then return eme.attr.namespace or ""; end
	-- Fallback for legacy OMEMO clients without EME
	local omemo = stanza:get_child("encrypted", "eu.siacs.conversations.axolotl");
	if omemo then return "eu.siacs.conversations.axolotl"; end
end

-- https://xeps.tigase.net//docs/push-notifications/encrypt/#41-discovering-support
local function account_disco_info(event)
	event.reply:tag("feature", {var=xmlns_push_encrypt}):up();
	event.reply:tag("feature", {var=xmlns_push_encrypt_aes_128_gcm}):up();
	event.reply:tag("feature", {var=xmlns_push_jingle}):up();
end
module:hook("account-disco-info", account_disco_info);

function handle_register(event)
	local encrypt = event.stanza:get_child("enable", xmlns_push):get_child("encrypt", xmlns_push_encrypt);
	if not encrypt then return; end

	local algorithm = encrypt.attr.alg;
	if algorithm ~= "aes-128-gcm" then
		event.origin.send(st.error_reply(
			event.stanza, "modify", "feature-not-implemented", "Unknown encryption algorithm"
		));
		return false;
	end

	local key_base64 = encrypt:get_text();
	local key_binary = base64.decode(key_base64);
	if not key_binary or #key_binary ~= 16 then
		event.origin.send(st.error_reply(
			event.stanza, "modify", "bad-request", "Invalid encryption key"
		));
		return false;
	end

	event.push_info.encryption = {
		algorithm = algorithm;
		key_base64 = key_base64;
	};
end

function handle_push(event)
	local encryption = event.push_info.encryption;
	if not encryption then return; end

	if encryption.algorithm ~= "aes-128-gcm" then
		event.reason = "Unsupported encryption algorithm: "..tostring(encryption.algorithm);
		return true;
	end

	local push_summary = event.push_summary;

	local original_stanza = event.original_stanza;
	local is_encrypted_msg = detect_stanza_encryption(original_stanza);
	local body;
	if is_encrypted_msg then
		-- TODO: localization
		body = "You have received an encrypted message";
	else
		body = original_stanza:get_child_text("body");
		if body and #body > 255 then
			body = body:sub(1, 255);
			if not valid_utf8(body) then
				body = body:gsub("[\194-\244][\128-\191]*$", "");
			end
		end
	end

	local push_payload = {
		unread = tonumber(push_summary["message-count"]) or 1;
		sender = jid.bare(original_stanza.attr.from);
		message = body;
	};

	if original_stanza.name == "message" then
		if original_stanza.attr.type == "groupchat" then
			push_payload.type = "groupchat";
			push_payload.nickname = jid.resource(original_stanza.attr.from);
		elseif original_stanza.attr.type ~= "error" then
			local jmi_propose = original_stanza:get_child("propose", xmlns_jmi);
			if jmi_propose then
				push_payload.type = "call";
				push_payload.sid = jmi_propose.attr.id;
				local media_types = set.new();
				for description in jmi_propose:childtags("description", xmlns_jingle_apps_rtp) do
					local media_type = description.attr.media;
					if media_type then
						media_types:add(media_type);
					end
				end
				push_payload.media = array.collect(media_types:items());
				push_payload.sender = original_stanza.attr.from;
			else
				push_payload.type = "chat";
			end
		end
	elseif original_stanza.name == "presence"
	and original_stanza.attr.type == "subscribe" then
		push_payload.type = "subscribe";
	end

	local iv = random.bytes(12);
	local key_binary = base64.decode(encryption.key_base64);
	local push_json = json.encode(push_payload);

	-- FIXME: luaossl does not expose the EVP_CTRL_GCM_GET_TAG API, so we append 16 NUL bytes
	-- Siskin does not validate the tag anyway.
	local encrypted_payload = base64.encode(ciphers.new("AES-128-GCM"):encrypt(key_binary, iv):final(push_json)..string.rep("\0", 16));
	local encrypted_element = st.stanza("encrypted", { xmlns = xmlns_push_encrypt, iv = base64.encode(iv) })
		:text(encrypted_payload);
	if push_payload.type == "call" then
		encrypted_element.attr.type = "voip";
		event.important = true;
	end
	-- Replace the unencrypted notification data with the encrypted one
	event.notification_payload
		:remove_children("x", "jabber:x:data")
		:add_child(encrypted_element);
end

module:hook("cloud_notify/registration", handle_register);
module:hook("cloud_notify/push", handle_push, 1);