fanotify: record name info for FAN_DIR_MODIFY event

For FAN_DIR_MODIFY event, allocate a variable size event struct to store
the dir entry name along side the directory file handle.

At this point, name info reporting is not yet implemented, so trying to
set FAN_DIR_MODIFY in mark mask will return -EINVAL.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Amir Goldstein <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/notify/fanotify/fanotify.c

···
 		fanotify_fh_equal(&ffe1->object_fh, &ffe2->object_fh);
 }
 
+static bool fanotify_name_event_equal(struct fanotify_name_event *fne1,
+				      struct fanotify_name_event *fne2)
+{
+	/*
+	 * Do not merge name events without dir fh.
+	 * FAN_DIR_MODIFY does not encode object fh, so it may be empty.
+	 */
+	if (!fne1->dir_fh.len)
+		return false;
+
+	if (fne1->name_len != fne2->name_len ||
+	    !fanotify_fh_equal(&fne1->dir_fh, &fne2->dir_fh))
+		return false;
+
+	return !memcmp(fne1->name, fne2->name, fne1->name_len);
+}
+
 static bool should_merge(struct fsnotify_event *old_fsn,
 			 struct fsnotify_event *new_fsn)
 {
···
 
 		return fanotify_fid_event_equal(FANOTIFY_FE(old),
 						FANOTIFY_FE(new));
+	case FANOTIFY_EVENT_TYPE_FID_NAME:
+		return fanotify_name_event_equal(FANOTIFY_NE(old),
+						 FANOTIFY_NE(new));
 	default:
 		WARN_ON_ONCE(1);
 	}
···
 	void *buf = fh->buf;
 	int err;
 
+	if (!inode)
+		goto out;
+
 	dwords = 0;
 	err = -ENOENT;
 	type = exportfs_encode_inode_fh(inode, NULL, &dwords, NULL);
···
 			    type, bytes, err);
 	kfree(ext_buf);
 	*fanotify_fh_ext_buf_ptr(fh) = NULL;
+out:
 	/* Report the event without a file identifier on encode error */
 	fh->type = FILEID_INVALID;
 	fh->len = 0;
···
 struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 					    struct inode *inode, u32 mask,
 					    const void *data, int data_type,
+					    const struct qstr *file_name,
 					    __kernel_fsid_t *fsid)
 {
 	struct fanotify_event *event = NULL;
 	struct fanotify_fid_event *ffe = NULL;
+	struct fanotify_name_event *fne = NULL;
 	gfp_t gfp = GFP_KERNEL_ACCOUNT;
 	struct inode *id = fanotify_fid_inode(inode, mask, data, data_type);
 	const struct path *path = fsnotify_data_path(data, data_type);
···
 		goto init;
 	}
 
+	/*
+	 * For FAN_DIR_MODIFY event, we report the fid of the directory and
+	 * the name of the modified entry.
+	 * Allocate an fanotify_name_event struct and copy the name.
+	 */
+	if (mask & FAN_DIR_MODIFY && !(WARN_ON_ONCE(!file_name))) {
+		fne = kmalloc(sizeof(*fne) + file_name->len + 1, gfp);
+		if (!fne)
+			goto out;
+
+		event = &fne->fae;
+		event->type = FANOTIFY_EVENT_TYPE_FID_NAME;
+		fne->name_len = file_name->len;
+		strcpy(fne->name, file_name->name);
+		goto init;
+	}
+
 	if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
 		ffe = kmem_cache_alloc(fanotify_fid_event_cachep, gfp);
 		if (!ffe)
···
 		event->type = FANOTIFY_EVENT_TYPE_PATH;
 	}
 
-init: __maybe_unused
+init:
 	/*
 	 * Use the victim inode instead of the watching inode as the id for
 	 * event queue, so event reported on parent is merged with event
···
 	else
 		event->pid = get_pid(task_tgid(current));
 
-	if (fanotify_event_object_fh(event)) {
-		ffe->object_fh.len = 0;
-		if (fsid)
-			ffe->fsid = *fsid;
-		if (id)
-			fanotify_encode_fh(&ffe->object_fh, id, gfp);
-	} else if (fanotify_event_has_path(event)) {
+	if (fsid && fanotify_event_fsid(event))
+		*fanotify_event_fsid(event) = *fsid;
+
+	if (fanotify_event_object_fh(event))
+		fanotify_encode_fh(fanotify_event_object_fh(event), id, gfp);
+
+	if (fanotify_event_dir_fh(event))
+		fanotify_encode_fh(fanotify_event_dir_fh(event), id, gfp);
+
+	if (fanotify_event_has_path(event)) {
 		struct path *p = fanotify_event_path(event);
 
 		if (path) {
···
 	}
 
 	event = fanotify_alloc_event(group, inode, mask, data, data_type,
-				     &fsid);
+				     file_name, &fsid);
 	ret = -ENOMEM;
 	if (unlikely(!event)) {
 		/*
···
 	kmem_cache_free(fanotify_fid_event_cachep, ffe);
 }
 
+static void fanotify_free_name_event(struct fanotify_event *event)
+{
+	struct fanotify_name_event *fne = FANOTIFY_NE(event);
+
+	if (fanotify_fh_has_ext_buf(&fne->dir_fh))
+		kfree(fanotify_fh_ext_buf(&fne->dir_fh));
+	kfree(fne);
+}
+
 static void fanotify_free_event(struct fsnotify_event *fsn_event)
 {
 	struct fanotify_event *event;
···
 		break;
 	case FANOTIFY_EVENT_TYPE_FID:
 		fanotify_free_fid_event(event);
+		break;
+	case FANOTIFY_EVENT_TYPE_FID_NAME:
+		fanotify_free_name_event(event);
 		break;
 	default:
 		WARN_ON_ONCE(1);

fs/notify/fanotify/fanotify.h

···
  * be freed and which concrete struct it may be cast to.
  */
 enum fanotify_event_type {
-	FANOTIFY_EVENT_TYPE_FID,
+	FANOTIFY_EVENT_TYPE_FID, /* fixed length */
+	FANOTIFY_EVENT_TYPE_FID_NAME, /* variable length */
 	FANOTIFY_EVENT_TYPE_PATH,
 	FANOTIFY_EVENT_TYPE_PATH_PERM,
 };
···
 	return container_of(event, struct fanotify_fid_event, fae);
 }
 
+struct fanotify_name_event {
+	struct fanotify_event fae;
+	__kernel_fsid_t fsid;
+	struct fanotify_fh dir_fh;
+	u8 name_len;
+	char name[0];
+};
+
+static inline struct fanotify_name_event *
+FANOTIFY_NE(struct fanotify_event *event)
+{
+	return container_of(event, struct fanotify_name_event, fae);
+}
+
 static inline __kernel_fsid_t *fanotify_event_fsid(struct fanotify_event *event)
 {
 	if (event->type == FANOTIFY_EVENT_TYPE_FID)
 		return &FANOTIFY_FE(event)->fsid;
+	else if (event->type == FANOTIFY_EVENT_TYPE_FID_NAME)
+		return &FANOTIFY_NE(event)->fsid;
 	else
 		return NULL;
 }
···
 		return NULL;
 }
 
+static inline struct fanotify_fh *fanotify_event_dir_fh(
+						struct fanotify_event *event)
+{
+	if (event->type == FANOTIFY_EVENT_TYPE_FID_NAME)
+		return &FANOTIFY_NE(event)->dir_fh;
+	else
+		return NULL;
+}
+
 static inline int fanotify_event_object_fh_len(struct fanotify_event *event)
 {
 	struct fanotify_fh *fh = fanotify_event_object_fh(event);
 
 	return fh ? fh->len : 0;
+}
+
+static inline bool fanotify_event_has_name(struct fanotify_event *event)
+{
+	return event->type == FANOTIFY_EVENT_TYPE_FID_NAME;
+}
+
+static inline int fanotify_event_name_len(struct fanotify_event *event)
+{
+	return fanotify_event_has_name(event) ?
+		FANOTIFY_NE(event)->name_len : 0;
 }
 
 struct fanotify_path_event {
···
 struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 					    struct inode *inode, u32 mask,
 					    const void *data, int data_type,
+					    const struct qstr *file_name,
 					    __kernel_fsid_t *fsid);

fs/notify/fanotify/fanotify_user.c

···
 	struct fanotify_event_info_fid info = { };
 	struct file_handle handle = { };
 	unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh_buf;
-	size_t fh_len = fh->len;
+	size_t fh_len = fh ? fh->len : 0;
 	size_t len = fanotify_fid_info_len(fh_len);
 
 	if (!len)
···
 	group->memcg = get_mem_cgroup_from_mm(current->mm);
 
 	oevent = fanotify_alloc_event(group, NULL, FS_Q_OVERFLOW, NULL,
-				      FSNOTIFY_EVENT_NONE, NULL);
+				      FSNOTIFY_EVENT_NONE, NULL, NULL);
 	if (unlikely(!oevent)) {
 		fd = -ENOMEM;
 		goto out_destroy_group;