[pmg-devel] applied: [PATCH pmg-api v8] fix #2971: DKIM: add setting to use From header when signing
Stoiko Ivanov
s.ivanov at proxmox.com
Mon Feb 26 17:34:36 CET 2024
applied with a few follow-ups on top, which hopefully make things clearer
(and shorter). Maybe you want to check them out.
tested this in my setup and managed to get a mail signed with this code
delivered to my private gmail inbox (through a few intermediate relays)
Thanks for seeing this through and the continued improvements!
On Mon, 26 Feb 2024 15:03:02 +0100
Maximiliano Sandoval <m.sandoval at proxmox.com> wrote:
> Following RFC 5322 [2], we add an option to use the address from the
> `From:` header instead of the Envelope From address.
>
> From RFC 7489 [1]:
>
> To illustrate, in relaxed mode, if a validated DKIM signature
> successfully verifies with a "d=" domain of "example.com", and the
> RFC5322.From address is "alerts at news.example.com", the DKIM "d="
> domain and the RFC5322.From domain are considered to be "in
> alignment". In strict mode, this test would fail, since the "d="
> domain does not exactly match the FQDN of the address.
>
> Tested with the following command:
>
> swaks --from foo at envelope.domain --to EMAIL -s PMG_ADDR:26 --data "Date: %DATE%\nTo: %TO_ADDRESS%\nFrom: bar at header.domain\nSubject: test %DATE%\nMessage-Id: <%MESSAGEID%>\nX-Mailer: swaks v%SWAKS_VERSION% jetmore.org/john/code/swaks/\n%NEW_HEADERS%\n%BODY%\n"
>
> Where EMAIL and PMG_ADDR are given adequate values, and envelope.domain
> and header.domain are in the 'Sign Domains' list.
>
> [1] https://datatracker.ietf.org/doc/html/rfc7489#section-3.1.1
> [2] https://datatracker.ietf.org/doc/html/rfc5322#section-3.6.2
>
> Signed-off-by: Maximiliano Sandoval <m.sandoval at proxmox.com>
> ---
> Differences from v7:
> - Simplify code counting the number of senders
> - `die` when the sender count is not 1
>
> Differences from v6:
> - Do not use uppercase in commit title
> - Rename dkim_use_domain to dkim-use-domain
>
> src/PMG/Config.pm | 8 +++++++
> src/PMG/DKIMSign.pm | 48 ++++++++++++++++++++++++++++++++++------
> src/PMG/RuleDB/Accept.pm | 3 +--
> src/PMG/RuleDB/BCC.pm | 3 +--
> src/bin/pmg-smtp-filter | 1 +
> 5 files changed, 52 insertions(+), 11 deletions(-)
>
> diff --git a/src/PMG/Config.pm b/src/PMG/Config.pm
> index 71d4c0b..0c5419e 100644
> --- a/src/PMG/Config.pm
> +++ b/src/PMG/Config.pm
> @@ -134,6 +134,12 @@ EODESC
> description => "Default DKIM selector",
> type => 'string', format => 'dns-name', #see RFC6376 3.1
> },
> + 'dkim-use-domain' => {
> + description => "Whether to sign using the address from the header or the envelope.",
> + type => 'string',
> + enum => [qw(header envelope)],
> + default => 'envelope',
> + },
> };
> }
>
> @@ -152,6 +158,7 @@ sub options {
> dkim_sign => { optional => 1 },
> dkim_sign_all_mail => { optional => 1 },
> dkim_selector => { optional => 1 },
> + 'dkim-use-domain' => { optional => 1 },
> };
> }
>
> @@ -1808,6 +1815,7 @@ my $pmg_service_params = {
> dkim_selector => 1,
> dkim_sign => 1,
> dkim_sign_all_mail => 1,
> + 'dkim-use-domain' => 1,
> },
> };
>
> diff --git a/src/PMG/DKIMSign.pm b/src/PMG/DKIMSign.pm
> index 08197f8..093ff34 100644
> --- a/src/PMG/DKIMSign.pm
> +++ b/src/PMG/DKIMSign.pm
> @@ -2,6 +2,8 @@ package PMG::DKIMSign;
>
> use strict;
> use warnings;
> +use Email::Address::XS qw(parse_email_addresses);
> +use Email::Address::XS;
> use Mail::DKIM::Signer;
> use Mail::DKIM::TextWrap;
> use Crypt::OpenSSL::RSA;
> @@ -53,11 +55,16 @@ sub create_signature {
>
> #determines which domain should be used for signing based on the e-mailaddress
> sub signing_domain {
> - my ($self, $sender_email) = @_;
> -
> - my @parts = split('@', $sender_email);
> - die "no domain in sender e-mail\n" if scalar(@parts) < 2;
> - my $input_domain = $parts[-1];
> + my ($self, $sender_email, $entity, $use_domain) = @_;
> +
> + my $input_domain;
> + if ($use_domain eq 'header') {
> + $input_domain = parse_headers_for_signing($entity);
> + } else {
> + my @parts = split('@', $sender_email);
> + die "no domain in sender e-mail\n" if scalar(@parts) < 2;
> + $input_domain = $parts[-1];
> + }
>
> if ($self->{sign_all}) {
> $self->domain($input_domain) if $self->{sign_all};
> @@ -84,8 +91,35 @@ sub signing_domain {
> }
>
>
> +sub parse_headers_for_signing {
> + # Following RFC 7489 [1], we only sign emails with exactly one sender in the
> + # From header.
> + #
> + # [1] https://datatracker.ietf.org/doc/html/rfc7489#section-6.6.1
> + my ($entity) = @_;
> +
> + my $from_count = 0;
> + my $domain;
> +
> + my @from_headers = $entity->head->get('from');
> + foreach my $from_header (@from_headers) {
> + my @addresses = parse_email_addresses($from_header);
> + $from_count += scalar(@addresses);
> + $domain = $addresses[0]->host() if scalar(@addresses) > 0;
> + }
> +
> + die "there is more than one sender in the header" if $from_count > 1;
> + die "there is no sender in the header" if $from_count == 0;
> + return $domain;
> +}
> +
> +
> sub sign_entity {
> - my ($entity, $selector, $sender, $sign_all) = @_;
> + my ($entity, $dkim, $sender) = @_;
> +
> + my $sign_all = $dkim->{sign_all};
> + my $use_domain = $dkim->{use_domain};
> + my $selector = $dkim->{selector};
>
> die "no selector provided\n" if ! $selector;
>
> @@ -110,7 +144,7 @@ sub sign_entity {
>
> $signer->extended_headers($extended_headers);
>
> - if ($signer->signing_domain($sender)) {
> + if ($signer->signing_domain($sender, $entity, $use_domain)) {
> $entity->print($signer);
> my $signature = $signer->create_signature();
> $entity->head->add('DKIM-Signature', $signature, 0);
> diff --git a/src/PMG/RuleDB/Accept.pm b/src/PMG/RuleDB/Accept.pm
> index 4ebd6da..d14c2fb 100644
> --- a/src/PMG/RuleDB/Accept.pm
> +++ b/src/PMG/RuleDB/Accept.pm
> @@ -102,8 +102,7 @@ sub execute {
>
> if ($dkim->{sign}) {
> eval {
> - $entity = PMG::DKIMSign::sign_entity($entity,
> - $dkim->{selector}, $msginfo->{sender}, $dkim->{sign_all});
> + $entity = PMG::DKIMSign::sign_entity($entity, $dkim, $msginfo->{sender});
> };
> syslog('warning',
> "Could not create DKIM-Signature - disabling Signing: $@") if $@;
> diff --git a/src/PMG/RuleDB/BCC.pm b/src/PMG/RuleDB/BCC.pm
> index 0f016f8..65b6fb5 100644
> --- a/src/PMG/RuleDB/BCC.pm
> +++ b/src/PMG/RuleDB/BCC.pm
> @@ -142,8 +142,7 @@ sub execute {
> my $dkim = $msginfo->{dkim} // {};
> if ($dkim->{sign}) {
> eval {
> - $entity = PMG::DKIMSign::sign_entity($entity,
> - $dkim->{selector}, $msginfo->{sender}, $dkim->{sign_all});
> + $entity = PMG::DKIMSign::sign_entity($entity, $dkim, $msginfo->{sender});
> };
> syslog('warning',
> "Could not create DKIM-Signature - disabling Signing: $@") if $@;
> diff --git a/src/bin/pmg-smtp-filter b/src/bin/pmg-smtp-filter
> index dc7128c..6061459 100755
> --- a/src/bin/pmg-smtp-filter
> +++ b/src/bin/pmg-smtp-filter
> @@ -636,6 +636,7 @@ sub handle_smtp {
> my $dkim_sign = $msginfo->{trusted} && $pmg_cfg->get('admin', 'dkim_sign');
> if ($dkim_sign) {
> $msginfo->{dkim}->{sign} = $dkim_sign;
> + $msginfo->{dkim}->{use_domain} = $pmg_cfg->get('admin', 'dkim-use-domain');
> $msginfo->{dkim}->{sign_all} = $pmg_cfg->get('admin', 'dkim_sign_all_mail');
> $msginfo->{dkim}->{selector} = $pmg_cfg->get('admin', 'dkim_selector');
> }
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