Lennart Poettering
775ae35403
This substantially beefs up the local DNS stub feature set in order to allow local clients to do DNSSEC validation through the stub. Previously we'd return NOTIMP if we'd get a DO or DO+CD lookup. With this change we'll instead: 1. If we get DO+CD requests (i.e. DNSSEC with no local checking) we'll proxy DNS queries and response mostly unmodified to/from upstream DNS servers if possible (this is called "bypass" mode). We will patch in new request IDs, (and patch them back out on reply), so that we can sanely keep track of things. We'll also maintain a minimal local cache for such lookups, always keeping the whole DNS packets in it (if we reply from cache we'll patch the TTLs of all included RRs). 2. If we get DO requests without CD (i.e. DNSSEC with local checking) we'll resolve and validate locally. In this mode we will not proxy packets, but generate our own. We will however cache the combination of answer RRs (along with their packet section assignments) we got back in the cache, and use this information to generate reply packets from the DNS stub. In both cases: if we determine a lookup is to be answered from LLMNR or mDNS we'll always revert to non-DNSSEC, non-proxy operation as before. Answers will lack the DO bit then, since the data cannot be validated via DNSSEC by the clients. To make this logic more debuggable, this also adds query flags for turning off RR sources. i.e. cache/network/zone/trust anchor/local synthesis may now be disabled individually for each lookup. The cache is substantially updated to make all this work: in addition to caching simple RRs for lookup RR keys, we'll now cache the whole packets and the whole combination of RRs, so that we can answer DO and DO+CD replies sensibly according to the rules described above. This sounds wasteful, but given that the DnsResourceRecord/DnsResourceKey/DnsAnswer/DnsPacket objects are all ref-counted and we try to merge references the actual additional memory used should be limited (but this might be something to optimize further later on). To implement classic RR key lookups and new-style packet proxy lookups (i.e. the ones necessary for DO+CD packet proxying, as described above) DnsTransaction and DnsQuery objects now always maintain either a DnsResourceKey/DnsQuestion as lookup key or a DnsPacket for "bypass" mode. Fixes: #4621 #17218
System and Service Manager
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