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implement dnssec-awareness throughout code, and dane for incoming/outgoing mail delivery

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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.
This commit is contained in:
Mechiel Lukkien
2023-10-10 12:09:35 +02:00
parent c4324fdaa1
commit daa908e9f4
177 changed files with 12907 additions and 3131 deletions
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55
dkim/dkim.go
View File

@ -38,7 +38,7 @@ import (
var xlog = mlog.New("dkim")
var (
metricDKIMSign = promauto.NewCounterVec(
metricSign = promauto.NewCounterVec(
prometheus.CounterOpts{
Name: "mox_dkim_sign_total",
Help: "DKIM messages signings, label key is the type of key, rsa or ed25519.",
@ -47,7 +47,7 @@ var (
"key",
},
)
metricDKIMVerify = promauto.NewHistogramVec(
metricVerify = promauto.NewHistogramVec(
prometheus.HistogramOpts{
Name: "mox_dkim_verify_duration_seconds",
Help: "DKIM verify, including lookup, duration and result.",
@ -113,10 +113,11 @@ var (
// To decide what to do with a message, both the signature parameters and the DNS
// TXT record have to be consulted.
type Result struct {
Status Status
Sig *Sig // Parsed form of DKIM-Signature header. Can be nil for invalid DKIM-Signature header.
Record *Record // Parsed form of DKIM DNS record for selector and domain in Sig. Optional.
Err error // If Status is not StatusPass, this error holds the details and can be checked using errors.Is.
Status Status
Sig *Sig // Parsed form of DKIM-Signature header. Can be nil for invalid DKIM-Signature header.
Record *Record // Parsed form of DKIM DNS record for selector and domain in Sig. Optional.
RecordAuthentic bool // Whether DKIM DNS record was DNSSEC-protected. Only valid if Sig is non-nil.
Err error // If Status is not StatusPass, this error holds the details and can be checked using errors.Is.
}
// todo: use some io.Writer to hash the body and the header.
@ -157,10 +158,10 @@ func Sign(ctx context.Context, localpart smtp.Localpart, domain dns.Domain, c co
switch sel.Key.(type) {
case *rsa.PrivateKey:
sig.AlgorithmSign = "rsa"
metricDKIMSign.WithLabelValues("rsa").Inc()
metricSign.WithLabelValues("rsa").Inc()
case ed25519.PrivateKey:
sig.AlgorithmSign = "ed25519"
metricDKIMSign.WithLabelValues("ed25519").Inc()
metricSign.WithLabelValues("ed25519").Inc()
default:
return "", fmt.Errorf("internal error, unknown pivate key %T", sel.Key)
}
@ -267,7 +268,9 @@ func Sign(ctx context.Context, localpart smtp.Localpart, domain dns.Domain, c co
//
// A requested record is <selector>._domainkey.<domain>. Exactly one valid DKIM
// record should be present.
func Lookup(ctx context.Context, resolver dns.Resolver, selector, domain dns.Domain) (rstatus Status, rrecord *Record, rtxt string, rerr error) {
//
// authentic indicates if DNS results were DNSSEC-verified.
func Lookup(ctx context.Context, resolver dns.Resolver, selector, domain dns.Domain) (rstatus Status, rrecord *Record, rtxt string, authentic bool, rerr error) {
log := xlog.WithContext(ctx)
start := timeNow()
defer func() {
@ -275,14 +278,14 @@ func Lookup(ctx context.Context, resolver dns.Resolver, selector, domain dns.Dom
}()
name := selector.ASCII + "._domainkey." + domain.ASCII + "."
records, err := dns.WithPackage(resolver, "dkim").LookupTXT(ctx, name)
records, lookupResult, err := dns.WithPackage(resolver, "dkim").LookupTXT(ctx, name)
if dns.IsNotFound(err) {
// ../rfc/6376:2608
// We must return StatusPermerror. We may want to return StatusTemperror because in
// practice someone will start using a new key before DNS changes have propagated.
return StatusPermerror, nil, "", fmt.Errorf("%w: dns name %q", ErrNoRecord, name)
return StatusPermerror, nil, "", lookupResult.Authentic, fmt.Errorf("%w: dns name %q", ErrNoRecord, name)
} else if err != nil {
return StatusTemperror, nil, "", fmt.Errorf("%w: dns name %q: %s", ErrDNS, name, err)
return StatusTemperror, nil, "", lookupResult.Authentic, fmt.Errorf("%w: dns name %q: %s", ErrDNS, name, err)
}
// ../rfc/6376:2612
@ -298,7 +301,7 @@ func Lookup(ctx context.Context, resolver dns.Resolver, selector, domain dns.Dom
var isdkim bool
r, isdkim, err = ParseRecord(s)
if err != nil && isdkim {
return StatusPermerror, nil, txt, fmt.Errorf("%w: %s", ErrSyntax, err)
return StatusPermerror, nil, txt, lookupResult.Authentic, fmt.Errorf("%w: %s", ErrSyntax, err)
} else if err != nil {
// Hopefully the remote MTA admin discovers the configuration error and fix it for
// an upcoming delivery attempt, in case we rejected with temporary status.
@ -310,7 +313,7 @@ func Lookup(ctx context.Context, resolver dns.Resolver, selector, domain dns.Dom
// ../rfc/6376:1609
// ../rfc/6376:2584
if record != nil {
return StatusTemperror, nil, "", fmt.Errorf("%w: dns name %q", ErrMultipleRecords, name)
return StatusTemperror, nil, "", lookupResult.Authentic, fmt.Errorf("%w: dns name %q", ErrMultipleRecords, name)
}
record = r
txt = s
@ -318,9 +321,9 @@ func Lookup(ctx context.Context, resolver dns.Resolver, selector, domain dns.Dom
}
if record == nil {
return status, nil, "", err
return status, nil, "", lookupResult.Authentic, err
}
return StatusNeutral, record, txt, nil
return StatusNeutral, record, txt, lookupResult.Authentic, nil
}
// Verify parses the DKIM-Signature headers in a message and verifies each of them.
@ -346,7 +349,7 @@ func Verify(ctx context.Context, resolver dns.Resolver, smtputf8 bool, policy fu
alg = r.Sig.Algorithm()
}
status := string(r.Status)
metricDKIMVerify.WithLabelValues(alg, status).Observe(duration)
metricVerify.WithLabelValues(alg, status).Observe(duration)
}
if len(results) == 0 {
@ -373,26 +376,26 @@ func Verify(ctx context.Context, resolver dns.Resolver, smtputf8 bool, policy fu
if err != nil {
// ../rfc/6376:2503
err := fmt.Errorf("parsing DKIM-Signature header: %w", err)
results = append(results, Result{StatusPermerror, nil, nil, err})
results = append(results, Result{StatusPermerror, nil, nil, false, err})
continue
}
h, canonHeaderSimple, canonDataSimple, err := checkSignatureParams(ctx, sig)
if err != nil {
results = append(results, Result{StatusPermerror, nil, nil, err})
results = append(results, Result{StatusPermerror, nil, nil, false, err})
continue
}
// ../rfc/6376:2560
if err := policy(sig); err != nil {
err := fmt.Errorf("%w: %s", ErrPolicy, err)
results = append(results, Result{StatusPolicy, nil, nil, err})
results = append(results, Result{StatusPolicy, nil, nil, false, err})
continue
}
br := bufio.NewReader(&moxio.AtReader{R: r, Offset: int64(bodyOffset)})
status, txt, err := verifySignature(ctx, resolver, sig, h, canonHeaderSimple, canonDataSimple, hdrs, verifySig, br, ignoreTestMode)
results = append(results, Result{status, sig, txt, err})
status, txt, authentic, err := verifySignature(ctx, resolver, sig, h, canonHeaderSimple, canonDataSimple, hdrs, verifySig, br, ignoreTestMode)
results = append(results, Result{status, sig, txt, authentic, err})
}
return results, nil
}
@ -477,15 +480,15 @@ func checkSignatureParams(ctx context.Context, sig *Sig) (hash crypto.Hash, cano
}
// lookup the public key in the DNS and verify the signature.
func verifySignature(ctx context.Context, resolver dns.Resolver, sig *Sig, hash crypto.Hash, canonHeaderSimple, canonDataSimple bool, hdrs []header, verifySig []byte, body *bufio.Reader, ignoreTestMode bool) (Status, *Record, error) {
func verifySignature(ctx context.Context, resolver dns.Resolver, sig *Sig, hash crypto.Hash, canonHeaderSimple, canonDataSimple bool, hdrs []header, verifySig []byte, body *bufio.Reader, ignoreTestMode bool) (Status, *Record, bool, error) {
// ../rfc/6376:2604
status, record, _, err := Lookup(ctx, resolver, sig.Selector, sig.Domain)
status, record, _, authentic, err := Lookup(ctx, resolver, sig.Selector, sig.Domain)
if err != nil {
// todo: for temporary errors, we could pass on information so caller returns a 4.7.5 ecode, ../rfc/6376:2777
return status, nil, err
return status, nil, authentic, err
}
status, err = verifySignatureRecord(record, sig, hash, canonHeaderSimple, canonDataSimple, hdrs, verifySig, body, ignoreTestMode)
return status, record, err
return status, record, authentic, err
}
// verify a DKIM signature given the record from dns and signature from the email message.