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firewall: fix 32-bit int truncation and optimize CryptoRandIntn #1358

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6d89f07
firewall: fix 32-bit int truncation
bitromortac Jul 21, 2026
cf7e538
firewall: optimize CryptoRandIntn with sync.Pool
bitromortac Jul 21, 2026
1eddc53
docs: add release notes for privacy mapper refactoring
bitromortac Jul 21, 2026
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6 changes: 6 additions & 0 deletions docs/release-notes/release-notes-0.17.1.md
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,12 @@
-V`](https://github.com/lightninglabs/lightning-terminal/pull/1337): The `-V`
flag now prints litd's version instead of the integrated lnd version.

* [Refactor privacy mapper to prevent 32-bit truncation and optimize
allocations](https://github.com/lightninglabs/lightning-terminal/pull/1358):
Refactored the privacy mapper's random number generation to use `int64`
instead of `int` to prevent architecture-dependent truncation on 32-bit
runtimes, and introduced a `sync.Pool` for `*big.Int` to optimize allocations.

## RPC Updates

## Integrated Binary Updates
Expand Down
69 changes: 48 additions & 21 deletions firewall/privacy_mapper.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,9 +7,11 @@ import (
"encoding/json"
"errors"
"fmt"
"math"
"math/big"
"strconv"
"strings"
"sync"
"time"

"github.com/btcsuite/btcd/chaincfg/chainhash"
Expand Down Expand Up @@ -61,14 +63,14 @@ var _ mid.RequestInterceptor = (*PrivacyMapper)(nil)
// requests to their real values and vice versa for responses.
type PrivacyMapper struct {
db firewalldb.PrivacyMapper
randIntn func(int) (int, error)
randIntn func(int64) (int64, error)
sessionDB firewalldb.SessionDB
}

// NewPrivacyMapper returns a new instance of PrivacyMapper. The randIntn
// function is used to draw randomness for request field obfuscation.
func NewPrivacyMapper(newDB firewalldb.PrivacyMapper,
randIntn func(int) (int, error),
randIntn func(int64) (int64, error),
sessionDB firewalldb.SessionDB) *PrivacyMapper {

return &PrivacyMapper{
Expand Down Expand Up @@ -379,7 +381,7 @@ func handleGetInfoResponse(db firewalldb.PrivacyMapDB,

func handleFwdHistoryResponse(db firewalldb.PrivacyMapDB,
flags session.PrivacyFlags,
randIntn func(int) (int, error)) func(ctx context.Context,
randIntn func(int64) (int64, error)) func(ctx context.Context,
r *lnrpc.ForwardingHistoryResponse) (proto.Message, error) {

return func(ctx context.Context, r *lnrpc.ForwardingHistoryResponse) (
Expand Down Expand Up @@ -582,7 +584,7 @@ func handleListChannelsRequest(db firewalldb.PrivacyMapDB,

func handleListChannelsResponse(db firewalldb.PrivacyMapDB,
flags session.PrivacyFlags,
randIntn func(int) (int, error)) func(ctx context.Context,
randIntn func(int64) (int64, error)) func(ctx context.Context,
r *lnrpc.ListChannelsResponse) (proto.Message, error) {

return func(ctx context.Context, r *lnrpc.ListChannelsResponse) (
Expand Down Expand Up @@ -866,7 +868,7 @@ func handleUpdatePolicyResponse(db firewalldb.PrivacyMapDB,

func handleWalletBalanceResponse(_ firewalldb.PrivacyMapDB,
flags session.PrivacyFlags,
randIntn func(int) (int, error)) func(ctx context.Context,
randIntn func(int64) (int64, error)) func(ctx context.Context,
r *lnrpc.WalletBalanceResponse) (proto.Message, error) {

return func(_ context.Context, r *lnrpc.WalletBalanceResponse) (
Expand Down Expand Up @@ -945,7 +947,7 @@ func handleWalletBalanceResponse(_ firewalldb.PrivacyMapDB,

func handleClosedChannelsResponse(db firewalldb.PrivacyMapDB,
flags session.PrivacyFlags,
randIntn func(int) (int, error)) func(ctx context.Context,
randIntn func(int64) (int64, error)) func(ctx context.Context,
r *lnrpc.ClosedChannelsResponse) (proto.Message, error) {

return func(ctx context.Context, r *lnrpc.ClosedChannelsResponse) (
Expand Down Expand Up @@ -1065,7 +1067,7 @@ func handleClosedChannelsResponse(db firewalldb.PrivacyMapDB,
// channel.
func obfuscatePendingChannel(ctx context.Context,
c *lnrpc.PendingChannelsResponse_PendingChannel,
tx firewalldb.PrivacyMapTx, randIntn func(int) (int, error),
tx firewalldb.PrivacyMapTx, randIntn func(int64) (int64, error),
flags session.PrivacyFlags) (
*lnrpc.PendingChannelsResponse_PendingChannel, error) {

Expand Down Expand Up @@ -1142,7 +1144,7 @@ func obfuscatePendingChannel(ctx context.Context,

func handlePendingChannelsResponse(db firewalldb.PrivacyMapDB,
flags session.PrivacyFlags,
randIntn func(int) (int, error)) func(ctx context.Context,
randIntn func(int64) (int64, error)) func(ctx context.Context,
r *lnrpc.PendingChannelsResponse) (proto.Message, error) {

return func(ctx context.Context, r *lnrpc.PendingChannelsResponse) (
Expand Down Expand Up @@ -1729,7 +1731,7 @@ func handleConnectPeerRequest(db firewalldb.PrivacyMapDB,
}

// maybeHideAmount hides an amount if the privacy flag is not set.
func maybeHideAmount(flags session.PrivacyFlags, randIntn func(int) (int,
func maybeHideAmount(flags session.PrivacyFlags, randIntn func(int64) (int64,
error), a int64) (int64, error) {

if !flags.Contains(session.ClearAmounts) {
Expand All @@ -1748,15 +1750,20 @@ func maybeHideAmount(flags session.PrivacyFlags, randIntn func(int) (int,

// hideAmount symmetrically randomizes an amount around a given relative
// variation interval. relativeVariation should be between 0 and 1.
func hideAmount(randIntn func(n int) (int, error), relativeVariation float64,
amount uint64) (uint64, error) {
func hideAmount(randIntn func(n int64) (int64, error),
relativeVariation float64, amount uint64) (uint64, error) {

if relativeVariation < 0 || relativeVariation > 1 {
return 0, fmt.Errorf("hide amount: relative variation is not "+
"between allowed bounds of [0, 1], is %v",
relativeVariation)
}

if amount > math.MaxInt64 {
return 0, fmt.Errorf("hide amount: amount %d overflows "+
"int64", amount)
}
Comment thread
bitromortac marked this conversation as resolved.

if amount == 0 {
return 0, nil
}
Expand All @@ -1765,8 +1772,13 @@ func hideAmount(randIntn func(n int) (int, error), relativeVariation float64,
// between 0 and 1.
fuzzInterval := uint64(float64(amount) * relativeVariation)

amountMin := int(amount - fuzzInterval)
amountMax := int(amount + fuzzInterval)
if amount+fuzzInterval > math.MaxInt64 {
return 0, fmt.Errorf("hide amount: amount %d with variation "+
"overflows int64", amount)
}

amountMin := int64(amount - fuzzInterval)
amountMax := int64(amount + fuzzInterval)

randAmount, err := randBetween(randIntn, amountMin, amountMax)
if err != nil {
Expand All @@ -1778,7 +1790,7 @@ func hideAmount(randIntn func(n int) (int, error), relativeVariation float64,

// hideTimestamp symmetrically randomizes a unix timestamp given an absolute
// variation interval. The random input is expected to be rand.Intn.
func hideTimestamp(randIntn func(n int) (int, error),
func hideTimestamp(randIntn func(n int64) (int64, error),
absoluteVariation time.Duration,
timestamp time.Time) (time.Time, error) {

Expand All @@ -1802,18 +1814,20 @@ func hideTimestamp(randIntn func(n int) (int, error),
timeMax := timestamp.Add(absoluteVariation)

timeNs, err := randBetween(
randIntn, int(timeMin.UnixNano()), int(timeMax.UnixNano()),
randIntn, timeMin.UnixNano(), timeMax.UnixNano(),
)
if err != nil {
return time.Time{}, err
}

return time.Unix(0, int64(timeNs)), nil
return time.Unix(0, timeNs), nil
}

// randBetween generates a random number between [min, max) given a source of
// randomness.
func randBetween(randIntn func(int) (int, error), min, max int) (int, error) {
func randBetween(randIntn func(int64) (int64, error),
min, max int64) (int64, error) {

if max < min {
return 0, fmt.Errorf("min is not allowed to be greater than "+
"max, (min: %v, max: %v)", min, max)
Expand All @@ -1833,7 +1847,7 @@ func randBetween(randIntn func(int) (int, error), min, max int) (int, error) {
}

// hideBool generates a random bool given a random input.
func hideBool(randIntn func(n int) (int, error)) (bool, error) {
func hideBool(randIntn func(n int64) (int64, error)) (bool, error) {
random, err := randIntn(2)
if err != nil {
return false, err
Expand All @@ -1844,18 +1858,31 @@ func hideBool(randIntn func(n int) (int, error)) (bool, error) {
return random >= 1, nil
}

// bigIntPool is a pool of *big.Int values to avoid frequent heap allocations in
// CryptoRandIntn.
var bigIntPool = sync.Pool{
New: func() any {
return new(big.Int)
},
}

// CryptoRandIntn generates a random number between [0, n).
func CryptoRandIntn(n int) (int, error) {
func CryptoRandIntn(n int64) (int64, error) {
if n == 0 {
return 0, nil
}

nBig, err := rand.Int(rand.Reader, big.NewInt(int64(n)))
nBig := bigIntPool.Get().(*big.Int)
defer bigIntPool.Put(nBig)

nBig.SetInt64(n)

randBig, err := rand.Int(rand.Reader, nBig)
if err != nil {
return 0, err
}

return int(nBig.Int64()), nil
return randBig.Int64(), nil
}

// ObfuscateConfig alters the config string by replacing sensitive data with
Expand Down
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