From: Michael Tremer <michael.tremer@ipfire.org>
Date: Sat, 16 May 2026 12:56:46 +0000 (+0100)
Subject: knot-resolver: Create a prototype for a DHCP leases integration
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4795f2c3d277bc56d288c1f8f04414fad8ede501;p=ipfire-2.x.git

knot-resolver: Create a prototype for a DHCP leases integration

This module will implement a policy handler which can be used to fetch
any current DHCP leases from a SQLite3 database.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
---

diff --git a/config/knot-resolver/kresd.conf b/config/knot-resolver/kresd.conf
index 5d77e19c2..0515796f6 100644
--- a/config/knot-resolver/kresd.conf
+++ b/config/knot-resolver/kresd.conf
@@ -93,6 +93,7 @@ local CA_FILE = "/etc/ssl/cert.pem"
 -- Load useful modules
 modules = {
 	'hints > iterate',  -- Allow loading /etc/hosts or custom root hints
+	'leases',
 	'stats',            -- Track internal statistics
 	'predict',          -- Prefetch expiring/frequent records
 	'ta_sentinel',
diff --git a/config/knot-resolver/leases.lua b/config/knot-resolver/leases.lua
new file mode 100644
index 000000000..a78a800c5
--- /dev/null
+++ b/config/knot-resolver/leases.lua
@@ -0,0 +1,170 @@
+-- Load modules
+local sqlite3 = require("lsqlite3")
+
+local DB_PATH = "/var/lib/knot-resolver/dhcp-leases.db"
+local TTL = 60
+
+local M = {}
+local db
+local sql_fwd
+local sql_rev
+
+local function log_error(s)
+	print(s)
+end
+
+local function log_debug(s)
+	print(s)
+end
+
+-- Initializes the module
+function M.init()
+	-- Open the database
+	db = sqlite3.open(DB_PATH, sqlite3.OPEN_READONLY)
+
+	-- Fail if we cannot open the database
+	if not db then
+		log_error("leases: Failed to open " .. DB_PATH)
+		return -1
+	end
+
+	-- Don't ever block
+	db:exec("PRAGMA query_only = 1")
+
+	-- Prepare the forward lookup query
+	sql_fwd = db:prepare(
+		"SELECT address FROM leases WHERE hostname = ?1 COLLATE NOCASE LIMIT 1"
+	)
+
+	-- Prepare the reverse lookup query
+	sql_rev = db:prepare(
+		"SELECT hostname FROM leases WHERE address = ?1 LIMIT 1"
+	)
+end
+
+-- Cleans up the module
+function M.deinit()
+	-- Cleanup the statements
+	if sql_fwd then
+		sql_fwd:finalize()
+	end
+	if sql_rev then
+		sql_rev:finalize()
+	end
+
+	-- Close the database
+	if db then
+		db:close()
+	end
+end
+
+-- Parses an IPv4 address from the reverse pointer query name
+local function address_from_reverse_pointer(qname)
+	local d, c, b, a = qname:match("^(%d+)%.(%d+)%.(%d+)%.(%d+)%.in%-addr%.arpa%.$")
+
+	-- Return nil if we could not parse the name
+	if not a or not b or not c or not d then
+		return
+	end
+
+	-- Concatenate the address
+	return string.format("%s.%s.%s.%s", a, b, c, d)
+end
+
+local function lookup_fwd(hostname)
+	-- Reset the statement
+	sql_fwd:reset()
+
+	-- Bind the query name
+	sql_fwd:bind_values(hostname)
+
+	-- Execute the statement
+	if sql_fwd:step() == sqlite3.ROW then
+		local address = sql_fwd:get_value(0)
+
+		-- Convert the address to wire format
+		if address then
+			return kres.str2ip(address)
+		end
+        end
+end
+
+local function lookup_rev(qname)
+	-- Parse the address from the query name
+	local address = address_from_reverse_pointer(qname)
+
+	-- Fail if we could not parse the address
+	if not address then
+		return
+	end
+
+	-- Reset the statement
+	sql_rev:reset()
+
+	-- Bind the address
+	sql_rev:bind_values(address)
+
+	-- Execute the statement
+	if sql_rev:step() == sqlite3.ROW then
+		local hostname = sql_rev:get_value(0)
+
+		-- Convert the hostname to wire format
+		if hostname then
+			return todname(hostname)
+		end
+	end
+end
+
+-- Function that will try to answer the query
+function M.answer()
+	return function(state, req)
+		-- Fetch the current query
+		local query = req:current()
+
+		-- Fetch the query name
+		local qname = kres.dname2str(query.sname)
+
+		-- Fetch the query type
+		local qtype = query.stype
+
+		-- Log action
+		log_debug(
+			string.format("Called for %s (%d)", qname, qtype)
+		)
+
+		local answer = {}
+
+		-- Is this a forward lookup?
+		if qtype == kres.type.A then
+			-- Perform a forward lookup
+			local address = lookup_fwd(qname)
+
+			if address then
+				answer[qtype] = { rdata = address, ttl = TTL }
+			end
+
+		-- Or is this a reverse lookup?
+		elseif qtype == kres.type.PTR then
+			-- Perform a reverse lookup
+			local hostname = lookup_rev(qname)
+
+			if hostname then
+				answer[qtype] = { rdata = hostname, ttl = TTL }
+			end
+		end
+
+		-- If we have an answer, use the policy module to send it
+		if answer then
+			answer = policy.ANSWER(answer)
+
+		-- Otherwise we send NXDOMAIN
+		else
+			answer = policy.DENY
+		end
+
+		-- Pass the state and request
+		return answer(state, req)
+	end
+end
+
+return M
diff --git a/config/rootfiles/common/knot-resolver b/config/rootfiles/common/knot-resolver
index a30943786..4ac4c4b91 100644
--- a/config/rootfiles/common/knot-resolver
+++ b/config/rootfiles/common/knot-resolver
@@ -76,6 +76,7 @@ usr/lib/knot-resolver/kres_modules/http/topojson.js
 usr/lib/knot-resolver/kres_modules/http_doh.lua
 usr/lib/knot-resolver/kres_modules/http_tls_cert.lua
 usr/lib/knot-resolver/kres_modules/http_trace.lua
+usr/lib/knot-resolver/kres_modules/leases.lua
 usr/lib/knot-resolver/kres_modules/nsid.so
 usr/lib/knot-resolver/kres_modules/policy.lua
 usr/lib/knot-resolver/kres_modules/predict.lua
diff --git a/lfs/knot-resolver b/lfs/knot-resolver
index cd24639d2..0404f8e05 100644
--- a/lfs/knot-resolver
+++ b/lfs/knot-resolver
@@ -82,6 +82,10 @@ $(TARGET) : $(patsubst %,$(DIR_DL)/%,$(objects))
 	cd $(DIR_APP) && ninja -C builddir/ $(MAKETUNING)
 	cd $(DIR_APP) && ninja -C builddir/ install
 
+	# Install the leases module
+	install -v -m 644 $(DIR_SRC)/config/knot-resolver/leases.lua \
+		/usr/lib/knot-resolver/kres_modules/leases.lua
+
 	# Create cache directory
 	-mkdir -pv /var/cache/knot-resolver
 	chown kresd:kresd /var/cache/knot-resolver