LXR linux/fs/verity/measure.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Ioctl to get a verity file's digest
   4 *
   5 * Copyright 2019 Google LLC
   6 */
   7
   8#include "fsverity_private.h"
   9
  10#include <linux/uaccess.h>
  11
  12/**
  13 * fsverity_ioctl_measure() - get a verity file's digest
  14 * @filp: file to get digest of
  15 * @_uarg: user pointer to fsverity_digest
  16 *
  17 * Retrieve the file digest that the kernel is enforcing for reads from a verity
  18 * file.  See the "FS_IOC_MEASURE_VERITY" section of
  19 * Documentation/filesystems/fsverity.rst for the documentation.
  20 *
  21 * Return: 0 on success, -errno on failure
  22 */
  23int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
  24{
  25        const struct inode *inode = file_inode(filp);
  26        struct fsverity_digest __user *uarg = _uarg;
  27        const struct fsverity_info *vi;
  28        const struct fsverity_hash_alg *hash_alg;
  29        struct fsverity_digest arg;
  30
  31        vi = fsverity_get_info(inode);
  32        if (!vi)
  33                return -ENODATA; /* not a verity file */
  34        hash_alg = vi->tree_params.hash_alg;
  35
  36        /*
  37         * The user specifies the digest_size their buffer has space for; we can
  38         * return the digest if it fits in the available space.  We write back
  39         * the actual size, which may be shorter than the user-specified size.
  40         */
  41
  42        if (get_user(arg.digest_size, &uarg->digest_size))
  43                return -EFAULT;
  44        if (arg.digest_size < hash_alg->digest_size)
  45                return -EOVERFLOW;
  46
  47        memset(&arg, 0, sizeof(arg));
  48        arg.digest_algorithm = hash_alg - fsverity_hash_algs;
  49        arg.digest_size = hash_alg->digest_size;
  50
  51        if (copy_to_user(uarg, &arg, sizeof(arg)))
  52                return -EFAULT;
  53
  54        if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size))
  55                return -EFAULT;
  56
  57        return 0;
  58}
  59EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
  60