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(f: 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(to: uarg, from: &arg, n: sizeof(arg)))
52 return -EFAULT;
53
54 if (copy_to_user(to: uarg->digest, from: vi->file_digest, n: 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 * @raw_digest: (out) the raw file digest
65 * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value
66 * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value
67 *
68 * Retrieves the fsverity digest of the given file. The file must have been
69 * opened at least once since the inode was last loaded into the inode cache;
70 * otherwise this function will not recognize when fsverity is enabled.
71 *
72 * The file's fsverity digest consists of @raw_digest in combination with either
73 * @alg or @halg. (The caller can choose which one of @alg or @halg to use.)
74 *
75 * IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since
76 * @raw_digest is meaningless without knowing which algorithm it uses! fsverity
77 * provides no security guarantee for users who ignore the algorithm ID, even if
78 * they use the digest size (since algorithms can share the same digest size).
79 *
80 * Return: The size of the raw digest in bytes, or 0 if the file doesn't have
81 * fsverity enabled.
82 */
83int fsverity_get_digest(struct inode *inode,
84 u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
85 u8 *alg, enum hash_algo *halg)
86{
87 const struct fsverity_info *vi;
88 const struct fsverity_hash_alg *hash_alg;
89
90 vi = fsverity_get_info(inode);
91 if (!vi)
92 return 0; /* not a verity file */
93
94 hash_alg = vi->tree_params.hash_alg;
95 memcpy(raw_digest, vi->file_digest, hash_alg->digest_size);
96 if (alg)
97 *alg = hash_alg - fsverity_hash_algs;
98 if (halg)
99 *halg = hash_alg->algo_id;
100 return hash_alg->digest_size;
101}
102EXPORT_SYMBOL_GPL(fsverity_get_digest);
103

source code of linux/fs/verity/measure.c