When query processing hits a delegation from a locally configured zone,
an attempt may be made to look for a better answer in the cache. In
such a case, the zone-sourced delegation data is set aside and the
lookup is retried using the cache database. When that lookup is
completed, a decision is made whether the answer found in the cache is
better than the answer found in the zone.
Currently, if the zone-sourced answer turns out to be better than the
one found in the cache:
- qctx->zdb is not restored into qctx->db,
- qctx->node, holding the zone database node found, is not even saved.
Thus, in such a case both qctx->db and qctx->node will point at cache
data. This is not an issue for BIND versions which do not support
mirror zones because in these versions non-recursive queries always
cause the zone-sourced delegation to be returned and thus the
non-recursive part of query_delegation() is never reached if the
delegation is coming from a zone. With mirror zones, however,
non-recursive queries may cause cache lookups even after a zone
delegation is found. Leaving qctx->db assigned to the cache database
when query_delegation() determines that the zone-sourced delegation is
the best answer to the client's query prevents DS records from being
added to delegations coming from mirror zones. Fix this issue by
keeping the zone database and zone node in qctx while the cache is
searched for an answer and then restoring them into qctx->db and
qctx->node, respectively, if the zone-sourced delegation turns out to be
the best answer. Since this change means that qctx->zdb cannot be used
as the glue database any more as it will be reset to NULL by RESTORE(),
ensure that qctx->db is not a cache database before attaching it to
qctx->client->query.gluedb.
Furthermore, current code contains a conditional statement which
prevents a mirror zone from being used as a source of glue records.
Said statement was added to prevent assertion failures caused by
attempting to use a zone database's glue cache for finding glue for an
NS RRset coming from a cache database. However, that check is overly
strict since it completely prevents glue from being added to delegations
coming from mirror zones. With the changes described above in place,
the scenario this check was preventing can no longer happen, so remove
the aforementioned check.
If qctx->zdb is not NULL, qctx->zfname will also not be NULL;
qctx->zsigrdataset may be NULL in such a case, but query_putrdataset()
handles pointers to NULL pointers gracefully. Remove redundant
conditional expressions to make the cleanup code in query_freedata()
match the corresponding sequences of SAVE() / RESTORE() macros more
closely.
Update named_zone_reusable() so that it does not consider a zone to be
eligible for reuse if its old value of the "mirror" option differs from
the new one. This causes "rndc reconfig" to create a new zone structure
whenever the value of the "mirror" option is changed, which ensures that
the previous zone database is not reused and that flags are properly set
in responses sourced from zones whose "mirror" setting was changed at
runtime.
If transferring or loading a mirror zone fails, resolution should still
succeed by means of falling back to regular recursive queries.
Currently, though, if a slave zone is present in the zone table and not
loaded, a SERVFAIL response is generated. Thus, mirror zones need
special handling in this regard.
Add a new dns_zt_find() flag, DNS_ZTFIND_MIRROR, and set it every time a
domain name is looked up rather than a zone itself. Handle that flag in
dns_zt_find() in such a way that a mirror zone which is expired or not
yet loaded is ignored when looking up domain names, but still possible
to find when the caller wants to know whether the zone is configured.
This causes a fallback to recursion when mirror zone data is unavailable
without making unloaded mirror zones invisible to code checking a zone's
existence.
When a resolver is a regular slave (i.e. not a mirror) for some zone,
non-recursive queries for names below that slaved zone will return a
delegation sourced from it. This behavior is suboptimal for mirror
zones as their contents should rather be treated as validated, cached
DNS responses. Modify query_delegation() and query_zone_delegation() to
permit clients allowed cache access to check its contents for a better
answer when responding to non-recursive queries.
Make ns3 mirror the "root" zone from ns1 and query the former for a
properly signed record below the root. Ensure ns1 is not queried during
resolution and that the AD bit is set in the response.
Update axfr_commit() so that all incoming versions of a mirror zone
transferred using AXFR are verified before being used. If zone
verification fails, discard the received version of the zone, wait until
the next refresh and retry.
