Merge pull request #12862 from omoerbeek/rec-recursion-bound

rec: bound maximum recursion depth to 16.

pdns/recursordist/docs/settings.rst

@@ -1296,7 +1296,7 @@ This setting, which defaults to 3600 seconds, puts a maximum on the amount of ti
 ``max-recursion-depth``
 -----------------------
 -  Integer
--  Default: 40
+-  Default: 16
 
 Total maximum number of internal recursion calls the server may use to answer a single query.
 0 means unlimited.
@@ -1308,6 +1308,10 @@ If `qname-minimization`_ is enabled, the fallback code in case of a failing reso
 
     Before 4.1.0, this settings was unlimited.
 
+.. versionchanged:: 4.9.0
+
+   Before 4.9.0 this setting's default was 40 and the limit on ``CNAME`` chains (fixed at 16) acted as a bound on he recursion depth.
+
 .. _setting-max-tcp-clients:
 
 ``max-tcp-clients``

pdns/recursordist/rec-main.cc

@@ -2882,7 +2882,7 @@ static void initArgs()
   ::arg().set("max-ns-per-resolve", "Maximum number of NS records to consider to resolve a name, 0 is no limit") = "13";
   ::arg().set("max-ns-address-qperq", "Maximum outgoing NS address queries per query") = "10";
   ::arg().set("max-total-msec", "Maximum total wall-clock time per query in milliseconds, 0 for unlimited") = "7000";
-  ::arg().set("max-recursion-depth", "Maximum number of internal recursion calls per query, 0 for unlimited") = "40";
+  ::arg().set("max-recursion-depth", "Maximum number of internal recursion calls per query, 0 for unlimited") = "16";
   ::arg().set("max-udp-queries-per-round", "Maximum number of UDP queries processed per recvmsg() round, before returning back to normal processing") = "10000";
   ::arg().set("protobuf-use-kernel-timestamp", "Compute the latency of queries in protobuf messages by using the timestamp set by the kernel when the query was received (when available)") = "";
   ::arg().set("distribution-pipe-buffer-size", "Size in bytes of the internal buffer of the pipe used by the distributor to pass incoming queries to a worker thread") = "0";