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 | */ |
23 | int 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 | } |
59 | EXPORT_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 | */ |
83 | int 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 | } |
102 | EXPORT_SYMBOL_GPL(fsverity_get_digest); |
103 | |