aaa94120be0f2c64b03859b5ced697e009ca2b4e
2
Commits
| Author | SHA1 | Message | Date | |
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  mixandClaude Opus 5.5
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ec08c8606b |
audit 2c: the From: parser port checked against OpenDKIM's signing itself
test / test (push) Canceled after 0s
The last check of the port, and the plan's last line of stage 2c. Through
Postfix the sender check refuses most lines before OpenDKIM sees them, so
TestPortAgainstOpenDKIM (internal/milter) talks to OpenDKIM directly:
test/upstream/opendkim-probe.sh starts OpenDKIM from the SelfPost image in
a throwaway container, with keys and a refile SigningTable for three
names, and the test plays it each From: line through go-milter's client,
as a client OpenDKIM trusts (127.0.0.1, InternalHosts' default). For each
line the d= of the signature OpenDKIM adds must be the domain the port
predicts - its address, the domain cut to DKIM_MAXHOSTNAMELEN, the whole
cut to MAXADDRESS, matched against "^.*@<domain>$" case-insensitive as
dkimf_apply_signtable() matches - or neither signs.
Run on the test server, 2026-10-15 (OpenDKIM Filter v2.11.0 from the
image): 385 lines - both shared files and lines composed from display
names plain, quoted, escaped and encoded, comments nested and open,
groups, lists, brackets, source routes, domain literals and quoted local
parts, with the other sender's name and the server's in each place - 385
agree, 287 signed. The two lines padded so that, cut at 256 bytes, they
end in "@other.e2e.test" are signed by OpenDKIM with other.e2e.test's key:
the danger the sender check's 256-byte rule (
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mixandClaude Opus 5.5
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3584adcbc2 |
sender check: From: read with OpenDKIM's own parser; L8 closed
test / test (push) Canceled after 0s
Audit 2026-10-12, stage 2c, the owner's decision of 2026-10-14: the check
decides by the address OpenDKIM signs for, whatever a display name or a
comment holds.
internal/milter/mailparse.go ports libopendkim's dkim_mail_parse() with
dkim_mail_first_special(), dkim_mail_token() and
dkim_mail_matching_paren() from Debian's opendkim 2.11.0~beta2-8+deb12u1,
line for line: the '<' form, group and list punctuation, an '@' before the
first ':', ';' or ',' deciding where the address starts, source routes
dropped, quoted strings and domain literals kept with their delimiters,
comments skipped, whitespace between atoms one space, no encoded word
decoded; and the C's own quirks ("@d" gives d as the local part too).
testdata/mailparse_harness.c compiles the C from the image's source; the
test feeds it and the port 200 019 lines (the hand-written cases and
200 000 random ones over the specials) - 93 443 parse and agree byte for
byte, 106 576 fail and agree on the error (on an error the C leaves its
in-place result unterminated, and OpenDKIM uses neither part then).
judge(): one From: field and one address stay required (moreAfter: only
list or group punctuation may follow); what OpenDKIM cannot read is
refused (mlfi_eoh() would not sign it); the address is lower-cased in
ASCII only, as dkimf_lowercase() and Postfix's tables do. Found reading
dkimf_apply_signtable(): OpenDKIM matches its refile SigningTable against
"user@domain" printed into MAXADDRESS + 1 = 257 bytes, so a longer address
is matched cut short - a quoted local part padded to end there in
"@another.tenant" would be signed with that tenant's key while its real
domain is the application's. Such an address (over 256 bytes) is refused;
one that fits is matched whole. The display-name and comment scan, the
"one @ outside quotes" rule and the SigningTable reader (Signers) go; the
check asks for header values with their leading space as OpenDKIM does
(OptHeaderLeadingSpace; Postfix keeps a v2 milter's event mask, milter8.c
milter8_negotiate()).
L8 closed: refused or passed no longer depends on other domains of the
server; security.md's accepted risk is struck. The shared other-sender
lines are now held to "never signed for the other sender": unit test (a
passed line is read at the application's domain) and e2e (a passed line
arrives signed for the application's domain, none for the other).
Documents: architecture "How the header is read", security's sender
check paragraph, the guide; the help topic per
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