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87 lines
2.8 KiB
Go
87 lines
2.8 KiB
Go
// Package iprev checks if an IP has a reverse DNS name configured and that the
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// reverse DNS name resolves back to the IP (RFC 8601, Section 3).
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package iprev
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import (
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"context"
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"errors"
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"fmt"
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"log/slog"
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"net"
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"time"
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"github.com/mjl-/mox/dns"
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"github.com/mjl-/mox/mlog"
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"github.com/mjl-/mox/stub"
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)
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var xlog = mlog.New("iprev", nil)
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var (
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MetricIPRev stub.HistogramVec = stub.HistogramVecIgnore{}
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)
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// Lookup errors.
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var (
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ErrNoRecord = errors.New("iprev: no reverse dns record")
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ErrDNS = errors.New("iprev: dns lookup") // Temporary error.
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)
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// ../rfc/8601:1082
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// Status is the result of a lookup.
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type Status string
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const (
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StatusPass Status = "pass" // Reverse and forward lookup results were in agreement.
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StatusFail Status = "fail" // Reverse and forward lookup results were not in agreement, but at least the reverse name does exist.
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StatusTemperror Status = "temperror" // Temporary error, e.g. DNS timeout.
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StatusPermerror Status = "permerror" // Permanent error and later retry is unlikely to succeed. E.g. no PTR record.
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)
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// Lookup checks whether an IP has a proper reverse & forward
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// DNS configuration. I.e. that it is explicitly associated with its domain name.
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//
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// A PTR lookup is done on the IP, resulting in zero or more names. These names are
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// forward resolved (A or AAAA) until the original IP address is found. The first
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// matching name is returned as "name". All names, matching or not, are returned as
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// "names".
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//
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// If a temporary error occurred, rerr is set.
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func Lookup(ctx context.Context, resolver dns.Resolver, ip net.IP) (rstatus Status, name string, names []string, authentic bool, rerr error) {
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log := xlog.WithContext(ctx)
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start := time.Now()
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defer func() {
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MetricIPRev.ObserveLabels(float64(time.Since(start))/float64(time.Second), string(rstatus))
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log.Debugx("iprev lookup result", rerr,
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slog.Any("ip", ip),
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slog.Any("status", rstatus),
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slog.Duration("duration", time.Since(start)))
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}()
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revNames, result, revErr := dns.WithPackage(resolver, "iprev").LookupAddr(ctx, ip.String())
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if dns.IsNotFound(revErr) {
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return StatusPermerror, "", nil, result.Authentic, ErrNoRecord
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} else if revErr != nil {
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return StatusTemperror, "", nil, result.Authentic, fmt.Errorf("%w: %s", ErrDNS, revErr)
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}
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var lastErr error
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authentic = result.Authentic
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for _, rname := range revNames {
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ips, result, err := dns.WithPackage(resolver, "iprev").LookupIP(ctx, "ip", rname)
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authentic = authentic && result.Authentic
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for _, fwdIP := range ips {
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if ip.Equal(fwdIP) {
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return StatusPass, rname, revNames, authentic, nil
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}
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}
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if err != nil && !dns.IsNotFound(err) {
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lastErr = err
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}
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}
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if lastErr != nil {
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return StatusTemperror, "", revNames, authentic, fmt.Errorf("%w: %s", ErrDNS, lastErr)
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}
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return StatusFail, "", revNames, authentic, nil
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}
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