From 281661c01e4a7562c9579a950036f82dbc7c04d4 Mon Sep 17 00:00:00 2001
From: Art Cancro <ajc@citadel.org>
Date: Mon, 29 Nov 2021 14:24:06 -0500
Subject: [PATCH] Mail to a mailing list room must be from a subscriber (or a
 logged in user) otherwise incoming message is rejected.

---
 citadel/internet_addressing.c    | 33 ++++++++++++++++++++++++++++++--
 citadel/internet_addressing.h    |  1 +
 citadel/modules/smtp/serv_smtp.c | 10 ++++++++++
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/citadel/internet_addressing.c b/citadel/internet_addressing.c
index 429272586..6fb485b1a 100644
--- a/citadel/internet_addressing.c
+++ b/citadel/internet_addressing.c
@@ -1655,8 +1655,7 @@ void CtdlSetEmailAddressesForUser(char *requested_user, char *new_emailaddrs)
 /*
  * Auto-generate an Internet email address for a user account
  */
-void AutoGenerateEmailAddressForUser(struct ctdluser *user)
-{
+void AutoGenerateEmailAddressForUser(struct ctdluser *user) {
 	char synthetic_email_addr[1024];
 	int i, j;
 	int u = 0;
@@ -1688,3 +1687,33 @@ void AutoGenerateEmailAddressForUser(struct ctdluser *user)
 	strncpy(CC->user.emailaddrs, synthetic_email_addr, sizeof(user->emailaddrs));
 	syslog(LOG_DEBUG, "user_ops: auto-generated email address <%s> for <%s>", synthetic_email_addr, user->fullname);
 }
+
+
+// Determine whether the supplied email address is subscribed to the supplied room's mailing list service.
+int is_email_subscribed_to_list(char *email, char *room_name) {
+	struct ctdlroom room;
+	long roomnum;
+	char *roomnetconfig;
+	int found_it = 0;
+
+	if (CtdlGetRoom(&room, room_name)) {
+		return(0);					// room not found, so definitely not subscribed
+	}
+	roomnum = room.QRnumber;
+	roomnetconfig = LoadRoomNetConfigFile(roomnum);
+	if (roomnetconfig == NULL) {
+		return(0);
+	}
+
+	// We're going to do a very sloppy match here and simply search for the specified email address
+	// anywhere in the room's netconfig.  If you don't like this, fix it yourself.
+	if (bmstrcasestr(roomnetconfig, email)) {
+		found_it = 1;
+	}
+	else {
+		found_it = 0;
+	}
+
+	free(roomnetconfig);
+	return(found_it);
+}
diff --git a/citadel/internet_addressing.h b/citadel/internet_addressing.h
index 4b12ee74d..443033561 100644
--- a/citadel/internet_addressing.h
+++ b/citadel/internet_addressing.h
@@ -21,6 +21,7 @@ struct CtdlMessage *convert_internet_message_buf(StrBuf **rfc822);
 int CtdlIsMe(char *addr, int addr_buf_len);
 int CtdlHostAlias(char *fqdn);
 char *harvest_collected_addresses(struct CtdlMessage *msg);
+int is_email_subscribed_to_list(char *email, char *room_name);
 
 /* 
  * Values that can be returned by CtdlHostAlias()
diff --git a/citadel/modules/smtp/serv_smtp.c b/citadel/modules/smtp/serv_smtp.c
index a74e2bb9f..549a29165 100644
--- a/citadel/modules/smtp/serv_smtp.c
+++ b/citadel/modules/smtp/serv_smtp.c
@@ -715,6 +715,16 @@ void smtp_rcpt(void) {
 		return;
 	}
 
+	if (
+		(valid->num_room > 0)						// If it's mail to a room (mailing list)...
+		&& (SMTP->message_originated_locally == 0)			// ...and also inbound Internet mail...
+		&& (is_email_subscribed_to_list((char *)ChrPtr(SMTP->from), valid->recp_room) == 0)	// ...and not a subscriber
+	) {
+		cprintf("551 <%s> - This mailing list only accepts messages from subscribers.\r\n", ChrPtr(SMTP->OneRcpt));
+		free_recipients(valid);
+		return;
+	}
+
 	cprintf("250 RCPT ok <%s>\r\n", ChrPtr(SMTP->OneRcpt));
 	if (StrLength(SMTP->recipients) > 0) {
 		StrBufAppendBufPlain(SMTP->recipients, HKEY(","), 0);
-- 
2.30.2