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1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* | |
ed45e201 | 3 | * Ioctl to get a verity file's digest |
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4 | * |
5 | * Copyright 2019 Google LLC | |
6 | */ | |
7 | ||
8 | #include "fsverity_private.h" | |
9 | ||
10 | #include <linux/uaccess.h> | |
11 | ||
12 | /** | |
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13 | * fsverity_ioctl_measure() - get a verity file's digest |
14 | * @filp: file to get digest of | |
6377a38b | 15 | * @_uarg: user pointer to fsverity_digest |
4dd893d8 | 16 | * |
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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 | |
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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(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 | ||
ed45e201 | 54 | if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size)) |
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55 | return -EFAULT; |
56 | ||
57 | return 0; | |
58 | } | |
59 | EXPORT_SYMBOL_GPL(fsverity_ioctl_measure); | |
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60 | |
61 | /** | |
62 | * fsverity_get_digest() - get a verity file's digest | |
63 | * @inode: inode to get digest of | |
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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 | |
246d9216 | 67 | * |
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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. | |
246d9216 | 71 | * |
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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. | |
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82 | */ |
83 | int fsverity_get_digest(struct inode *inode, | |
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84 | u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE], |
85 | u8 *alg, enum hash_algo *halg) | |
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86 | { |
87 | const struct fsverity_info *vi; | |
88 | const struct fsverity_hash_alg *hash_alg; | |
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89 | |
90 | vi = fsverity_get_info(inode); | |
91 | if (!vi) | |
74836ecb | 92 | return 0; /* not a verity file */ |
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93 | |
94 | hash_alg = vi->tree_params.hash_alg; | |
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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; | |
246d9216 | 101 | } |
74836ecb | 102 | EXPORT_SYMBOL_GPL(fsverity_get_digest); |