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https://github.com/mjl-/mox.git
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daa908e9f4
the vendored dns resolver code is a copy of the go stdlib dns resolver, with awareness of the "authentic data" (i.e. dnssec secure) added, as well as support for enhanced dns errors, and looking up tlsa records (for dane). ideally it would be upstreamed, but the chances seem slim. dnssec-awareness is added to all packages, e.g. spf, dkim, dmarc, iprev. their dnssec status is added to the Received message headers for incoming email. but the main reason to add dnssec was for implementing dane. with dane, the verification of tls certificates can be done through certificates/public keys published in dns (in the tlsa records). this only makes sense (is trustworthy) if those dns records can be verified to be authentic. mox now applies dane to delivering messages over smtp. mox already implemented mta-sts for webpki/pkix-verification of certificates against the (large) pool of CA's, and still enforces those policies when present. but it now also checks for dane records, and will verify those if present. if dane and mta-sts are both absent, the regular opportunistic tls with starttls is still done. and the fallback to plaintext is also still done. mox also makes it easy to setup dane for incoming deliveries, so other servers can deliver with dane tls certificate verification. the quickstart now generates private keys that are used when requesting certificates with acme. the private keys are pre-generated because they must be static and known during setup, because their public keys must be published in tlsa records in dns. autocert would generate private keys on its own, so had to be forked to add the option to provide the private key when requesting a new certificate. hopefully upstream will accept the change and we can drop the fork. with this change, using the quickstart to setup a new mox instance, the checks at internet.nl result in a 100% score, provided the domain is dnssec-signed and the network doesn't have any issues.
92 lines
3 KiB
Go
92 lines
3 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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"net"
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"time"
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"github.com/prometheus/client_golang/prometheus"
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"github.com/prometheus/client_golang/prometheus/promauto"
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"github.com/mjl-/mox/dns"
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"github.com/mjl-/mox/mlog"
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)
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var xlog = mlog.New("iprev")
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var (
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metricIPRev = promauto.NewHistogramVec(
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prometheus.HistogramOpts{
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Name: "mox_iprev_lookup_total",
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Help: "Number of iprev lookups.",
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Buckets: []float64{0.001, 0.005, 0.01, 0.05, 0.100, 0.5, 1, 5, 10, 20, 30},
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},
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[]string{"status"},
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)
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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")
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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.WithLabelValues(string(rstatus)).Observe(float64(time.Since(start)) / float64(time.Second))
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log.Debugx("iprev lookup result", rerr, mlog.Field("ip", ip), mlog.Field("status", rstatus), mlog.Field("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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