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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
//go:build !ts_omit_tailnetlock
package tka
import (
"fmt"
"os"
"tailscale.com/types/tkatype"
)
// Types implementing Signer can sign update messages.
type Signer interface {
// SignAUM returns signatures for the AUM encoded by the given AUMSigHash.
SignAUM(tkatype.AUMSigHash) ([]tkatype.Signature, error)
}
// UpdateBuilder implements a builder for changes to the tailnet
// key authority.
//
// Finalize must be called to compute the update messages, which
// must then be applied to all Authority objects using Inform().
type UpdateBuilder struct {
a *Authority
signer Signer
state State
parent AUMHash
out []AUM
}
func (b *UpdateBuilder) mkUpdate(update AUM) error {
prevHash := make([]byte, len(b.parent))
copy(prevHash, b.parent[:])
update.PrevAUMHash = prevHash
if b.signer != nil {
sigs, err := b.signer.SignAUM(update.SigHash())
if err != nil {
return fmt.Errorf("signing failed: %v", err)
}
update.Signatures = append(update.Signatures, sigs...)
}
if err := update.StaticValidate(); err != nil {
return fmt.Errorf("generated update was invalid: %v", err)
}
state, err := b.state.applyVerifiedAUM(update)
if err != nil {
return fmt.Errorf("update cannot be applied: %v", err)
}
b.state = state
b.parent = update.Hash()
b.out = append(b.out, update)
return nil
}
// AddKey adds a new key to the authority.
func (b *UpdateBuilder) AddKey(key Key) error {
keyID, err := key.ID()
if err != nil {
return err
}
if _, err := b.state.GetKey(keyID); err == nil {
return fmt.Errorf("cannot add key %v: already exists", key)
}
if len(b.state.Keys) >= maxKeys {
return fmt.Errorf("cannot add key %v: maximum number of keys reached", key)
}
return b.mkUpdate(AUM{MessageKind: AUMAddKey, Key: &key})
}
// RemoveKey removes a key from the authority.
func (b *UpdateBuilder) RemoveKey(keyID tkatype.KeyID) error {
if _, err := b.state.GetKey(keyID); err != nil {
return fmt.Errorf("failed reading key %x: %v", keyID, err)
}
return b.mkUpdate(AUM{MessageKind: AUMRemoveKey, KeyID: keyID})
}
// SetKeyVote updates the number of votes of an existing key.
func (b *UpdateBuilder) SetKeyVote(keyID tkatype.KeyID, votes uint) error {
if _, err := b.state.GetKey(keyID); err != nil {
return fmt.Errorf("failed reading key %x: %v", keyID, err)
}
return b.mkUpdate(AUM{MessageKind: AUMUpdateKey, Votes: &votes, KeyID: keyID})
}
// SetKeyMeta updates key-value metadata stored against an existing key.
//
// TODO(tom): Provide an API to update specific values rather than the whole
// map.
func (b *UpdateBuilder) SetKeyMeta(keyID tkatype.KeyID, meta map[string]string) error {
if _, err := b.state.GetKey(keyID); err != nil {
return fmt.Errorf("failed reading key %x: %v", keyID, err)
}
return b.mkUpdate(AUM{MessageKind: AUMUpdateKey, Meta: meta, KeyID: keyID})
}
func (b *UpdateBuilder) generateCheckpoint() error {
// Compute the checkpoint state.
state := b.a.state
for i, update := range b.out {
var err error
if state, err = state.applyVerifiedAUM(update); err != nil {
return fmt.Errorf("applying update %d: %v", i, err)
}
}
// Checkpoints can't specify a parent AUM.
state.LastAUMHash = nil
return b.mkUpdate(AUM{MessageKind: AUMCheckpoint, State: &state})
}
// checkpointEvery sets how often a checkpoint AUM should be generated.
const checkpointEvery = 50
// Finalize returns the set of update message to actuate the update.
func (b *UpdateBuilder) Finalize(storage Chonk) ([]AUM, error) {
var (
needCheckpoint bool = true
cursor AUMHash = b.a.Head()
)
for i := len(b.out); i < checkpointEvery; i++ {
aum, err := storage.AUM(cursor)
if err != nil {
if err == os.ErrNotExist {
// The available chain is shorter than the interval to checkpoint at.
needCheckpoint = false
break
}
return nil, fmt.Errorf("reading AUM (%v): %v", cursor, err)
}
if aum.MessageKind == AUMCheckpoint {
needCheckpoint = false
break
}
parent, hasParent := aum.Parent()
if !hasParent {
// We've hit the genesis update, so the chain is shorter than the interval to checkpoint at.
needCheckpoint = false
break
}
cursor = parent
}
if needCheckpoint {
if err := b.generateCheckpoint(); err != nil {
return nil, fmt.Errorf("generating checkpoint: %v", err)
}
}
// Check no AUMs were applied in the meantime
if len(b.out) > 0 {
if parent, _ := b.out[0].Parent(); parent != b.a.Head() {
return nil, fmt.Errorf("updates no longer apply to head: based on %x but head is %x", parent, b.a.Head())
}
}
return b.out, nil
}
// NewUpdater returns a builder you can use to make changes to
// the tailnet key authority.
//
// The provided signer function, if non-nil, is called with each update
// to compute and apply signatures.
//
// Updates are specified by calling methods on the returned UpdatedBuilder.
// Call Finalize() when you are done to obtain the specific update messages
// which actuate the changes.
func (a *Authority) NewUpdater(signer Signer) *UpdateBuilder {
return &UpdateBuilder{
a: a,
signer: signer,
parent: a.Head(),
state: a.state,
}
}
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