// SPDX-License-Identifier: GPL-2.0-only
  /*
   * umd - User mode driver support
   */
  #include <linux/shmem_fs.h>
  #include <linux/pipe_fs_i.h>

  #include <linux/mount.h>
  #include <linux/fs_struct.h>
  #include <linux/task_work.h>

  #include <linux/usermode_driver.h>

  static struct vfsmount *blob_to_mnt(const void *data, size_t len, const char *name)
  {
  	struct file_system_type *type;
  	struct vfsmount *mnt;
  	struct file *file;
  	ssize_t written;
  	loff_t pos = 0;
  
  	type = get_fs_type("tmpfs");
  	if (!type)
  		return ERR_PTR(-ENODEV);
  
  	mnt = kern_mount(type);
  	put_filesystem(type);
  	if (IS_ERR(mnt))
  		return mnt;
  
  	file = file_open_root(mnt->mnt_root, mnt, name, O_CREAT | O_WRONLY, 0700);
  	if (IS_ERR(file)) {
  		mntput(mnt);
  		return ERR_CAST(file);
  	}
  
  	written = kernel_write(file, data, len, &pos);
  	if (written != len) {
  		int err = written;
  		if (err >= 0)
  			err = -ENOMEM;
  		filp_close(file, NULL);
  		mntput(mnt);
  		return ERR_PTR(err);
  	}
  
  	fput(file);
  
  	/* Flush delayed fput so exec can open the file read-only */
  	flush_delayed_fput();
  	task_work_run();
  	return mnt;
  }
  
  /**
   * umd_load_blob - Remember a blob of bytes for fork_usermode_driver
   * @info: information about usermode driver
   * @data: a blob of bytes that can be executed as a file
   * @len:  The lentgh of the blob
   *
   */
  int umd_load_blob(struct umd_info *info, const void *data, size_t len)
  {
  	struct vfsmount *mnt;
  
  	if (WARN_ON_ONCE(info->wd.dentry || info->wd.mnt))
  		return -EBUSY;
  
  	mnt = blob_to_mnt(data, len, info->driver_name);
  	if (IS_ERR(mnt))
  		return PTR_ERR(mnt);
  
  	info->wd.mnt = mnt;
  	info->wd.dentry = mnt->mnt_root;
  	return 0;
  }
  EXPORT_SYMBOL_GPL(umd_load_blob);
  
  /**
   * umd_unload_blob - Disassociate @info from a previously loaded blob
   * @info: information about usermode driver
   *
   */
  int umd_unload_blob(struct umd_info *info)
  {
  	if (WARN_ON_ONCE(!info->wd.mnt ||
  			 !info->wd.dentry ||
  			 info->wd.mnt->mnt_root != info->wd.dentry))
  		return -EINVAL;
  
  	kern_unmount(info->wd.mnt);
  	info->wd.mnt = NULL;
  	info->wd.dentry = NULL;
  	return 0;
  }
  EXPORT_SYMBOL_GPL(umd_unload_blob);

  static int umd_setup(struct subprocess_info *info, struct cred *new)
  {

  	struct umd_info *umd_info = info->data;

  	struct file *from_umh[2];
  	struct file *to_umh[2];
  	int err;
  
  	/* create pipe to send data to umh */
  	err = create_pipe_files(to_umh, 0);
  	if (err)
  		return err;
  	err = replace_fd(0, to_umh[0], 0);
  	fput(to_umh[0]);
  	if (err < 0) {
  		fput(to_umh[1]);
  		return err;
  	}
  
  	/* create pipe to receive data from umh */
  	err = create_pipe_files(from_umh, 0);
  	if (err) {
  		fput(to_umh[1]);
  		replace_fd(0, NULL, 0);
  		return err;
  	}
  	err = replace_fd(1, from_umh[1], 0);
  	fput(from_umh[1]);
  	if (err < 0) {
  		fput(to_umh[1]);
  		replace_fd(0, NULL, 0);
  		fput(from_umh[0]);
  		return err;
  	}

  	set_fs_pwd(current->fs, &umd_info->wd);

  	umd_info->pipe_to_umh = to_umh[1];
  	umd_info->pipe_from_umh = from_umh[0];

  	umd_info->tgid = get_pid(task_tgid(current));

  	return 0;
  }
  
  static void umd_cleanup(struct subprocess_info *info)
  {

  	struct umd_info *umd_info = info->data;

  
  	/* cleanup if umh_setup() was successful but exec failed */
  	if (info->retval) {

  		fput(umd_info->pipe_to_umh);
  		fput(umd_info->pipe_from_umh);

  		put_pid(umd_info->tgid);
  		umd_info->tgid = NULL;

  	}
  }
  
  /**

   * fork_usermode_driver - fork a usermode driver
   * @info: information about usermode driver (shouldn't be NULL)

   *

   * Returns either negative error or zero which indicates success in
   * executing a usermode driver. In such case 'struct umd_info *info'

   * is populated with two pipes and a tgid of the process. The caller is

   * responsible for health check of the user process, killing it via

   * tgid, and closing the pipes when user process is no longer needed.

   */

  int fork_usermode_driver(struct umd_info *info)

  {

  	struct subprocess_info *sub_info;

  	const char *argv[] = { info->driver_name, NULL };

  	int err;

  	if (WARN_ON_ONCE(info->tgid))
  		return -EBUSY;

  	err = -ENOMEM;

  	sub_info = call_usermodehelper_setup(info->driver_name,
  					     (char **)argv, NULL, GFP_KERNEL,

  					     umd_setup, umd_cleanup, info);
  	if (!sub_info)
  		goto out;

  	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);

  out:

  	return err;
  }

  EXPORT_SYMBOL_GPL(fork_usermode_driver);