With cache_enable = true, one cache entry was shared by every client
asking the same name against the same upstream: the cache key
({Qtype, Qclass, Name, Upstream}) and the osResolver hot-cache/singleflight
key ("name:qtype:") both ignored the EDNS Client Subnet (ECS). A response
tailored for subnet A was therefore served to subnet B.
A cached answer's records are scoped to the network that generated them
(RFC 7871 §7.3), so sharing them across subnets returns the wrong
CDN/policy answer. Rewriting only the ECS option on the shared answer is
worse: forwarders that validate the echoed ECS (e.g. dnsmasq with
add-subnet) then accept the wrong-subnet answer instead of rejecting it as
a mismatch.
Partition both cache paths by a canonical ECS tuple (family, source-prefix,
masked address) via the new dnscache.CanonicalECS: the LRU key gains an ECS
field and the singleflight/hot-cache key appends the canonical ECS. Same
subnet still shares an entry; different subnets (or address families) never
do. Only a request with no ECS option collapses to the shared empty
partition; a carried /0 keeps its own family-scoped token, since it is
forwarded with an ECS option and must stay distinguishable from a no-ECS
query (RFC 7871 §7.3.1). SetCacheReply no longer touches ECS and only
reconciles the EDNS Cookie.
Adds real cache-path regression tests (LRU and osResolver hot cache) that
serve a different A record per subnet and verify the second subnet never
receives the first's record.
Fixes https://github.com/Control-D-Inc/ctrld/issues/324
For cached or singleflight messages, the edns0 cookie is currently
shared among all of them, causing mismatch cookie warning from clients.
The ctrld proxy should re-set client cookies for each request
separately, even though they use the same shared answer.
Cuong Manh Le