fs/verity/measure.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * fs/verity/measure.c: ioctl to get a verity file's measurement
   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 measurement
  14  * @filp: file to get measurement of
  15  * @_uarg: user pointer to fsverity_digest
  16  *
  17  * Retrieve the file measurement that the kernel is enforcing for reads from a
  18  * verity 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  */
  23 int 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->measurement, hash_alg->digest_size))
  55                 return -EFAULT;
  56
  57         return 0;
  58 }
  59 EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);