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implement "requiretls", rfc 8689

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with requiretls, the tls verification mode/rules for email deliveries can be
changed by the sender/submitter. in two ways:

1. "requiretls" smtp extension to always enforce verified tls (with mta-sts or
dnssec+dane), along the entire delivery path until delivery into the final
destination mailbox (so entire transport is verified-tls-protected).

2. "tls-required: no" message header, to ignore any tls and tls verification
errors even if the recipient domain has a policy that requires tls verification
(mta-sts and/or dnssec+dane), allowing delivery of non-sensitive messages in
case of misconfiguration/interoperability issues (at least useful for sending
tls reports).

we enable requiretls by default (only when tls is active), for smtp and
submission. it can be disabled through the config.

for each delivery attempt, we now store (per recipient domain, in the account
of the sender) whether the smtp server supports starttls and requiretls. this
support is shown (after having sent a first message) in the webmail when
sending a message (the previous 3 bars under the address input field are now 5
bars, the first for starttls support, the last for requiretls support). when
all recipient domains for a message are known to implement requiretls,
requiretls is automatically selected for sending (instead of "default" tls
behaviour). users can also select the "fallback to insecure" to add the
"tls-required: no" header.

new metrics are added for insight into requiretls errors and (some, not yet
all) cases where tls-required-no ignored a tls/verification error.

the admin can change the requiretls status for messages in the queue. so with
default delivery attempts, when verified tls is required by failing, an admin
could potentially change the field to "tls-required: no"-behaviour.

messages received (over smtp) with the requiretls option, get a comment added
to their Received header line, just before "id", after "with".
This commit is contained in:
Mechiel Lukkien
2023-10-24 10:06:16 +02:00
parent 0e5e16b3d0
commit 2f5d6069bf
31 changed files with 1102 additions and 274 deletions
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31
queue/queue.go
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@ -99,6 +99,21 @@ type Msg struct {
// admin interface. If empty (the default for a submitted message), regular routing
// rules apply.
Transport string
// RequireTLS influences TLS verification during delivery.
//
// If nil, the recipient domain policy is followed (MTA-STS and/or DANE), falling
// back to optional opportunistic non-verified STARTTLS.
//
// If RequireTLS is true (through SMTP REQUIRETLS extension or webmail submit),
// MTA-STS or DANE is required, as well as REQUIRETLS support by the next hop
// server.
//
// If RequireTLS is false (through messag header "TLS-Required: No"), the recipient
// domain's policy is ignored if it does not lead to a successful TLS connection,
// i.e. falling back to SMTP delivery with unverified STARTTLS or plain text.
RequireTLS *bool
// ../rfc/8689:250
}
// Sender of message as used in MAIL FROM.
@ -180,7 +195,7 @@ func Count(ctx context.Context) (int, error) {
// this data is used as the message when delivering the DSN and the remote SMTP
// server supports SMTPUTF8. If the remote SMTP server does not support SMTPUTF8,
// the regular non-utf8 message is delivered.
func Add(ctx context.Context, log *mlog.Log, senderAccount string, mailFrom, rcptTo smtp.Path, has8bit, smtputf8 bool, size int64, messageID string, msgPrefix []byte, msgFile *os.File, dsnutf8Opt []byte) (int64, error) {
func Add(ctx context.Context, log *mlog.Log, senderAccount string, mailFrom, rcptTo smtp.Path, has8bit, smtputf8 bool, size int64, messageID string, msgPrefix []byte, msgFile *os.File, dsnutf8Opt []byte, requireTLS *bool) (int64, error) {
// todo: Add should accept multiple rcptTo if they are for the same domain. so we can queue them for delivery in one (or just a few) session(s), transferring the data only once. ../rfc/5321:3759
if Localserve {
@ -221,7 +236,7 @@ func Add(ctx context.Context, log *mlog.Log, senderAccount string, mailFrom, rcp
}()
now := time.Now()
qm := Msg{0, now, senderAccount, mailFrom.Localpart, mailFrom.IPDomain, rcptTo.Localpart, rcptTo.IPDomain, formatIPDomain(rcptTo.IPDomain), 0, nil, now, nil, "", has8bit, smtputf8, size, messageID, msgPrefix, dsnutf8Opt, ""}
qm := Msg{0, now, senderAccount, mailFrom.Localpart, mailFrom.IPDomain, rcptTo.Localpart, rcptTo.IPDomain, formatIPDomain(rcptTo.IPDomain), 0, nil, now, nil, "", has8bit, smtputf8, size, messageID, msgPrefix, dsnutf8Opt, "", requireTLS}
if err := tx.Insert(&qm); err != nil {
return 0, err
@ -339,6 +354,18 @@ func Drop(ctx context.Context, ID int64, toDomain string, recipient string) (int
return n, nil
}
// SaveRequireTLS updates the RequireTLS field of the message with id.
func SaveRequireTLS(ctx context.Context, id int64, requireTLS *bool) error {
return DB.Write(ctx, func(tx *bstore.Tx) error {
m := Msg{ID: id}
if err := tx.Get(&m); err != nil {
return fmt.Errorf("get message: %w", err)
}
m.RequireTLS = requireTLS
return tx.Update(&m)
})
}
type ReadReaderAtCloser interface {
io.ReadCloser
io.ReaderAt