fsnotify: send event with parent/name info to sb/mount/non-dir marks

Similar to events "on child" to watching directory, send event
with parent/name info if sb/mount/non-dir marks are interested in
parent/name info.

The FS_EVENT_ON_CHILD flag can be set on sb/mount/non-dir marks to specify
interest in parent/name info for events on non-directory inodes.

Events on "orphan" children (disconnected dentries) are sent without
parent/name info.

Events on directories are sent with parent/name info only if the parent
directory is watching.

After this change, even groups that do not subscribe to events on
children could get an event with mark iterator type TYPE_CHILD and
without mark iterator type TYPE_INODE if fanotify has marks on the same
objects.

dnotify and inotify event handlers can already cope with that situation.
audit does not subscribe to events that are possible on child, so won't
get to this situation. nfsd does not access the marks iterator from its
event handler at the moment, so it is not affected.

This is a bit too fragile, so we should prepare all groups to cope with
mark type TYPE_CHILD preferably using a generic helper.

Link: https://lore.kernel.org/r/20200716084230.30611-16-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 61 insertions, 13 deletions

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 4a762c8c4a29..494d5d70323f 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -142,38 +142,81 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode)
 	spin_unlock(&inode->i_lock);
 }
 
+/* Are inode/sb/mount interested in parent and name info with this event? */
+static bool fsnotify_event_needs_parent(struct inode *inode, struct mount *mnt,
+					__u32 mask)
+{
+	__u32 marks_mask = 0;
+
+	/* We only send parent/name to inode/sb/mount for events on non-dir */
+	if (mask & FS_ISDIR)
+		return false;
+
+	/* Did either inode/sb/mount subscribe for events with parent/name? */
+	marks_mask |= fsnotify_parent_needed_mask(inode->i_fsnotify_mask);
+	marks_mask |= fsnotify_parent_needed_mask(inode->i_sb->s_fsnotify_mask);
+	if (mnt)
+		marks_mask |= fsnotify_parent_needed_mask(mnt->mnt_fsnotify_mask);
+
+	/* Did they subscribe for this event with parent/name info? */
+	return mask & marks_mask;
+}
+
 /*
  * Notify this dentry's parent about a child's events with child name info
- * if parent is watching.
- * Notify only the child without name info if parent is not watching.
+ * if parent is watching or if inode/sb/mount are interested in events with
+ * parent and name info.
+ *
+ * Notify only the child without name info if parent is not watching and
+ * inode/sb/mount are not interested in events with parent and name info.
  */
 int __fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data,
 		      int data_type)
 {
+	const struct path *path = fsnotify_data_path(data, data_type);
+	struct mount *mnt = path ? real_mount(path->mnt) : NULL;
 	struct inode *inode = d_inode(dentry);
 	struct dentry *parent;
+	bool parent_watched = dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED;
+	__u32 p_mask;
 	struct inode *p_inode = NULL;
 	struct name_snapshot name;
 	struct qstr *file_name = NULL;
 	int ret = 0;
 
+	/*
+	 * Do inode/sb/mount care about parent and name info on non-dir?
+	 * Do they care about any event at all?
+	 */
+	if (!inode->i_fsnotify_marks && !inode->i_sb->s_fsnotify_marks &&
+	    (!mnt || !mnt->mnt_fsnotify_marks) && !parent_watched)
+		return 0;
+
 	parent = NULL;
-	if (!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED))
+	if (!parent_watched && !fsnotify_event_needs_parent(inode, mnt, mask))
 		goto notify;
 
+	/* Does parent inode care about events on children? */
 	parent = dget_parent(dentry);
 	p_inode = parent->d_inode;
-
-	if (unlikely(!fsnotify_inode_watches_children(p_inode))) {
+	p_mask = fsnotify_inode_watches_children(p_inode);
+	if (unlikely(parent_watched && !p_mask))
 		__fsnotify_update_child_dentry_flags(p_inode);
-	} else if (p_inode->i_fsnotify_mask & mask & ALL_FSNOTIFY_EVENTS) {
+
+	/*
+	 * Include parent/name in notification either if some notification
+	 * groups require parent info (!parent_watched case) or the parent is
+	 * interested in this event.
+	 */
+	if (!parent_watched || (mask & p_mask & ALL_FSNOTIFY_EVENTS)) {
 		/* When notifying parent, child should be passed as data */
 		WARN_ON_ONCE(inode != fsnotify_data_inode(data, data_type));
 
 		/* Notify both parent and child with child name info */
 		take_dentry_name_snapshot(&name, dentry);
 		file_name = &name.name;
-		mask |= FS_EVENT_ON_CHILD;
+		if (parent_watched)
+			mask |= FS_EVENT_ON_CHILD;
 	}
 
 notify:
@@ -349,8 +392,8 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 		inode = dir;
 	} else if (mask & FS_EVENT_ON_CHILD) {
 		/*
-		 * Event on child - report on TYPE_INODE to dir
-		 * and on TYPE_CHILD to child.
+		 * Event on child - report on TYPE_INODE to dir if it is
+		 * watching children and on TYPE_CHILD to child.
 		 */
 		child = inode;
 		inode = dir;
@@ -364,14 +407,17 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 	 * SRCU because we have no references to any objects and do not
 	 * need SRCU to keep them "alive".
 	 */
-	if (!inode->i_fsnotify_marks && !sb->s_fsnotify_marks &&
+	if (!sb->s_fsnotify_marks &&
 	    (!mnt || !mnt->mnt_fsnotify_marks) &&
+	    (!inode || !inode->i_fsnotify_marks) &&
 	    (!child || !child->i_fsnotify_marks))
 		return 0;
 
-	marks_mask = inode->i_fsnotify_mask | sb->s_fsnotify_mask;
+	marks_mask = sb->s_fsnotify_mask;
 	if (mnt)
 		marks_mask |= mnt->mnt_fsnotify_mask;
+	if (inode)
+		marks_mask |= inode->i_fsnotify_mask;
 	if (child)
 		marks_mask |= child->i_fsnotify_mask;
 
@@ -386,14 +432,16 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 
 	iter_info.srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
 
-	iter_info.marks[FSNOTIFY_OBJ_TYPE_INODE] =
-		fsnotify_first_mark(&inode->i_fsnotify_marks);
 	iter_info.marks[FSNOTIFY_OBJ_TYPE_SB] =
 		fsnotify_first_mark(&sb->s_fsnotify_marks);
 	if (mnt) {
 		iter_info.marks[FSNOTIFY_OBJ_TYPE_VFSMOUNT] =
 			fsnotify_first_mark(&mnt->mnt_fsnotify_marks);
 	}
+	if (inode) {
+		iter_info.marks[FSNOTIFY_OBJ_TYPE_INODE] =
+			fsnotify_first_mark(&inode->i_fsnotify_marks);
+	}
 	if (child) {
 		iter_info.marks[FSNOTIFY_OBJ_TYPE_CHILD] =
 			fsnotify_first_mark(&child->i_fsnotify_marks);