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// Copyright (C) 2019-2023 Algorand, Inc.
// This file is part of go-algorand
//
// go-algorand is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// go-algorand is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with go-algorand. If not, see <https://www.gnu.org/licenses/>.
package dnssec
import (
"context"
"fmt"
"strings"
"time"
"github.com/algorand/go-deadlock"
"github.com/miekg/dns"
)
// TrustQuerier wraps Querier and trusted root anchor retrieval for better testability
type TrustQuerier interface {
Querier
GetRootAnchorDS() ([]dns.DS, error)
}
type trustChain struct {
client TrustQuerier
trustedZones map[string]trustedZone
mu deadlock.RWMutex
}
func makeTrustChain(c TrustQuerier) *trustChain {
return &trustChain{
client: c,
trustedZones: make(map[string]trustedZone),
}
}
// QueryWrapper implements TrustQuerier
// GetRootAnchor is forwared to MakeRootTrustAnchor
type QueryWrapper struct {
Querier
}
// GetRootAnchorDS returns DS from a real trust anchor
func (qw QueryWrapper) GetRootAnchorDS() (dss []dns.DS, err error) {
a, err := MakeRootTrustAnchor()
if err != nil {
return
}
return a.ToDS(), nil
}
// must be called with the lock taken
func (t *trustChain) removeSelfAndChildren(zone string) {
for k := range t.trustedZones {
if strings.HasSuffix(k, zone) {
delete(t.trustedZones, k)
}
}
}
// ensure checks that all zones from root till fqZoneName are valid and places them into a cache.
// It also performs cache invalidation: if child-parent authentication fails because of keys mismatch
// then parent zone is updated from the network and the process repeats.
// For example, example.com. is represented by 3 trusted zones: [".", "com.", "example.com."]
func (t *trustChain) ensure(ctx context.Context, fqZoneName string, keytags []uint16) error {
// get zones from . to fqZoneName
zones, err := splitToZones(fqZoneName)
if err != nil {
return err
}
zoneIdx := 0
refreshedZones := make([]bool, len(zones)) // indexes of refreshed zones during the loop iterations
// the loop goes over zones and cached trust chain and creates new entries if needed.
// cache invalidation happens in these three cases:
// 1. no ZSK in parent zone to check newly obtained DS
// Explanation: DS is stored in parent and signed with its ZSK. If no such keys in the cache then ZSK rotation happened.
// 2. DNSKEY signature (RRSIG) expired
// 3. no ZSK in the last zone in cache
// Explanation: server rotated ZSK and the cache does not have key to authenticate response.
//
// worst case: the last zone fails to find ZSK, it triggers refreshing back to root
// causing 2 * len(zones) iterations
// makeTrustedZone does not return cacheOutdated and refreshedZones has indication that the root was already updated
// and the second fallback to the root zone will fail
// this would not survive after granular locks and concurrent underlying zones removal
t.mu.Lock()
defer t.mu.Unlock()
for {
zone := zones[zoneIdx]
tz, ok := t.trustedZones[zone]
if !ok {
if refreshedZones[zoneIdx] {
return fmt.Errorf("cache outdated for already updated zone %s", zone)
}
var cacheOutdated bool
parentZone := trustedZone{}
if zoneIdx > 0 {
parentZone = t.trustedZones[zones[zoneIdx-1]]
}
if tz, cacheOutdated, err = makeTrustedZone(ctx, zone, parentZone, t.client, time.Now()); err != nil {
return err
}
if cacheOutdated {
// Failed to validate DS using cached parent's keys
// restart loop from parent
zoneIdx--
if zoneIdx < 0 {
return fmt.Errorf("logic error: cache outdated for root zone")
}
parentZoneName := zones[zoneIdx]
t.removeSelfAndChildren(parentZoneName)
continue
}
// successfully created a new zone, record it
t.trustedZones[zone] = tz
refreshedZones[zoneIdx] = true
}
if tz.isExpired(time.Now()) {
// remove current and all child zones and restart with the same zone
t.removeSelfAndChildren(zone)
continue
}
if zoneIdx == len(zones)-1 {
// for the last zone also ensure that ZSK used to sign user-requested RR are also in place
if !tz.checkKeys(keytags) {
if refreshedZones[zoneIdx] {
return fmt.Errorf("ZSK %v not found in zone %s", keytags, fqZoneName)
}
// seems like the latest zone
t.removeSelfAndChildren(zone)
continue
}
}
zoneIdx++
if zoneIdx >= len(zones) {
break
}
}
return nil
}
func (t *trustChain) getDNSKey(fqZoneName string, keyTag uint16) (key *dns.DNSKEY, found bool) {
t.mu.RLock()
trustedZone, ok := t.trustedZones[fqZoneName]
t.mu.RUnlock()
if !ok {
return
}
k, found := trustedZone.zsk[keyTag]
return &k, found
}
// Authenticate verifies a given rrset and its signatures validity down to the trusted root.
// Following steps are done:
// 1. Ensure the trust chain is valid. This requires keys' signature check back to the root if not cached
// 2. Check the signature using authenticated DNSKEY
func (t *trustChain) Authenticate(ctx context.Context, rrSet []dns.RR, rrSig []dns.RRSIG) (err error) {
if len(rrSig) == 0 {
return fmt.Errorf("empty RRSIG")
}
signer := rrSig[0].SignerName
// sanity check: ensure all RRSIG contain the same signer, it must be the parent zone
for i := 1; i < len(rrSig); i++ {
if signer != rrSig[i].SignerName {
return fmt.Errorf("signer name mismatch: %s vs %s", signer, rrSig[i].SignerName)
}
}
fqdn := dns.Fqdn(signer)
keytags := make([]uint16, 0, len(rrSig))
for _, sig := range rrSig {
keytags = append(keytags, sig.KeyTag)
}
// 1. ensure trust from the root to the signer
// 2. check the keys are in place
err = t.ensure(ctx, fqdn, keytags)
if err != nil {
return err
}
for _, sig := range rrSig {
// get already authenticated ZSK
key, ok := t.getDNSKey(fqdn, sig.KeyTag)
if !ok {
// skip, trustChain.ensure checks that at least one keytag is available
continue
}
if err = sig.Verify(key, rrSet); err == nil {
return nil
}
}
return err
}
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