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rekey_fsm.go
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rekey_fsm.go
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// Copyright 2017 Keybase Inc. All rights reserved.
// Use of this source code is governed by a BSD
// license that can be found in the LICENSE file.
package libkbfs
import (
"context"
"fmt"
"sync"
"time"
"github.com/keybase/client/go/kbfs/data"
"github.com/keybase/client/go/kbfs/kbfssync"
"github.com/keybase/client/go/kbfs/tlf"
"github.com/keybase/client/go/logger"
)
/*
This file defines a finite state machine (FSM) for rekey operation scheduling.
The state chart is described in following dot graph:
digraph rekeyFSM {
graph [rankdir=LR]
start [shape=plaintext]
Idle -> Idle [label="*"]
Scheduled -> Scheduled [label="*"]
Started -> Started [label="*"]
start -> Idle
Idle -> Scheduled [label=Request]
Scheduled -> Scheduled [label="Request,RekeyNotNeeded"]
Scheduled -> Started [label=Timeup]
Started -> Scheduled [label="Finished(TTL valid && (rekey done || needs paper))"]
Started -> Idle [label="Finished (*)"]
}
*/
// CtxRekeyTagKey is the type used for unique context tags within an
// enqueued Rekey.
type CtxRekeyTagKey int
const (
// CtxRekeyIDKey is the type of the tag for unique operation IDs
// within an enqueued Rekey.
CtxRekeyIDKey CtxRekeyTagKey = iota
)
// CtxRekeyOpID is the display name for the unique operation
// enqueued rekey ID tag.
const CtxRekeyOpID = "REKEYID"
type rekeyEventType int
const (
_ rekeyEventType = iota
rekeyRequestEvent
rekeyFinishedEvent
rekeyTimeupEvent
rekeyNotNeededEvent
rekeyKickoffEvent
rekeyShutdownEvent
rekeyCancelEventForTest
)
func (e rekeyEventType) String() string {
switch e {
case rekeyRequestEvent:
return "rekeyRequestEvent"
case rekeyFinishedEvent:
return "rekeyFinishedEvent"
case rekeyTimeupEvent:
return "rekeyTimeupEvent"
case rekeyNotNeededEvent:
return "rekeyNotNeededEvent"
case rekeyShutdownEvent:
return "rekeyShutdownEvent"
case rekeyKickoffEvent:
return "rekeyKickoffEvent"
case rekeyCancelEventForTest:
return "rekeyCancelEventForTest"
default:
return "unknown"
}
}
// rekeyTask describes a rekey task.
type rekeyTask struct {
// timeout, if non-nil, causes rekey to fail if it takes more than this
// duration since it enters rekeyStateStarted.
timeout *time.Duration
ttl int
promptPaper bool
ctx *protectedContext
}
// rekeyRequest describes a rekey request.
type rekeyRequest struct {
// delay is the duration to wait for since the request enters the FSM until
// starting the rekey.
delay time.Duration
rekeyTask
}
// rekeyFinished describes a rekeyFinishedEvent. It contains results from an
// actual rekey operation.
type rekeyFinished struct {
RekeyResult
err error
}
// RekeyEvent describes an event to send into the RekeyFSM. A function, e.g.,
// NewRekeyRequestEvent, should be used to construct one.
type RekeyEvent struct {
eventType rekeyEventType
request *rekeyRequest
finished *rekeyFinished
}
func (e RekeyEvent) String() string {
switch e.eventType {
case rekeyRequestEvent:
return fmt.Sprintf("%s [%#+v]", e.eventType, e.request)
case rekeyFinishedEvent:
return fmt.Sprintf("%s [%#+v]", e.eventType, e.finished)
default:
return e.eventType.String()
}
}
func newRekeyRequestEvent(req rekeyRequest) RekeyEvent {
return RekeyEvent{
eventType: rekeyRequestEvent,
request: &req,
}
}
func newRekeyRequestEventWithContext(ctx context.Context) RekeyEvent {
return newRekeyRequestEvent(rekeyRequest{
delay: 0,
rekeyTask: rekeyTask{
timeout: nil,
promptPaper: false,
ttl: rekeyInitialTTL,
ctx: newProtectedContext(ctx, nil),
},
})
}
// NewRekeyRequestWithPaperPromptEvent creates a non-delayed rekey request
// Event that causes a paper prompt.
func NewRekeyRequestWithPaperPromptEvent() RekeyEvent {
e := NewRekeyRequestEvent()
d := rekeyWithPromptWaitTimeDefault
e.request.promptPaper = true
e.request.timeout = &d
return e
}
// NewRekeyRequestEvent creates a non-delayed rekey request Event.
func NewRekeyRequestEvent() RekeyEvent {
return newRekeyRequestEventWithContext(CtxWithRandomIDReplayable(
context.Background(), CtxRekeyIDKey, CtxRekeyOpID, nil))
}
// NewRekeyNotNeededEvent creates a rekeyNotNeededEvent typed event. If the FSM
// is in rekeyStateScheduled, this causes FSM to unset paperkey prompt. In
// other states nothing happens. This event is sent to the FSM when we see a MD
// update with rekey flag unset. It can be an indication that an old
// outstanding rekey request has been served by another device, or just a
// regular rekey updates.
func NewRekeyNotNeededEvent() RekeyEvent {
return RekeyEvent{
eventType: rekeyNotNeededEvent,
}
}
func newRekeyFinishedEvent(res RekeyResult, err error) RekeyEvent {
return RekeyEvent{
eventType: rekeyFinishedEvent,
finished: &rekeyFinished{
RekeyResult: res,
err: err,
},
}
}
func newRekeyTimeupEvent() RekeyEvent {
return RekeyEvent{
eventType: rekeyTimeupEvent,
}
}
func newRekeyShutdownEvent() RekeyEvent {
return RekeyEvent{
eventType: rekeyShutdownEvent,
}
}
func newRekeyKickoffEvent() RekeyEvent {
return RekeyEvent{
eventType: rekeyKickoffEvent,
}
}
func newRekeyCancelEventForTest() RekeyEvent {
return RekeyEvent{
eventType: rekeyCancelEventForTest,
}
}
// rekeyState models a state in the FSM. rekeyFSM keeps exactly one instance of
// rekeyState at any given time.
type rekeyState interface {
// reactToEvent defines how this state reacts to an event. Implementations of
// rekeyState should handle necessary transition actions in reactToEvent(),
// and return a new rekeyState instance after transition is finished.
// rekeyFSM sends event to the rekeyState instance it holds whenever it
// receives an event, and use the returned rekeyState instance as new state.
// It's OK to return the receiver itself as "new" state.
//
// rekeyFSM runs an event loop in a dedicated goroutine that calls
// reactToEvent and updates states. In other words, it's safe to assume
// reactToEvent is only called within the same goroutine, and that it's
// impossible that multiple reactToEvent calls are issued concurrently.
reactToEvent(event RekeyEvent) rekeyState
}
type rekeyStateIdle struct {
fsm *rekeyFSM
}
func newRekeyStateIdle(fsm *rekeyFSM) *rekeyStateIdle {
return &rekeyStateIdle{fsm: fsm}
}
func (r *rekeyStateIdle) reactToEvent(event RekeyEvent) rekeyState {
switch event.eventType {
case rekeyRequestEvent:
return newRekeyStateScheduled(r.fsm,
event.request.delay, event.request.rekeyTask)
default:
return r
}
}
type rekeyStateScheduled struct {
fsm *rekeyFSM
timer *time.Timer
deadline time.Time
task rekeyTask
}
func newRekeyStateScheduled(
fsm *rekeyFSM, delay time.Duration, task rekeyTask) *rekeyStateScheduled {
task.ctx.setLogger(fsm.log)
return &rekeyStateScheduled{
fsm: fsm,
timer: time.AfterFunc(delay, func() {
fsm.Event(newRekeyTimeupEvent())
}),
deadline: time.Now().Add(delay),
task: task,
}
}
func (r *rekeyStateScheduled) reactToEvent(event RekeyEvent) rekeyState {
switch event.eventType {
case rekeyTimeupEvent:
// This blocks (which inheritently blocks the entire FSM) if too many
// are active.
if r.fsm.fbo.config.GetRekeyFSMLimiter().WaitToStart(
r.task.ctx.context()) != nil {
return r
}
return newRekeyStateStarted(r.fsm, r.task)
case rekeyRequestEvent:
if r.task.promptPaper && !event.request.promptPaper {
// KBFS-2251: If fbo concludes that paper key would be needed in
// order for rekey to proceed, it writes a MD to mdserver with
// rekey set at the same time. To prevent the FSM from being kicked
// of to rekeyStateStarted right away after receiving this update
// (through FoldersNeedRekey) from mdserver, we just reuse the same
// timer if r.task.promptPaper is set.
//
// If the request has promptPaper set, then it's from the KBFS
// client, likely due to a read request. In this case, we should
// shorten the wait timer according the the request.
r.fsm.log.CDebugf(r.task.ctx.context(), "Reusing existing timer "+
"without possibly shortening due to r.task.promptPaper==true")
return r
}
task := r.task
task.promptPaper = task.promptPaper || event.request.promptPaper
if task.timeout == nil {
task.timeout = event.request.timeout
}
task.ttl = event.request.ttl
task.ctx.maybeReplaceContext(event.request.ctx.context())
if !r.deadline.After(time.Now().Add(event.request.delay)) {
r.fsm.log.CDebugf(task.ctx.context(), "Reusing existing timer")
r.task = task
return r
}
r.timer.Stop()
return newRekeyStateScheduled(r.fsm, event.request.delay, task)
case rekeyNotNeededEvent:
// KBFS-2254: if another device finished rekey, we should unset the
// paperkey prompt so that if this other device goes offline before a
// third device triggers a rekey request, the timer can be preempted.
// What if the FoldersNeedRekey call comes in before this and we still
// miss the rekey request? Well now we also send a rekey request into
// the FSM on MD updates with rekey flag set. Since the MD updates are
// applied in order, and that FSM's state transition is
// single-goroutined, we are safe here.
r.task.promptPaper = false
return r
case rekeyKickoffEvent:
r.timer.Reset(time.Millisecond)
return r
case rekeyCancelEventForTest:
r.timer.Stop()
return newRekeyStateIdle(r.fsm)
case rekeyShutdownEvent:
r.timer.Stop()
return r
default:
return r
}
}
type rekeyStateStarted struct {
fsm *rekeyFSM
task rekeyTask
}
func newRekeyStateStarted(fsm *rekeyFSM, task rekeyTask) *rekeyStateStarted {
ctx := task.ctx.context()
var cancel context.CancelFunc
if task.timeout != nil {
ctx, cancel = context.WithTimeout(task.ctx.context(), *task.timeout)
}
go func() {
defer fsm.fbo.config.GetRekeyFSMLimiter().Done()
if cancel != nil {
defer cancel()
}
fsm.log.CDebugf(ctx, "Processing rekey for %s", fsm.fbo.folderBranch.Tlf)
var res RekeyResult
err := fsm.fbo.doMDWriteWithRetryUnlessCanceled(ctx,
func(lState *kbfssync.LockState) (err error) {
res, err = fsm.fbo.rekeyLocked(ctx, lState, task.promptPaper)
return err
})
fsm.log.CDebugf(ctx, "Rekey finished with res=%#+v, error=%v", res, err)
fsm.Event(newRekeyFinishedEvent(res, err))
}()
return &rekeyStateStarted{
fsm: fsm,
task: task,
}
}
func (r *rekeyStateStarted) reactToEvent(event RekeyEvent) rekeyState {
switch event.eventType {
case rekeyFinishedEvent:
ttl := r.task.ttl - 1
r.fsm.log.CDebugf(r.task.ctx.context(),
"Rekey finished, ttl: %d -> %d", r.task.ttl, ttl)
if ttl <= 0 {
r.fsm.log.CDebugf(r.task.ctx.context(),
"Not scheduling new rekey because TTL expired")
return newRekeyStateIdle(r.fsm)
}
switch event.finished.err {
case nil:
default:
r.fsm.log.CDebugf(r.task.ctx.context(),
"Rekey errored; scheduling new rekey in %s", rekeyRecheckInterval)
return newRekeyStateScheduled(r.fsm, rekeyRecheckInterval, rekeyTask{
timeout: r.task.timeout,
promptPaper: r.task.promptPaper,
ttl: ttl,
ctx: r.task.ctx,
})
}
d := r.fsm.fbo.config.RekeyWithPromptWaitTime()
if event.finished.NeedsPaperKey {
r.fsm.log.CDebugf(r.task.ctx.context(),
"Scheduling rekey due to NeedsPaperKey==true")
return newRekeyStateScheduled(r.fsm, d, rekeyTask{
timeout: &d,
promptPaper: true,
ttl: ttl,
ctx: r.task.ctx,
})
}
if event.finished.DidRekey {
// We enqueue the rekey here again, in case we missed a device due to a
// race condition. This is specifically for the situation where user
// provisions two devices in a row, and the key update for the 2nd device
// only comes in after rekey for a TLF is done, which didn't include the
// second device. At this point, there wouldn't be a new MD with rekey
// bit set since it's already set. As a result, the TLF won't get rekeyed
// for the second device until the next 1-hour timer triggers another
// scan.
r.fsm.log.CDebugf(r.task.ctx.context(),
"Scheduling rekey (recheck) due to DidRekey==true")
return newRekeyStateScheduled(r.fsm, rekeyRecheckInterval, rekeyTask{
timeout: nil,
promptPaper: false,
ttl: ttl,
ctx: r.task.ctx,
})
}
r.fsm.log.CDebugf(r.task.ctx.context(),
"Not scheduling rekey because no more rekeys or rechecks are needed")
return newRekeyStateIdle(r.fsm)
default:
return r
}
}
type rekeyFSMListener struct {
repeatedly bool
onEvent func(RekeyEvent)
}
type rekeyFSM struct {
shutdownCh chan struct{}
reqs chan RekeyEvent
fbo *folderBranchOps
log logger.Logger
current rekeyState
muListeners sync.Mutex
listeners map[rekeyEventType][]rekeyFSMListener
}
// NewRekeyFSM creates a new rekey FSM.
func NewRekeyFSM(fbo *folderBranchOps) RekeyFSM {
fsm := &rekeyFSM{
reqs: make(chan RekeyEvent, fbo.config.Mode().RekeyQueueSize()),
shutdownCh: make(chan struct{}),
fbo: fbo,
log: fbo.config.MakeLogger("RekeyFSM"),
listeners: make(map[rekeyEventType][]rekeyFSMListener),
}
fsm.current = newRekeyStateIdle(fsm)
if fbo.bType == standard {
go fsm.loop()
}
return fsm
}
func (m *rekeyFSM) loop() {
reqs := m.reqs
for {
select {
case e := <-reqs:
next := m.current.reactToEvent(e)
if e.eventType == rekeyShutdownEvent {
// Set reqs to nil so on next iteration, we will skip any
// content in reqs. So if there are multiple
// rekeyShutdownEvent, we won't close m.shutdownCh multiple
// times.
reqs = nil
close(m.shutdownCh)
} else {
// Only log if we're not shutting down, otherwise `go vet`
// yells at us in tests.
m.log.Debug("RekeyFSM transition: %T + %s -> %T",
m.current, e, next)
}
m.current = next
m.triggerCallbacksForTest(e)
case <-m.shutdownCh:
return
}
}
}
// Event implements RekeyFSM interface for rekeyFSM.
func (m *rekeyFSM) Event(event RekeyEvent) {
select {
case m.reqs <- event:
case <-m.shutdownCh:
}
}
// Shutdown implements RekeyFSM interface for rekeyFSM.
func (m *rekeyFSM) Shutdown() {
m.Event(newRekeyShutdownEvent())
}
func (m *rekeyFSM) triggerCallbacksForTest(e RekeyEvent) {
var cbs []rekeyFSMListener
func() {
m.muListeners.Lock()
defer m.muListeners.Unlock()
cbs = m.listeners[e.eventType]
m.listeners[e.eventType] = nil
for _, cb := range cbs {
if cb.repeatedly {
m.listeners[e.eventType] = append(
m.listeners[e.eventType], cb)
}
}
}()
for _, cb := range cbs {
cb.onEvent(e)
}
}
// listenOnEvent implements RekeyFSM interface for rekeyFSM.
func (m *rekeyFSM) listenOnEvent(
event rekeyEventType, callback func(RekeyEvent), repeatedly bool) {
m.muListeners.Lock()
defer m.muListeners.Unlock()
m.listeners[event] = append(m.listeners[event], rekeyFSMListener{
onEvent: callback,
repeatedly: repeatedly,
})
}
func getRekeyFSM(ctx context.Context, ops KBFSOps, tlfID tlf.ID) RekeyFSM {
switch o := ops.(type) {
case *KBFSOpsStandard:
return o.getOpsNoAdd(
ctx, data.FolderBranch{
Tlf: tlfID,
Branch: data.MasterBranch,
}).rekeyFSM
default:
panic("unknown KBFSOps")
}
}
// RequestRekeyAndWaitForOneFinishEvent sends a rekey request to the FSM
// associated with tlfID, and wait for exact one rekeyFinished event. This can
// be useful for waiting for a rekey result in tests.
//
// Note that the supplied ctx is injected to the rekey task, so canceling ctx
// would actually cancel the rekey.
//
// Currently this is only used in tests and RekeyFile. Normal rekey activities
// should go through the FSM asychronously.
func RequestRekeyAndWaitForOneFinishEvent(ctx context.Context,
ops KBFSOps, tlfID tlf.ID) (res RekeyResult, err error) {
fsm := getRekeyFSM(ctx, ops, tlfID)
rekeyWaiter := make(chan struct{})
fsm.listenOnEvent(rekeyFinishedEvent, func(e RekeyEvent) {
res = e.finished.RekeyResult
err = e.finished.err
close(rekeyWaiter)
}, false)
fsm.Event(newRekeyRequestEventWithContext(ctx))
<-rekeyWaiter
return res, err
}