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Use crypto/rand for upstream DNS transaction IDs #3020

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Merged
Benjamin Elder (BenTheElder) merged 1 commit into from
Oct 21, 2026
Merged

Use crypto/rand for upstream DNS transaction IDs #3020

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10 changes: 7 additions & 3 deletions internal/atunnel/dns/pendingreq.go
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,8 @@ package dns

import (
"bytes"
"math/rand/v2"
"crypto/rand"
"encoding/binary"
"net"
"sync"
"time"
Expand Down Expand Up @@ -110,11 +111,14 @@ func (p *pendingRequests) record(
clientAddr net.Addr,
upstreams []string,
) (uint16, bool) {
// Probe from a random starting ID so upstream transaction IDs are not predictable.
var buf [2]byte
_, _ = rand.Read(buf[:])
start := binary.BigEndian.Uint16(buf[:])

p.mu.Lock()
defer p.mu.Unlock()

// Probe from a random starting ID so upstream transaction IDs are not predictable.
start := uint16(rand.Uint32())
upstreamID, ok := p.inUse.FindFirstUnsetFrom(start)
if !ok {
p.limiter.inFlight.release()
Expand Down
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