s2s: SASL EXTERNAL

1 files changed, 211 insertions, 0 deletions

diff --git a/util/certverification.lua b/util/certverification.lua
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+++ b/util/certverification.lua
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+-- Prosody IM
+-- Copyright (C) 2010 Matthew Wild
+-- Copyright (C) 2010 Paul Aurich
+--
+-- This project is MIT/X11 licensed. Please see the
+-- COPYING file in the source package for more information.
+--
+
+-- TODO: I feel a fair amount of this logic should be integrated into Luasec,
+-- so that everyone isn't re-inventing the wheel.  Dependencies on
+-- IDN libraries complicate that.
+
+
+-- [TLS-CERTS] - http://tools.ietf.org/html/draft-saintandre-tls-server-id-check-10
+-- [XMPP-CORE] - http://tools.ietf.org/html/draft-ietf-xmpp-3920bis-18
+-- [SRV-ID]    - http://tools.ietf.org/html/rfc4985
+-- [IDNA]      - http://tools.ietf.org/html/rfc5890
+-- [LDAP]      - http://tools.ietf.org/html/rfc4519
+-- [PKIX]      - http://tools.ietf.org/html/rfc5280
+
+local nameprep = require "util.encodings".stringprep.nameprep;
+local idna_to_ascii = require "util.encodings".idna.to_ascii;
+local log = require "util.logger".init("certverification");
+
+module "certverification"
+
+local oid_commonname = "2.5.4.3"; -- [LDAP] 2.3
+local oid_subjectaltname = "2.5.29.17"; -- [PKIX] 4.2.1.6
+local oid_xmppaddr = "1.3.6.1.5.5.7.8.5"; -- [XMPP-CORE]
+local oid_dnssrv   = "1.3.6.1.5.5.7.8.7"; -- [SRV-ID]
+
+-- Compare a hostname (possibly international) with asserted names
+-- extracted from a certificate.
+-- This function follows the rules laid out in
+-- sections 4.4.1 and 4.4.2 of [TLS-CERTS]
+--
+-- A wildcard ("*") all by itself is allowed only as the left-most label
+local function compare_dnsname(host, asserted_names)
+	-- TODO: Sufficient normalization?  Review relevant specs.
+	local norm_host = idna_to_ascii(host)
+	if norm_host == nil then
+		log("info", "Host %s failed IDNA ToASCII operation", host)
+		return false
+	end
+
+	norm_host = norm_host:lower()
+
+	local host_chopped = norm_host:gsub("^[^.]+%.", "") -- everything after the first label
+
+	for i=1,#asserted_names do
+		local name = asserted_names[i]
+		if norm_host == name:lower() then
+			log("debug", "Cert dNSName %s matched hostname", name);
+			return true
+		end
+
+		-- Allow the left most label to be a "*"
+		if name:match("^%*%.") then
+			local rest_name = name:gsub("^[^.]+%.", "")
+			if host_chopped == rest_name:lower() then
+				log("debug", "Cert dNSName %s matched hostname", name);
+				return true
+			end
+		end
+	end
+
+	return false
+end
+
+-- Compare an XMPP domain name with the asserted id-on-xmppAddr
+-- identities extracted from a certificate.  Both are UTF8 strings.
+--
+-- Per [XMPP-CORE], matches against asserted identities don't include
+-- wildcards, so we just do a normalize on both and then a string comparison
+--
+-- TODO: Support for full JIDs?
+local function compare_xmppaddr(host, asserted_names)
+	local norm_host = nameprep(host)
+
+	for i=1,#asserted_names do
+		local name = asserted_names[i]
+
+		-- We only want to match against bare domains right now, not
+		-- those crazy full-er JIDs.
+		if name:match("[@/]") then
+			log("debug", "Ignoring xmppAddr %s because it's not a bare domain", name)
+		else
+			local norm_name = nameprep(name)
+			if norm_name == nil then
+				log("info", "Ignoring xmppAddr %s, failed nameprep!", name)
+			else
+				if norm_host == norm_name then
+					log("debug", "Cert xmppAddr %s matched hostname", name)
+					return true
+				end
+			end
+		end
+	end
+
+	return false
+end
+
+-- Compare a host + service against the asserted id-on-dnsSRV (SRV-ID)
+-- identities extracted from a certificate.
+--
+-- Per [SRV-ID], the asserted identities will be encoded in ASCII via ToASCII.
+-- Comparison is done case-insensitively, and a wildcard ("*") all by itself
+-- is allowed only as the left-most non-service label.
+local function compare_srvname(host, service, asserted_names)
+	local norm_host = idna_to_ascii(host)
+	if norm_host == nil then
+		log("info", "Host %s failed IDNA ToASCII operation", host);
+		return false
+	end
+
+	-- Service names start with a "_"
+	if service:match("^_") == nil then service = "_"..service end
+
+	norm_host = norm_host:lower();
+	local host_chopped = norm_host:gsub("^[^.]+%.", "") -- everything after the first label
+
+	for i=1,#asserted_names do
+		local asserted_service, name = asserted_names[i]:match("^(_[^.]+)%.(.*)");
+		if service == asserted_service then
+			if norm_host == name:lower() then
+				log("debug", "Cert SRVName %s matched hostname", name);
+				return true;
+			end
+
+			-- Allow the left most label to be a "*"
+			if name:match("^%*%.") then
+				local rest_name = name:gsub("^[^.]+%.", "")
+				if host_chopped == rest_name:lower() then
+					log("debug", "Cert SRVName %s matched hostname", name)
+					return true
+				end
+			end
+			if norm_host == name:lower() then
+				log("debug", "Cert SRVName %s matched hostname", name);
+				return true
+			end
+		end
+	end
+
+	return false
+end
+
+function verify_identity(host, service, cert)
+	local ext = cert:extensions()
+	if ext[oid_subjectaltname] then
+		local sans = ext[oid_subjectaltname];
+
+		-- Per [TLS-CERTS] 4.3, 4.4.4, "a client MUST NOT seek a match for a
+		-- reference identifier if the presented identifiers include a DNS-ID
+		-- SRV-ID, URI-ID, or any application-specific identifier types"
+		local had_supported_altnames = false
+
+		if sans[oid_xmppaddr] then
+			had_supported_altnames = true
+			if compare_xmppaddr(host, sans[oid_xmppaddr]) then return true end
+		end
+
+		if sans[oid_dnssrv] then
+			had_supported_altnames = true
+			-- Only check srvNames if the caller specified a service
+			if service and compare_srvname(host, service, sans[oid_dnssrv]) then return true end
+		end
+
+		if sans["dNSName"] then
+			had_supported_altnames = true
+			if compare_dnsname(host, sans["dNSName"]) then return true end
+		end
+
+		-- We don't need URIs, but [TLS-CERTS] is clear.
+		if sans["uniformResourceIdentifier"] then
+			had_supported_altnames = true
+		end
+
+		if had_supported_altnames then return false end
+	end
+
+	-- Extract a common name from the certificate, and check it as if it were
+	-- a dNSName subjectAltName (wildcards may apply for, and receive,
+	-- cat treats)
+	--
+	-- Per [TLS-CERTS] 1.5, a CN-ID is the Common Name from a cert subject
+	-- which has one and only one Common Name
+	local subject = cert:subject()
+	local cn = nil
+	for i=1,#subject do
+		local dn = subject[i]
+		if dn["oid"] == oid_commonname then
+			if cn then
+				log("info", "Certificate has multiple common names")
+				return false
+			end
+
+			cn = dn["value"];
+		end
+	end
+
+	if cn then
+		-- Per [TLS-CERTS] 4.4.4, follow the comparison rules for dNSName SANs.
+		return compare_dnsname(host, { cn })
+	end
+
+	-- If all else fails, well, why should we be any different?
+	return false
+end
+
+return _M;