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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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52
smtpclient/client_test.go
View File

@ -36,6 +36,8 @@ func TestClient(t *testing.T) {
ctx := context.Background()
log := mlog.New("smtpclient")
mlog.SetConfig(map[string]mlog.Level{"": mlog.LevelTrace})
type options struct {
pipelining bool
ecodes bool
@ -43,13 +45,15 @@ func TestClient(t *testing.T) {
starttls bool
eightbitmime bool
smtputf8 bool
requiretls bool
ehlo bool
tlsMode TLSMode
tlsHostname dns.Domain
need8bitmime bool
needsmtputf8 bool
auths []string // Allowed mechanisms.
tlsMode TLSMode
tlsHostname dns.Domain
need8bitmime bool
needsmtputf8 bool
needsrequiretls bool
auths []string // Allowed mechanisms.
nodeliver bool // For server, whether client will attempt a delivery.
}
@ -146,6 +150,9 @@ func TestClient(t *testing.T) {
if opts.smtputf8 {
writeline("250-SMTPUTF8")
}
if opts.requiretls && haveTLS {
writeline("250-REQUIRETLS")
}
if opts.auths != nil {
writeline("250-AUTH " + strings.Join(opts.auths, " "))
}
@ -260,6 +267,7 @@ func TestClient(t *testing.T) {
result <- nil
}()
// todo: should abort tests more properly. on client failures, we may be left with hanging test.
go func() {
defer func() {
x := recover()
@ -268,7 +276,8 @@ func TestClient(t *testing.T) {
}
}()
fail := func(format string, args ...any) {
result <- fmt.Errorf("client: %w", fmt.Errorf(format, args...))
err := fmt.Errorf("client: %w", fmt.Errorf(format, args...))
result <- err
panic("stop")
}
c, err := New(ctx, log, clientConn, opts.tlsMode, localhost, opts.tlsHostname, auths, nil, nil, nil)
@ -279,7 +288,7 @@ func TestClient(t *testing.T) {
result <- nil
return
}
err = c.Deliver(ctx, "postmaster@mox.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), opts.need8bitmime, opts.needsmtputf8)
err = c.Deliver(ctx, "postmaster@mox.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), opts.need8bitmime, opts.needsmtputf8, opts.needsrequiretls)
if (err == nil) != (expDeliverErr == nil) || err != nil && !errors.Is(err, expDeliverErr) {
fail("first deliver: got err %v, expected %v", err, expDeliverErr)
}
@ -288,7 +297,7 @@ func TestClient(t *testing.T) {
if err != nil {
fail("reset: %v", err)
}
err = c.Deliver(ctx, "postmaster@mox.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), opts.need8bitmime, opts.needsmtputf8)
err = c.Deliver(ctx, "postmaster@mox.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), opts.need8bitmime, opts.needsmtputf8, opts.needsrequiretls)
if (err == nil) != (expDeliverErr == nil) || err != nil && !errors.Is(err, expDeliverErr) {
fail("second deliver: got err %v, expected %v", err, expDeliverErr)
}
@ -327,11 +336,13 @@ test
smtputf8: true,
starttls: true,
ehlo: true,
requiretls: true,
tlsMode: TLSStrictStartTLS,
tlsHostname: dns.Domain{ASCII: "mox.example"},
need8bitmime: true,
needsmtputf8: true,
tlsMode: TLSStrictStartTLS,
tlsHostname: dns.Domain{ASCII: "mox.example"},
need8bitmime: true,
needsmtputf8: true,
needsrequiretls: true,
}
test(msg, options{}, nil, nil, nil, nil)
@ -346,6 +357,7 @@ test
test(msg, options{ehlo: true, auths: []string{"SCRAM-SHA-1"}}, []sasl.Client{sasl.NewClientSCRAMSHA1("test", "test")}, nil, nil, nil)
test(msg, options{ehlo: true, auths: []string{"SCRAM-SHA-256"}}, []sasl.Client{sasl.NewClientSCRAMSHA256("test", "test")}, nil, nil, nil)
// todo: add tests for failing authentication, also at various stages in SCRAM
test(msg, options{ehlo: true, requiretls: false, needsrequiretls: true, nodeliver: true}, nil, nil, ErrRequireTLSUnsupported, nil)
// Set an expired certificate. For non-strict TLS, we should still accept it.
// ../rfc/7435:424
@ -441,7 +453,7 @@ func TestErrors(t *testing.T) {
panic(err)
}
msg := ""
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false)
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false, false)
var xerr Error
if err == nil || !errors.Is(err, ErrStatus) || !errors.As(err, &xerr) || !xerr.Permanent {
panic(fmt.Errorf("got %#v, expected ErrStatus with Permanent", err))
@ -461,7 +473,7 @@ func TestErrors(t *testing.T) {
panic(err)
}
msg := ""
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false)
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false, false)
var xerr Error
if err == nil || !errors.Is(err, ErrStatus) || !errors.As(err, &xerr) || xerr.Permanent {
panic(fmt.Errorf("got %#v, expected ErrStatus with not-Permanent", err))
@ -483,7 +495,7 @@ func TestErrors(t *testing.T) {
panic(err)
}
msg := ""
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false)
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false, false)
var xerr Error
if err == nil || !errors.Is(err, ErrStatus) || !errors.As(err, &xerr) || xerr.Permanent {
panic(fmt.Errorf("got %#v, expected ErrStatus with not-Permanent", err))
@ -507,7 +519,7 @@ func TestErrors(t *testing.T) {
panic(err)
}
msg := ""
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false)
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false, false)
var xerr Error
if err == nil || !errors.Is(err, ErrStatus) || !errors.As(err, &xerr) || !xerr.Permanent {
panic(fmt.Errorf("got %#v, expected ErrStatus with Permanent", err))
@ -543,7 +555,7 @@ func TestErrors(t *testing.T) {
panic(err)
}
msg := ""
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false)
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false, false)
var xerr Error
if err == nil || !errors.Is(err, ErrStatus) || !errors.As(err, &xerr) || xerr.Permanent {
panic(fmt.Errorf("got %#v, expected ErrStatus with non-Permanent", err))
@ -574,14 +586,14 @@ func TestErrors(t *testing.T) {
}
msg := ""
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false)
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false, false)
var xerr Error
if err == nil || !errors.Is(err, ErrStatus) || !errors.As(err, &xerr) || xerr.Permanent {
panic(fmt.Errorf("got %#v, expected ErrStatus with non-Permanent", err))
}
// Another delivery.
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false)
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false, false)
if err == nil || !errors.Is(err, ErrStatus) || !errors.As(err, &xerr) || !xerr.Permanent {
panic(fmt.Errorf("got %#v, expected ErrStatus with Permanent", err))
}
@ -604,7 +616,7 @@ func TestErrors(t *testing.T) {
}
msg := ""
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false)
err = c.Deliver(ctx, "postmaster@other.example", "mjl@mox.example", int64(len(msg)), strings.NewReader(msg), false, false, false)
var xerr Error
if err == nil || !errors.Is(err, ErrStatus) || !errors.As(err, &xerr) || !xerr.Permanent {
panic(fmt.Errorf("got %#v, expected ErrStatus with Permanent", err))