95 lines
2.2 KiB
Go
95 lines
2.2 KiB
Go
// Package dnsreverse implements the dns_reverse module.
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// It enriches already-known hosts by performing reverse-DNS lookups
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// for every host that has no hostname recorded yet.
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package dnsreverse
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import (
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"context"
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"fmt"
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"log/slog"
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"net"
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"strings"
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"time"
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"github.com/cereda-systems/nexus-scanner/internal/db"
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)
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// Module enriches hosts in the database with reverse-DNS hostnames.
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type Module struct {
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site string
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store *db.Store
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log *slog.Logger
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}
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// New returns a new dns_reverse module.
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func New(site string, store *db.Store) *Module {
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return &Module{
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site: site,
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store: store,
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log: slog.With("module", "dns_reverse"),
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}
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}
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func (m *Module) Name() string { return "dns_reverse" }
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func (m *Module) Interval() time.Duration { return 10 * time.Minute }
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// Run looks up hostnames for all hosts that have none recorded yet.
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func (m *Module) Run(ctx context.Context) error {
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scanID, err := m.store.BeginScan(m.Name())
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if err != nil {
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return fmt.Errorf("begin scan: %w", err)
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}
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scanErr := m.scan(ctx)
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if endErr := m.store.EndScan(scanID, scanErr); endErr != nil {
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m.log.Error("record scan end", "err", endErr)
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}
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return scanErr
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}
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func (m *Module) scan(ctx context.Context) error {
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hosts, err := m.store.ListHosts("")
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if err != nil {
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return fmt.Errorf("list hosts: %w", err)
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}
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resolved := 0
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for _, h := range hosts {
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// Skip hosts that already have a hostname.
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if h.Hostname != "" {
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continue
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}
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select {
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case <-ctx.Done():
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return ctx.Err()
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default:
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}
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names, err := net.DefaultResolver.LookupAddr(ctx, h.IP)
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if err != nil {
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// A lookup failure is not fatal — continue with the next host.
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m.log.Debug("reverse lookup failed", "ip", h.IP, "err", err)
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continue
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}
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if len(names) == 0 {
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continue
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}
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// LookupAddr returns FQDNs with a trailing dot — strip it.
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hostname := strings.TrimSuffix(names[0], ".")
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h.Hostname = hostname
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if err := m.store.UpsertHost(h); err != nil {
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m.log.Error("upsert host", "ip", h.IP, "err", err)
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continue
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}
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m.log.Info("hostname resolved", "ip", h.IP, "hostname", hostname)
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resolved++
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}
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m.log.Info("scan complete", "checked", len(hosts), "resolved", resolved)
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return nil
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}
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