eloop: Fix cases where a socket is reopened from a timeout/signal handler

It was possible for a registered eloop socket handler to be unregistered
and re-registered for a re-opened socket with the same fd from a timeout
or signal handler. If such a case happened with the old socket having a
pending event waiting for processing, some eloop combinations could end
up calling the new handler function with the new socket and get stuck
waiting for an event that has not yet happened on the new socket. This
happened with timeout and signal handlers with all eloop.c types. In
addition to that, the epoll case could also trigger this when a socket
handler re-registered a re-opened socket.

Fix these by checking whether there has been socket handler changes
during processing and break the processing round by going back to
select/poll/epoll for an updated result if any changes are done during
the eloop handler calls before processing the old socket results.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/utils/eloop.c

@@ -61,11 +61,8 @@ struct eloop_signal {
 struct eloop_sock_table {
 	int count;
 	struct eloop_sock *table;
-#ifdef CONFIG_ELOOP_EPOLL
 	eloop_event_type type;
-#else /* CONFIG_ELOOP_EPOLL */
 	int changed;
-#endif /* CONFIG_ELOOP_EPOLL */
 };
 
 struct eloop_data {
@@ -256,9 +253,7 @@ static int eloop_sock_table_add_sock(struct eloop_sock_table *table,
 	table->table = tmp;
 	eloop.max_sock = new_max_sock;
 	eloop.count++;
-#ifndef CONFIG_ELOOP_EPOLL
 	table->changed = 1;
-#endif /* CONFIG_ELOOP_EPOLL */
 	eloop_trace_sock_add_ref(table);
 
 #ifdef CONFIG_ELOOP_EPOLL
@@ -314,9 +309,7 @@ static void eloop_sock_table_remove_sock(struct eloop_sock_table *table,
 	}
 	table->count--;
 	eloop.count--;
-#ifndef CONFIG_ELOOP_EPOLL
 	table->changed = 1;
-#endif /* CONFIG_ELOOP_EPOLL */
 	eloop_trace_sock_add_ref(table);
 #ifdef CONFIG_ELOOP_EPOLL
 	if (epoll_ctl(eloop.epollfd, EPOLL_CTL_DEL, sock, NULL) < 0) {
@@ -523,6 +516,10 @@ static void eloop_sock_table_dispatch(struct epoll_event *events, int nfds)
 			continue;
 		table->handler(table->sock, table->eloop_data,
 			       table->user_data);
+		if (eloop.readers.changed ||
+		    eloop.writers.changed ||
+		    eloop.exceptions.changed)
+			break;
 	}
 }
 #endif /* CONFIG_ELOOP_EPOLL */
@@ -991,6 +988,11 @@ void eloop_run(void)
 				   , strerror(errno));
 			goto out;
 		}
+
+		eloop.readers.changed = 0;
+		eloop.writers.changed = 0;
+		eloop.exceptions.changed = 0;
+
 		eloop_process_pending_signals();
 
 		/* check if some registered timeouts have occurred */
@@ -1012,6 +1014,19 @@ void eloop_run(void)
 		if (res <= 0)
 			continue;
 
+		if (eloop.readers.changed ||
+		    eloop.writers.changed ||
+		    eloop.exceptions.changed) {
+			 /*
+			  * Sockets may have been closed and reopened with the
+			  * same FD in the signal or timeout handlers, so we
+			  * must skip the previous results and check again
+			  * whether any of the currently registered sockets have
+			  * events.
+			  */
+			continue;
+		}
+
 #ifdef CONFIG_ELOOP_POLL
 		eloop_sock_table_dispatch(&eloop.readers, &eloop.writers,
 					  &eloop.exceptions, eloop.pollfds_map,