Previously, when answering from the cache, and when minimal-responses
was not set, we added the best known zone cut to the authority section
of the response message, using dns_db_findzonecut() to look it up in
the DNS cache. Since the DNS cache will no longer be used to store
parent-side NS RRsets, it will now be possible for an ancestor node
to be used as the zone cut, leading to the wrong NS record being
included.
There are various ways we could correct this:
1. Use dns_deleg_lookup() instead of dns_db_findzonecut() to find the
zone cut. But currently, the deleg database stores only the server
addresses for the delegation, not the full NS RRset; this would need
to be changed.
2. Look up <name>/NS whenever we cache a referral; that way we'll get
the child-side NS RRset and cache that, and we can retrieve it when
building the response.
But the solution chosen here is simply not to look up the NS record
when answering from the cache, effectively making "minimal-responses
yes;" mandatory for queries answered from the cache.
System tests have been updated as needed, so they no longer expect
NS RRsets in the authority section of recursive responses.
Make the maximum number of processed delegation nameservers configurable
via the new 'max-delegation-servers' option (default: 13), replacing the
hardcoded NS_PROCESSING_LIMIT (20).
The default is reduced to 13 to precisely match the maximum number of
root servers that can fit into a classic 512-byte UDP payload. This
provides a natural, historically sound cap that mitigates resource
exhaustion and amplification attacks from artificially inflated or
misconfigured delegations.
The configuration option is strictly bounded between 1 and 100 to ensure
resolver stability.
Update Sphinx-related Python packages to their current versions pulled
in by "pip install sphinx-rtd-theme" run in a fresh Debian "bookworm"
container.
ANY queries are widely abused by attackers doing reflection attacks as
they return the largest answers. Enable minimal ANY answers by default
to reduce the attack surface of the DNS servers.
Update documentation, removing the mention of statements being
implicitely "fixed" if they are defined out of range (for
`edns-version`, `edns-udp-size`, `max-udp-size`, `no-cookie-udp-size`
and `padding`) as the ranges are now enforced.
After a couple releases, it appears that the minimum version can be
increased without much trouble.
Because meson only requires python 3.7 or greater, most supported
distributions can run a newer meson without having to deal with
additional dependencies or a new python version.
Since the "tkey-gssapi-credential" statement has been previously
deprecated, mark it as ancient and remove all code related to it:
- The code processing the "tkey-gssapi-credential" statement in the
configuration is the only user of the dst_gssapi_acquirecred() and
dst_gssapi_releasecred() functions, so remove them along with their
static helper functions and a backup definition of the
GSS_KRB5_MECHANISM macro.
- When calling gss_accept_sec_context(), pass GSS_C_NO_CREDENTIAL
instead of the credential acquired by gss_acquire_cred().
(Previously, NULL was passed when "tkey-gssapi-credential" was not
specified. Kerberos headers define GSS_C_NO_CREDENTIAL as
(gss_cred_id_t) 0, so the logic was effectively the same, but using
the GSS_C_NO_CREDENTIAL macro is more appropriate.) This renders
the 'cred' parameter for dst_gssapi_acceptctx() redundant, so remove
it from the prototype of the latter. (Contrary to what the
documentation for dst_gssapi_acceptctx() claims,
dst_gssapi_releasecred() does not need to subsequently be called to
free the GSS-API context; a dst_gssapi_deletectx() call in
gssapi_destroy() takes care of that when the dynamically generated
TSIG key is destroyed.)
- Remove the 'gsscred' member from struct dns_tkeyctx, along with its
related dns_gss_cred_id_t typedef.
Update the relevant sections of the ARM and code comments accordingly.
This makes the "tkey-gssapi-keytab" statement the only way to set up
GSS-TSIG in named.
Remove redundant code from bin/named/tkeyconf.c while at it.
To prevent spoofed unsigned DNAME responses being accepted retry
response with unsigned DNAMEs over TCP if the response is not TSIG
signed or there isn't a good DNS CLIENT COOKIE.
