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wgengine, ipn/ipnlocal: route PeerForIP through LocalBackend's live data

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userspaceEngine.PeerForIP read from e.netMap.Peers and
e.lastCfgFull.Peers, both of which go stale when peers arrive via
netmap deltas (which skip Engine.SetNetworkMap and Engine.Reconfig).
Every PeerForIP caller (Engine.Ping, the TSMP disco-key handler,
pendopen diagnostics, tsdial.Dialer.UseNetstackForIP, and
LocalBackend.GetPeerEndpointChanges) would report "no matching peer"
for freshly-added peers.

Fix it the same way SetPeerByIPPacketFunc fixed the outbound packet
hot path: have LocalBackend install a callback that reads the live
nodeBackend. nb.NodeByAddr is built from both SelfNode and Peers
(updateNodeByAddrLocked), so a single lookup covers the common case
with IsSelf set when the matched node ID is SelfNode's. The subnet-
route / exit-node-default-route slow path goes through a new
Engine.PeerKeyForIP that exposes the engine's AllowedIPs BART table
(the same table the outbound packet hot path already consults, with
exit-node selection honored), and resolves the matched key back to a
NodeView via the live nodeBackend.

Updates #12542

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I0d4b0d8997c8e796b7367c46b49b61d4fdc717b0
This commit is contained in:
Brad Fitzpatrick
2026-06-23 14:37:15 -07:00
committed by Brad Fitzpatrick
parent e9ae398199
commit d4f2917c1b
5 changed files with 392 additions and 58 deletions
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wgengine/wgengine.go
+37 -1
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@@ -100,9 +100,45 @@ type Engine interface {
ResetAndStop() (*Status, error)
// PeerForIP returns the node to which the provided IP routes,
// if any. If none is found, (nil, false) is returned.
// if any. If none is found, (zero, false) is returned.
//
// Despite the name, it can return the self node (with
// PeerForIP.IsSelf set). It handles Tailscale IPs, subnet-routed
// IPs, and exit-node global internet IPs, returning whichever
// node would handle that traffic.
//
// This is the cold path used by Ping, TSMP, pendopen diagnostics,
// and debug endpoints. It uses the same underlying data structures
// as the wireguard-go outbound packet path
// ([Engine.SetPeerByIPPacketFunc]), but is slower because it
// returns richer data (a full NodeView, the matched route prefix,
// and the IsSelf flag) requiring extra lookups.
//
// In production, the lookup is implemented by LocalBackend and
// plumbed in via [Engine.SetPeerForIPFunc]; the engine itself holds
// no peer-lookup state on this path.
PeerForIP(netip.Addr) (_ PeerForIP, ok bool)
// SetPeerForIPFunc installs a callback used by [Engine.PeerForIP].
// It parallels [Engine.SetPeerByIPPacketFunc] but serves the
// cold-path control lookups (Ping, TSMP, pendopen diagnostics,
// [tsdial.Dialer.UseNetstackForIP], debug endpoints).
//
// If fn is nil, PeerForIP returns (zero, false) for every IP.
//
// LocalBackend installs a func backed by the live nodeBackend for
// exact-match and self addresses, with [Engine.PeerKeyForIP]
// supplying the subnet-route / exit-node fallback.
SetPeerForIPFunc(fn func(netip.Addr) (_ PeerForIP, ok bool))
// PeerKeyForIP returns the peer's NodePublic and the matched prefix
// for the longest-prefix match of ip in the engine's AllowedIPs
// table (the wireguard config most recently installed via
// [Engine.Reconfig]). Exit-node selection is honored: an unselected
// exit node's 0.0.0.0/0 is not matched. It is the same table the
// outbound packet hot path consults via [Engine.SetPeerByIPPacketFunc].
PeerKeyForIP(netip.Addr) (_ key.NodePublic, _ netip.Prefix, ok bool)
// GetFilter returns the current packet filter, if any.
GetFilter() *filter.Filter