fanotify: ignore events on directories unless specifically requested

fanotify has a very limited number of events it sends on directories.  The
usefulness of these events is yet to be seen and still we send them.  This
is particularly painful for mount marks where one might receive many of
these useless events.  As such this patch will drop events on IS_DIR()
inodes unless they were explictly requested with FAN_ON_DIR.

This means that a mark on a directory without FAN_EVENT_ON_CHILD or
FAN_ON_DIR is meaningless and will result in no events ever (although it
will still be allowed since detecting it is hard)

Signed-off-by: Eric Paris <eparis@redhat.com>

fs/notify/fanotify/fanotify.c

@@ -131,6 +131,7 @@ static int fanotify_handle_event(struct fsnotify_group *group,
 	BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 	BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 	BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
+	BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 
 	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
@@ -195,6 +196,10 @@ static bool fanotify_should_send_event(struct fsnotify_group *group,
 		BUG();
 	}
 
+	if (S_ISDIR(path->dentry->d_inode->i_mode) &&
+	    (marks_ignored_mask & FS_ISDIR))
+		return false;
+
 	if (event_mask & marks_mask & ~marks_ignored_mask)
 		return true;
 

fs/notify/fanotify/fanotify_user.c

@@ -570,6 +570,12 @@ static __u32 fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark,
 		if (flags & FAN_MARK_IGNORED_SURV_MODIFY)
 			fsn_mark->flags |= FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY;
 	}
+
+	if (!(flags & FAN_MARK_ONDIR)) {
+		__u32 tmask = fsn_mark->ignored_mask | FAN_ONDIR;
+		fsnotify_set_mark_ignored_mask_locked(fsn_mark, tmask);
+	}
+
 	spin_unlock(&fsn_mark->lock);
 
 	return mask & ~oldmask;
@@ -766,6 +772,12 @@ SYSCALL_DEFINE(fanotify_mark)(int fanotify_fd, unsigned int flags,
 	default:
 		return -EINVAL;
 	}
+
+	if (mask & FAN_ONDIR) {
+		flags |= FAN_MARK_ONDIR;
+		mask &= ~FAN_ONDIR;
+	}
+
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 	if (mask & ~(FAN_ALL_EVENTS | FAN_ALL_PERM_EVENTS | FAN_EVENT_ON_CHILD))
 #else

include/linux/fanotify.h

@@ -10,13 +10,15 @@
 #define FAN_CLOSE_NOWRITE	0x00000010	/* Writtable file closed */
 #define FAN_OPEN		0x00000020	/* File was opened */
 
-#define FAN_EVENT_ON_CHILD	0x08000000	/* interested in child events */
-
 #define FAN_Q_OVERFLOW		0x00004000	/* Event queued overflowed */
 
 #define FAN_OPEN_PERM		0x00010000	/* File open in perm check */
 #define FAN_ACCESS_PERM		0x00020000	/* File accessed in perm check */
 
+#define FAN_ONDIR		0x40000000	/* event occurred against dir */
+
+#define FAN_EVENT_ON_CHILD	0x08000000	/* interested in child events */
+
 /* helper events */
 #define FAN_CLOSE		(FAN_CLOSE_WRITE | FAN_CLOSE_NOWRITE) /* close */
 
@@ -47,6 +49,10 @@
 #define FAN_MARK_IGNORED_MASK	0x00000020
 #define FAN_MARK_IGNORED_SURV_MODIFY	0x00000040
 #define FAN_MARK_FLUSH		0x00000080
+#ifdef __KERNEL__
+/* not valid from userspace, only kernel internal */
+#define FAN_MARK_ONDIR		0x00000100
+#endif
 
 #define FAN_ALL_MARK_FLAGS	(FAN_MARK_ADD |\
 				 FAN_MARK_REMOVE |\