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appc,feature/conn25: prevent clients from forwarding DNS requests and

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modifying DNS responses for domains they are also connectors for

For Connectors 2025, determine if a client is configured as a
connector and what domains it is a connector for. When acting as a
client, don't install Split DNS routes to other connectors for those
domains, and don't alter DNS responses for those domains. The responses
are forwarded back to the original client, which in turn does the alteration,
swapping the real IP for a Magic IP.

A client is also a connector for a domain if it has tags that overlap
with tags in the configured policy, and --advertise-connector=true
in the prefs (not in the self-node Hostinfo from the netmap). We use the prefs
as the source of truth because control only gets a copy from the prefs, and
may drift. And the AppConnector field is currently zeroed out in the
self-node Hostinfo from control.

The extension adds a ProfileStateChange hook to process prefs changes,
and the config type is split into prefs and nodeview sub-configs.

Fixes tailscale/corp#39317

Signed-off-by: Michael Ben-Ami <mzb@tailscale.com>
This commit is contained in:
Michael Ben-Ami
2026-04-07 15:54:52 -04:00
committed by mzbenami
parent 4f47c3c93d
commit 1dc08f4d41
5 changed files with 437 additions and 121 deletions
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appc/conn25.go
+18 -5
View File
@@ -16,7 +16,7 @@ import (
const AppConnectorsExperimentalAttrName = "tailscale.com/app-connectors-experimental"
func isEligibleConnector(peer tailcfg.NodeView) bool {
func isPeerEligibleConnector(peer tailcfg.NodeView) bool {
if !peer.Valid() || !peer.Hostinfo().Valid() {
return false
}
@@ -39,7 +39,7 @@ func sortByPreference(ns []tailcfg.NodeView) {
func PickConnector(nb ipnext.NodeBackend, app appctype.Conn25Attr) []tailcfg.NodeView {
appTagsSet := set.SetOf(app.Connectors)
matches := nb.AppendMatchingPeers(nil, func(n tailcfg.NodeView) bool {
if !isEligibleConnector(n) {
if !isPeerEligibleConnector(n) {
return false
}
for _, t := range n.Tags().All() {
@@ -55,7 +55,7 @@ func PickConnector(nb ipnext.NodeBackend, app appctype.Conn25Attr) []tailcfg.Nod
// PickSplitDNSPeers looks at the netmap peers capabilities and finds which peers
// want to be connectors for which domains.
func PickSplitDNSPeers(hasCap func(c tailcfg.NodeCapability) bool, self tailcfg.NodeView, peers map[tailcfg.NodeID]tailcfg.NodeView) map[string][]tailcfg.NodeView {
func PickSplitDNSPeers(hasCap func(c tailcfg.NodeCapability) bool, self tailcfg.NodeView, peers map[tailcfg.NodeID]tailcfg.NodeView, isSelfEligibleConnector bool) map[string][]tailcfg.NodeView {
var m map[string][]tailcfg.NodeView
if !hasCap(AppConnectorsExperimentalAttrName) {
return m
@@ -65,21 +65,34 @@ func PickSplitDNSPeers(hasCap func(c tailcfg.NodeCapability) bool, self tailcfg.
return m
}
tagToDomain := make(map[string][]string)
selfTags := set.SetOf(self.Tags().AsSlice())
selfRoutedDomains := set.Set[string]{}
for _, app := range apps {
for _, tag := range app.Connectors {
tagToDomain[tag] = append(tagToDomain[tag], app.Domains...)
domains := tagToDomain[tag]
domains = slices.Grow(domains, len(app.Domains))
for _, d := range app.Domains {
if isSelfEligibleConnector && selfTags.Contains(tag) {
selfRoutedDomains.Add(d)
}
domains = append(domains, d)
}
tagToDomain[tag] = domains
}
}
// NodeIDs are Comparable, and we have a map of NodeID to NodeView anyway, so
// use a Set of NodeIDs to deduplicate, and populate into a []NodeView later.
var work map[string]set.Set[tailcfg.NodeID]
for _, peer := range peers {
if !isEligibleConnector(peer) {
if !isPeerEligibleConnector(peer) {
continue
}
for _, t := range peer.Tags().All() {
domains := tagToDomain[t]
for _, domain := range domains {
if selfRoutedDomains.Contains(domain) {
continue
}
if work[domain] == nil {
mak.Set(&work, domain, set.Set[tailcfg.NodeID]{})
}