From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate001.proxmox.com (gate001.proxmox.com [IPv6:2a0f:8001:1:32::40]) by lore.proxmox.com (Postfix) with ESMTPS id E708C1FF0AA for ; Tue, 20 Oct 2026 16:35:34 +0200 (CEST) Received: from gate001.proxmox.com (localhost.localdomain [127.0.0.1]) by gate001.proxmox.com (Proxmox) with ESMTP id B2BA3216B5; Tue, 20 Oct 2026 16:35:34 +0200 (CEST) From: Shannon Sterz To: pbs-devel@lists.proxmox.com Subject: [PATCH proxmox v3] fix #7814: send-mail: normalize LF line endings to CRLF endings Date: Tue, 20 Oct 2026 16:34:35 +0200 Message-ID: <20261020143437.333073-1-s.sterz@proxmox.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1792506927150 X-SPAM-LEVEL: Spam detection results: 0 AWL 0.773 Adjusted score from AWL reputation of From: address DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment (newer systems) RCVD_IN_DNSWL_MED -2.3 Sender listed at https://www.dnswl.org/, medium trust SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record Message-ID-Hash: XHOYXCEPDZM6DU25GD5SVBYPUN3Q73XA X-Message-ID-Hash: XHOYXCEPDZM6DU25GD5SVBYPUN3Q73XA X-MailFrom: s.sterz@proxmox.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; loop; banned-address; emergency; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.10 Precedence: list List-Id: Proxmox Backup Server development discussion List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: RFC5321 Section 2.3.8 requires that mails do not contain bare CR or LF bytes. this patch normalizes unix style LF line endings to CRLF line endings. it also removes bare CR bytes. when text would be base64 encoded, CR bytes will be dropped, to keep the behavior for encoded and non-encoded text aligned. to comply with rfc 2045 section 6.8 and rfc 2047 section 4.1 line endings are also normalized before encoding them in headers and body text [1,2]. for filenames we now strip all control characters other than space (0x20). this should improve compliance with rfc 6266 section 4.3 [3]. while that section specifies the recipient should do such stripping, doing so before sending minimizes compatibility issues and avoids transfering useless information. also adds tests to encode this behavior. [1]: https://datatracker.ietf.org/doc/html/rfc2045#section-6.8 [2]: https://datatracker.ietf.org/doc/html/rfc2047#section-4.1 [3]: https://datatracker.ietf.org/doc/html/rfc6266/#section-4.3 Signed-off-by: Shannon Sterz --- Notes: v2: https://lore.proxmox.com/all/20260730140126.444424-1-s.sterz@proxmox.com/ changes since v2 (thanks @ Samuel Rufinatscha): * normalize line endings to CRLF and preserve existing CRLF line endings before base64 encoding according to rfc 2045 and 2047. * remove all control characters from filenames not just CR. * improve documentation. v1: https://lore.proxmox.com/all/20260714084719.68076-1-s.sterz@proxmox.com/ changes since v1 (thanks @ Lukas Wagner): * fixed a typo (than -> then) * adjusted how the capacity for forwarded messages that need to be normalized is calculated. proxmox-sendmail/src/lib.rs | 280 ++++++++++++++++++++++++++++++++---- 1 file changed, 256 insertions(+), 24 deletions(-) diff --git a/proxmox-sendmail/src/lib.rs b/proxmox-sendmail/src/lib.rs index b3ff56e5..45868c0f 100644 --- a/proxmox-sendmail/src/lib.rs +++ b/proxmox-sendmail/src/lib.rs @@ -63,6 +63,30 @@ fn encode_filename_formatted(filename: &str) -> String { format_encoded_text(&encoded, format_prefix, ";", 0, true) } +/// Normalizes line endings before base64 encoding bytes. Stripping bare CR bytes is necessary +/// according to RFC 5321 Section 2.3.8 +/// (https://datatracker.ietf.org/doc/html/rfc5321#section-2.3.8). RFC 2045 Section 6.8 +/// (https://datatracker.ietf.org/doc/html/rfc2045#section-6.8) and RFC 2047 Section 4.1 +/// (https://datatracker.ietf.org/doc/html/rfc2047#section-4.1) also specify that line endings +/// should be normalized to CRLF prior to base64 encoding in mime body text and header values. +fn normalize_line_endings_base64>(raw: T) -> String { + // this will always have enough capacity, since the worst case is a message consisting only + // of "\n" and that would exactly double in size. messages are also unlikely to be that big + // that the extra allocated space here really matters. so set the capacity to the upper + // bound to avoid more complex capacity calculations that would take more time to run. + let mut normalized: Vec = Vec::with_capacity(raw.as_ref().len() * 2); + + for byte in raw.as_ref() { + match byte { + b'\r' => continue, + b'\n' => normalized.extend_from_slice(b"\r\n"), + b => normalized.push(*b), + } + } + + proxmox_base64::encode(&normalized) +} + /// Helper function used to format text to not exceed line limits imposed by standards such as RFC /// 2045 Section 6.8 that specifies that Base64 content transfer encoded text "must be represented /// in lines of no more than 76 characters each". It also allows taking into account any necessary @@ -168,7 +192,7 @@ impl Recipient { if !name.is_ascii() { format!( "=?utf-8?B?{}?= <{}>", - proxmox_base64::encode(name), + normalize_line_endings_base64(name), self.email ) } else { @@ -199,7 +223,7 @@ impl Attachment<'_> { if self.filename.is_ascii() { let _ = write!(attachment, "{}", &self.filename); } else { - let encoded = proxmox_base64::encode(&self.filename); + let encoded = normalize_line_endings_base64(&self.filename); let prefix_fn = |line| { if Some(0) == line { "=?utf-8?B?" @@ -325,12 +349,27 @@ impl<'a> Mail<'a> { self } - /// Adds an attachment with a specified file name and mime-type to an email. + /// Adds an attachment with a specified filename and mime-type to an email. The filename will be + /// stripped of control characters for better compatibility. /// /// Note: Adding attachments triggers `multipart/mixed` mode. pub fn add_attachment(&mut self, filename: &str, mime_type: &str, content: &'a [u8]) { + // Since we strip control characters the length of the original filename is an absolute + // upper bound of the size of the final string. + let mut normalized: String = String::with_capacity(filename.len()); + + // RFC 6266 Section 4.3 (https://datatracker.ietf.org/doc/html/rfc6266/#section-4.3) says + // that recipients should remove things such as control characters from a filename. So since + // these should be stripped anyway, do that here already to avoid encoding them later. + for character in filename.chars() { + match character { + c if c <= '\x1f' || c == '\x7f' => continue, + c => normalized.push(c), + } + } + self.attachments.push(Attachment { - filename: filename.to_string(), + filename: normalized, mime: mime_type.to_string(), content, }); @@ -451,7 +490,10 @@ impl<'a> Mail<'a> { /// Forwards an email message to a given list of recipients. /// - /// `message` must be compatible with ``sendmail`` (the message is piped into stdin unmodified). + /// `message` must be compatible with ``sendmail``. The message is piped into `stdin` + /// unmodified. One exception is stripping bare CR bytes and normalizing LF line endings to + /// CRLF line endings in accordance with RFC 5321 Section 2.3.8 + /// (https://datatracker.ietf.org/doc/html/rfc5321#section-2.3.8). #[cfg(feature = "mail-forwarder")] pub fn forward( mailto: &[&str], @@ -485,11 +527,25 @@ impl<'a> Mail<'a> { .spawn() .with_context(|| "could not spawn sendmail process")?; + // this will always have enough capacity, since the worst case is a message consisting only + // of "\n" and that would exactly double in size. messages are also unlikely to be that big + // that the extra allocated space here really matters. so set the capacity to the upper + // bound to avoid more complex capacity calculations that would take more time to run. + let mut normalized_message: Vec = Vec::with_capacity(message.len() * 2); + + for byte in message { + match byte { + b'\r' => continue, + b'\n' => normalized_message.extend_from_slice(b"\r\n"), + b => normalized_message.push(*b), + } + } + sendmail_process .stdin .take() .unwrap() - .write_all(message) + .write_all(&normalized_message) .with_context(|| "couldn't write to sendmail stdin")?; sendmail_process @@ -520,7 +576,9 @@ impl<'a> Mail<'a> { write!(mail, "\n--{file_boundary}--")?; } - Ok(mail) + // normalize line endings from `\n` to `\r\n` and drop bare `\r` according to RFC 5321 + // 2.3.8: https://datatracker.ietf.org/doc/html/rfc5321#section-2.3.8 + Ok(mail.replace('\r', "").replace('\n', "\r\n")) } fn format_header( @@ -561,7 +619,7 @@ impl<'a> Mail<'a> { writeln!( header, "Subject: =?utf-8?B?{}?=", - proxmox_base64::encode(&self.subject) + normalize_line_endings_base64(&self.subject) )?; } else { writeln!(header, "Subject: {}", self.subject)?; @@ -571,7 +629,7 @@ impl<'a> Mail<'a> { writeln!( header, "From: =?utf-8?B?{}?= <{}>", - proxmox_base64::encode(&self.mail_author), + normalize_line_endings_base64(&self.mail_author), self.mail_from )?; } else { @@ -606,16 +664,18 @@ impl<'a> Mail<'a> { header.push_str("Auto-Submitted: auto-generated;\n"); for (key, value) in &self.headers { - // Strip CR/LF so an interpolated key or value cannot inject extra header lines. - let key = key.replace(['\r', '\n'], ""); - let value = value.replace(['\r', '\n'], ""); + // Strip LF so an interpolated key or value cannot inject extra header lines. Bare CR + // will be stripped for non-ASCII text before encoding and for ASCII text globally + // before finishing formatting. + let key = key.replace('\n', ""); + let value = value.replace('\n', ""); if value.is_ascii() { writeln!(header, "{key}: {value}")?; } else { writeln!( header, "{key}: =?utf-8?B?{}?=", - proxmox_base64::encode(&value) + normalize_line_endings_base64(&value) )?; } } @@ -653,7 +713,11 @@ impl<'a> Mail<'a> { body.push_str(&self.body_txt); } else { body.push_str("Content-Transfer-Encoding: base64\n\n"); - body.push_str(&encode_base64_formatted(&self.body_txt)); + // normalize line endings according to RFC 2045 Section 6.8 + // (https://datatracker.ietf.org/doc/html/rfc2045#section-6.8). + body.push_str(&encode_base64_formatted( + self.body_txt.replace('\r', "").replace('\n', "\r\n"), + )); } if let Some(html) = &self.body_html { @@ -666,7 +730,11 @@ impl<'a> Mail<'a> { body.push_str(html); } else { body.push_str("Content-Transfer-Encoding: base64\n\n"); - body.push_str(&encode_base64_formatted(html)); + // normalize line endings according to RFC 2045 Section 6.8 + // (https://datatracker.ietf.org/doc/html/rfc2045#section-6.8). + body.push_str(&encode_base64_formatted( + html.replace('\r', "").replace('\n', "\r\n"), + )); } write!(body, "\n--{html_boundary}--")?; @@ -895,8 +963,8 @@ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: base64 -VGhpcyB1dGYtOCBlbWFpbCBzaG91bGQgaGFuZGxlIGVtb2ppcwrwn6eR8J+TpwphbmQgd2Vp -cmQgZ2VybWFuIGNoYXJhY3RlcnM6IMO2w6TDvMOfCmFuZCBtb3JlLg=="#, +VGhpcyB1dGYtOCBlbWFpbCBzaG91bGQgaGFuZGxlIGVtb2ppcw0K8J+nkfCfk6cNCmFuZCB3 +ZWlyZCBnZXJtYW4gY2hhcmFjdGVyczogw7bDpMO8w58NCmFuZCBtb3JlLg=="#, ) } @@ -1140,10 +1208,10 @@ Content-Transfer-Encoding: 7bit ]; let mail = Mail::new( - "Sender Näme", - "from@example.com", - "Subject Linë", - "Lorem Ipsum Dolor Sit\nAmët", + "Sender Nä\rme", + "from@example.\rcom", + "Subject Linë\r", + "Lorem Ipsum Dolor \rSit\nAmët", ) .with_recipient_and_name("Receiver Näme", "receiver@example.com") .with_attachment("deadbeef.bin", "application/octet-stream", &bin) @@ -1176,14 +1244,14 @@ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: base64 -TG9yZW0gSXBzdW0gRG9sb3IgU2l0CkFtw6t0 +TG9yZW0gSXBzdW0gRG9sb3IgU2l0DQpBbcOrdA== ------_=_NextPart_002_1732806251 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: base64 -PGh0bWwgbGFuZz0iZGUtYXQiPjxoZWFkPjwvaGVhZD48Ym9keT4KCTxwcmU+CgkJTG9yZW0g -SXBzdW0gRMO2bG9yIFNpdCBBbWV0Cgk8L3ByZT4KPC9ib2R5PjwvaHRtbD4= +PGh0bWwgbGFuZz0iZGUtYXQiPjxoZWFkPjwvaGVhZD48Ym9keT4NCgk8cHJlPg0KCQlMb3Jl +bSBJcHN1bSBEw7Zsb3IgU2l0IEFtZXQNCgk8L3ByZT4NCjwvYm9keT48L2h0bWw+ ------_=_NextPart_002_1732806251-- ------_=_NextPart_001_1732806251 Content-Type: application/octet-stream; @@ -1344,4 +1412,168 @@ ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz assert_eq!(suffixed, out); } + + #[test] + fn line_endings_are_normalized_when_not_encoded() { + let bin: [u8; 63] = [ + 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, + 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, + 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, + 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, + 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0x0d, + ]; + + let mail = Mail::new( + "Se\rnder Name", + "fro\rm@example.com", + "Sub\rject Line", + "Lor\rem Ipsum Dolor Sit\nAmet", + ) + .with_recipient_and_name("R\receiver Name", "receive\rr@example.com") + .with_attachment("deadb\reef.bin", "application/octet-stream", &bin) + .with_html_alt("\n\t
\n\t\tLorem Ipsum Dolor Si\rt Amet\n\t
\n") + .with_header("X-CR-HEADE\r", "value\r"); + + let body = mail.format_mail(1732806251).expect("could not format mail"); + + assert!(body.is_ascii()); + + let expected = r#"Content-Type: multipart/mixed; + boundary="----_=_NextPart_001_1732806251" +MIME-Version: 1.0 +Subject: Subject Line +From: Sender Name +To: Receiver Name +Date: Thu, 28 Nov 2024 16:04:11 +0100 +Auto-Submitted: auto-generated; +X-CR-HEADE: value + +This is a multi-part message in MIME format. + +------_=_NextPart_001_1732806251 +Content-Type: multipart/alternative; boundary="----_=_NextPart_002_1732806251" +MIME-Version: 1.0 + +------_=_NextPart_002_1732806251 +Content-Type: text/plain; + charset="UTF-8" +Content-Transfer-Encoding: 7bit + +Lorem Ipsum Dolor Sit +Amet +------_=_NextPart_002_1732806251 +Content-Type: text/html; + charset="UTF-8" +Content-Transfer-Encoding: 7bit + + + 
+		Lorem Ipsum Dolor Sit Amet
+
+ +------_=_NextPart_002_1732806251-- +------_=_NextPart_001_1732806251 +Content-Type: application/octet-stream; + name="deadbeef.bin" +Content-Disposition: attachment; + filename*0*=UTF-8''deadbeef.bin +Content-Transfer-Encoding: base64 + +3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v +3q2+796tvu8N +------_=_NextPart_001_1732806251--"#; + + // manually compare here to ensure we split specifically only on `\r\n` line endings + + let lines1 = body.split("\r\n"); + let lines2 = expected.split("\n"); + + for ((i, line1), line2) in lines1.enumerate().zip(lines2) { + if !(line1.starts_with("Date:") && line2.starts_with("Date:")) { + assert_eq!(line1, line2, "lines at {i} do not match"); + } + } + + assert_eq!(body.lines().count(), expected.lines().count()); + } + + #[test] + fn line_endings_are_normalized_when_encoded() { + let bin: [u8; 63] = [ + 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, + 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, + 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, + 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, + 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0x0d, + ]; + + let mail = Mail::new( + "Se\rnder Näme", + "fro\rm@example.com", + "Sub\rject Linë", + "Lor\rem Ipsum \r\nDolor Sit\nAmët", + ) + .with_recipient_and_name("R\receiver Näme", "receive\rr@example.com") + .with_attachment("🐄💀.\x7fb\rin", "ima\rge/bmp", &bin) + .with_html_alt("\n\t
\r\n\t\tLorem Ipsum Dölor Si\rt Amet\n\t
\n") + .with_header("X-CR-HEADE\r", "valüe\r"); + + let body = mail.format_mail(1732806251).expect("could not format mail"); + + assert!(body.is_ascii()); + + let expected = r#"Content-Type: multipart/mixed; + boundary="----_=_NextPart_001_1732806251" +MIME-Version: 1.0 +Subject: =?utf-8?B?U3ViamVjdCBMaW7Dqw==?= +From: =?utf-8?B?U2VuZGVyIE7DpG1l?= +To: =?utf-8?B?UmVjZWl2ZXIgTsOkbWU=?= +Date: Thu, 28 Nov 2024 16:04:11 +0100 +Auto-Submitted: auto-generated; +X-CR-HEADE: =?utf-8?B?dmFsw7xl?= + +This is a multi-part message in MIME format. + +------_=_NextPart_001_1732806251 +Content-Type: multipart/alternative; boundary="----_=_NextPart_002_1732806251" +MIME-Version: 1.0 + +------_=_NextPart_002_1732806251 +Content-Type: text/plain; + charset="UTF-8" +Content-Transfer-Encoding: base64 + +TG9yZW0gSXBzdW0gDQpEb2xvciBTaXQNCkFtw6t0 +------_=_NextPart_002_1732806251 +Content-Type: text/html; + charset="UTF-8" +Content-Transfer-Encoding: base64 + +PGh0bWwgbGFuZz0iZGUtYXQiPjxoZWFkPjwvaGVhZD48Ym9keT4NCgk8cHJlPg0KCQlMb3Jl +bSBJcHN1bSBEw7Zsb3IgU2l0IEFtZXQNCgk8L3ByZT4NCjwvYm9keT48L2h0bWw+ +------_=_NextPart_002_1732806251-- +------_=_NextPart_001_1732806251 +Content-Type: image/bmp; + name="=?utf-8?B?8J+QhPCfkoAuYmlu?=" +Content-Disposition: attachment; + filename*0*=UTF-8''%F0%9F%90%84%F0%9F%92%80.bin +Content-Transfer-Encoding: base64 + +3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v +3q2+796tvu8N +------_=_NextPart_001_1732806251--"#; + + // manually compare here to ensure we split specifically only on `\r\n` line endings + + let lines1 = body.split("\r\n"); + let lines2 = expected.split("\n"); + + for ((i, line1), line2) in lines1.enumerate().zip(lines2) { + if !(line1.starts_with("Date:") && line2.starts_with("Date:")) { + assert_eq!(line1, line2, "lines at {i} do not match"); + } + } + + assert_eq!(body.lines().count(), expected.lines().count()); + } } -- 2.47.3