dmarc: a report is bounded, kept per domain, and ingested one at a time

Security review of the DMARC report path (Fable, 2026-10-11), which ran
for the first time in 2.0.0. No Critical or High finding. Fixed:

- Medium: a report was bounded only as 8 MiB of XML - some 160 000
  records or one name of megabytes, all of it rows and table cells. At
  most 5 000 records (more is ErrRejected, dropped), text fields cut to
  255 bytes on a character boundary, a record's count capped.
- Medium: the cap of 500 reports was for the whole server, so a stranger
  filing under one domain's address evicted every other domain's
  reports. PruneDMARCReports counts per domain.
- Low: the pipe service ran up to default_process_limit (100) commands
  at once against the panel's database; maxproc is 1.
- Low: the reason logged for a dropped message carried the sender's
  bytes (header line, zip entry name) as they came; cut to 200 bytes and
  reduced to printable ASCII, zip entry names quoted.
- Low: SELFPOST_DATA_DIR / SELFPOST_DB_PATH with whitespace or "$" would
  reach the command through export_environment as another path; refused
  at start when DMARC ingest is on.

Left as they are, told to the owner: the parse-failure count is a
lifetime figure shown under "This week"; a report larger than the
command reads is dropped as unreadable; nested multipart is not searched.

The hub's Retention line follows the design commit before this one.
security.md: the review, and the accepted-risk entry says what a
stranger can and cannot do now. The roadmap no longer calls the review
pending.

  go vet ./cmd/... ./internal/dmarc/ ./internal/store/: ok
  go test ./cmd/... ./internal/dmarc/ ./internal/store/ ./internal/web/...: ok
  make e2e on the test server (with the port-25 scenarios of the next
  commit): ok

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

docs/guide.md

@@ -891,7 +891,7 @@ sees the *Ingest* box — whether ingest works, the last report received, report
 kept this week and parse failures. Open a domain's roll-up from the list or
 from *DMARC reports* in the domain page's menu. A user with the *domain* role
 sees the reports of the domains assigned to them, without the *Ingest* box.
-Summaries are pruned (500 kept, 90 days max).
+Summaries are pruned (500 kept for each domain, 90 days max).
 
 A message that is not a report the relay keeps — unreadable as an aggregate
 report, about a domain not sent from here, or delivered to another domain's

docs/roadmap.md

@@ -47,7 +47,8 @@ development convenience): **panel-redesign** shipped as `2.0.0` (2026-10-11); th
 **inbound-antispam-panel** (`2.1.0`), built in the new component kit —
 styling its two screens once instead of twice. panel-docs shipped in
 [CHANGELOG.md](../CHANGELOG.md) `[1.8.0]`; dmarc-reports in `[1.7.0]`
-(security review of the ingest path pending); domain-stats-auto-ratelimit in
+(its ingest path first ran in `2.0.0` and was reviewed on 2026-10-11, see
+[security.md](security.md)); domain-stats-auto-ratelimit in
 `[1.6.0]`; send-log-retention in `[1.5.0]`; inbound-relay in `[1.4.0]`;
 queue-retries in `[1.3.1]`; the 2026-08-13 full-tree review follow-ups are in
 `[1.3.0]`. Candidates need explicit agreement before they join the queue.

docs/security.md

@@ -26,7 +26,14 @@ the user form did not end that user's sessions, internal errors reached forms a
 (see [Authentication and sessions](#authentication-and-sessions) and [Errors
 shown to users](#errors-shown-to-users)); two deliberate behaviours are
 recorded under Accepted risks (upstream of a delegated inbound domain, profile
-saved without the password).
+saved without the password). The 2026-10-11 review (Fable) covered the DMARC
+report path from port 25 to the report pages, which ran for the first time in
+2.0.0 - the 2026-08-19 pass read code that Postfix could not yet start: no
+Critical or High finding; a report's size was bounded only as bytes (now 5 000
+records, 255 bytes a field), the retention cap was one for the whole server
+(now per domain), the delivery command could run a hundred at once (now one),
+and the reason logged for a dropped message carried the sender's bytes as they
+came (now cut and reduced to printable ASCII).
 (2) **Accepted risks** —
 deliberate departures beyond the mandatory, recorded so the decision is not
 lost.
@@ -274,8 +281,15 @@ deferred item from the roadmap.
   reporters are arbitrary third parties and the mailbox address is published in
   DNS. The ingest already constrains the meaningful part — a report cannot be
   filed under a domain this instance does not host, and the claimed domain is
-  cross-checked against the `+tag` of the delivery address — and the data is
-  advisory statistics only; nothing enforces off it. The trigger to revisit is
+  cross-checked against the `+tag` of the delivery address (effective since
+  2.0.0: before it the recipient never reached the command) — and the data is
+  advisory statistics only; nothing enforces off it. What a stranger can do is
+  limited to a domain that chose a SelfPost-hosted address, through that
+  address: file reports under it, replace one whose reporter and id they know,
+  and fill that domain's 500 — not another domain's. A message that is not a
+  report the relay keeps is dropped, not bounced (the envelope sender is the
+  author's to write); a genuine report the parser cannot read is lost the same
+  way, with a count and a line in the mail log. The trigger to revisit is
   any feature that lets report contents drive an automatic action (policy
   changes, rate limiting, alerting an operator into a config change).
 - **The application auth-IP allow-list is enforced fail-open.** The check runs