audit 2c: findings of the two reviews

Technical review (Opus, 11 findings, 2 medium) and security review (Fable,
no high or medium) of 3c86280..HEAD. Both confirm the port gives
dkim_mail_parse()'s result on every input it parses, and that no line the
check passes is signed with another domain's key.

- F1 (medium): OpenDKIM's parser takes lines no mail program reads as one
  address - "ceo@bank.com:me@mine.com", "Name <ceo@bank.com:me@mine.com>",
  "<b@evil.com, a@mine.com>", "ceo@bank.com <me@mine.com>",
  "ceo@bank.com@mine.com" - and signs for the last while a lenient reader
  shows the first. The line must now also be one address in RFC 5322's
  grammar (net/mail, display names in any charset passed through), at the
  domain OpenDKIM signs for. A quoted display name may still hold anything.
- F2 (medium): the bindings were asked about OpenDKIM's form of the
  address, quotes and all, so "x"@mine.com passed for an application
  holding @mine.com while x@mine.com belonged to another. They are now
  asked about the reader's address, its local part unquoted, as Postfix
  holds the envelope's.
- F3 / security (low): Bindings.Allowed and DomainOf fold case in ASCII
  only: Postfix folds as Unicode (casefold.c, ICU), but every key and
  login the panel writes is ASCII, and the Unicode fold let the Kelvin sign
  pass for "k" (net/mail then refuses such a line on the domain test).
- F4 (low): a TERM between "postfix start-fg &" and "child=$!" is no longer
  lost: the wrapper stops Postfix as soon as the pid is known.
- F5 (low): for startsecs after a start any failed reload passed as "not
  running". postfix-reload is now build/postfix-reload.sh: exit 75 when
  master -t says no master runs, else exec postfix reload; RunOnce returns
  EndError with the status, and only 75 is taken as done. supervisor.State
  goes.
- F6 (low): crashexit spares postfix-reload too - a reload that could not
  be spawned is reported to whoever asked, not a reason to stop the
  container.
- F7 (low): a certs/ that is itself a link is resolved before the walk
  (filepath.WalkDir does not follow its root).
- F8 (low): at shutdown the tailer reads what is left of the rotated
  file before saving its place. Not changed: a refusal line still waiting
  on the old file at shutdown is not kept - the panel writes refused rows
  itself, only a kill loses one, and that window is the minute's grace.
- F9 (low): pct read as text - empty or unreadable is 100, the rest held
  to 0..100.
- F10 (low): the directory is synced after sasldb2's rename.
- F11 (low): POSTFIX_STARTSECS by expr, so "010" or "08" in
  MILTER_WAIT_TIMEOUT are decimal, not octal or an error.
- Security (low): pagehide also empties defaultValue - the input's value
  attribute and the textarea's text - not only .value. A sasldb2.new left
  by a killed panel is removed at start (entrypoint) and never archived.
  security.md says that links under certs/ are followed and by whom they
  can be placed.

Tests: sender check cases for F1 (four lines), F2 (a bound address
quoted, for its owner and for another), F3; EndError's state and status;
pct cases. architecture.md and CHANGELOG describe the reader rule. Stand
(2026-10-15, make e2e, exit 0); go vet and go test ./... pass on the
server (24 packages).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/milter/sender.go

@@ -3,8 +3,11 @@ package milter
 import (
 	"context"
 	"fmt"
+	"io"
 	"log"
+	"mime"
 	"net"
+	"net/mail"
 	"net/textproto"
 	"os"
 	"strings"
@@ -201,13 +204,19 @@ func splitTableLine(line string) (key, value string, ok bool) {
 // whole domain (assumptions B-PS1). The bare local part MA_FIND_DEFAULT also
 // tries for a local domain is never a key here: every key the panel writes
 // has an "@" (internal/postfix renderSenderLoginMaps).
+//
+// Case is folded in ASCII only. Postfix folds as Unicode (src/util/casefold.c
+// with ICU, which Debian builds with), but every key and login the panel
+// writes is ASCII; a Unicode fold would only let a look-alike pass - the
+// Kelvin sign for "k" - for an address OpenDKIM, folding ASCII, does not
+// sign (review of stage 2c).
 func (b *Bindings) Allowed(login, addr string) (bool, error) {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 	if err := b.fresh(); err != nil {
 		return false, err
 	}
-	login, addr = strings.ToLower(login), strings.ToLower(addr)
+	login, addr = asciiLower(login), asciiLower(addr)
 	keys := []string{addr}
 	// recipient_delimiter is "+" (build/postfix-config.sh), so an
 	// application listed as invoices@ may also send as invoices+march@.
@@ -256,7 +265,7 @@ func (b *Bindings) DomainOf(login string) string {
 	if b.fresh() != nil {
 		return ""
 	}
-	return b.domainOf[strings.ToLower(login)]
+	return b.domainOf[asciiLower(login)]
 }
 
 // Refusals is where the check leaves the send-log rows of what it refused.
@@ -384,7 +393,8 @@ func (s *senderSession) judge() (shown, why string, err error) {
 		// OpenDKIM takes the first; a reader may show the others.
 		return shown, "it must be one address", nil
 	}
-	addr := r.user + "@" + asciiLower(r.domain)
+	signedDomain := asciiLower(r.domain)
+	addr := r.user + "@" + signedDomain
 	// OpenDKIM matches its SigningTable against "user@domain" as
 	// snprintf() leaves it in a buffer of MAXADDRESS + 1 = 257 bytes
 	// (opendkim.c, dkimf_apply_signtable(); libopendkim/dkim-internal.h).
@@ -394,8 +404,26 @@ func (s *senderSession) judge() (shown, why string, err error) {
 	if len(addr) > 256 {
 		return printable(addr), "the address is longer than OpenDKIM reads whole", nil
 	}
-	shown = printable(addr)
-	ok, err := s.bind.Allowed(s.login, asciiLower(addr))
+	// The address a mail program shows. OpenDKIM's parser reads lines no
+	// standard reader takes for one address - "ceo@bank.com:me@mine.com",
+	// "ceo@bank.com <me@mine.com>", "<b@evil.com, a@mine.com>" - and signs
+	// for the last of them while a lenient program shows the first. So the
+	// line must also be one address in RFC 5322's grammar (net/mail), at the
+	// domain OpenDKIM signs for; a quoted display name may say anything.
+	// And that address, its local part unquoted as Postfix holds the
+	// envelope's (Postfix 3.7.11, src/global/tok822_parse.c), is the one
+	// held against the bindings: "x"@mine.com is x@mine.com, which may be
+	// another application's (review of stage 2c, F1, F2).
+	list, perr := fromParser.ParseList(unfold(raw))
+	if perr != nil || len(list) != 1 {
+		return shown, "it must be one address, as a mail program reads it", nil
+	}
+	seen := asciiLower(list[0].Address)
+	if domainOf(seen) != signedDomain {
+		return shown, "a mail program would show another address than the one signed", nil
+	}
+	shown = printable(seen)
+	ok, err := s.bind.Allowed(s.login, seen)
 	if err != nil {
 		return shown, "", fmt.Errorf("sender bindings: %w", err)
 	}
@@ -405,6 +433,20 @@ func (s *senderSession) judge() (shown, why string, err error) {
 	return shown, "", nil
 }
 
+// fromParser reads the From: line as a mail program would. A display name
+// encoded in a charset Go does not convert (windows-1251, koi8-r, ...) is
+// still a display name: its bytes are passed through unread.
+var fromParser = mail.AddressParser{WordDecoder: &mime.WordDecoder{
+	CharsetReader: func(charset string, input io.Reader) (io.Reader, error) { return input, nil },
+}}
+
+// unfold joins the lines of a folded header value (RFC 5322 2.2.3): a line
+// break is dropped, the white space that follows it stays. Postfix hands a
+// milter the line breaks as LF (assumptions B-PM12).
+func unfold(v string) string {
+	return strings.NewReplacer("\r\n", "", "\n", "", "\r", "").Replace(v)
+}
+
 // asciiLower lower-cases A-Z only, as OpenDKIM's dkimf_lowercase() and
 // Postfix's table lookups do; strings.ToLower would also fold characters
 // outside ASCII - the Kelvin sign to "k" - into names they are not.

internal/milter/sender_test.go

@@ -20,6 +20,8 @@ import (
 // example.org, and two applications share shop.example.org.
 const senderMaps = `@news.example.net news
 @shop.example.org shop,shop2
+desk@shop.example.org shop2
+@kiosk.example.net kiosk
 invoices@example.org billing
 billing@example.org billing
 `
@@ -102,9 +104,24 @@ func TestSenderCheck(t *testing.T) {
 		{"a stranger's address in the display name", "shop", [][2]string{from(`"someone@gmail.example" <a@shop.example.org>`)}, true, ""},
 		{"another sender in an encoded display name", "shop", [][2]string{from("=?utf-8?q?director=40example=2Eorg?= <a@shop.example.org>")}, true, ""},
 		{"a stranger's address in a comment", "shop", [][2]string{from("a@shop.example.org (someone@gmail.example)")}, true, ""},
-		{"an unquoted address as the display name", "shop", [][2]string{from("director@example.org <a@shop.example.org>")}, true, ""},
+		{"an unquoted address as the display name", "shop", [][2]string{from("director@example.org <a@shop.example.org>")}, false, "as a mail program reads it"},
 		{"another domain inside a quoted local part", "shop", [][2]string{from(`"director@example.org"@shop.example.org`)}, true, ""},
-		{"no local part: OpenDKIM takes the domain for it", "shop", [][2]string{from("@shop.example.org")}, true, ""},
+		{"no local part: OpenDKIM takes the domain for it", "shop", [][2]string{from("@shop.example.org")}, false, "as a mail program reads it"},
+		// Lines OpenDKIM signs for the application's domain while a lenient
+		// mail program shows another address first (review of stage 2c, F1).
+		{"another address before a colon", "shop", [][2]string{from("ceo@bank.example:me@shop.example.org")}, false, "as a mail program reads it"},
+		{"a route-like colon inside the brackets", "shop", [][2]string{from("Name <ceo@bank.example:me@shop.example.org>")}, false, "as a mail program reads it"},
+		{"a list inside the brackets", "shop", [][2]string{from("<b@evil.example, a@shop.example.org>")}, false, "as a mail program reads it"},
+		{"an address with two @", "shop", [][2]string{from("ceo@bank.example@shop.example.org")}, false, "as a mail program reads it"},
+		// An address bound to another application, its local part quoted
+		// (F2): a reader and Postfix take "desk" for desk.
+		{"another application's address, quoted", "shop", [][2]string{from(`"desk"@shop.example.org`)}, false, "not an address this application sends as"},
+		{"its own bound address, quoted", "shop2", [][2]string{from(`"desk"@shop.example.org`)}, true, ""},
+		// A look-alike of the domain in a character a Unicode fold maps
+		// to ASCII (F3): OpenDKIM would not sign it, and it is not the
+		// application's.
+		{"the Kelvin sign for k in the domain", "kiosk", [][2]string{from("a@\u212Aiosk.example.net")}, false, "a mail program would show another address"},
+		{"the same domain in ASCII", "kiosk", [][2]string{from("a@kiosk.example.net")}, true, ""},
 
 		{"another registered domain", "shop", [][2]string{from("director@example.org")}, false, "not an address this application sends as"},
 		{"the server's own name", "shop", [][2]string{from("postmaster@mail.example.org")}, false, "not an address this application sends as"},