Set the default maximum DNS UDP packet size to 1232.

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

Thanks to Xiang Li for the prompt.

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

Change-Id: I7326e1a5f2ce2a69f3a8c166c3d6d79f1f5955dd

diff --git a/CHANGELOG b/CHANGELOG
index 35c1b06..45316f8 100644 (file)
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -28,6 +28,14 @@ Backpored patch
        first query completes, the answer can be sent to all the
        clients who asked. Refer: CERT CVE-2020-25686.
 
+    Set the default maximum DNS UDP packet sice to 1232. This
+    has been the recommended value since 2020 because it's the
+    largest value that avoid fragmentation, and fragmentation
+    is just not reliable on the modern internet, especially
+    for IPv6. It's still possible to override this with
+    --edns-packet-max for special circumstances.
+
+
 version 2.79
        Fix parsing of CNAME arguments, which are confused by extra spaces.
        Thanks to Diego Aguirre for spotting the bug.

diff --git a/man/dnsmasq.8 b/man/dnsmasq.8
index bd99b48..2e1df49 100644 (file)
--- a/man/dnsmasq.8
+++ b/man/dnsmasq.8
@@ -168,7 +168,8 @@ 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 67a5ac5..c924908 100644 (file)
--- a/src/config.h
+++ b/src/config.h
@@ -21,7 +21,7 @@
 #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 1280 /* "go anywhere" UDP packet size */
 #define KEYBLOCK_LEN 40 /* choose to minimise fragmentation when storing DNSSEC keys */
 #define DNSSEC_WORK 50 /* Max number of queries to validate one question */