From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [212.224.123.68]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.proxmox.com (Postfix) with ESMTPS id C9DE4C05A3 for ; Wed, 10 Jan 2024 22:39:51 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id A5A5094D6 for ; Wed, 10 Jan 2024 22:39:21 +0100 (CET) Received: from proxmox-new.maurer-it.com (proxmox-new.maurer-it.com [94.136.29.106]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by firstgate.proxmox.com (Proxmox) with ESMTPS for ; Wed, 10 Jan 2024 22:39:19 +0100 (CET) Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id A604246FFC for ; Wed, 10 Jan 2024 22:39:19 +0100 (CET) Date: Wed, 10 Jan 2024 22:39:17 +0100 From: Stoiko Ivanov To: Maximiliano Sandoval Cc: pmg-devel@lists.proxmox.com Message-ID: <20240110223917.49438535@rosa.proxmox.com> In-Reply-To: <20240103145329.538668-1-m.sandoval@proxmox.com> References: <20240103145329.538668-1-m.sandoval@proxmox.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SPAM-LEVEL: Spam detection results: 0 AWL 0.088 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record T_SCC_BODY_TEXT_LINE -0.01 - URIBL_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to URIBL was blocked. See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block for more information. [config.pm, ietf.org, dkimsign.pm, bcc.pm, accept.pm, jetmore.org] Subject: Re: [pmg-devel] [RFC PATCH] fix-2971: DKIM: Add setting to use From header when signing X-BeenThere: pmg-devel@lists.proxmox.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: Proxmox Mail Gateway development discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 10 Jan 2024 21:39:51 -0000 Thanks for tackling this! Finally got around to look a bit into the RFCs... (and currently don't think the premises of DMARC work too well with many e-mail setups (not only lists)) the bugreport has gained quite a few comments and further suggestions that we should consider: * fixed signing domain for all mails (something the DKIM RFC orginally envisioned) * signing bounces to not have them generate DMARC reports (maybe even a general fallback from envelope-from (RFC5321.From) to header-from (RFC5322.From) if the former would not be signed, but the latter would? * out-of-office mails at least the first two might make sense to consider (out-of-office mails usually are sent as bounce (empty 5321.from)) maybe the setting could be "dkim_prefer_rfc5322_domain" (better names more than welcome), and the choice on, which domain to actually use for the 'd=' tag in the signature could be done in PMG::DKIMSign::signing_domain. to sign bounces originating from PMG (e.g. the daily spam and admin reports) - you'd need to add the DKIM-signing to PMG::Utils::reinject_local_mail (and to test what happens with mails sent via '/usr/sbin/sendmail' on the PMG (e.g. smartd-messages and cronjob-outputs). The changes do neither to happen with this patchset nor do you need to do them, but maybe some of it offers itself for implementation, but please mention 'partially fixes #2971' somewhere. Some documentation for this would be needed as well. further comments inline: On Wed, 3 Jan 2024 15:53:29 +0100 Maximiliano Sandoval wrote: > We add an option to use the address from the `From:` header instead of > the Envelope From address. Following RFC 5322 [2], we use the `Sender:` > header when there are multiple addresses in the `From:` header. sorry, I know I pointed you in that direction - but the DMARC rfc (where this enhancement request initially originated) says - most of those cases don't happen in DMARC protected domains (reality might have a different view on that): https://datatracker.ietf.org/doc/html/rfc7489#section-6.6.1 so we can probably spare ourselves the going through multiple headers, and can take the part after the first '@' until either EOL or '>' as domain (but please verify this with the acceptable syntax in rfc 5322) > > From RFC 6376 [1]: wrong rfc - this is from the dmarc-one: https://datatracker.ietf.org/doc/html/rfc7489#section-3.1.1 (DKIM itself doesn't require the signing domain to occur anywhere in the SMTP-dialogue, or the mail-headers or body: https://datatracker.ietf.org/doc/html/rfc6376#section-3.11 (INFORMATIVE DISCUSSION)) > > 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@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. > > Current Problems: > > - `dkim_sign_rfc5322` is probably not a descriptive name for the setting > - The setting description might be improved upon > > Tested with the following command: > > swaks --from foo@bar1 --to EMAIL -s PMG_ADDR:26 --data "Date: %DATE%\nTo: %TO_ADDRESS%\nFrom: foo@bar2\nSubject: test %DATE%\nMessage-Id: <%MESSAGEID%>\nX-Mailer: swaks v%SWAKS_VERSION% jetmore.org/john/code/swaks/\n%NEW_HEADERS%\n%BODY%\n" > > [1] https://datatracker.ietf.org/doc/html/rfc6376 > [2] https://datatracker.ietf.org/doc/html/rfc5322#section-3.6.2 > > Signed-off-by: Maximiliano Sandoval > --- > src/PMG/Config.pm | 7 +++++++ > src/PMG/DKIMSign.pm | 43 +++++++++++++++++++++++++++++++++++++++- > src/PMG/RuleDB/Accept.pm | 2 +- > src/PMG/RuleDB/BCC.pm | 2 +- > src/bin/pmg-smtp-filter | 1 + > 5 files changed, 52 insertions(+), 3 deletions(-) > > diff --git a/src/PMG/Config.pm b/src/PMG/Config.pm > index 7339e0d..b6c61e1 100644 > --- a/src/PMG/Config.pm > +++ b/src/PMG/Config.pm > @@ -134,6 +134,11 @@ EODESC > description => "Default DKIM selector", > type => 'string', format => 'dns-name', #see RFC6376 3.1 > }, > + dkim_sign_rfc5322 => { > + description => "Whether to use the address from the From header when DKIM signing outbound mails.", > + type => 'boolean', > + default => 0, > + }, > }; > } > > @@ -152,6 +157,7 @@ sub options { > dkim_sign => { optional => 1 }, > dkim_sign_all_mail => { optional => 1 }, > dkim_selector => { optional => 1 }, > + dkim_sign_rfc5322 => { optional => 1 }, > }; > } > > @@ -1788,6 +1794,7 @@ my $pmg_service_params = { > dkim_selector => 1, > dkim_sign => 1, > dkim_sign_all_mail => 1, > + dkim_sign_rfc5322 => 1, > }, > }; > > diff --git a/src/PMG/DKIMSign.pm b/src/PMG/DKIMSign.pm > index 08197f8..009313d 100644 > --- a/src/PMG/DKIMSign.pm > +++ b/src/PMG/DKIMSign.pm > @@ -84,8 +84,49 @@ sub signing_domain { > } > > > +sub parse_signing_sender { > + # If there is exactly one single address in the 'From' header we use that > + # address for signing, otherwise we use the 'Sender' header. > + my ($entity) = @_; > + > + my $from_count = 0; > + my @from_headers = $entity->head->get('from'); > + foreach my $from_header (@from_headers) { > + my @senders = split(',', $from_header); this won't work in a robust manner - consider the following (valid) from header: ``` From: "Ivanov, Stoiko" ``` > + $from_count += scalar(@senders); > + } > + > + if ($from_count > 1) { > + my $send_count = 0; > + my @send_headers = $entity->head->get('sender'); > + foreach my $send_header (@send_headers) { > + my @senders = split(',', $send_header); > + $send_count += scalar(@senders); > + } > + if ($send_count > 1) { > + syslog('warning', "Email has more than one address in its 'Sender' " . > + "it won't be signed. See RFC 5322 Section 3.6.2"); > + } elsif ($send_count == 1) { > + return $entity->head->get('sender', 0); > + } else { > + syslog('warning', "Email has multiple addresses in its 'From' header " . > + "and no 'Sender' header, it won't be signed. See RFC 5322 Section 3.6.2"); > + } > + } elsif ($from_count == 1) { > + return $entity->head->get('from', 0); > + } > +} > + > + > sub sign_entity { > - my ($entity, $selector, $sender, $sign_all) = @_; > + my ($entity, $dkim, $sender) = @_; > + > + my $sign_all = $dkim->{sign_all}; > + my $selector = $dkim->{selector}; > + > + if ($dkim->{sign_rfc5322}) { > + $sender = parse_signing_sender($entity); > + } > > die "no selector provided\n" if ! $selector; > > diff --git a/src/PMG/RuleDB/Accept.pm b/src/PMG/RuleDB/Accept.pm > index 4ebd6da..2e1bfa7 100644 > --- a/src/PMG/RuleDB/Accept.pm > +++ b/src/PMG/RuleDB/Accept.pm > @@ -103,7 +103,7 @@ sub execute { > if ($dkim->{sign}) { > eval { > $entity = PMG::DKIMSign::sign_entity($entity, > - $dkim->{selector}, $msginfo->{sender}, $dkim->{sign_all}); > + $dkim, $msginfo->{sender}); > }; > syslog('warning', > "Could not create DKIM-Signature - disabling Signing: $@") if $@; > diff --git a/src/PMG/RuleDB/BCC.pm b/src/PMG/RuleDB/BCC.pm > index 0f016f8..6db48af 100644 > --- a/src/PMG/RuleDB/BCC.pm > +++ b/src/PMG/RuleDB/BCC.pm > @@ -143,7 +143,7 @@ sub execute { > if ($dkim->{sign}) { > eval { > $entity = PMG::DKIMSign::sign_entity($entity, > - $dkim->{selector}, $msginfo->{sender}, $dkim->{sign_all}); > + $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 7da3de8..549dbd4 100755 > --- a/src/bin/pmg-smtp-filter > +++ b/src/bin/pmg-smtp-filter > @@ -627,6 +627,7 @@ sub handle_smtp { > my $dkim_sign = $msginfo->{trusted} && $pmg_cfg->get('admin', 'dkim_sign'); > if ($dkim_sign) { > $msginfo->{dkim}->{sign} = $dkim_sign; > + $msginfo->{dkim}->{sign_rfc5322} = $pmg_cfg->get('admin', 'dkim_sign_rfc5322'); > $msginfo->{dkim}->{sign_all} = $pmg_cfg->get('admin', 'dkim_sign_all_mail'); > $msginfo->{dkim}->{selector} = $pmg_cfg->get('admin', 'dkim_selector'); > }