[patch] djbdns-dnscache-configurable-truncate-size-nov6.patch

djbdns-dnscache-configurable-truncate-size-nov6.patch (text/plain), 2.53 KB, created by Jaco Kroon on 2024-02-23 06:27:44 UTC

From: Jaco Kroon <[e-mail]>
Date: Tue, 24 Oct 2023 06:36:10 +0200
Subject: [PATCH] dnscache: Enable larger truncation

This variation conflicts with the IPv6 patch.

This is a workaround for https://forum.mikrotik.com/viewtopic.php?t=200627
where Mikrotik doesn't fall back if the UDP response is truncated.

This is done by enabling larger (configurable) than 512 byte responses on UDP
such that Mikrotik doesn't have a need to revert to TCP.  Since it's impossible
to truly know the maximum size of a DNS response trivially this is made
configurable and the upper limit is arbitrarily capped to 16KB.

Signed-off-by: Jaco Kroon <[e-mail]>
diff -bru djbdns-1.05.o/dnscache.c djbdns-1.05/dnscache.c
--- djbdns-1.05.o/dnscache.c	2024-02-23 08:05:00.037623680 +0200
+++ djbdns-1.05/dnscache.c	2024-02-23 08:18:26.320580927 +0200
@@ -52,6 +52,7 @@
 static char buf[1024];
 uint64 numqueries = 0;
 
+static unsigned int truncate_len = 512;
 
 static int udp53;
 
@@ -77,7 +78,7 @@
 {
   if (!u[j].active) return;
   response_id(u[j].id);
-  if (response_len > 512) response_tc();
+  if (response_len > truncate_len) response_tc();
   socket_send4(udp53,response,response_len,u[j].ip,u[j].port);
   log_querydone(&u[j].active,response_len);
   u[j].active = 0; --uactive;
@@ -430,6 +431,15 @@
   if (!cache_init(cachesize))
     strerr_die3x(111,FATAL,"not enough memory for cache of size ",x);
 
+  x = env_get("TRUNCATELEN");
+  if (x) {
+    scan_ulong(x,&truncate_len);
+    if (truncate_len < 512)
+      truncate_len = 512;
+    if (truncate_len > 16384)
+      truncate_len = 16384;
+  }
+
   if (env_get("HIDETTL"))
     response_hidettl();
   if (env_get("FORWARDONLY"))
diff -Nbrau djbdns-1.05.o/server.c djbdns-1.05/server.c
--- djbdns-1.05.o/server.c	2001-02-11 23:11:45.000000000 +0200
+++ djbdns-1.05/server.c	2024-02-23 08:19:40.020855813 +0200
@@ -83,6 +83,7 @@
 {
   char *x;
   int udp53;
+  unsigned int truncate_len = 512;
 
   x = env_get("IP");
   if (!x)
@@ -105,11 +106,19 @@
 
   buffer_putsflush(buffer_2,starting);
 
+  x = env_get("TRUNCATELEN");
+  if (x) {
+    scan_ulong(x,&truncate_len);
+    if (truncate_len < 512)
+      truncate_len = 512;
+    if (truncate_len > 16384)
+      truncate_len = 16384;
+  }
   for (;;) {
     len = socket_recv4(udp53,buf,sizeof buf,ip,&port);
     if (len < 0) continue;
     if (!doit()) continue;
-    if (response_len > 512) response_tc();
+    if (response_len > truncate_len) response_tc();
     socket_send4(udp53,response,response_len,ip,port);
     /* may block for buffer space; if it fails, too bad */
   }