fanotify: report parent fid + child fid

Add support for FAN_REPORT_FID | FAN_REPORT_DIR_FID.
Internally, it is implemented as a private case of reporting both
parent and child fids and name, the parent and child fids are recorded
in a variable length fanotify_name_event, but there is no name.

It should be noted that directory modification events are recorded
in fixed size fanotify_fid_event when not reporting name, just like
with group flags FAN_REPORT_FID.

Link: https://lore.kernel.org/r/20200716084230.30611-23-amir73il@gmail.comSigned-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/notify/fanotify/fanotify.c

@@ -535,7 +535,7 @@ static struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 		/*
 		 * With both flags FAN_REPORT_DIR_FID and FAN_REPORT_FID, we
 		 * report the child fid for events reported on a non-dir child
-		 * in addition to reporting the parent fid and child name.
+		 * in addition to reporting the parent fid and maybe child name.
 		 */
 		if ((fid_mode & FAN_REPORT_FID) &&
 		    id != dirid && !(mask & FAN_ONDIR))
@@ -552,12 +552,18 @@ static struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 		 *
 		 * For event on non-directory that is reported to parent, we
 		 * record the fid of the parent and the name of the child.
+		 *
+		 * Even if not reporting name, we need a variable length
+		 * fanotify_name_event if reporting both parent and child fids.
 		 */
-		if ((fid_mode & FAN_REPORT_NAME) &&
-		    ((mask & ALL_FSNOTIFY_DIRENT_EVENTS) ||
-		     !(mask & FAN_ONDIR)))
+		if (!(fid_mode & FAN_REPORT_NAME)) {
+			name_event = !!child;
+			file_name = NULL;
+		} else if ((mask & ALL_FSNOTIFY_DIRENT_EVENTS) ||
+			   !(mask & FAN_ONDIR)) {
 			name_event = true;
 		}
+	}
 
 	/*
 	 * For queues with unlimited length lost events are not expected and
@@ -575,7 +581,7 @@ static struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 
 	if (fanotify_is_perm_event(mask)) {
 		event = fanotify_alloc_perm_event(path, gfp);
-	} else if (name_event && file_name) {
+	} else if (name_event && (file_name || child)) {
 		event = fanotify_alloc_name_event(id, fsid, file_name, child,
 						  gfp);
 	} else if (fid_mode) {

fs/notify/fanotify/fanotify_user.c

@@ -371,7 +371,8 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
 
 	/* Event info records order is: dir fid + name, child fid */
 	if (fanotify_event_dir_fh_len(event)) {
-		info_type = FAN_EVENT_INFO_TYPE_DFID_NAME;
+		info_type = info->name_len ? FAN_EVENT_INFO_TYPE_DFID_NAME :
+					     FAN_EVENT_INFO_TYPE_DFID;
 		ret = copy_info_to_user(fanotify_event_fsid(event),
 					fanotify_info_dir_fh(info),
 					info_type, fanotify_info_name(info),
@@ -957,18 +958,10 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
 
 	/*
 	 * Child name is reported with parent fid so requires dir fid.
-	 * If reporting child name, we can report both child fid and dir fid.
+	 * We can report both child fid and dir fid with or without name.
 	 */
-	switch (fid_mode) {
-	case 0:
-	case FAN_REPORT_FID:
-	case FAN_REPORT_DIR_FID:
-	case FAN_REPORT_DFID_NAME:
-	case FAN_REPORT_DFID_NAME | FAN_REPORT_FID:
-		break;
-	default:
+	if ((fid_mode & FAN_REPORT_NAME) && !(fid_mode & FAN_REPORT_DIR_FID))
 		return -EINVAL;
-	}
 
 	user = get_current_user();
 	if (atomic_read(&user->fanotify_listeners) > FANOTIFY_DEFAULT_MAX_LISTENERS) {