From 09584bd33578b0f1ea7f173d06dbe2532336a7b1 Mon Sep 17 00:00:00 2001
From: Jan Engelhardt <jengelh@inai.de>
Date: Mon, 30 May 2022 02:42:10 +0200
Subject: [PATCH] emsmdb, zcore: perform dot-stuffing ahead of SMTP DATA

Certain lines in a mail have special meaning to certain components in
the chain, such as lines beginning with "From " in the Unix mbox
format, or lines beginning with a "." in a SMTP DATA command.

When regular mail is prepared for export, MIME::write_content always
applies a transform, and that is base64 or, (since recently)
alternatively, quoted-printable. The base64 transform naturally
"defuses" lines since neither "From " nor "." are possible with the
base64 output alphabet. The QP encoder specifically looks for the
special pattern and force-encodes them. By doing all that, no SMTP
dot-stuffing would be needed.

However, S/MIME is not classified as regular mail and would be copied
verbatim to the SMTP channel, which is incorrect.

Change the send routines to explicitly do SMTP-style dot-stuffing.

References: GXF-30, GXL-84
---
 exch/emsmdb/common_util.cpp | 6 ++++++
 exch/zcore/common_util.cpp  | 6 ++++++
 lib/email/mail.cpp          | 6 +++---
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/exch/emsmdb/common_util.cpp b/exch/emsmdb/common_util.cpp
index 5609e5711..3666fd7d3 100644
--- a/exch/emsmdb/common_util.cpp
+++ b/exch/emsmdb/common_util.cpp
@@ -1676,6 +1676,12 @@ BOOL common_util_send_mail(MAIL *pmail,
 	char last_command[1024];
 	char last_response[1024];
 	
+	MAIL dot_encoded(pmail->pmime_pool);
+	if (pmail->check_dot()) {
+		if (!pmail->transfer_dot(&dot_encoded, true))
+			return false;
+		pmail = &dot_encoded;
+	}
 	int sockd = gx_inet_connect(g_smtp_ip, g_smtp_port, 0);
 	if (sockd < 0) {
 		log_err("Cannot connect to SMTP server [%s]:%hu: %s",
diff --git a/exch/zcore/common_util.cpp b/exch/zcore/common_util.cpp
index 58956127a..64449cea7 100644
--- a/exch/zcore/common_util.cpp
+++ b/exch/zcore/common_util.cpp
@@ -1360,6 +1360,12 @@ static BOOL common_util_send_mail(MAIL *pmail,
 	char last_command[1024];
 	char last_response[1024];
 	
+	MAIL dot_encoded(pmail->pmime_pool);
+	if (pmail->check_dot()) {
+		if (!pmail->transfer_dot(&dot_encoded, true))
+			return false;
+		pmail = &dot_encoded;
+	}
 	int sockd = gx_inet_connect(g_smtp_ip, g_smtp_port, 0);
 	if (sockd < 0) {
 		log_err("Cannot connect to SMTP server [%s]:%hu: %s",
diff --git a/lib/email/mail.cpp b/lib/email/mail.cpp
index e3382a7ce..7167adcb0 100644
--- a/lib/email/mail.cpp
+++ b/lib/email/mail.cpp
@@ -827,12 +827,12 @@ bool MAIL::dup(MAIL *pmail_dst)
 }
 
 /*
- *	apply or reverse-apply dot-stuffing mail object into a clean object
+ *	add or remove dot-stuffing; copies into a clean object
  *	@param
  *		pmail_src [in]			mail source object
  *		pmail_dst [in, out]		mail destination object
  */
-bool MAIL::transfer_dot(MAIL *pmail_dst, bool fwd)
+bool MAIL::transfer_dot(MAIL *pmail_dst, bool add_dot)
 {
 	auto pmail_src = this;
 	unsigned int size;
@@ -866,7 +866,7 @@ bool MAIL::transfer_dot(MAIL *pmail_dst, bool fwd)
 		size ++;
 		pbuff[offset + size] = '\n';
 		size ++;
-		if (fwd) {
+		if (add_dot) {
 			if (pbuff[offset] == '.') {
 				memmove(&pbuff[offset+1], &pbuff[offset], size);
 				++size;