From: =?utf-8?b?T25kxZllaiBTdXLDvQ==?= <ondrej@isc.org>
Date: Mon, 17 Jun 2024 11:40:40 +0200
Subject: Be smarter about refusing to add many RR types to the database

Instead of outright refusing to add new RR types to the cache, be a bit
smarter:

1. If the new header type is in our priority list, we always add either
   positive or negative entry at the beginning of the list.

2. If the new header type is negative entry, and we are over the limit,
   we mark it as ancient immediately, so it gets evicted from the cache
   as soon as possible.

3. Otherwise add the new header after the priority headers (or at the
   head of the list).

4. If we are over the limit, evict the last entry on the normal header
   list.

(cherry picked from commit 57cd34441a1b4ecc9874a4a106c2c95b8d7a3120)
---
 lib/dns/rbtdb.c | 27 ++++++++++-----------------
 1 file changed, 10 insertions(+), 17 deletions(-)

diff --git a/lib/dns/rbtdb.c b/lib/dns/rbtdb.c
index 4332215..5179f94 100644
--- a/lib/dns/rbtdb.c
+++ b/lib/dns/rbtdb.c
@@ -6260,19 +6260,13 @@ update_recordsandxfrsize(bool add, rbtdb_version_t *rbtversion,
 	RWUNLOCK(&rbtversion->rwlock, isc_rwlocktype_write);
 }
 
-#ifndef DNS_RBTDB_MAX_RTYPES
-#define DNS_RBTDB_MAX_RTYPES 100
-#endif /* DNS_RBTDB_MAX_RTYPES */
-
 static bool
 overmaxtype(dns_rbtdb_t *rbtdb, uint32_t ntypes) {
-	UNUSED(rbtdb);
-
-	if (DNS_RBTDB_MAX_RTYPES == 0) {
+	if (rbtdb->maxtypepername == 0) {
 		return (false);
 	}
 
-	return (ntypes >= DNS_RBTDB_MAX_RTYPES);
+	return (ntypes >= rbtdb->maxtypepername);
 }
 
 static bool
@@ -6370,7 +6364,6 @@ add32(dns_rbtdb_t *rbtdb, dns_rbtnode_t *rbtnode, const dns_name_t *nodename,
 					set_ttl(rbtdb, topheader, 0);
 					mark_header_ancient(rbtdb, topheader);
 				}
-				ntypes = 0; /* Always add the negative entry */
 				goto find_header;
 			}
 			/*
@@ -6395,11 +6388,9 @@ add32(dns_rbtdb_t *rbtdb, dns_rbtnode_t *rbtnode, const dns_name_t *nodename,
 			 * check for an extant non-ancient NODATA ncache
 			 * entry which covers the same type as the RRSIG.
 			 */
-			ntypes = 0;
 			for (topheader = rbtnode->data; topheader != NULL;
 			     topheader = topheader->next)
 			{
-				++ntypes;
 				if ((topheader->type ==
 				     RBTDB_RDATATYPE_NCACHEANY) ||
 				    (newheader->type == sigtype &&
@@ -6444,12 +6435,16 @@ add32(dns_rbtdb_t *rbtdb, dns_rbtnode_t *rbtnode, const dns_name_t *nodename,
 		}
 	}
 
-	ntypes = 0;
 	for (topheader = rbtnode->data; topheader != NULL;
 	     topheader = topheader->next)
 	{
-		++ntypes;
-		if (prio_type(topheader->type)) {
+		if (IS_CACHE(rbtdb) && ACTIVE(topheader, now)) {
+			++ntypes;
+			expireheader = topheader;
+		} else if (!IS_CACHE(rbtdb)) {
+			++ntypes;
+		}
+		if (prio_header(topheader)) {
 			prioheader = topheader;
 		}
 		if (topheader->type == newheader->type ||
@@ -6806,9 +6801,7 @@ find_header:
 			/*
 			 * No rdatasets of the given type exist at the node.
 			 */
-			if (rbtdb->maxtypepername > 0 &&
-			    ntypes >= rbtdb->maxtypepername)
-			{
+			if (!IS_CACHE(rbtdb) && overmaxtype(rbtdb, ntypes)) {
 				free_rdataset(rbtdb, rbtdb->common.mctx,
 					      newheader);
 				return (DNS_R_TOOMANYRECORDS);