monitor: Clean up fd sets on monitor disconnect

Fd sets are shared by all monitor connections.  Fd sets are considered
to be in use while at least one monitor is connected.  When the last
monitor disconnects, all fds that are members of an fd set with no
outstanding dup references are closed.  This prevents any fd leakage
associated with a client disconnect prior to using a passed fd.

Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

monitor.c

@@ -200,6 +200,7 @@ struct Monitor {
 
 static QLIST_HEAD(mon_list, Monitor) mon_list;
 static QLIST_HEAD(mon_fdsets, MonFdset) mon_fdsets;
+static int mon_refcount;
 
 static mon_cmd_t mon_cmds[];
 static mon_cmd_t info_cmds[];
@@ -2391,7 +2392,8 @@ static void monitor_fdset_cleanup(MonFdset *mon_fdset)
     MonFdsetFd *mon_fdset_fd_next;
 
     QLIST_FOREACH_SAFE(mon_fdset_fd, &mon_fdset->fds, next, mon_fdset_fd_next) {
-        if (mon_fdset_fd->removed) {
+        if (mon_fdset_fd->removed ||
+                (QLIST_EMPTY(&mon_fdset->dup_fds) && mon_refcount == 0)) {
             close(mon_fdset_fd->fd);
             g_free(mon_fdset_fd->opaque);
             QLIST_REMOVE(mon_fdset_fd, next);
@@ -2405,6 +2407,16 @@ static void monitor_fdset_cleanup(MonFdset *mon_fdset)
     }
 }
 
+static void monitor_fdsets_cleanup(void)
+{
+    MonFdset *mon_fdset;
+    MonFdset *mon_fdset_next;
+
+    QLIST_FOREACH_SAFE(mon_fdset, &mon_fdsets, next, mon_fdset_next) {
+        monitor_fdset_cleanup(mon_fdset);
+    }
+}
+
 AddfdInfo *qmp_add_fd(bool has_fdset_id, int64_t fdset_id, bool has_opaque,
                       const char *opaque, Error **errp)
 {
@@ -4824,9 +4836,12 @@ static void monitor_control_event(void *opaque, int event)
         data = get_qmp_greeting();
         monitor_json_emitter(mon, data);
         qobject_decref(data);
+        mon_refcount++;
         break;
     case CHR_EVENT_CLOSED:
         json_message_parser_destroy(&mon->mc->parser);
+        mon_refcount--;
+        monitor_fdsets_cleanup();
         break;
     }
 }
@@ -4867,6 +4882,12 @@ static void monitor_event(void *opaque, int event)
             readline_show_prompt(mon->rs);
         }
         mon->reset_seen = 1;
+        mon_refcount++;
+        break;
+
+    case CHR_EVENT_CLOSED:
+        mon_refcount--;
+        monitor_fdsets_cleanup();
         break;
     }
 }