view mod_xhtmlim/mod_xhtmlim.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
parents 1f68287138e3
children
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-- XEP-0071: XHTML-IM sanitizing

local assert = assert;

local st = require "util.stanza";
local url = require "socket.url";

local no_styles = module:get_option_boolean("strip_xhtml_style", true);

-- Tables from XEP-0071
local xeptables = [[
<body/>	class, id, title; style
<head/>	profile
<html/>	version
<title/>
<abbr/>	class, id, title; style
<acronym/>	class, id, title; style
<address/>	class, id, title; style
<blockquote/>	class, id, title; style; cite
<br/>	class, id, title; style
<cite/>	class, id, title; style
<code/>	class, id, title; style
<dfn/>	class, id, title; style
<div/>	class, id, title; style
<em/>	class, id, title; style
<h1/>	class, id, title; style
<h2/>	class, id, title; style
<h3/>	class, id, title; style
<h4/>	class, id, title; style
<h5/>	class, id, title; style
<h6/>	class, id, title; style
<kbd/>	class, id, title; style
<p/>	class, id, title; style
<pre/>	class, id, title; style
<q/>	class, id, title; style; cite
<samp/>	class, id, title; style
<span/>	class, id, title; style
<strong/>	class, id, title; style
<var/>	class, id, title; style
<a/>	class, id, title; style; accesskey, charset, href, hreflang, rel, rev, tabindex, type
<dl/>	class, id, title; style
<dt/>	class, id, title; style
<dd/>	class, id, title; style
<ol/>	class, id, title; style
<ul/>	class, id, title; style
<li/>	class, id, title; style
<img/>	class, id, title; style; alt, height, longdesc, src, width
]];

-- map of whitelisted tag names to set of allowed attributes
local tags = {}; -- { string : { string : boolean } }

for tag, attrs in xeptables:gmatch("<(%w+)/>([^\n]*)") do
	tags[tag] = { xmlns = true, ["xml:lang"] = true };
	for attr in attrs:gmatch("%w+") do
		tags[tag][attr] = true;
	end
	if no_styles then
		tags[tag]["style"] = nil;
	end
end

-- module:log("debug", "tags = %s;", require "util.serialization".serialize(tags));

-- TODO Decide if disallowed tags should be bounced or silently discarded.
-- XEP says "ignore" and replace tag with text content, but that would
-- need a different transform which can't use `maptags`.
if not module:get_option_boolean("bounce_invalid_xhtml", false) then
	assert = function (x) return x end
end

local function sanitize_xhtml(tag)
	-- module:log("debug", "sanitize_xhtml(<{%s}%s>)", tag.attr.xmlns, tag.name);
	if tag.attr.xmlns == "http://www.w3.org/1999/xhtml" then
		local allowed = assert(tags[tag.name], tag.name);
		if allowed then
			for attr, value in pairs(tag.attr) do
				if not allowed[attr] then
					-- module:log("debug", "Removing disallowed attribute %q from <%s>", attr, tag.name);
					tag.attr[attr] = nil;
				elseif attr == "src" or attr == "href" then
					local urlattr = url.parse(value);
					local scheme = urlattr and urlattr.scheme;
					if scheme ~= "http" and scheme ~= "https" and scheme ~= "mailto" and scheme ~= "xmpp" and scheme ~= "cid" then
						tag.attr[attr] = "https://url.was.invalid/";
					end
				end
			end
		else
			tag.name = "span"
			tag.attr = { xmlns = "http://www.w3.org/1999/xhtml" }
		end
		-- Check child tags
		tag:maptags(sanitize_xhtml);
		-- This tag is clean!
		return tag;
	end
	-- Not xhtml, probably best to discard it
	return nil;
end

-- Check for xhtml-im, sanitize if exists
local function message_handler(event)
	local stanza = event.stanza;
	if stanza:get_child("html", "http://jabber.org/protocol/xhtml-im") then
		stanza = st.clone(stanza);
		if pcall(function() -- try
			stanza:get_child("html", "http://jabber.org/protocol/xhtml-im"):maptags(sanitize_xhtml);
		end) then
			event.stanza = stanza;
		else -- catch
			if stanza.attr.type ~= "error" then
				event.origin.send(st.error_reply(stanza, "modify", "not-acceptable", "Stanza contained illegal XHTML-IM tag"));
			end
			return true;
		end
	end
end

-- Stanzas received from clients
module:hook("pre-message/bare", message_handler, 71);
module:hook("pre-message/full", message_handler, 71);
module:hook("pre-message/host", message_handler, 71);

-- Stanzas about to be delivered to clients
module:hook("message/bare", message_handler, 71);
module:hook("message/full", message_handler, 71);