infrastructure/mox
1
0
Fork 0
mirror of https://github.com/mjl-/mox.git synced 2025-07-15 10:54:35 +03:00
Code Issues Packages Projects Releases Wiki Activity

add config option to disable tls client auth during tls handshakes

Browse Source 
to work around clients, like the gmail smtp client, that tries to
authenticate with a webpki-issued certificate (which we don't know).

i tried specifying a list of accepted (subjects of) CA certs during the
tls handshake (with just 1 entry, with "xmox.nl" as common name), which
clients can use to influence their cert selection.  however, the gmail
smtp client ignores it, so not a solution for the issue where this was
raised. also, specifying a list of accepted certs could cause other
clients to not send their client cert anymore, breaking existing setups.

i also considered only asking for tls client auth when at least one
account has a tls pubkey configured. but decided against it since any
account can add one on their own (without system admin interaction),
changing behaviour of the system and potentially breaking existing
submission/tls configs.

we now also print the "subject" and "issuer" of certs when tls client
auth fails, should be useful for future debugging.

for issue #359
This commit is contained in:
Mechiel Lukkien
2025-06-09 12:26:58 +02:00
parent f5b8c64b84
commit 833a67fe3d
9 changed files with 55 additions and 35 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
smtpserver/fuzz_test.go
View File

@ -113,7 +113,7 @@ func FuzzServer(f *testing.F) {
const viaHTTPS = false
err := serverConn.SetDeadline(time.Now().Add(time.Second))
flog(err, "set server deadline")
serve("test", cid, dns.Domain{ASCII: "mox.example"}, nil, serverConn, resolver, submission, false, viaHTTPS, 100<<10, false, false, false, nil, 0)
serve("test", cid, dns.Domain{ASCII: "mox.example"}, nil, serverConn, resolver, submission, false, viaHTTPS, false, 100<<10, false, false, false, nil, 0)
cid++
}

35
smtpserver/server.go
View File

@ -206,12 +206,14 @@ func Listen() {
listener := mox.Conf.Static.Listeners[name]
var tlsConfig, tlsConfigDelivery *tls.Config
var noTLSClientAuth bool
if listener.TLS != nil {
tlsConfig = listener.TLS.Config
// For SMTP delivery, if we get a TLS handshake for an SNI hostname that we don't
// allow, we'll fallback to a certificate for the listener hostname instead of
// causing the connection to fail. May improve interoperability.
tlsConfigDelivery = listener.TLS.ConfigFallback
noTLSClientAuth = listener.TLS.ClientAuthDisabled
}
maxMsgSize := listener.SMTPMaxMessageSize
@ -234,7 +236,7 @@ func Listen() {
// https://github.com/golang/go/issues/70232.
tlsConfigDelivery.SessionTicketsDisabled = listener.SMTP.TLSSessionTicketsDisabled == nil || *listener.SMTP.TLSSessionTicketsDisabled
}
listen1("smtp", name, ip, port, hostname, tlsConfigDelivery, false, false, maxMsgSize, false, listener.SMTP.RequireSTARTTLS, !listener.SMTP.NoRequireTLS, listener.SMTP.DNSBLZones, firstTimeSenderDelay)
listen1("smtp", name, ip, port, hostname, tlsConfigDelivery, false, false, noTLSClientAuth, maxMsgSize, false, listener.SMTP.RequireSTARTTLS, !listener.SMTP.NoRequireTLS, listener.SMTP.DNSBLZones, firstTimeSenderDelay)
}
}
if listener.Submission.Enabled {
@ -244,7 +246,7 @@ func Listen() {
}
port := config.Port(listener.Submission.Port, 587)
for _, ip := range listener.IPs {
listen1("submission", name, ip, port, hostname, tlsConfig, true, false, maxMsgSize, !listener.Submission.NoRequireSTARTTLS, !listener.Submission.NoRequireSTARTTLS, true, nil, 0)
listen1("submission", name, ip, port, hostname, tlsConfig, true, false, noTLSClientAuth, maxMsgSize, !listener.Submission.NoRequireSTARTTLS, !listener.Submission.NoRequireSTARTTLS, true, nil, 0)
}
}
@ -255,7 +257,7 @@ func Listen() {
}
port := config.Port(listener.Submissions.Port, 465)
for _, ip := range listener.IPs {
listen1("submissions", name, ip, port, hostname, tlsConfig, true, true, maxMsgSize, true, true, true, nil, 0)
listen1("submissions", name, ip, port, hostname, tlsConfig, true, true, noTLSClientAuth, maxMsgSize, true, true, true, nil, 0)
}
}
}
@ -263,7 +265,7 @@ func Listen() {
var servers []func()
func listen1(protocol, name, ip string, port int, hostname dns.Domain, tlsConfig *tls.Config, submission, xtls bool, maxMessageSize int64, requireTLSForAuth, requireTLSForDelivery, requireTLS bool, dnsBLs []dns.Domain, firstTimeSenderDelay time.Duration) {
func listen1(protocol, name, ip string, port int, hostname dns.Domain, tlsConfig *tls.Config, submission, xtls, noTLSClientAuth bool, maxMessageSize int64, requireTLSForAuth, requireTLSForDelivery, requireTLS bool, dnsBLs []dns.Domain, firstTimeSenderDelay time.Duration) {
log := mlog.New("smtpserver", nil)
addr := net.JoinHostPort(ip, fmt.Sprintf("%d", port))
if os.Getuid() == 0 {
@ -297,7 +299,7 @@ func listen1(protocol, name, ip string, port int, hostname dns.Domain, tlsConfig
// Package is set on the resolver by the dkim/spf/dmarc/etc packages.
resolver := dns.StrictResolver{Log: log.Logger}
go serve(name, mox.Cid(), hostname, tlsConfig, conn, resolver, submission, xtls, false, maxMessageSize, requireTLSForAuth, requireTLSForDelivery, requireTLS, dnsBLs, firstTimeSenderDelay)
go serve(name, mox.Cid(), hostname, tlsConfig, conn, resolver, submission, xtls, false, noTLSClientAuth, maxMessageSize, requireTLSForAuth, requireTLSForDelivery, requireTLS, dnsBLs, firstTimeSenderDelay)
}
}
@ -321,10 +323,11 @@ type conn struct {
origConn net.Conn
conn net.Conn
tls bool
extRequireTLS bool // Whether to announce and allow the REQUIRETLS extension.
viaHTTPS bool // Whether the connection came in via the HTTPS port (using TLS ALPN).
resolver dns.Resolver
tls bool
extRequireTLS bool // Whether to announce and allow the REQUIRETLS extension.
viaHTTPS bool // Whether the connection came in via the HTTPS port (using TLS ALPN).
noTLSClientAuth bool
resolver dns.Resolver
// The "x" in the readers and writes indicate Read and Write errors use panic to
// propagate the error.
xbr *bufio.Reader
@ -435,7 +438,7 @@ func (c *conn) loginAttempt(useTLS bool, authMech string) store.LoginAttempt {
// makeTLSConfig makes a new tls config that is bound to the connection for
// possible client certificate authentication in case of submission.
func (c *conn) makeTLSConfig() *tls.Config {
if !c.submission {
if !c.submission || c.noTLSClientAuth {
return c.baseTLSConfig
}
@ -540,7 +543,7 @@ func (c *conn) tlsClientAuthVerifyPeerCertParsed(cert *x509.Certificate) error {
if err == bstore.ErrAbsent {
la.Result = store.AuthBadCredentials
}
return fmt.Errorf("looking up tls public key with fingerprint %s: %v", fp, err)
return fmt.Errorf("looking up tls public key with fingerprint %s, subject %q, issuer %q: %v", fp, cert.Subject, cert.Issuer, err)
}
la.LoginAddress = pubKey.LoginAddress
@ -620,7 +623,7 @@ func (c *conn) xtlsHandshakeAndAuthenticate(conn net.Conn) {
cancel()
cs := tlsConn.ConnectionState()
if cs.DidResume && len(cs.PeerCertificates) > 0 {
if cs.DidResume && len(cs.PeerCertificates) > 0 && !c.noTLSClientAuth {
// Verify client after session resumption.
err := c.tlsClientAuthVerifyPeerCertParsed(cs.PeerCertificates[0])
if err != nil {
@ -634,6 +637,7 @@ func (c *conn) xtlsHandshakeAndAuthenticate(conn net.Conn) {
slog.String("ciphersuite", ciphersuite),
slog.String("sni", cs.ServerName),
slog.Bool("resumed", cs.DidResume),
slog.Bool("notlsclientauth", c.noTLSClientAuth),
slog.Int("clientcerts", len(cs.PeerCertificates)),
}
if c.account != nil {
@ -860,10 +864,10 @@ var cleanClose struct{} // Sentinel value for panic/recover indicating clean clo
func ServeTLSConn(listenerName string, hostname dns.Domain, conn *tls.Conn, tlsConfig *tls.Config, submission, viaHTTPS bool, maxMsgSize int64, requireTLS bool) {
log := mlog.New("smtpserver", nil)
resolver := dns.StrictResolver{Log: log.Logger}
serve(listenerName, mox.Cid(), hostname, tlsConfig, conn, resolver, submission, true, viaHTTPS, maxMsgSize, true, true, requireTLS, nil, 0)
serve(listenerName, mox.Cid(), hostname, tlsConfig, conn, resolver, submission, true, viaHTTPS, true, maxMsgSize, true, true, requireTLS, nil, 0)
}
func serve(listenerName string, cid int64, hostname dns.Domain, tlsConfig *tls.Config, nc net.Conn, resolver dns.Resolver, submission, xtls, viaHTTPS bool, maxMessageSize int64, requireTLSForAuth, requireTLSForDelivery, requireTLS bool, dnsBLs []dns.Domain, firstTimeSenderDelay time.Duration) {
func serve(listenerName string, cid int64, hostname dns.Domain, tlsConfig *tls.Config, nc net.Conn, resolver dns.Resolver, submission, xtls, viaHTTPS, noTLSClientAuth bool, maxMessageSize int64, requireTLSForAuth, requireTLSForDelivery, requireTLS bool, dnsBLs []dns.Domain, firstTimeSenderDelay time.Duration) {
var localIP, remoteIP net.IP
if a, ok := nc.LocalAddr().(*net.TCPAddr); ok {
localIP = a.IP
@ -890,6 +894,7 @@ func serve(listenerName string, cid int64, hostname dns.Domain, tlsConfig *tls.C
submission: submission,
tls: xtls,
viaHTTPS: viaHTTPS,
noTLSClientAuth: noTLSClientAuth,
extRequireTLS: requireTLS,
resolver: resolver,
lastlog: time.Now(),
@ -1209,7 +1214,7 @@ func (c *conn) cmdHello(p *parser, ehlo bool) {
// case, or it would trigger the mechanism downgrade detection.
mechs = "SCRAM-SHA-256-PLUS SCRAM-SHA-256 SCRAM-SHA-1-PLUS SCRAM-SHA-1 CRAM-MD5 PLAIN LOGIN"
}
if c.tls && len(c.conn.(*tls.Conn).ConnectionState().PeerCertificates) > 0 && !c.viaHTTPS {
if c.tls && len(c.conn.(*tls.Conn).ConnectionState().PeerCertificates) > 0 && !c.viaHTTPS && !c.noTLSClientAuth {
mechs = "EXTERNAL " + mechs
}
c.xbwritelinef("250-AUTH %s", mechs)

6
smtpserver/server_test.go
View File

@ -257,7 +257,7 @@ func (ts *testserver) runRaw(fn func(clientConn net.Conn)) {
defer func() { <-serverdone }()
go func() {
serve("test", ts.cid-2, dns.Domain{ASCII: "mox.example"}, ts.serverConfig, serverConn, ts.resolver, ts.submission, ts.immediateTLS, false, 100<<20, false, false, ts.requiretls, ts.dnsbls, 0)
serve("test", ts.cid-2, dns.Domain{ASCII: "mox.example"}, ts.serverConfig, serverConn, ts.resolver, ts.submission, ts.immediateTLS, false, false, 100<<20, false, false, ts.requiretls, ts.dnsbls, 0)
close(serverdone)
}()
@ -476,7 +476,7 @@ func TestSubmission(t *testing.T) {
tlsConfig := &tls.Config{
Certificates: []tls.Certificate{fakeCert(ts.t, false)},
}
serve("test", ts.cid-2, dns.Domain{ASCII: "mox.example"}, tlsConfig, serverConn, ts.resolver, ts.submission, ts.immediateTLS, false, 100<<20, false, false, false, ts.dnsbls, 0)
serve("test", ts.cid-2, dns.Domain{ASCII: "mox.example"}, tlsConfig, serverConn, ts.resolver, ts.submission, ts.immediateTLS, false, false, 100<<20, false, false, false, ts.dnsbls, 0)
close(serverdone)
}()
@ -1426,7 +1426,7 @@ func TestNonSMTP(t *testing.T) {
tlsConfig := &tls.Config{
Certificates: []tls.Certificate{fakeCert(ts.t, false)},
}
serve("test", ts.cid-2, dns.Domain{ASCII: "mox.example"}, tlsConfig, serverConn, ts.resolver, ts.submission, false, false, 100<<20, false, false, false, ts.dnsbls, 0)
serve("test", ts.cid-2, dns.Domain{ASCII: "mox.example"}, tlsConfig, serverConn, ts.resolver, ts.submission, false, false, false, 100<<20, false, false, false, ts.dnsbls, 0)
close(serverdone)
}()