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 */
fsverity_ioctl_measure(struct file * filp,void __user * _uarg)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);
60
