diff --git a/fs/incfs/vfs.c b/fs/incfs/vfs.c
index aae918963a76..f911c5eb9290 100644
--- a/fs/incfs/vfs.c
+++ b/fs/incfs/vfs.c
@@ -135,6 +135,11 @@ static const struct file_operations incfs_file_ops = {
 	.compat_ioctl = dispatch_ioctl
 };
 
+enum FILL_PERMISSION {
+	CANT_FILL = 0,
+	CAN_FILL = 1,
+};
+
 static const struct file_operations incfs_pending_read_file_ops = {
 	.read = pending_reads_read,
 	.poll = pending_reads_poll,
@@ -1284,6 +1289,9 @@ static long ioctl_fill_blocks(struct file *f, void __user *arg)
 	if (!df)
 		return -EBADF;
 
+	if ((uintptr_t)f->private_data != CAN_FILL)
+		return -EPERM;
+
 	if (copy_from_user(&fill_blocks, usr_fill_blocks, sizeof(fill_blocks)))
 		return -EFAULT;
 
@@ -1336,6 +1344,53 @@ static long ioctl_fill_blocks(struct file *f, void __user *arg)
 	return i;
 }
 
+static long ioctl_permit_fill(struct file *f, void __user *arg)
+{
+	struct incfs_permit_fill __user *usr_permit_fill = arg;
+	struct incfs_permit_fill permit_fill;
+	long error = 0;
+	struct file *file = 0;
+
+	if (f->f_op != &incfs_pending_read_file_ops)
+		return -EPERM;
+
+	if (copy_from_user(&permit_fill, usr_permit_fill, sizeof(permit_fill)))
+		return -EFAULT;
+
+	file = fget(permit_fill.file_descriptor);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	if (file->f_op != &incfs_file_ops) {
+		error = -EPERM;
+		goto out;
+	}
+
+	if (file->f_inode->i_sb != f->f_inode->i_sb) {
+		error = -EPERM;
+		goto out;
+	}
+
+	switch ((uintptr_t)file->private_data) {
+	case CANT_FILL:
+		file->private_data = (void *)CAN_FILL;
+		break;
+
+	case CAN_FILL:
+		pr_debug("CAN_FILL already set");
+		break;
+
+	default:
+		pr_warn("Invalid file private data");
+		error = -EFAULT;
+		goto out;
+	}
+
+out:
+	fput(file);
+	return error;
+}
+
 static long ioctl_read_file_signature(struct file *f, void __user *arg)
 {
 	struct incfs_get_file_sig_args __user *args_usr_ptr = arg;
@@ -1393,6 +1448,8 @@ static long dispatch_ioctl(struct file *f, unsigned int req, unsigned long arg)
 		return ioctl_create_file(mi, (void __user *)arg);
 	case INCFS_IOC_FILL_BLOCKS:
 		return ioctl_fill_blocks(f, (void __user *)arg);
+	case INCFS_IOC_PERMIT_FILL:
+		return ioctl_permit_fill(f, (void __user *)arg);
 	case INCFS_IOC_READ_FILE_SIGNATURE:
 		return ioctl_read_file_signature(f, (void __user *)arg);
 	default:
@@ -1823,9 +1880,10 @@ static int file_open(struct inode *inode, struct file *file)
 		goto out;
 	}
 
-	if (S_ISREG(inode->i_mode))
+	if (S_ISREG(inode->i_mode)) {
 		err = make_inode_ready_for_data_ops(mi, inode, backing_file);
-	else if (S_ISDIR(inode->i_mode)) {
+		file->private_data = (void *)CANT_FILL;
+	} else if (S_ISDIR(inode->i_mode)) {
 		struct dir_file *dir = NULL;
 
 		dir = incfs_open_dir_file(mi, backing_file);
diff --git a/include/uapi/linux/incrementalfs.h b/include/uapi/linux/incrementalfs.h
index 2efc53f591ef..fd65f575cdf0 100644
--- a/include/uapi/linux/incrementalfs.h
+++ b/include/uapi/linux/incrementalfs.h
@@ -51,13 +51,23 @@
 	_IOR(INCFS_IOCTL_BASE_CODE, 31, struct incfs_get_file_sig_args)
 
 /*
- * Fill in one or more data block
+ * Fill in one or more data block. This may only be called on a handle
+ * passed as a parameter to INCFS_IOC_PERMIT_FILLING
  *
  * Returns number of blocks filled in, or error if none were
  */
 #define INCFS_IOC_FILL_BLOCKS                                                  \
 	_IOR(INCFS_IOCTL_BASE_CODE, 32, struct incfs_fill_blocks)
 
+/*
+ * Permit INCFS_IOC_FILL_BLOCKS on the given file descriptor
+ * May only be called on .pending_reads file
+ *
+ * Returns 0 on success or error
+ */
+#define INCFS_IOC_PERMIT_FILL                                                  \
+	_IOW(INCFS_IOCTL_BASE_CODE, 33, struct incfs_permit_fill)
+
 enum incfs_compression_alg {
 	COMPRESSION_NONE = 0,
 	COMPRESSION_LZ4 = 1
@@ -139,6 +149,17 @@ struct incfs_fill_blocks {
 	__aligned_u64 fill_blocks;
 };
 
+/*
+ * Permit INCFS_IOC_FILL_BLOCKS on the given file descriptor
+ * May only be called on .pending_reads file
+ *
+ * Argument for INCFS_IOC_PERMIT_FILL
+ */
+struct incfs_permit_fill {
+	/* File to permit fills on */
+	__u32 file_descriptor;
+};
+
 enum incfs_hash_tree_algorithm {
 	INCFS_HASH_TREE_NONE = 0,
 	INCFS_HASH_TREE_SHA256 = 1
diff --git a/tools/testing/selftests/filesystems/incfs/incfs_test.c b/tools/testing/selftests/filesystems/incfs/incfs_test.c
index 1cd1226f4e44..7031561c0173 100644
--- a/tools/testing/selftests/filesystems/incfs/incfs_test.c
+++ b/tools/testing/selftests/filesystems/incfs/incfs_test.c
@@ -204,15 +204,43 @@ static char *get_index_filename(const char *mnt_dir, incfs_uuid_t id)
 	return strdup(path);
 }
 
-int open_file_by_id(char *mnt_dir, incfs_uuid_t id)
+int open_file_by_id(const char *mnt_dir, incfs_uuid_t id, bool use_ioctl)
 {
 	char *path = get_index_filename(mnt_dir, id);
+	int cmd_fd = open_commands_file(mnt_dir);
 	int fd = open(path, O_RDWR);
+	struct incfs_permit_fill permit_fill = {
+		.file_descriptor = fd,
+	};
+	int error = 0;
 
-	free(path);
 	if (fd < 0) {
 		print_error("Can't open file by id.");
+		error = -errno;
+		goto out;
+	}
+
+	if (use_ioctl && ioctl(cmd_fd, INCFS_IOC_PERMIT_FILL, &permit_fill)) {
+		print_error("Failed to call PERMIT_FILL");
+		error = -errno;
+		goto out;
+	}
+
+	if (ioctl(fd, INCFS_IOC_PERMIT_FILL, &permit_fill) != -1 ||
+	    errno != EPERM) {
+		print_error(
+			"Successfully called PERMIT_FILL on non pending_read file");
 		return -errno;
+		goto out;
+	}
+
+out:
+	free(path);
+	close(cmd_fd);
+
+	if (error) {
+		close(fd);
+		return error;
 	}
 
 	return fd;
@@ -258,12 +286,6 @@ static int emit_test_blocks(char *mnt_dir, struct test_file *file,
 	int i = 0;
 	int blocks_written = 0;
 
-	fd = open_file_by_id(mnt_dir, file->id);
-	if (fd <= 0) {
-		error = -errno;
-		goto out;
-	}
-
 	for (i = 0; i < block_count; i++) {
 		int block_index = blocks[i];
 		bool compress = (file->index + block_index) % 2 == 0;
@@ -315,6 +337,24 @@ static int emit_test_blocks(char *mnt_dir, struct test_file *file,
 	}
 
 	if (!error) {
+		fd = open_file_by_id(mnt_dir, file->id, false);
+		if (fd < 0) {
+			error = -errno;
+			goto out;
+		}
+		write_res = ioctl(fd, INCFS_IOC_FILL_BLOCKS, &fill_blocks);
+		if (write_res >= 0) {
+			ksft_print_msg("Wrote to file via normal fd error\n");
+			error = -EPERM;
+			goto out;
+		}
+
+		close(fd);
+		fd = open_file_by_id(mnt_dir, file->id, true);
+		if (fd < 0) {
+			error = -errno;
+			goto out;
+		}
 		write_res = ioctl(fd, INCFS_IOC_FILL_BLOCKS, &fill_blocks);
 		if (write_res < 0)
 			error = -errno;
@@ -706,7 +746,6 @@ static int load_hash_tree(const char *mount_dir, struct test_file *file)
 	int err;
 	int i;
 	int fd;
-	char *file_path;
 	struct incfs_fill_blocks fill_blocks = {
 		.count = file->mtree_block_count,
 	};
@@ -729,9 +768,7 @@ static int load_hash_tree(const char *mount_dir, struct test_file *file)
 		};
 	}
 
-	file_path  = concat_file_name(mount_dir, file->name);
-	fd = open(file_path, O_RDWR);
-	free(file_path);
+	fd = open_file_by_id(mount_dir, file->id, false);
 	if (fd < 0) {
 		err = errno;
 		goto failure;
@@ -739,7 +776,19 @@ static int load_hash_tree(const char *mount_dir, struct test_file *file)
 
 	err = ioctl(fd, INCFS_IOC_FILL_BLOCKS, &fill_blocks);
 	close(fd);
+	if (err >= 0) {
+		err = -EPERM;
+		goto failure;
+	}
+
+	fd = open_file_by_id(mount_dir, file->id, true);
+	if (fd < 0) {
+		err = errno;
+		goto failure;
+	}
 
+	err = ioctl(fd, INCFS_IOC_FILL_BLOCKS, &fill_blocks);
+	close(fd);
 	if (err < fill_blocks.count)
 		err = errno;
 	else {