From eb92fb32b746f2104b0f370b5b295bb8dd4bd5e5 Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Tue, 7 Mar 2023 22:07:46 +0000
Subject: [PATCH] Set the default maximum DNS UDP packet size to 1232.

http://www.dnsflagday.net/2020/ refers.

Thanks to Xiang Li for the prompt.

CVE: CVE-2023-28450
Upstream-Status: Backport [https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=eb92fb32b746f2104b0f370b5b295bb8dd4bd5e5]

Signed-off-by: Peter Marko <peter.marko@siemens.com>
---
 man/dnsmasq.8 | 3 ++-
 src/config.h  | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/man/dnsmasq.8 b/man/dnsmasq.8
index 41e2e04..5acb935 100644
--- a/man/dnsmasq.8
+++ b/man/dnsmasq.8
@@ -183,7 +183,8 @@ to zero completely disables DNS function, leaving only DHCP and/or TFTP.
 .TP
 .B \-P, --edns-packet-max=<size>
 Specify the largest EDNS.0 UDP packet which is supported by the DNS
-forwarder. Defaults to 4096, which is the RFC5625-recommended size.
+forwarder. Defaults to 1232, which is the recommended size following the
+DNS flag day in 2020. Only increase if you know what you are doing.
 .TP
 .B \-Q, --query-port=<query_port>
 Send outbound DNS queries from, and listen for their replies on, the
diff --git a/src/config.h b/src/config.h
index 1e7b30f..37b374e 100644
--- a/src/config.h
+++ b/src/config.h
@@ -19,7 +19,7 @@
 #define CHILD_LIFETIME 150 /* secs 'till terminated (RFC1035 suggests > 120s) */
 #define TCP_MAX_QUERIES 100 /* Maximum number of queries per incoming TCP connection */
 #define TCP_BACKLOG 32  /* kernel backlog limit for TCP connections */
-#define EDNS_PKTSZ 4096 /* default max EDNS.0 UDP packet from RFC5625 */
+#define EDNS_PKTSZ 1232 /* default max EDNS.0 UDP packet from from  /dnsflagday.net/2020 */
 #define SAFE_PKTSZ 1232 /* "go anywhere" UDP packet size, see https://dnsflagday.net/2020/ */
 #define KEYBLOCK_LEN 40 /* choose to minimise fragmentation when storing DNSSEC keys */
 #define DNSSEC_WORK 50 /* Max number of queries to validate one question */
-- 
2.20.1

