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ipnlocal: accept a new opts.UpdatePrefs field.

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This is needed because the original opts.Prefs field was at some point
subverted for use in frontend->backend state migration for backward
compatibility on some platforms. We still need that feature, but we
also need the feature of providing the full set of prefs from
`tailscale up`, *not* including overwriting the prefs.Persist keys, so
we can't use the original field from `tailscale up`.

`tailscale up` had attempted to compensate for that by doing SetPrefs()
before Start(), but that violates the ipn.Backend contract, which says
you should call Start() before anything else (that's why it's called
Start()). As a result, doing SetPrefs({ControlURL=...,
WantRunning=true}) would cause a connection to the *previous* control
server (because WantRunning=true), and then connect to the *new*
control server only after running Start().

This problem may have been avoided before, but only by pure luck.

It turned out to be relatively harmless since the connection to the old
control server was immediately closed and replaced anyway, but it
created a race condition that could have caused spurious notifications
or rejected keys if the server responded quickly.

As already covered by existing TODOs, a better fix would be to have
Start() get out of the business of state migration altogether. But
we're approaching a release so I want to make the minimum possible fix.

Fixes #1840.

Signed-off-by: Avery Pennarun <apenwarr@tailscale.com>
This commit is contained in:
Avery Pennarun
2021-05-04 04:26:07 -04:00
parent 7dbbe0c7c7
commit 6d10655dc3
4 changed files with 45 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
ipn/ipnlocal/local.go
View File

@@ -633,16 +633,18 @@ func (b *LocalBackend) getNewControlClientFunc() clientGen {
//
// b.mu must be held.
func (b *LocalBackend) startIsNoopLocked(opts ipn.Options) bool {
// Options has 4 fields; check all of them:
// Options has 5 fields; check all of them:
// * FrontendLogID
// * StateKey
// * Prefs
// * UpdatePrefs
// * AuthKey
return b.state == ipn.Running &&
b.hostinfo != nil &&
b.hostinfo.FrontendLogID == opts.FrontendLogID &&
b.stateKey == opts.StateKey &&
opts.Prefs == nil &&
opts.UpdatePrefs == nil &&
opts.AuthKey == ""
}
@@ -717,6 +719,12 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
return fmt.Errorf("loading requested state: %v", err)
}
if opts.UpdatePrefs != nil {
newPrefs := opts.UpdatePrefs
newPrefs.Persist = b.prefs.Persist
b.prefs = newPrefs
}
wantRunning := b.prefs.WantRunning
if wantRunning {
if err := b.initMachineKeyLocked(); err != nil {
@@ -779,6 +787,10 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
debugFlags = append([]string{"netstack"}, debugFlags...)
}
// TODO(apenwarr): The only way to change the ServerURL is to
// re-run b.Start(), because this is the only place we create a
// new controlclient. SetPrefs() allows you to overwrite ServerURL,
// but it won't take effect until the next Start().
cc, err := b.getNewControlClientFunc()(controlclient.Options{
GetMachinePrivateKey: b.createGetMachinePrivateKeyFunc(),
Logf: logger.WithPrefix(b.logf, "control: "),