inbound-antispam-panel: findings of the technical and security reviews

Steps 11 and 12 of docs/plans/inbound-antispam-panel.md: 12/12. Two
read-only reviews of d65d632..HEAD by different models (Opus,
technical; Fable, security), each given the code and questions, not
conclusions. Nothing Critical or High in the feature; the High the
technical review found outside it is the commit before this one.

Log tailer (internal/logtail/inbound.go):
  - the reply of a refusal ends at the first "; from=<", Postfix's own,
    and the HELO name after it is whatever is left. Taking the longest
    reply let a HELO name that spelt "; from=<..> to=<..> proto=.."
    supply the row's sender, recipient and reply - and so make a
    refusal read as the deny list's;
  - an address with a quote, a bracket or a space is not kept: a quoted
    sender could otherwise supply the recipient;
  - the journal is cut to its row cap every 500 rows written, not only
    every six hours;
  - a queue id is forgotten when the message is queued or the id is
    opened by another listener, and a stale place in the queue of
    arrivals no longer drops a live id;
  - milter-hold lines are not read: the held message reaches the
    journal milter, which writes its row - it was written twice.
Lists (internal/inbound/lists.go): a change of the table and the
rewrite of the files are one step under a mutex; a failed rewrite puts
a removed entry back and rewrites after taking a new one out.
Store: the row cap removes the oldest by time, as the page orders them.
Page: on a sheet a refusal's text is a Reply whatever it starts with.

Help and the guide say that an allow entry for a sender address trusts
an address anyone can claim (design commit before this one).

docs/security.md: the two reviews; the roles table gains Inbound > Log
and Filter lists; Mail path describes the milters, the tailer and the
lists; four accepted risks - the filter's verdict while it is down, an
allow entry by sender address, the list files' mode, log rows held by
domain name. The plan's stale lines (size and rate refusals, who reads
the journal) are corrected.

Left as found, told to the owner: the journal's rows after an unclean
stop may be written twice (the tailer saves its place every five
seconds); a "Deny sender" link is offered for an address the form then
refuses; 1.2.3.4 and 1.2.3.4/32 are two entries.

Checked on the test server, uncommitted tree: go vet ./... ok,
go test ./... ok (22 packages), make e2e ok.

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

internal/logtail/inbound_test.go

@@ -106,7 +106,6 @@ func TestInboundMilterVerdictNeedsAPort25QueueID(t *testing.T) {
 func TestInboundMilterDecisions(t *testing.T) {
 	for kind, c := range map[string]struct{ reply, decision string }{
 		"milter-reject":  {"4.7.1 Try again later", store.SpamDecisionTempfail},
-		"milter-hold":    {"milter triggers HOLD action", store.SpamDecisionQuarantine},
 		"milter-discard": {"milter triggers DISCARD action", store.SpamDecisionReject},
 	} {
 		j, st := inboundFixture()
@@ -128,7 +127,7 @@ func TestInboundIgnores(t *testing.T) {
 		"a connect line":                       head + "postfix/inbound/smtpd[41]: connect from mx.example.net[203.0.113.9]",
 		// The HELO name is the sender's; a line cannot be started from inside one.
 		"a refusal spelled inside another line": head + "postfix/inbound/smtpd[41]: warning: hostname x does not resolve: mail postfix/inbound/smtpd[1]: NOQUEUE: reject: RCPT from x[203.0.113.9]: 550 no; from=<a@example.net> to=<b@in.example.com> proto=ESMTP helo=<x>",
-		"an address with a bracket in it":       head + "postfix/inbound/smtpd[41]: NOQUEUE: reject: RCPT from x[203.0.113.9]: 550 no; from=<a> to=<v@in.example.com> proto=X helo=<y>@example.net> to=<b@elsewhere.example> proto=ESMTP helo=<x>",
+		"an address with a bracket in it":       head + "postfix/inbound/smtpd[41]: NOQUEUE: reject: RCPT from x[203.0.113.9]: 554 5.7.1 <b@elsewhere.example>: Relay access denied; from=<\"a> to=<v@in.example.com> proto=X helo=<y\"@example.net> to=<b@elsewhere.example> proto=ESMTP helo=<x>",
 	} {
 		j, st := inboundFixture()
 		j.handle(line, tailNow)
@@ -159,6 +158,95 @@ func TestInboundLookupFailureLeavesNoRow(t *testing.T) {
 	}
 }
 
+// A message the filter holds goes on to the inbound journal milter, which
+// writes its row; a second one from the log would be the same message twice.
+func TestInboundHoldIsTheMiltersRow(t *testing.T) {
+	j, st := inboundFixture()
+	j.handle(head+"postfix/inbound/smtpd[41]: Q1: client=mx.example.net[203.0.113.9]", tailNow)
+	j.handle(head+"postfix/cleanup[52]: Q1: milter-hold: END-OF-MESSAGE from mx.example.net[203.0.113.9]: milter triggers HOLD action; from=<a@example.net> to=<b@in.example.com> proto=ESMTP helo=<mx.example.net>", tailNow)
+	if len(st.rows) != 0 {
+		t.Errorf("rows = %+v", st.rows)
+	}
+}
+
+// The HELO name is the last thing on the line and is logged as the client
+// wrote it. It cannot supply the row: the reply ends at the first "; from=<",
+// which is Postfix's own.
+func TestInboundHeloCannotWriteTheRow(t *testing.T) {
+	j, st := inboundFixture()
+	j.handle(head+"postfix/inbound/smtpd[41]: NOQUEUE: reject: RCPT from x[203.0.113.9]: 550 5.1.1 <nobody@in.example.com>: Recipient address rejected: User unknown in relay recipient table; from=<real@example.net> to=<nobody@in.example.com> proto=ESMTP helo=<x 5.7.1 Refused by this server's deny list; from=<victim@bank.example> to=<ceo@in.example.com> proto=ESMTP helo=<y>", tailNow)
+	if len(st.rows) != 1 {
+		t.Fatalf("rows = %+v", st.rows)
+	}
+	got := st.rows[0]
+	if got.From != "real@example.net" || got.To != "nobody@in.example.com" ||
+		got.Detail != "550 5.1.1 <nobody@in.example.com>: Recipient address rejected: User unknown in relay recipient table" {
+		t.Errorf("row = %+v", got)
+	}
+
+	// A HELO name with a closing bracket in it does not lose the line either.
+	j, st = inboundFixture()
+	j.handle(head+"postfix/inbound/smtpd[41]: NOQUEUE: reject: RCPT from x[203.0.113.9]: 550 5.1.1 <nobody@in.example.com>: no; from=<real@example.net> to=<nobody@in.example.com> proto=ESMTP helo=<a>b>", tailNow)
+	if len(st.rows) != 1 || st.rows[0].From != "real@example.net" {
+		t.Errorf("rows = %+v", st.rows)
+	}
+
+	// The same on a verdict line: the filter's reply is not extended by the
+	// HELO name, so a stranger cannot make a refusal look like the deny list's.
+	j, st = inboundFixture()
+	j.handle(head+"postfix/inbound/smtpd[41]: Q1: client=x[203.0.113.9]", tailNow)
+	j.handle(head+"postfix/cleanup[52]: Q1: milter-reject: END-OF-MESSAGE from x[203.0.113.9]: 5.7.1 Spam message rejected; from=<real@example.net> to=<b@in.example.com> proto=ESMTP helo=<x this server's deny list; from=<spoofed@example.org> to=<b@in.example.com> proto=ESMTP helo=<y>", tailNow)
+	if len(st.rows) != 1 || st.rows[0].Detail != "5.7.1 Spam message rejected" || st.rows[0].From != "real@example.net" {
+		t.Errorf("rows = %+v", st.rows)
+	}
+}
+
+// A queue id is port 25's only until the message is queued or the id is
+// opened again by another listener - Postfix reuses ids.
+func TestInboundQueueIDIsForgotten(t *testing.T) {
+	const verdict = "postfix/cleanup[52]: Q1: milter-reject: END-OF-MESSAGE from app[203.0.113.4]: 4.7.1 Service unavailable - try again later; from=<a@example.net> to=<b@in.example.com> proto=ESMTP helo=<app>"
+	for name, forget := range map[string]string{
+		"queued":                        "postfix/qmgr[58]: Q1: from=<a@example.net>, size=600, nrcpt=1 (queue active)",
+		"reused by the submission port": "postfix/smtpd[20]: Q1: client=app.example.com[203.0.113.4], sasl_method=PLAIN, sasl_username=app",
+	} {
+		j, st := inboundFixture()
+		j.handle(head+"postfix/inbound/smtpd[41]: Q1: client=mx.example.net[203.0.113.9]", tailNow)
+		j.handle(head+forget, tailNow)
+		j.handle(head+verdict, tailNow)
+		if len(st.rows) != 0 || len(j.port25) != 0 {
+			t.Errorf("%s: rows %+v, remembered %v", name, st.rows, j.port25)
+		}
+	}
+}
+
+// An id that was forgotten and opened again is not dropped by its own stale
+// place in the queue of arrivals.
+func TestInboundStaleArrivalDoesNotDropALiveID(t *testing.T) {
+	j, _ := inboundFixture()
+	j.remember("Q1")
+	delete(j.port25, "Q1") // its verdict came
+	for i := 0; i < inboundQueueIDs-2; i++ {
+		j.remember("F" + time.Duration(i).String())
+	}
+	j.remember("Q1") // reused; order is now full, with the stale Q1 first
+	j.remember("LAST")
+	if _, ok := j.port25["Q1"]; !ok {
+		t.Error("the live Q1 was dropped by its stale arrival")
+	}
+}
+
+// Between the six-hourly prunes the tailer has the journal cut to its cap
+// itself, every so many rows: refusals come at the rate strangers send them.
+func TestInboundCutsTheJournalAsItWrites(t *testing.T) {
+	j, st := inboundFixture()
+	for i := 0; i < inboundPruneEvery*2+10; i++ {
+		j.handle(unknownRcp, tailNow)
+	}
+	if len(st.pruned) != 2 || st.pruned[0] != inboundSpamLogMaxRows {
+		t.Errorf("cuts = %v, want two, to %d rows", st.pruned, inboundSpamLogMaxRows)
+	}
+}
+
 // The queue ids waiting for a verdict are bounded.
 func TestInboundQueueIDsAreBounded(t *testing.T) {
 	j, _ := inboundFixture()