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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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16
queue/submit.go
View File

@ -16,6 +16,7 @@ import (
"github.com/mjl-/mox/mlog"
"github.com/mjl-/mox/mox-"
"github.com/mjl-/mox/sasl"
"github.com/mjl-/mox/smtp"
"github.com/mjl-/mox/smtpclient"
"github.com/mjl-/mox/store"
)
@ -51,11 +52,20 @@ func deliverSubmit(cid int64, qlog *mlog.Log, resolver dns.Resolver, dialer smtp
qlog.Debug("queue deliversubmit result", mlog.Field("host", transport.DNSHost), mlog.Field("port", port), mlog.Field("attempt", m.Attempts), mlog.Field("permanent", permanent), mlog.Field("secodeopt", secodeOpt), mlog.Field("errmsg", errmsg), mlog.Field("ok", success), mlog.Field("duration", time.Since(start)))
}()
// We don't have to attempt SMTP-DANE for submission, since it only applies to SMTP
// relaying on port 25. ../rfc/7672:1261
// todo: SMTP-DANE should be used when relaying on port 25.
// ../rfc/7672:1261
// todo: for submission, understand SRV records, and even DANE.
// If submit was done with REQUIRETLS extension for SMTP, we must verify TLS
// certificates. If our submission connection is not configured that way, abort.
requireTLS := m.RequireTLS != nil && *m.RequireTLS
if requireTLS && tlsMode != smtpclient.TLSStrictStartTLS && tlsMode != smtpclient.TLSStrictImmediate {
errmsg = fmt.Sprintf("transport %s: message requires verified tls but transport does not verify tls", transportName)
fail(qlog, m, backoff, true, dsn.NameIP{}, smtp.SePol7MissingReqTLS, errmsg)
return
}
dialctx, dialcancel := context.WithTimeout(context.Background(), 30*time.Second)
defer dialcancel()
if m.DialedIPs == nil {
@ -165,7 +175,7 @@ func deliverSubmit(cid int64, qlog *mlog.Log, resolver dns.Resolver, dialer smtp
deliverctx, delivercancel := context.WithTimeout(context.Background(), time.Duration(60+size/(1024*1024))*time.Second)
defer delivercancel()
err = client.Deliver(deliverctx, m.Sender().String(), m.Recipient().String(), size, msgr, req8bit, reqsmtputf8)
err = client.Deliver(deliverctx, m.Sender().String(), m.Recipient().String(), size, msgr, req8bit, reqsmtputf8, requireTLS)
if err != nil {
qlog.Infox("delivery failed", err)
}