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)

diff --git a/lib/dns/rbtdb.c b/lib/dns/rbtdb.c
index 66ace122a2786fd1d47f54878a5e172a0568c4ba..5c2f0b252d6dfe6b254fe045e491000aacf83a3b 100644 (file)
--- a/lib/dns/rbtdb.c
+++ b/lib/dns/rbtdb.c
@@ -6258,6 +6258,24 @@ update_recordsandxfrsize(bool add, rbtdb_version_t *rbtversion,
        RWUNLOCK(&rbtversion->rwlock, isc_rwlocktype_write);
 }
 
+static bool
+overmaxtype(dns_rbtdb_t *rbtdb, uint32_t ntypes) {
+       if (rbtdb->maxtypepername == 0) {
+               return (false);
+       }
+
+       return (ntypes >= rbtdb->maxtypepername);
+}
+
+static bool
+prio_header(rdatasetheader_t *header) {
+       if (NEGATIVE(header) && prio_type(RBTDB_RDATATYPE_EXT(header->type))) {
+               return (true);
+       }
+
+       return (prio_type(header->type));
+}
+
 /*
  * write lock on rbtnode must be held.
  */
@@ -6269,7 +6287,7 @@ add32(dns_rbtdb_t *rbtdb, dns_rbtnode_t *rbtnode, const dns_name_t *nodename,
        rbtdb_changed_t *changed = NULL;
        rdatasetheader_t *topheader = NULL, *topheader_prev = NULL;
        rdatasetheader_t *header = NULL, *sigheader = NULL;
-       rdatasetheader_t *prioheader = NULL;
+       rdatasetheader_t *prioheader = NULL, *expireheader = NULL;
        unsigned char *merged = NULL;
        isc_result_t result;
        bool header_nx;
@@ -6344,7 +6362,6 @@ 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;
                        }
                        /*
@@ -6356,6 +6373,7 @@ add32(dns_rbtdb_t *rbtdb, dns_rbtnode_t *rbtnode, const dns_name_t *nodename,
                        {
                                if (topheader->type == sigtype) {
                                        sigheader = topheader;
+                                       break;
                                }
                        }
                        negtype = RBTDB_RDATATYPE_VALUE(covers, 0);
@@ -6368,11 +6386,9 @@ 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 &&
@@ -6417,12 +6433,16 @@ 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 ||
@@ -6791,9 +6811,7 @@ 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);
@@ -6801,7 +6819,7 @@ find_header:
 
                        newheader->down = NULL;
 
-                       if (prio_type(newheader->type)) {
+                       if (prio_header(newheader)) {
                                /* This is a priority type, prepend it */
                                newheader->next = rbtnode->data;
                                rbtnode->data = newheader;
@@ -6814,6 +6832,31 @@ find_header:
                                newheader->next = rbtnode->data;
                                rbtnode->data = newheader;
                        }
+
+                       if (IS_CACHE(rbtdb) && overmaxtype(rbtdb, ntypes)) {
+                               if (expireheader == NULL) {
+                                       expireheader = newheader;
+                               }
+                               if (NEGATIVE(newheader) &&
+                                   !prio_header(newheader))
+                               {
+                                       /*
+                                        * Add the new non-priority negative
+                                        * header to the database only
+                                        * temporarily.
+                                        */
+                                       expireheader = newheader;
+                               }
+
+                               set_ttl(rbtdb, expireheader, 0);
+                               mark_header_ancient(rbtdb, expireheader);
+                               /*
+                                * FIXME: In theory, we should mark the RRSIG
+                                * and the header at the same time, but there is
+                                * no direct link between those two header, so
+                                * we would have to check the whole list again.
+                                */
+                       }
                }
        }