text: // SPDX-License-Identifier: GPL-2.0
  /*
   * fs/verity/measure.c: ioctl to get a verity file's measurement
   *
   * Copyright 2019 Google LLC
   */
  
  #include "fsverity_private.h"
  
  #include <linux/uaccess.h>
  
  /**
   * fsverity_ioctl_measure() - get a verity file's measurement
   * @filp: file to get measurement of
   * @_uarg: user pointer to fsverity_digest
   *
   * Retrieve the file measurement that the kernel is enforcing for reads from a
   * verity file.  See the "FS_IOC_MEASURE_VERITY" section of
   * Documentation/filesystems/fsverity.rst for the documentation.
   *
   * Return: 0 on success, -errno on failure
   */
  int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
  {
  	const struct inode *inode = file_inode(filp);
  	struct fsverity_digest __user *uarg = _uarg;
  	const struct fsverity_info *vi;
  	const struct fsverity_hash_alg *hash_alg;
  	struct fsverity_digest arg;
  
  	vi = fsverity_get_info(inode);
  	if (!vi)
  		return -ENODATA; /* not a verity file */
  	hash_alg = vi->tree_params.hash_alg;
  
  	/*
  	 * The user specifies the digest_size their buffer has space for; we can
  	 * return the digest if it fits in the available space.  We write back
  	 * the actual size, which may be shorter than the user-specified size.
  	 */
  
  	if (get_user(arg.digest_size, &uarg->digest_size))
  		return -EFAULT;
  	if (arg.digest_size < hash_alg->digest_size)
  		return -EOVERFLOW;
  
  	memset(&arg, 0, sizeof(arg));
  	arg.digest_algorithm = hash_alg - fsverity_hash_algs;
  	arg.digest_size = hash_alg->digest_size;
  
  	if (copy_to_user(uarg, &arg, sizeof(arg)))
  		return -EFAULT;
  
  	if (copy_to_user(uarg->digest, vi->measurement, hash_alg->digest_size))
  		return -EFAULT;
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
  