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
61/**
62 * fsverity_get_digest() - get a verity file's digest
63 * @inode: inode to get digest of
64 * @digest: (out) pointer to the digest
65 * @alg: (out) pointer to the hash algorithm enumeration
66 *
67 * Return the file hash algorithm and digest of an fsverity protected file.
68 * Assumption: before calling this, the file must have been opened.
69 *
70 * Return: 0 on success, -errno on failure
71 */
72int fsverity_get_digest(struct inode *inode,
73			u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
74			enum hash_algo *alg)
75{
76	const struct fsverity_info *vi;
77	const struct fsverity_hash_alg *hash_alg;
78
79	vi = fsverity_get_info(inode);
80	if (!vi)
81		return -ENODATA; /* not a verity file */
82
83	hash_alg = vi->tree_params.hash_alg;
84	memcpy(digest, vi->file_digest, hash_alg->digest_size);
85	*alg = hash_alg->algo_id;
86	return 0;
87}