iproto: fix assertion on dropping of a new connection

We need to handle case of dropping new connection. When
net_send_greeting() is executed the connection can be closed due to
iproto_drop_connections() call.

Note that in the test the Tarantool crashes for another reason. Due to
access after sleep to the connection that is destroyed so its memory is
poisoned. Yet we visit net_send_greeting() too in the test with patch so
original issue is verified too. We also need to test that such
a connection is closed. This will be done in EE version.

Closes tarantool#9717

NO_DOC=bugfix

changelogs/unreleased/gh-9717-fix-crash-on-new-connection-drop.md

@@ -0,0 +1,3 @@
+## bugfix/core
+
+* Fixed a crash on dropping a just accepted connection (gh-9717).

src/box/iproto.cc

@@ -918,6 +918,8 @@ struct iproto_connection
 	 * connection.
 	 */
 	struct cmsg cancel_msg;
+	/** Set if connection is accepted in TX. */
+	bool is_established;
 };
 
 /** Returns a string suitable for logging. */
@@ -1663,6 +1665,7 @@ iproto_connection_new(struct iproto_thread *iproto_thread)
 	con->session = NULL;
 	con->is_in_replication = false;
 	con->is_drop_pending = false;
+	con->is_established = false;
 	rlist_create(&con->in_stop_list);
 	rlist_create(&con->tx.inprogress);
 	rlist_add_entry(&iproto_thread->connections, con, in_connections);
@@ -3329,6 +3332,11 @@ net_send_greeting(struct cmsg *m)
 {
 	struct iproto_msg *msg = (struct iproto_msg *) m;
 	struct iproto_connection *con = msg->connection;
+	if (con->is_drop_pending) {
+		iproto_connection_close(con);
+		iproto_msg_delete(msg);
+		return;
+	}
 	if (msg->close_connection) {
 		struct obuf *out = msg->wpos.obuf;
 		int64_t nwr = iostream_writev(&con->io, out->iov,
@@ -3345,6 +3353,7 @@ net_send_greeting(struct cmsg *m)
 		iproto_msg_delete(msg);
 		return;
 	}
+	con->is_established = true;
 	con->wend = msg->wpos;
 	/*
 	 * Connect is synchronous, so no one could have been
@@ -3988,9 +3997,16 @@ iproto_do_cfg_f(struct cbus_call_msg *m)
 			 * cannot close them as usual. Anyway we cancel
 			 * replication fibers as well and close connection
 			 * after replication is breaked.
+			 *
+			 * Do not close connection that is not yet
+			 * established. Otherwise session
+			 * on_connect/on_disconnect callbacks may be
+			 * executed in reverse order in case of yields
+			 * in on_connect callbacks.
 			 */
 			if (!con->is_in_replication &&
-			    con->state == IPROTO_CONNECTION_ALIVE)
+			    con->state == IPROTO_CONNECTION_ALIVE &&
+			    con->is_established)
 				iproto_connection_close(con);
 			/*
 			 * Do not wait deletion of connection that called

test/box-luatest/shutdown_test.lua

@@ -1,5 +1,6 @@
 local server = require('luatest.server')
 local utils = require('luatest.utils')
+local justrun = require('test.justrun')
 local fio = require('fio')
 local popen = require('popen')
 local fiber = require('fiber')
@@ -74,6 +75,33 @@ g_crash.test_shutdown_during_snapshot_on_signal = function(cg)
     t.assert_equals(status.exit_code, 0)
 end
 
+-- Test shutdown when new iproto connection is accepted but
+-- not yet fully established.
+g_crash.test_shutdown_during_new_connection = function(cg)
+    local script = [[
+        local net = require('net.box')
+        local fiber = require('fiber')
+
+        local sock = 'unix/:./iproto.sock'
+        box.cfg{listen = sock}
+        local cond = fiber.cond()
+        local in_trigger = false
+        box.session.on_connect(function()
+            in_trigger = true
+            cond:signal()
+            fiber.sleep(1)
+        end)
+        net.connect(sock, {wait_connected = false})
+        while not in_trigger do
+            cond:wait()
+        end
+        os.exit()
+    ]]
+    local result = justrun.tarantool(cg.workdir, {}, {'-e', script},
+                                     {nojson = true, quote_args = true})
+    t.assert_equals(result.exit_code, 0)
+end
+
 local g = t.group()
 
 g.before_each(function(cg)