On LLMNR we never want to retry stream connections (since local TCP
connections should work, and we don't want to unnecessarily delay
operation), explicitly remember whether we already tried one, instead of
deriving this from a still stored stream object. This way, we can free
the stream early, without forgetting that we tried it.
Previously the calls for emitting DNS UDP packets were just called
dns_{transacion|scope}_emit(), but the one to establish a DNS TCP
connection was called dns_transaction_open_tcp(). Clean this up, and
rename them dns_{transaction|scope}_emit_udp() and
dns_transaction_open_tcp().
This adds a mode that makes resolved automatically downgrade from DNSSEC
support to classic non-DNSSEC resolving if the configured DNS server is
not capable of DNSSEC. Enabling this mode increases compatibility with
crappy network equipment, but of course opens up the system to
downgrading attacks.
The new mode can be enabled by setting DNSSEC=downgrade-ok in
resolved.conf. DNSSEC=yes otoh remains a "strict" mode, where DNS
resolving rather fails then allow downgrading.
Downgrading is done:
- when the server does not support EDNS0+DO
- or when the server supports it but does not augment returned RRs with
RRSIGs. The latter is detected when requesting DS or SOA RRs for the
root domain (which is necessary to do proofs for unsigned data)
Previously, if we couldn't reach a server via UDP we'd generate an
MAX_ATTEMPTS transaction result, but if we couldn't reach it via TCP
we'd generate a RESOURCES transaction result. While it is OK to generate
two different errors I think, "RESOURCES" is certainly a misnomer.
Introduce a new transaction result "CONNECTION_FAILURE" instead.
Previously, we'd insist on an RRSIG for all DS/NSEC/NSEC3 RRs. With this
change we don't do that anymore, but also allow unsigned DS/NSEC/NSEC3
if we can prove that the zone they are located in is unsigned.
This collects statistical data about transactions, dnssec verifications
and the cache, and exposes it over the bus. The systemd-resolve-host
tool learns new options to query these statistics and reset them.
Be stricter when searching suitable NSEC3 RRs for proof: generalize the
check we use to find suitable NSEC3 RRs, in nsec3_is_good(), and add
additional checks, such as checking whether all NSEC3 RRs use the same
parameters, have the same suffix and so on.
When doing an NSEC3 proof, before detrmining whether a name is the
closest encloser we first need to figure out the longest common suffix
we have with any NSEC3 RR in the reply.
Note that this is still not complete, one additional step is still
missing: when we verified that a wildcard RRset is properly signed, we
still need to do an NSEC/NSEC3 proof that no more specific RRset exists.
Otherwise if we have an A lookup that failed DNSSEC validation, but an
AAAA lookup that succeeded, we might end up using the A data, but we
really should not.
Let's simplify usage and memory management of DnsResourceRecord's
dns_resource_record_to_string() call: cache the formatted string as
part of the object, and return it on subsequent calls, freeing it when
the DnsResourceRecord itself is freed.
If there are multiple SOA RRs, and we look for a suitable one covering
our request, then make sure to pick the one that is furthest away from
the root name, not just the first one we encounter.
Let's make sure we propagate the DNSSEC validation status from an
auxiliary DNSSEC transaction back to the originating transaction, to
improve the error messages we generate.
We have many types of failure for a transaction, and
DNS_TRANSACTION_FAILURE was just one specific one of them, if the server
responded with a non-zero RCODE. Hence let's rename this, to indicate
which kind of failure this actually refers to.
This adds a new DnsAnswer item flag "DNS_ANSWER_SHARED_OWNER" which is
set for mDNS RRs that lack the cache-flush bit. The cache-flush bit is
removed from the DnsResourceRecord object in favour of this.
This also splits out the code that removes previous entries when adding
new positive ones into a new separate call dns_cache_remove_previous().
Let's use dns_cache_remove() rather than
dns_cache_item_remove_and_free() to destroy the cache, since the former
requires far fewer hash table lookups.
When we receieve a TTL=0 RR, then let's only flush that specific RR and
not the whole RRset.
On mDNS with RRsets that a shared-owner this is how specific RRs are
removed from the set, hence support this. And on non-mDNS the whole
RRset will already be removed much earlier in dns_cache_put() hence
there's no reason remove it again.
