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-- SPDX-License-Identifier: GPL-3.0-or-later
-- Module implementing RFC 8145 section 5
-- Signaling Trust Anchor Knowledge in DNS using Key Tag Query
local kres = require('kres')
local ffi = require('ffi')
local M = {}
M.layer = {}
-- transform trust anchor keyset structure for one domain name (in wire format)
-- to signalling query name like _ta-keytag1-keytag2.example.com.
-- Returns:
-- string constructed from valid keytags
-- nil if no valid keytag is present in keyset
local function prepare_query_name(keyset, name)
if not keyset then return nil end
local keytags = {}
for _, key in ipairs(keyset) do
if key.state == "Valid" then
table.insert(keytags, key.key_tag)
end
end
if next(keytags) == nil then return nil end
table.sort(keytags)
local query = "_ta"
for _, tag in pairs(keytags) do
query = string.format("%s-%04x", query, tag)
end
if name == "\0" then
return query .. "."
else
return query .. "." .. kres.dname2str(name)
end
end
-- construct keytag query for valid keys and send it as asynchronous query
-- (does nothing if no valid keys are present at given domain name)
local function send_ta_query(domain)
local keyset = trust_anchors.keysets[domain]
local qname = prepare_query_name(keyset, domain)
if qname ~= nil then
log_info(ffi.C.LOG_GRP_TASIGNALING, "signalling query triggered: %s", qname)
-- asynchronous query
-- we do not care about result or from where it was obtained
event.after(0, function ()
resolve(qname, kres.type.NULL, kres.class.IN, "NONAUTH")
end)
end
end
-- act on DNSKEY queries which were not answered from cache
function M.layer.consume(state, req, pkt)
-- First check for standard "cached packets": PKT_SIZE_NOWIRE, for efficiency.
if pkt.size ~= -1 and pkt:qtype() == kres.type.DNSKEY then
local qry = req:current()
if not qry.flags.CACHED then
send_ta_query(qry:name())
end
end
return state -- do not interfere with normal query processing
end
return M
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