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types: consider subnet routes as source identity in ACL matching

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CanAccess and CanAccessRoute only used a node's Tailscale IPs as
source identity when matching ACL rules. A subnet router acting on
behalf of its advertised subnets was invisible to ACLs that reference
subnet CIDRs as source (e.g. src=10.88.8.0/24 dst=10.99.9.0/24).

Extend both functions to also check whether the node's approved
subnet routes overlap the matcher's source set. This makes subnet
routers visible to each other when ACLs reference their subnet CIDRs,
enabling subnet-to-subnet traffic routing.

The new checks are guarded by len(subnetRoutes) > 0, so non-router
nodes (the vast majority) pay zero additional cost.

Fixes #3157
This commit is contained in:
Ubuntu
2026-04-02 13:23:23 +00:00
parent 45d5544736
commit ea85dcbc14
1 changed files with 49 additions and 13 deletions
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hscontrol/types/node.go
+49 -13
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@@ -324,23 +324,39 @@ func (node *Node) CanAccess(matchers []matcher.Match, node2 *Node) bool {
allowedIPs := node2.IPs()
for _, matcher := range matchers {
if !matcher.SrcsContainsIPs(src...) {
continue
if matcher.SrcsContainsIPs(src...) {
if matcher.DestsContainsIP(allowedIPs...) {
return true
}
// Check if the node has access to routes that might be part of a
// smaller subnet that is served from node2 as a subnet router.
if matcher.DestsOverlapsPrefixes(node2.SubnetRoutes()...) {
return true
}
// If the dst is "the internet" and node2 is an exit node, allow access.
if matcher.DestsIsTheInternet() && node2.IsExitNode() {
return true
}
}
if matcher.DestsContainsIP(allowedIPs...) {
return true
}
// A subnet router acts on behalf of its advertised subnets.
// If the node's approved subnet routes overlap the source set,
// check whether node2 (or its subnets) is in the destination set.
if srcRoutes := node.SubnetRoutes(); len(srcRoutes) > 0 &&
matcher.SrcsOverlapsPrefixes(srcRoutes...) {
if matcher.DestsContainsIP(allowedIPs...) {
return true
}
// Check if the node has access to routes that might be part of a
// smaller subnet that is served from node2 as a subnet router.
if matcher.DestsOverlapsPrefixes(node2.SubnetRoutes()...) {
return true
}
if matcher.DestsOverlapsPrefixes(node2.SubnetRoutes()...) {
return true
}
// If the dst is "the internet" and node2 is an exit node, allow access.
if matcher.DestsIsTheInternet() && node2.IsExitNode() {
return true
if matcher.DestsIsTheInternet() && node2.IsExitNode() {
return true
}
}
}
@@ -349,6 +365,7 @@ func (node *Node) CanAccess(matchers []matcher.Match, node2 *Node) bool {
func (node *Node) CanAccessRoute(matchers []matcher.Match, route netip.Prefix) bool {
src := node.IPs()
subnetRoutes := node.SubnetRoutes()
for _, matcher := range matchers {
if matcher.SrcsContainsIPs(src...) && matcher.DestsOverlapsPrefixes(route) {
@@ -358,6 +375,25 @@ func (node *Node) CanAccessRoute(matchers []matcher.Match, route netip.Prefix) b
if matcher.SrcsOverlapsPrefixes(route) && matcher.DestsContainsIP(src...) {
return true
}
// A subnet router acts on behalf of its advertised subnets.
// If the node's approved subnet routes overlap the source set
// and the route overlaps the destination set, the router needs
// this route to forward traffic from its local subnet.
if len(subnetRoutes) > 0 {
if matcher.SrcsOverlapsPrefixes(subnetRoutes...) &&
matcher.DestsOverlapsPrefixes(route) {
return true
}
// Reverse: traffic from the route's subnet is destined for
// this node's subnets; the router needs the route for return
// traffic.
if matcher.SrcsOverlapsPrefixes(route) &&
matcher.DestsOverlapsPrefixes(subnetRoutes...) {
return true
}
}
}
return false