From: Vladimír Čunát <vladimir.cunat@nic.cz>
Date: Mon, 3 Aug 2026 11:57:51 +0000 (+0200)
Subject: serve_stale: avoid SIGSEGV from a LuaJIT bug
X-Git-Tag: v6.4.2~4^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=710efa0f775efbbdc91656e35a5a31a7ec90ec23;p=thirdparty%2Fknot-resolver.git

serve_stale: avoid SIGSEGV from a LuaJIT bug

The debugging and fix was really submitted by
David Komárek from Whalebone.io
---

diff --git a/NEWS b/NEWS
index 08ac8dfae..d2b8aa2d2 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,7 @@ Knot Resolver 6.4.2 (2026-08-dd)
 Bugfixes
 --------
 - cache: avoid excessive logging introduced in the last release (!1869)
+- /options/serve-stale: avoid SIGSEGV from a LuaJIT bug (#957)
 
 
 Knot Resolver 6.4.1 (2026-07-22)
diff --git a/modules/serve_stale/serve_stale.lua b/modules/serve_stale/serve_stale.lua
index d1b18f90e..73362a9a7 100644
--- a/modules/serve_stale/serve_stale.lua
+++ b/modules/serve_stale/serve_stale.lua
@@ -7,15 +7,17 @@ local ffi = require('ffi')
 -- approximately at multiples of KR_CONN_RTT_MAX.
 M.timeout = 3*sec
 
-M.callback = ffi.cast("kr_stale_cb",
-	function (ttl) --, name, type, qry)
-		--log_debug(ffi.C.SRVSTALE, '   => called back with TTL: ' .. tostring(ttl))
-		if ttl + 3600 * 24 > 0 then -- at most one day stale
-			return 1
-		else
-			return -1
-		end
-	end)
+local function stale_cb(ttl) --, name, type, qry)
+	--log_debug(ffi.C.SRVSTALE, '   => called back with TTL: ' .. tostring(ttl))
+	if ttl + 3600 * 24 > 0 then -- at most one day stale
+		return 1
+	else
+		return -1
+	end
+end
+-- Work around a LuaJIT bug: https://github.com/LuaJIT/LuaJIT/issues/1498
+jit.off(stale_cb)
+M.callback = ffi.cast("kr_stale_cb", stale_cb)
 
 M.layer = {
 	produce = function (state, req)