check/authorize_sender: Implement MAIL FROM, From header authorization for local senders

Closes #268.

docs/man/maddy-filters.5.scd

@@ -872,3 +872,91 @@ X-Spam-Flag and X-Spam-Score are added to the header irregardless of value.
 
 Flags to pass to the rspamd server.
 See https://rspamd.com/doc/architecture/protocol.html for details.
+
+## MAIL FROM and From authorization (check.authorize_sender)
+
+This check verifies that envelope and header sender addresses belong
+to the authenticated user. Address ownership is established via table
+that maps each user account to a email address it is allowed to use.
+There are some special cases, see user_to_email description below.
+
+```
+check.authorize_sender {
+    prepare_email identity
+    user_to_email identity
+    check_header yes
+
+    unauth_action reject
+    no_match_action reject
+    malformed_action reject
+    err_action reject
+
+    auth_normalize precis_casefold_email
+    from_normalize precis_casefold_email
+}
+```
+```
+check {
+    authorize_sender { ... }
+}
+```
+
+## Configuration directives
+
+*Syntax:* user_to_email _table_ ++
+*Default:* identity
+
+Table to use for lookups. Result of the lookup should contain either the
+domain name, the full email address or "*" string. If it is just domain - user
+will be allowed to use any mailbox within a domain as a sender address.
+If result contains "*" - user will be allowed to use any address.
+
+*Syntax:* check_header _boolean_ ++
+*Default:* yes
+
+Whether to verify header sender in addition to envelope.
+
+Either Sender or From field value should match the
+authorization identity.
+
+*Syntax:* unauth_action _action_ ++
+*Default:* reject
+
+What to do if the user is not authenticated at all.
+
+*Syntax:* no_match_action _action_ ++
+*Default:* reject
+
+What to do if user is not allowed to use the sender address specified.
+
+*Syntax:* malformed_action _action_ ++
+*Default:* reject
+
+What to do if From or Sender header fields contain malformed values.
+
+*Syntax:* err_action _action_ ++
+*Default:* reject
+
+What to do if error happens during prepare_email or user_to_email lookup.
+
+*Syntax:* auth_normalize _action_ ++
+*Default:* precis_casefold_email
+
+Normalization function to apply to authorization username before
+further processing.
+
+Available options:
+- precis_casefold_email   PRECIS UsernameCaseMapped profile + U-labels form for domain
+- precis_casefold         PRECIS UsernameCaseMapped profile for the entire string
+- precis_email            PRECIS UsernameCasePreserved profile + U-labels form for domain
+- precis                  PRECIS UsernameCasePreserved profile for the entire string
+- casefold                Convert to lower case
+- noop                    Nothing
+
+*Syntax:* from_normalize _action_ ++
+*Default:* precis_casefold_email
+
+Normalization function to apply to email addresses before
+further processing.
+
+Available options are same as for auth_normalize.

framework/address/norm.go

@@ -19,11 +19,13 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 package address
 
 import (
+	"fmt"
 	"strings"
 	"unicode/utf8"
 
 	"github.com/foxcpp/maddy/framework/dns"
 	"golang.org/x/net/idna"
+	"golang.org/x/text/secure/precis"
 	"golang.org/x/text/unicode/norm"
 )
 
@@ -112,3 +114,41 @@ func IsASCII(s string) bool {
 	}
 	return true
 }
+
+// PRECISFold applies UsernameCaseMapped to the local part and dns.ForLookup
+// to domain part of the address.
+func PRECISFold(addr string) (string, error) {
+	return precisEmail(addr, precis.UsernameCaseMapped)
+}
+
+// PRECIS applies UsernameCasePreserved to the local part and dns.ForLookup
+// to domain part of the address.
+func PRECIS(addr string) (string, error) {
+	return precisEmail(addr, precis.UsernameCasePreserved)
+}
+
+func precisEmail(addr string, profile *precis.Profile) (string, error) {
+	mbox, domain, err := Split(addr)
+	if err != nil {
+		return "", fmt.Errorf("address: precis: %w", err)
+	}
+
+	// PRECISFold is not included in the regular address.ForLookup since it reduces
+	// the range of valid addresses to a subset of actually valid values.
+	// PRECISFold is a matter of our own local policy, not a general rule for all
+	// email addresses.
+
+	// Side note: For used profiles, there is no practical difference between
+	// CompareKey and String.
+	mbox, err = profile.CompareKey(mbox)
+	if err != nil {
+		return "", fmt.Errorf("address: precis: %w", err)
+	}
+
+	domain, err = dns.ForLookup(domain)
+	if err != nil {
+		return "", fmt.Errorf("address: precis: %w", err)
+	}
+
+	return mbox + "@" + domain, nil
+}

framework/module/table.go

@@ -18,7 +18,9 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 package module
 
-// Tabele is the interface implemented by module that implementation string-to-string
+import "context"
+
+// Table is the interface implemented by module that implementation string-to-string
 // translation.
 //
 // Modules implementing this interface should be registered with prefix
@@ -27,6 +29,12 @@ type Table interface {
 	Lookup(s string) (string, bool, error)
 }
 
+// MultiTable is the interface that module can implement in addition to Table
+// if it can provide multiple values as a lookup result.
+type MultiTable interface {
+	LookupMulti(ctx context.Context, s string) ([]string, error)
+}
+
 type MutableTable interface {
 	Table
 	Keys() ([]string, error)

internal/authz/lookup.go

@@ -0,0 +1,40 @@
+package authz
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/foxcpp/maddy/framework/address"
+	"github.com/foxcpp/maddy/framework/module"
+)
+
+func AuthorizeEmailUse(ctx context.Context, username, addr string, mapping module.Table) (bool, error) {
+	_, domain, err := address.Split(addr)
+	if err != nil {
+		return false, fmt.Errorf("authz: %w", err)
+	}
+
+	var validEmails []string
+	if multi, ok := mapping.(module.MultiTable); ok {
+		validEmails, err = multi.LookupMulti(ctx, username)
+		if err != nil {
+			return false, fmt.Errorf("authz: %w", err)
+		}
+	} else {
+		validEmail, ok, err := mapping.Lookup(username)
+		if err != nil {
+			return false, fmt.Errorf("authz: %w", err)
+		}
+		if ok {
+			validEmails = []string{validEmail}
+		}
+	}
+
+	for _, ent := range validEmails {
+		if ent == domain || ent == "*" || ent == addr {
+			return true, nil
+		}
+	}
+
+	return false, nil
+}

internal/authz/normalization.go

@@ -0,0 +1,23 @@
+package authz
+
+import (
+	"strings"
+
+	"github.com/foxcpp/maddy/framework/address"
+	"golang.org/x/text/secure/precis"
+)
+
+// NormalizeFuncs defines configurable normalization functions to be used
+// in authentication and authorization routines.
+var NormalizeFuncs = map[string]func(string) (string, error){
+	"precis_casefold_email": address.PRECISFold,
+	"precis_casefold":       precis.UsernameCaseMapped.CompareKey,
+	"precis_email":          address.PRECIS,
+	"precis":                precis.UsernameCasePreserved.CompareKey,
+	"casefold": func(s string) (string, error) {
+		return strings.ToLower(s), nil
+	},
+	"noop": func(s string) (string, error) {
+		return s, nil
+	},
+}

internal/check/authorize_sender/authorize_sender.go

@@ -0,0 +1,311 @@
+/*
+Maddy Mail Server - Composable all-in-one email server.
+Copyright © 2019-2020 Max Mazurov <fox.cpp@disroot.org>, Maddy Mail Server contributors
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+package authorize_sender
+
+import (
+	"context"
+	"fmt"
+	"net/mail"
+
+	"github.com/emersion/go-message/textproto"
+	"github.com/foxcpp/maddy/framework/buffer"
+	"github.com/foxcpp/maddy/framework/config"
+	modconfig "github.com/foxcpp/maddy/framework/config/module"
+	"github.com/foxcpp/maddy/framework/exterrors"
+	"github.com/foxcpp/maddy/framework/log"
+	"github.com/foxcpp/maddy/framework/module"
+	"github.com/foxcpp/maddy/internal/authz"
+	"github.com/foxcpp/maddy/internal/table"
+	"github.com/foxcpp/maddy/internal/target"
+)
+
+const modName = "check.authorize_sender"
+
+type Check struct {
+	instName string
+	log      log.Logger
+
+	checkHeader  bool
+	emailPrepare module.Table
+	userToEmail  module.Table
+
+	unauthAction  modconfig.FailAction
+	noMatchAction modconfig.FailAction
+	errAction     modconfig.FailAction
+
+	fromNorm func(string) (string, error)
+	authNorm func(string) (string, error)
+}
+
+func New(_, instName string, _, inlineArgs []string) (module.Module, error) {
+	return &Check{
+		instName: instName,
+	}, nil
+}
+
+func (c *Check) Name() string {
+	return modName
+}
+
+func (c *Check) InstanceName() string {
+	return c.instName
+}
+
+func (c *Check) Init(cfg *config.Map) error {
+	cfg.Bool("debug", true, false, &c.log.Debug)
+
+	cfg.Bool("check_header", false, true, &c.checkHeader)
+
+	cfg.Custom("prepare_email", false, false, func() (interface{}, error) {
+		return &table.Identity{}, nil
+	}, modconfig.TableDirective, &c.emailPrepare)
+	cfg.Custom("user_to_email", false, false, func() (interface{}, error) {
+		return &table.Identity{}, nil
+	}, modconfig.TableDirective, &c.userToEmail)
+
+	cfg.Custom("unauth_action", false, false, func() (interface{}, error) {
+		return modconfig.FailAction{Reject: true}, nil
+	}, modconfig.FailActionDirective, &c.unauthAction)
+	cfg.Custom("no_match_action", false, false, func() (interface{}, error) {
+		return modconfig.FailAction{Reject: true}, nil
+	}, modconfig.FailActionDirective, &c.noMatchAction)
+	cfg.Custom("err_action", false, false, func() (interface{}, error) {
+		return modconfig.FailAction{Reject: true}, nil
+	}, modconfig.FailActionDirective, &c.errAction)
+
+	var (
+		authNormalize string
+		fromNormalize string
+		ok            bool
+	)
+	cfg.String("auth_normalize", false, false,
+		"precis_casefold_email", &authNormalize)
+	cfg.String("from_normalize", false, false,
+		"precis_casefold_email", &fromNormalize)
+
+	if _, err := cfg.Process(); err != nil {
+		return err
+	}
+
+	c.authNorm, ok = authz.NormalizeFuncs[authNormalize]
+	if !ok {
+		return fmt.Errorf("%v: unknown normalization function: %v", modName, authNormalize)
+	}
+	c.fromNorm, ok = authz.NormalizeFuncs[fromNormalize]
+	if !ok {
+		return fmt.Errorf("%v: unknown normalization function: %v", modName, fromNormalize)
+	}
+
+	return nil
+}
+
+type state struct {
+	c       *Check
+	msgMeta *module.MsgMetadata
+	log     log.Logger
+}
+
+func (c *Check) CheckStateForMsg(_ context.Context, msgMeta *module.MsgMetadata) (module.CheckState, error) {
+	return &state{
+		c:       c,
+		msgMeta: msgMeta,
+		log:     target.DeliveryLogger(c.log, msgMeta),
+	}, nil
+}
+
+func (s *state) authzSender(ctx context.Context, authName, email string) module.CheckResult {
+	if authName == "" {
+		return s.c.unauthAction.Apply(module.CheckResult{
+			Reason: &exterrors.SMTPError{
+				Code:         530,
+				EnhancedCode: exterrors.EnhancedCode{5, 7, 0},
+				Message:      "Authentication required",
+				CheckName:    modName,
+			}})
+	}
+
+	fromEmailNorm, err := s.c.fromNorm(email)
+	if err != nil {
+		return s.c.errAction.Apply(module.CheckResult{
+			Reason: &exterrors.SMTPError{
+				Code:         553,
+				EnhancedCode: exterrors.EnhancedCode{5, 1, 7},
+				Message:      "Unable to normalize sender address",
+				CheckName:    modName,
+				Err:          err,
+			}})
+	}
+	authNameNorm, err := s.c.authNorm(authName)
+	if err != nil {
+		return s.c.errAction.Apply(module.CheckResult{
+			Reason: &exterrors.SMTPError{
+				Code:         535,
+				EnhancedCode: exterrors.EnhancedCode{5, 7, 8},
+				Message:      "Unable to normalize authorization username",
+				CheckName:    modName,
+			}})
+	}
+
+	s.log.DebugMsg("normalized names", "from", fromEmailNorm, "auth", authNameNorm)
+
+	preparedEmail, ok, err := s.c.emailPrepare.Lookup(fromEmailNorm)
+	if err != nil {
+		return s.c.errAction.Apply(module.CheckResult{
+			Reason: &exterrors.SMTPError{
+				Code:         454,
+				EnhancedCode: exterrors.EnhancedCode{4, 7, 0},
+				Message:      "Internal error during policy check",
+				CheckName:    modName,
+				Err:          err,
+			}})
+	}
+	if !ok {
+		preparedEmail = fromEmailNorm
+	}
+
+	ok, err = authz.AuthorizeEmailUse(ctx, authNameNorm, preparedEmail, s.c.userToEmail)
+	if err != nil {
+		return s.c.errAction.Apply(module.CheckResult{
+			Reason: &exterrors.SMTPError{
+				Code:         454,
+				EnhancedCode: exterrors.EnhancedCode{4, 7, 0},
+				Message:      "Internal error during policy check",
+				CheckName:    modName,
+				Err:          err,
+			}})
+	}
+	if !ok {
+		return s.c.noMatchAction.Apply(module.CheckResult{
+			Reason: &exterrors.SMTPError{
+				Code:         553,
+				EnhancedCode: exterrors.EnhancedCode{5, 7, 0},
+				Message:      "Unauthorized use of sender address",
+				CheckName:    modName,
+			}})
+	}
+
+	return module.CheckResult{}
+}
+
+func (s *state) CheckConnection(_ context.Context) module.CheckResult {
+	return module.CheckResult{}
+}
+
+func (s *state) CheckSender(ctx context.Context, fromEmail string) module.CheckResult {
+	if s.msgMeta.Conn == nil {
+		s.log.Msg("skipping locally generated message")
+		return module.CheckResult{}
+	}
+	authName := s.msgMeta.Conn.AuthUser
+
+	return s.authzSender(ctx, authName, fromEmail)
+}
+
+func (s *state) CheckRcpt(_ context.Context, _ string) module.CheckResult {
+	return module.CheckResult{}
+}
+
+func (s *state) CheckBody(ctx context.Context, hdr textproto.Header, _ buffer.Buffer) module.CheckResult {
+	if !s.c.checkHeader {
+		return module.CheckResult{}
+	}
+	if s.msgMeta.Conn == nil {
+		s.log.Msg("skipping locally generated message")
+		return module.CheckResult{}
+	}
+	authName := s.msgMeta.Conn.AuthUser
+
+	fromHdr := hdr.Get("From")
+	if fromHdr == "" {
+		return s.c.errAction.Apply(module.CheckResult{
+			Reason: &exterrors.SMTPError{
+				Code:         550,
+				EnhancedCode: exterrors.EnhancedCode{5, 7, 0},
+				Message:      "Missing From header",
+				CheckName:    modName,
+			}})
+	}
+	list, err := mail.ParseAddressList(fromHdr)
+	if err != nil || len(list) == 0 {
+		return s.c.errAction.Apply(module.CheckResult{
+			Reason: &exterrors.SMTPError{
+				Code:         550,
+				EnhancedCode: exterrors.EnhancedCode{5, 7, 0},
+				Message:      "Malformed From header",
+				CheckName:    modName,
+				Err:          err,
+			}})
+	}
+	fromEmail := list[0].Address
+	if len(list) > 1 {
+		return s.c.errAction.Apply(module.CheckResult{
+			Reason: &exterrors.SMTPError{
+				Code:         550,
+				EnhancedCode: exterrors.EnhancedCode{5, 7, 0},
+				Message:      "Multiple From addresses are not allowed",
+				CheckName:    modName,
+				Err:          err,
+			}})
+	}
+
+	var senderAddr string
+	if senderHdr := hdr.Get("Sender"); senderHdr != "" {
+		sender, err := mail.ParseAddress(senderHdr)
+		if err != nil {
+			return s.c.errAction.Apply(module.CheckResult{
+				Reason: &exterrors.SMTPError{
+					Code:         550,
+					EnhancedCode: exterrors.EnhancedCode{5, 7, 0},
+					Message:      "Malformed Sender header",
+					CheckName:    modName,
+					Err:          err,
+				}})
+		}
+		senderAddr = sender.Address
+	}
+
+	res := s.authzSender(ctx, authName, fromEmail)
+	if res.Reason == nil {
+		return res
+	}
+
+	if senderAddr != "" && senderAddr != fromEmail {
+		res = s.authzSender(ctx, authName, senderAddr)
+		if res.Reason == nil {
+			return res
+		}
+	}
+
+	// Neither matched.
+	return s.c.noMatchAction.Apply(module.CheckResult{
+		Reason: &exterrors.SMTPError{
+			Code:         553,
+			EnhancedCode: exterrors.EnhancedCode{5, 7, 0},
+			Message:      "Unauthorized use of sender address",
+			CheckName:    modName,
+		}})
+}
+
+func (s *state) Close() error {
+	return nil
+}
+
+func init() {
+	module.Register(modName, New)
+}

internal/storage/imapsql/normalize.go

@@ -19,43 +19,15 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 package imapsql
 
 import (
-	"fmt"
 	"strings"
 
 	"github.com/foxcpp/maddy/framework/address"
-	"github.com/foxcpp/maddy/framework/dns"
 	"golang.org/x/text/secure/precis"
 )
 
 var normalizeFuncs = map[string]func(string) (string, error){
-	"precis_email": func(s string) (string, error) {
-		mbox, domain, err := address.Split(s)
-		if err != nil {
-			return "", fmt.Errorf("imapsql: username prepare: %w", err)
-		}
-
-		// PRECIS is not included in the regular address.ForLookup since it reduces
-		// the range of valid addresses to a subset of actually valid values.
-		// PRECIS is a matter of our own local policy, not a general rule for all
-		// email addresses.
-
-		// Side note: For used profiles, there is no practical difference between
-		// CompareKey and String.
-		mbox, err = precis.UsernameCaseMapped.CompareKey(mbox)
-		if err != nil {
-			return "", fmt.Errorf("imapsql: username prepare: %w", err)
-		}
-
-		domain, err = dns.ForLookup(domain)
-		if err != nil {
-			return "", fmt.Errorf("imapsql: username prepare: %w", err)
-		}
-
-		return mbox + "@" + domain, nil
-	},
-	"precis": func(s string) (string, error) {
-		return precis.UsernameCaseMapped.CompareKey(s)
-	},
+	"precis_email": address.PRECISFold,
+	"precis":       precis.UsernameCaseMapped.CompareKey,
 	"casefold": func(s string) (string, error) {
 		return strings.ToLower(s), nil
 	},

maddy.go

@@ -44,6 +44,7 @@ import (
 	_ "github.com/foxcpp/maddy/internal/auth/pass_table"
 	_ "github.com/foxcpp/maddy/internal/auth/plain_separate"
 	_ "github.com/foxcpp/maddy/internal/auth/shadow"
+	_ "github.com/foxcpp/maddy/internal/check/authorize_sender"
 	_ "github.com/foxcpp/maddy/internal/check/command"
 	_ "github.com/foxcpp/maddy/internal/check/dkim"
 	_ "github.com/foxcpp/maddy/internal/check/dns"

tests/conn.go

@@ -21,6 +21,7 @@ package tests
 import (
 	"bufio"
 	"crypto/tls"
+	"encoding/base64"
 	"fmt"
 	"io"
 	"net"
@@ -201,6 +202,20 @@ func (c *Conn) TLS() {
 	c.Scanner = bufio.NewScanner(c.Conn)
 }
 
+func (c *Conn) SMTPPlainAuth(username, password string, expectOk bool) {
+	c.T.Helper()
+
+	resp := append([]byte{0x00}, username...)
+	resp = append(resp, 0x00)
+	resp = append(resp, password...)
+	c.Writeln("AUTH PLAIN " + base64.StdEncoding.EncodeToString(resp))
+	if expectOk {
+		c.ExpectPattern("235 *")
+	} else {
+		c.ExpectPattern("*")
+	}
+}
+
 func (c *Conn) SMTPNegotation(ourName string, requireExts, blacklistExts []string) {
 	c.T.Helper()
 

tests/smtp_test.go

@@ -343,6 +343,77 @@ func TestDNSBLConfig2(tt *testing.T) {
 	conn.ExpectPattern("221 *")
 }
 
+func TestCheckAuthorizeSender(tt *testing.T) {
+	tt.Parallel()
+	t := tests.NewT(tt)
+	t.DNS(nil)
+	t.Port("smtp")
+	t.Config(`
+		smtp tcp://127.0.0.1:{env:TEST_PORT_smtp} {
+			hostname mx.maddy.test
+			tls off
+
+			auth dummy
+			defer_sender_reject off
+
+			source example1.org {
+				check {
+					authorize_sender {
+						auth_normalize precis_casefold
+						user_to_email static {
+							entry "test-user1" "test@example1.org"
+							entry "test-user2" "é@example1.org" 
+						}
+					}
+				}
+				deliver_to dummy
+			}
+			source example2.org {
+				check {
+					authorize_sender {
+						auth_normalize precis_casefold
+						prepare_email static {
+							entry "alias-to-test@example2.org" "test@example2.org"
+						}
+						user_to_email static {
+							entry "test-user1" "test@example2.org"
+							entry "test-user2" "test2@example2.org"
+						}
+					}
+				}
+				deliver_to dummy
+			}
+
+			default_source {
+				reject
+			}
+		}`)
+	t.Run(1)
+	defer t.Close()
+
+	c := t.Conn("smtp")
+	c.SMTPNegotation("client.maddy.test", nil, nil)
+	c.SMTPPlainAuth("test-user2", "1", true)
+	c.Writeln("MAIL FROM:<test@example1.org>")
+	c.ExpectPattern("5*") // rejected - user is not test-user1
+	c.Writeln("MAIL FROM:<test3@example1.org>")
+	c.ExpectPattern("5*") // rejected - unknown email
+	c.Writeln("MAIL FROM:<E\u0301@EXAMPLE1.org> SMTPUTF8")
+	c.ExpectPattern("2*") // OK - é@example1.org belongs to test-user2
+	c.Close()
+
+	c = t.Conn("smtp")
+	c.SMTPNegotation("client.maddy.test", nil, nil)
+	c.SMTPPlainAuth("test-user1", "1", true)
+	c.Writeln("MAIL FROM:<test2@example2.org>")
+	c.ExpectPattern("5*") // rejected - user is not test-user2
+	c.Writeln("MAIL FROM:<test@example2.org>")
+	c.ExpectPattern("2*") // OK - test@example2.org belongs to test-user
+	c.Writeln("MAIL FROM:<alias-to-test@example2.org>")
+	c.ExpectPattern("2*") // OK - test@example2.org belongs to test-user
+	c.Close()
+}
+
 func TestCheckCommand(tt *testing.T) {
 	tt.Parallel()
 	t := tests.NewT(tt)