Fix potential memory leak of tev->e_list by reordering list_add before epoll_ctl

This commit addresses a potential memory leak in tgt_event_add related to
tev->e_list. Previously, epoll_ctl(EPOLL_CTL_ADD) was called before
list_add. This sequence could lead to a race condition where the epoll event
is registered and immediately triggered, leading to EPOLL_CTL_DEL and
list_del being called before list_add, resulting in the event being removed
from epoll but never added to the list, causing a memory leak after calling
list_add (Because no one will call list_del to remove this tev->e_list anymore).

To prevent this, list_add is now called before epoll_ctl(EPOLL_CTL_ADD).
This ensures that the tev->e_list is added to the list before any
epoll events can be triggered, allowing proper cleanup by list_del in case
of an early EPOLL_CTL_DEL.

Signed-off-by: JK Chen <[email protected]>

Author: jkchen1095

usr/tgtd.c

@@ -217,12 +217,13 @@ int tgt_event_add(int fd, int events, event_handler_t handler, void *data)
 	memset(&ev, 0, sizeof(ev));
 	ev.events = events;
 	ev.data.ptr = tev;
+	list_add(&tev->e_list, &tgt_events_list);
 	err = epoll_ctl(ep_fd, EPOLL_CTL_ADD, fd, &ev);
 	if (err) {
 		eprintf("Cannot add fd, %m\n");
+		list_del(&tev->e_list);
 		free(tev);
-	} else
-		list_add(&tev->e_list, &tgt_events_list);
+	}
 
 	return err;
 }