git » chasquid » commit 216cf47

diff --git a/chasquid.go b/chasquid.go
index 80fb3af..640850d 100644
--- a/chasquid.go
+++ b/chasquid.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"expvar"
 	"flag"
 	"fmt"
@@ -19,6 +20,7 @@ import (
 	"blitiri.com.ar/go/chasquid/internal/maillog"
 	"blitiri.com.ar/go/chasquid/internal/normalize"
 	"blitiri.com.ar/go/chasquid/internal/smtpsrv"
+	"blitiri.com.ar/go/chasquid/internal/sts"
 	"blitiri.com.ar/go/chasquid/internal/systemd"
 	"blitiri.com.ar/go/chasquid/internal/userdb"
 
@@ -135,12 +137,18 @@ func main() {
 
 	dinfo := s.InitDomainInfo(conf.DataDir + "/domaininfo")
 
+	stsCache, err := sts.NewCache(conf.DataDir + "/sts-cache")
+	if err != nil {
+		log.Fatalf("Failed to initialize STS cache: %v", err)
+	}
+	go stsCache.PeriodicallyRefresh(context.Background())
+
 	localC := &courier.Procmail{
 		Binary:  conf.MailDeliveryAgentBin,
 		Args:    conf.MailDeliveryAgentArgs,
 		Timeout: 30 * time.Second,
 	}
-	remoteC := &courier.SMTP{Dinfo: dinfo}
+	remoteC := &courier.SMTP{Dinfo: dinfo, STSCache: stsCache}
 	s.InitQueue(conf.DataDir+"/queue", localC, remoteC)
 
 	// Load the addresses and listeners.
diff --git a/internal/courier/smtp.go b/internal/courier/smtp.go
index 159eee4..3fa98ad 100644
--- a/internal/courier/smtp.go
+++ b/internal/courier/smtp.go
@@ -1,6 +1,7 @@
 package courier
 
 import (
+	"context"
 	"crypto/tls"
 	"expvar"
 	"flag"
@@ -13,6 +14,7 @@ import (
 	"blitiri.com.ar/go/chasquid/internal/domaininfo"
 	"blitiri.com.ar/go/chasquid/internal/envelope"
 	"blitiri.com.ar/go/chasquid/internal/smtp"
+	"blitiri.com.ar/go/chasquid/internal/sts"
 	"blitiri.com.ar/go/chasquid/internal/trace"
 )
 
@@ -26,6 +28,11 @@ var (
 	smtpPort = flag.String("testing__outgoing_smtp_port", "25",
 		"port to use for outgoing SMTP connections, ONLY FOR TESTING")
 
+	// Enable STS policy checking; this is an experimental flag and will be
+	// removed in the future, once this is made the default.
+	enableSTS = flag.Bool("experimental__enable_sts", false,
+		"enable STS policy checking; EXPERIMENTAL")
+
 	// Fake MX records, used for testing only.
 	fakeMX = map[string][]string{}
 )
@@ -34,20 +41,25 @@ var (
 var (
 	tlsCount   = expvar.NewMap("chasquid/smtpOut/tlsCount")
 	slcResults = expvar.NewMap("chasquid/smtpOut/securityLevelChecks")
+
+	stsSecurityModes   = expvar.NewMap("chasquid/smtpOut/sts/mode")
+	stsSecurityResults = expvar.NewMap("chasquid/smtpOut/sts/security")
 )
 
 // SMTP delivers remote mail via outgoing SMTP.
 type SMTP struct {
-	Dinfo *domaininfo.DB
+	Dinfo    *domaininfo.DB
+	STSCache *sts.PolicyCache
 }
 
 func (s *SMTP) Deliver(from string, to string, data []byte) (error, bool) {
 	a := &attempt{
-		courier: s,
-		from:    from,
-		to:      to,
-		data:    data,
-		tr:      trace.New("Courier.SMTP", to),
+		courier:  s,
+		from:     from,
+		to:       to,
+		data:     data,
+		toDomain: envelope.DomainOf(to),
+		tr:       trace.New("Courier.SMTP", to),
 	}
 	defer a.tr.Finish()
 	a.tr.Debugf("%s  ->  %s", from, to)
@@ -57,8 +69,9 @@ func (s *SMTP) Deliver(from string, to string, data []byte) (error, bool) {
 		a.from = ""
 	}
 
-	toDomain := envelope.DomainOf(to)
-	mxs, err := lookupMXs(a.tr, toDomain)
+	a.stsPolicy = s.fetchSTSPolicy(a.tr, a.toDomain)
+
+	mxs, err := lookupMXs(a.tr, a.toDomain, a.stsPolicy)
 	if err != nil {
 		// Note this is considered a permanent error.
 		// This is in line with what other servers (Exim) do. However, the
@@ -104,6 +117,8 @@ type attempt struct {
 	toDomain    string
 	helloDomain string
 
+	stsPolicy *sts.Policy
+
 	tr *trace.Trace
 }
 
@@ -171,6 +186,18 @@ retry:
 	}
 	slcResults.Add("pass", 1)
 
+	if a.stsPolicy != nil && a.stsPolicy.Mode == sts.Enforce {
+		// The connection MUST be validated TLS.
+		// https://tools.ietf.org/html/draft-ietf-uta-mta-sts-03#section-4.2
+		if secLevel != domaininfo.SecLevel_TLS_SECURE {
+			stsSecurityResults.Add("fail", 1)
+			return a.tr.Errorf("invalid security level (%v) for STS policy",
+				secLevel), false
+		}
+		stsSecurityResults.Add("pass", 1)
+		a.tr.Debugf("STS policy: connection is using valid TLS")
+	}
+
 	if err = c.MailAndRcpt(a.from, a.to); err != nil {
 		return a.tr.Errorf("MAIL+RCPT %v", err), smtp.IsPermanent(err)
 	}
@@ -195,7 +222,29 @@ retry:
 	return nil, false
 }
 
-func lookupMXs(tr *trace.Trace, domain string) ([]string, error) {
+func (s *SMTP) fetchSTSPolicy(tr *trace.Trace, domain string) *sts.Policy {
+	if !*enableSTS {
+		return nil
+	}
+	if s.STSCache == nil {
+		return nil
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Minute)
+	defer cancel()
+
+	policy, err := s.STSCache.Fetch(ctx, domain)
+	if err != nil {
+		return nil
+	}
+
+	tr.Debugf("got STS policy")
+	stsSecurityModes.Add(string(policy.Mode), 1)
+
+	return policy
+}
+
+func lookupMXs(tr *trace.Trace, domain string, policy *sts.Policy) ([]string, error) {
 	if v, ok := fakeMX[domain]; ok {
 		return v, nil
 	}
@@ -239,12 +288,39 @@ func lookupMXs(tr *trace.Trace, domain string) ([]string, error) {
 	// This case is explicitly covered by the SMTP RFC.
 	// https://tools.ietf.org/html/rfc5321#section-5.1
 
-	// Cap the list of MXs to 5 hosts, to keep delivery attempt times sane
-	// and prevent abuse.
-	if len(mxs) > 5 {
+	mxs = filterMXs(tr, policy, mxs)
+	if len(mxs) == 0 {
+		tr.Errorf("domain %q has no valid MX/A record", domain)
+	} else if len(mxs) > 5 {
+		// Cap the list of MXs to 5 hosts, to keep delivery attempt times
+		// sane and prevent abuse.
 		mxs = mxs[:5]
 	}
 
 	tr.Debugf("MXs: %v", mxs)
 	return mxs, nil
 }
+
+func filterMXs(tr *trace.Trace, p *sts.Policy, mxs []string) []string {
+	if p == nil {
+		return mxs
+	}
+
+	filtered := []string{}
+	for _, mx := range mxs {
+		if p.MXIsAllowed(mx) {
+			filtered = append(filtered, mx)
+		} else {
+			tr.Printf("MX %q not allowed by policy, skipping", mx)
+		}
+	}
+
+	// We don't want to return an empty set if the mode is not enforce.
+	// This prevents failures for policies in reporting mode.
+	// https://tools.ietf.org/html/draft-ietf-uta-mta-sts-03#section-5.2
+	if len(filtered) == 0 && p.Mode != sts.Enforce {
+		filtered = mxs
+	}
+
+	return filtered
+}
diff --git a/internal/courier/smtp_test.go b/internal/courier/smtp_test.go
index 703acc3..e1e624c 100644
--- a/internal/courier/smtp_test.go
+++ b/internal/courier/smtp_test.go
@@ -23,7 +23,7 @@ func newSMTP(t *testing.T) (*SMTP, string) {
 		t.Fatal(err)
 	}
 
-	return &SMTP{dinfo}, dir
+	return &SMTP{dinfo, nil}, dir
 }
 
 // Fake server, to test SMTP out.