lib-smtp: server: Added max_recipients setting, which enforces a reci…

…pient limit per-transaction.

src/lib-smtp/smtp-server-cmd-rcpt.c

@@ -17,9 +17,9 @@ cmd_rcpt_check_state(struct smtp_server_cmd_ctx *cmd)
 {
 	struct smtp_server_connection *conn = cmd->conn;
 	struct smtp_server_command *command = cmd->cmd;
+	struct smtp_server_transaction *trans = conn->state.trans;
 
-	if (conn->state.pending_mail_cmds == 0 &&
-		conn->state.trans == NULL) {
+	if (conn->state.pending_mail_cmds == 0 && trans == NULL) {
 		if (command->hook_replied != NULL) {
 			conn->state.pending_rcpt_cmds--;
 			command->hook_replied = NULL;
@@ -28,6 +28,13 @@ cmd_rcpt_check_state(struct smtp_server_cmd_ctx *cmd)
 			503, "5.5.0", "MAIL needed first");
 		return FALSE;
 	}
+	if (conn->set.max_recipients > 0 && trans != NULL &&
+		smtp_server_transaction_rcpt_count(trans) >=
+			conn->set.max_recipients) {
+		smtp_server_reply(cmd,
+			451, "4.5.3", "Too many recipients");
+		return FALSE;
+	}
 
 	return TRUE;
 }

src/lib-smtp/smtp-server-connection.c

@@ -802,6 +802,8 @@ smtp_server_connection_alloc(struct smtp_server *server,
 		if (set->max_bad_commands > 0) {
 			conn->set.max_bad_commands = set->max_bad_commands;
 		}
+		if (set->max_recipients > 0)
+			conn->set.max_recipients = set->max_recipients;
 		smtp_command_limits_merge(&conn->set.command_limits,
 					  &set->command_limits);
 

src/lib-smtp/smtp-server.c

@@ -48,6 +48,7 @@ struct smtp_server *smtp_server_init(const struct smtp_server_settings *set)
 		set->max_pipelined_commands : 1);
 	server->set.max_bad_commands = (set->max_bad_commands > 0 ?
 		set->max_bad_commands : SMTP_SERVER_DEFAULT_MAX_BAD_COMMANDS);
+	server->set.max_recipients = set->max_recipients;
 	server->set.command_limits = set->command_limits;
 
 	if (set->xclient_extensions != NULL) {

src/lib-smtp/smtp-server.h

@@ -240,6 +240,10 @@ struct smtp_server_settings {
 	/* maximum number of sequential bad commands */
 	unsigned int max_bad_commands;
 
+	/* maximum number of recipients in a transaction
+	   (0 means unlimited, which is the default) */
+	unsigned int max_recipients;
+
 	/* command limits */
 	struct smtp_command_limits command_limits;
 

src/lib-smtp/test-smtp-server-errors.c

@@ -2,6 +2,7 @@
 
 #include "lib.h"
 #include "str.h"
+#include "array.h"
 #include "hostpid.h"
 #include "ioloop.h"
 #include "istream.h"
@@ -906,6 +907,108 @@ static void test_bad_ehlo(void)
 	test_end();
 }
 
+/*
+ * Too many recipients
+ */
+
+/* client */
+
+static void
+test_too_many_recipients_connected(struct client_connection *conn)
+{
+	(void)o_stream_send_str(conn->conn.output,
+		"EHLO frop\r\n"
+		"MAIL FROM:<sender@example.com>\r\n"
+		"RCPT TO:<recipient1@example.com>\r\n"
+		"RCPT TO:<recipient2@example.com>\r\n"
+		"RCPT TO:<recipient3@example.com>\r\n"
+		"RCPT TO:<recipient4@example.com>\r\n"
+		"RCPT TO:<recipient5@example.com>\r\n"
+		"RCPT TO:<recipient6@example.com>\r\n"
+		"RCPT TO:<recipient7@example.com>\r\n"
+		"RCPT TO:<recipient8@example.com>\r\n"
+		"RCPT TO:<recipient9@example.com>\r\n"
+		"RCPT TO:<recipient10@example.com>\r\n"
+		"RCPT TO:<recipient11@example.com>\r\n"
+		"DATA\r\n"
+		"0123456789ABCDEF0123456789ABCDEF\r\n"
+		"0123456789ABCDEF0123456789ABCDEF\r\n"
+		"0123456789ABCDEF0123456789ABCDEF\r\n"
+		"0123456789ABCDEF0123456789ABCDEF\r\n"
+		"0123456789ABCDEF0123456789ABCDEF\r\n"
+		"0123456789ABCDEF0123456789ABCDEF\r\n"
+		"0123456789ABCDEF0123456789ABCDEF\r\n"
+		".\r\n");
+}
+
+static void test_client_too_many_recipients(unsigned int index)
+{
+	test_client_connected = test_too_many_recipients_connected;
+	test_client_run(index);
+}
+
+/* server */
+
+static void
+test_server_too_many_recipients_trans_free(void *conn_ctx  ATTR_UNUSED,
+	struct smtp_server_transaction *trans ATTR_UNUSED)
+{
+	io_loop_stop(ioloop);
+}
+
+static int
+test_server_too_many_recipients_rcpt(void *conn_ctx ATTR_UNUSED,
+	struct smtp_server_cmd_ctx *cmd ATTR_UNUSED,
+	struct smtp_server_cmd_rcpt *data)
+{
+	if (debug) {
+		i_debug("RCPT TO:%s",
+			smtp_address_encode(data->path));
+	}
+	return 1;
+}
+
+static int
+test_server_too_many_recipients_data_begin(void *conn_ctx ATTR_UNUSED,
+	struct smtp_server_cmd_ctx *cmd,
+	struct smtp_server_transaction *trans,
+	struct istream *data_input ATTR_UNUSED)
+{
+	test_assert(array_count(&trans->rcpt_to) == 10);
+
+	smtp_server_reply(cmd, 250, "2.0.0", "OK");
+	return 1;
+}
+
+static void test_server_too_many_recipients
+(const struct smtp_server_settings *server_set)
+{
+	server_callbacks.conn_trans_free =
+		test_server_too_many_recipients_trans_free;
+	server_callbacks.conn_cmd_rcpt =
+		test_server_too_many_recipients_rcpt;
+	server_callbacks.conn_cmd_data_begin =
+		test_server_too_many_recipients_data_begin;
+	test_server_run(server_set);
+}
+
+/* test */
+
+static void test_too_many_recipients(void)
+{
+	struct smtp_server_settings smtp_server_set;
+
+	test_server_defaults(&smtp_server_set);
+	smtp_server_set.max_client_idle_time_msecs = 1000;
+	smtp_server_set.max_recipients = 10;
+
+	test_begin("too many recipients");
+	test_run_client_server(&smtp_server_set,
+		test_server_too_many_recipients,
+		test_client_too_many_recipients, 1);
+	test_end();
+}
+
 /*
  * All tests
  */
@@ -918,6 +1021,7 @@ static void (*const test_functions[])(void) = {
 	test_long_command,
 	test_big_data,
 	test_bad_ehlo,
+	test_too_many_recipients,
 	NULL
 };