fsnotify: annotate directory entry modification events

"dirent" events are referring to events that modify directory entries,
such as create,delete,rename. Those events should always be reported
on a watched directory, regardless if FS_EVENT_ON_CHILD is set
on the watch mask.

fsnotify_nameremove() and fsnotify_move() were modified to no longer
set the FS_EVENT_ON_CHILD event bit. This is a semantic change to
align with the "dirent" event definition. It has no effect on any
existing backend, because dnotify, inotify and audit always requets the
child events and fanotify does not get the delete,rename events.

The fsnotify_dirent() helper is used instead of fsnotify_parent() to
report a dirent event to dentry->d_parent without FS_EVENT_ON_CHILD
and regardless if parent has the FS_EVENT_ON_CHILD bit set.

Unlike fsnotify_parent(), fsnotify_dirent() assumes that dentry->d_name
and dentry->d_parent are stable. For fsnotify_create()/fsnotify_mkdir(),
this assumption is abviously correct. For fsnotify_nameremove(), it is
less trivial, so we use dget_parent() and take_dentry_name_snapshot() to
grab stable references.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

include/linux/fsnotify.h

@@ -17,8 +17,22 @@
 #include <linux/slab.h>
 #include <linux/bug.h>
 
+/*
+ * Notify this @dir inode about a change in the directory entry @dentry.
+ *
+ * Unlike fsnotify_parent(), the event will be reported regardless of the
+ * FS_EVENT_ON_CHILD mask on the parent inode.
+ */
+static inline int fsnotify_dirent(struct inode *dir, struct dentry *dentry,
+				  __u32 mask)
+{
+	return fsnotify(dir, mask, d_inode(dentry), FSNOTIFY_EVENT_INODE,
+			dentry->d_name.name, 0);
+}
+
 /* Notify this dentry's parent about a child's events. */
-static inline int fsnotify_parent(const struct path *path, struct dentry *dentry, __u32 mask)
+static inline int fsnotify_parent(const struct path *path,
+				  struct dentry *dentry, __u32 mask)
 {
 	if (!dentry)
 		dentry = path->dentry;
@@ -85,8 +99,8 @@ static inline void fsnotify_move(struct inode *old_dir, struct inode *new_dir,
 {
 	struct inode *source = moved->d_inode;
 	u32 fs_cookie = fsnotify_get_cookie();
-	__u32 old_dir_mask = (FS_EVENT_ON_CHILD | FS_MOVED_FROM);
-	__u32 new_dir_mask = (FS_EVENT_ON_CHILD | FS_MOVED_TO);
+	__u32 old_dir_mask = FS_MOVED_FROM;
+	__u32 new_dir_mask = FS_MOVED_TO;
 	const unsigned char *new_name = moved->d_name.name;
 
 	if (old_dir == new_dir)
@@ -128,15 +142,35 @@ static inline void fsnotify_vfsmount_delete(struct vfsmount *mnt)
 
 /*
  * fsnotify_nameremove - a filename was removed from a directory
+ *
+ * This is mostly called under parent vfs inode lock so name and
+ * dentry->d_parent should be stable. However there are some corner cases where
+ * inode lock is not held. So to be on the safe side and be reselient to future
+ * callers and out of tree users of d_delete(), we do not assume that d_parent
+ * and d_name are stable and we use dget_parent() and
+ * take_dentry_name_snapshot() to grab stable references.
  */
 static inline void fsnotify_nameremove(struct dentry *dentry, int isdir)
 {
+	struct dentry *parent;
+	struct name_snapshot name;
 	__u32 mask = FS_DELETE;
 
+	/* d_delete() of pseudo inode? (e.g. __ns_get_path() playing tricks) */
+	if (IS_ROOT(dentry))
+		return;
+
 	if (isdir)
 		mask |= FS_ISDIR;
 
-	fsnotify_parent(NULL, dentry, mask);
+	parent = dget_parent(dentry);
+	take_dentry_name_snapshot(&name, dentry);
+
+	fsnotify(d_inode(parent), mask, d_inode(dentry), FSNOTIFY_EVENT_INODE,
+		 name.name, 0);
+
+	release_dentry_name_snapshot(&name);
+	dput(parent);
 }
 
 /*
@@ -155,7 +189,7 @@ static inline void fsnotify_create(struct inode *inode, struct dentry *dentry)
 {
 	audit_inode_child(inode, dentry, AUDIT_TYPE_CHILD_CREATE);
 
-	fsnotify(inode, FS_CREATE, dentry->d_inode, FSNOTIFY_EVENT_INODE, dentry->d_name.name, 0);
+	fsnotify_dirent(inode, dentry, FS_CREATE);
 }
 
 /*
@@ -176,12 +210,9 @@ static inline void fsnotify_link(struct inode *dir, struct inode *inode, struct
  */
 static inline void fsnotify_mkdir(struct inode *inode, struct dentry *dentry)
 {
-	__u32 mask = (FS_CREATE | FS_ISDIR);
-	struct inode *d_inode = dentry->d_inode;
-
 	audit_inode_child(inode, dentry, AUDIT_TYPE_CHILD_CREATE);
 
-	fsnotify(inode, mask, d_inode, FSNOTIFY_EVENT_INODE, dentry->d_name.name, 0);
+	fsnotify_dirent(inode, dentry, FS_CREATE | FS_ISDIR);
 }
 
 /*