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From: Jaco Kroon <jaco@uls.co.za>
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 <jaco@uls.co.za>
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 */
}
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