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  *
  15  * Retrieve the file measurement that the kernel is enforcing for reads from a
  16  * verity file.  See the "FS_IOC_MEASURE_VERITY" section of
  17  * Documentation/filesystems/fsverity.rst for the documentation.
  18  *
  19  * Return: 0 on success, -errno on failure
  20  */
  21 int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
  22 {
  23         const struct inode *inode = file_inode(filp);
  24         struct fsverity_digest __user *uarg = _uarg;
  25         const struct fsverity_info *vi;
  26         const struct fsverity_hash_alg *hash_alg;
  27         struct fsverity_digest arg;
  28
  29         vi = fsverity_get_info(inode);
  30         if (!vi)
  31                 return -ENODATA; /* not a verity file */
  32         hash_alg = vi->tree_params.hash_alg;
  33
  34         /*
  35          * The user specifies the digest_size their buffer has space for; we can
  36          * return the digest if it fits in the available space.  We write back
  37          * the actual size, which may be shorter than the user-specified size.
  38          */
  39
  40         if (get_user(arg.digest_size, &uarg->digest_size))
  41                 return -EFAULT;
  42         if (arg.digest_size < hash_alg->digest_size)
  43                 return -EOVERFLOW;
  44
  45         memset(&arg, 0, sizeof(arg));
  46         arg.digest_algorithm = hash_alg - fsverity_hash_algs;
  47         arg.digest_size = hash_alg->digest_size;
  48
  49         if (copy_to_user(uarg, &arg, sizeof(arg)))
  50                 return -EFAULT;
  51
  52         if (copy_to_user(uarg->digest, vi->measurement, hash_alg->digest_size))
  53                 return -EFAULT;
  54
  55         return 0;
  56 }
  57 EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);