tailscale/ipn/ipnlocal/expiry.go

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// Copyright (c) 2023 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ipnlocal
import (
"time"
"tailscale.com/syncs"
"tailscale.com/tailcfg"
"tailscale.com/types/key"
"tailscale.com/types/logger"
"tailscale.com/types/netmap"
)
// For extra defense-in-depth, when we're testing expired nodes we check
// ControlTime against this 'epoch' (set to the approximate time that this code
// was written) such that if control (or Headscale, etc.) sends a ControlTime
// that's sufficiently far in the past, we can safely ignore it.
var flagExpiredPeersEpoch = time.Unix(1673373066, 0)
// If the offset between the current time and the time received from control is
// larger than this, we store an offset in our expiryManager to adjust future
// clock timings.
const minClockDelta = 1 * time.Minute
// expiryManager tracks the state of expired nodes and the delta from the
// current clock time to the time returned from control, and allows mutating a
// netmap to mark peers as expired based on the current delta-adjusted time.
type expiryManager struct {
// previouslyExpired stores nodes that have already expired so we can
// only log on state transitions.
previouslyExpired map[tailcfg.StableNodeID]bool
// clockDelta stores the delta between the current time and the time
// received from control such that:
// time.Now().Add(clockDelta) == MapResponse.ControlTime
clockDelta syncs.AtomicValue[time.Duration]
logf logger.Logf
timeNow func() time.Time
}
func newExpiryManager(logf logger.Logf) *expiryManager {
return &expiryManager{
previouslyExpired: map[tailcfg.StableNodeID]bool{},
logf: logf,
timeNow: time.Now,
}
}
// onControlTime is called whenever we receive a new timestamp from the control
// server to store the delta.
func (em *expiryManager) onControlTime(t time.Time) {
localNow := em.timeNow()
delta := t.Sub(localNow)
if delta.Abs() > minClockDelta {
em.logf("[v1] netmap: flagExpiredPeers: setting clock delta to %v", delta)
em.clockDelta.Store(delta)
} else {
em.clockDelta.Store(0)
}
}
// flagExpiredPeers updates mapRes.Peers, mutating all peers that have expired,
// taking into account any clock skew detected by using the ControlTime field
// in the MapResponse. We don't actually remove expired peers from the Peers
// array; instead, we clear some fields of the Node object, and set
// Node.Expired so other parts of the codebase can provide more clear error
// messages when attempting to e.g. ping an expired node.
//
// This is additionally a defense-in-depth against something going wrong with
// control such that we start seeing expired peers with a valid Endpoints or
// DERP field.
//
// This function is safe to call concurrently with onControlTime but not
// concurrently with any other call to flagExpiredPeers.
func (em *expiryManager) flagExpiredPeers(netmap *netmap.NetworkMap) {
localNow := em.timeNow()
// Adjust our current time by any saved delta to adjust for clock skew.
controlNow := localNow.Add(em.clockDelta.Load())
if controlNow.Before(flagExpiredPeersEpoch) {
em.logf("netmap: flagExpiredPeers: [unexpected] delta-adjusted current time is before hardcoded epoch; skipping")
return
}
for _, peer := range netmap.Peers {
// Nodes that don't expire have KeyExpiry set to the zero time;
// skip those and peers that are already marked as expired
// (e.g. from control).
if peer.KeyExpiry.IsZero() || peer.KeyExpiry.After(controlNow) {
delete(em.previouslyExpired, peer.StableID)
continue
} else if peer.Expired {
continue
}
if !em.previouslyExpired[peer.StableID] {
em.logf("[v1] netmap: flagExpiredPeers: clearing expired peer %v", peer.StableID)
em.previouslyExpired[peer.StableID] = true
}
// Actually mark the node as expired
peer.Expired = true
// Control clears the Endpoints and DERP fields of expired
// nodes; do so here as well. The Expired bool is the correct
// thing to set, but this replicates the previous behaviour.
//
// NOTE: this is insufficient to actually break connectivity,
// since we discover endpoints via DERP, and due to DERP return
// path optimization.
peer.Endpoints = nil
peer.DERP = ""
// Defense-in-depth: break the node's public key as well, in
// case something tries to communicate.
peer.Key = key.NodePublicWithBadOldPrefix(peer.Key)
}
}