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/bpf.h> |
11 | #include <linux/btf.h> |
12 | #include <linux/uaccess.h> |
13 | |
14 | /** |
15 | * fsverity_ioctl_measure() - get a verity file's digest |
16 | * @filp: file to get digest of |
17 | * @_uarg: user pointer to fsverity_digest |
18 | * |
19 | * Retrieve the file digest that the kernel is enforcing for reads from a verity |
20 | * file. See the "FS_IOC_MEASURE_VERITY" section of |
21 | * Documentation/filesystems/fsverity.rst for the documentation. |
22 | * |
23 | * Return: 0 on success, -errno on failure |
24 | */ |
25 | int fsverity_ioctl_measure(struct file *filp, void __user *_uarg) |
26 | { |
27 | const struct inode *inode = file_inode(f: filp); |
28 | struct fsverity_digest __user *uarg = _uarg; |
29 | const struct fsverity_info *vi; |
30 | const struct fsverity_hash_alg *hash_alg; |
31 | struct fsverity_digest arg; |
32 | |
33 | vi = fsverity_get_info(inode); |
34 | if (!vi) |
35 | return -ENODATA; /* not a verity file */ |
36 | hash_alg = vi->tree_params.hash_alg; |
37 | |
38 | /* |
39 | * The user specifies the digest_size their buffer has space for; we can |
40 | * return the digest if it fits in the available space. We write back |
41 | * the actual size, which may be shorter than the user-specified size. |
42 | */ |
43 | |
44 | if (get_user(arg.digest_size, &uarg->digest_size)) |
45 | return -EFAULT; |
46 | if (arg.digest_size < hash_alg->digest_size) |
47 | return -EOVERFLOW; |
48 | |
49 | memset(&arg, 0, sizeof(arg)); |
50 | arg.digest_algorithm = hash_alg - fsverity_hash_algs; |
51 | arg.digest_size = hash_alg->digest_size; |
52 | |
53 | if (copy_to_user(to: uarg, from: &arg, n: sizeof(arg))) |
54 | return -EFAULT; |
55 | |
56 | if (copy_to_user(to: uarg->digest, from: vi->file_digest, n: hash_alg->digest_size)) |
57 | return -EFAULT; |
58 | |
59 | return 0; |
60 | } |
61 | EXPORT_SYMBOL_GPL(fsverity_ioctl_measure); |
62 | |
63 | /** |
64 | * fsverity_get_digest() - get a verity file's digest |
65 | * @inode: inode to get digest of |
66 | * @raw_digest: (out) the raw file digest |
67 | * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value |
68 | * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value |
69 | * |
70 | * Retrieves the fsverity digest of the given file. The file must have been |
71 | * opened at least once since the inode was last loaded into the inode cache; |
72 | * otherwise this function will not recognize when fsverity is enabled. |
73 | * |
74 | * The file's fsverity digest consists of @raw_digest in combination with either |
75 | * @alg or @halg. (The caller can choose which one of @alg or @halg to use.) |
76 | * |
77 | * IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since |
78 | * @raw_digest is meaningless without knowing which algorithm it uses! fsverity |
79 | * provides no security guarantee for users who ignore the algorithm ID, even if |
80 | * they use the digest size (since algorithms can share the same digest size). |
81 | * |
82 | * Return: The size of the raw digest in bytes, or 0 if the file doesn't have |
83 | * fsverity enabled. |
84 | */ |
85 | int fsverity_get_digest(struct inode *inode, |
86 | u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE], |
87 | u8 *alg, enum hash_algo *halg) |
88 | { |
89 | const struct fsverity_info *vi; |
90 | const struct fsverity_hash_alg *hash_alg; |
91 | |
92 | vi = fsverity_get_info(inode); |
93 | if (!vi) |
94 | return 0; /* not a verity file */ |
95 | |
96 | hash_alg = vi->tree_params.hash_alg; |
97 | memcpy(raw_digest, vi->file_digest, hash_alg->digest_size); |
98 | if (alg) |
99 | *alg = hash_alg - fsverity_hash_algs; |
100 | if (halg) |
101 | *halg = hash_alg->algo_id; |
102 | return hash_alg->digest_size; |
103 | } |
104 | EXPORT_SYMBOL_GPL(fsverity_get_digest); |
105 | |
106 | #ifdef CONFIG_BPF_SYSCALL |
107 | |
108 | /* bpf kfuncs */ |
109 | __bpf_kfunc_start_defs(); |
110 | |
111 | /** |
112 | * bpf_get_fsverity_digest: read fsverity digest of file |
113 | * @file: file to get digest from |
114 | * @digest_ptr: (out) dynptr for struct fsverity_digest |
115 | * |
116 | * Read fsverity_digest of *file* into *digest_ptr*. |
117 | * |
118 | * Return: 0 on success, a negative value on error. |
119 | */ |
120 | __bpf_kfunc int bpf_get_fsverity_digest(struct file *file, struct bpf_dynptr_kern *digest_ptr) |
121 | { |
122 | const struct inode *inode = file_inode(f: file); |
123 | u32 dynptr_sz = __bpf_dynptr_size(ptr: digest_ptr); |
124 | struct fsverity_digest *arg; |
125 | const struct fsverity_info *vi; |
126 | const struct fsverity_hash_alg *hash_alg; |
127 | int out_digest_sz; |
128 | |
129 | if (dynptr_sz < sizeof(struct fsverity_digest)) |
130 | return -EINVAL; |
131 | |
132 | arg = __bpf_dynptr_data_rw(ptr: digest_ptr, len: dynptr_sz); |
133 | if (!arg) |
134 | return -EINVAL; |
135 | |
136 | if (!IS_ALIGNED((uintptr_t)arg, __alignof__(*arg))) |
137 | return -EINVAL; |
138 | |
139 | vi = fsverity_get_info(inode); |
140 | if (!vi) |
141 | return -ENODATA; /* not a verity file */ |
142 | |
143 | hash_alg = vi->tree_params.hash_alg; |
144 | |
145 | arg->digest_algorithm = hash_alg - fsverity_hash_algs; |
146 | arg->digest_size = hash_alg->digest_size; |
147 | |
148 | out_digest_sz = dynptr_sz - sizeof(struct fsverity_digest); |
149 | |
150 | /* copy digest */ |
151 | memcpy(arg->digest, vi->file_digest, min_t(int, hash_alg->digest_size, out_digest_sz)); |
152 | |
153 | /* fill the extra buffer with zeros */ |
154 | if (out_digest_sz > hash_alg->digest_size) |
155 | memset(arg->digest + arg->digest_size, 0, out_digest_sz - hash_alg->digest_size); |
156 | |
157 | return 0; |
158 | } |
159 | |
160 | __bpf_kfunc_end_defs(); |
161 | |
162 | BTF_KFUNCS_START(fsverity_set_ids) |
163 | BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS) |
164 | BTF_KFUNCS_END(fsverity_set_ids) |
165 | |
166 | static int bpf_get_fsverity_digest_filter(const struct bpf_prog *prog, u32 kfunc_id) |
167 | { |
168 | if (!btf_id_set8_contains(set: &fsverity_set_ids, id: kfunc_id)) |
169 | return 0; |
170 | |
171 | /* Only allow to attach from LSM hooks, to avoid recursion */ |
172 | return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0; |
173 | } |
174 | |
175 | static const struct btf_kfunc_id_set bpf_fsverity_set = { |
176 | .owner = THIS_MODULE, |
177 | .set = &fsverity_set_ids, |
178 | .filter = bpf_get_fsverity_digest_filter, |
179 | }; |
180 | |
181 | void __init fsverity_init_bpf(void) |
182 | { |
183 | register_btf_kfunc_id_set(prog_type: BPF_PROG_TYPE_LSM, s: &bpf_fsverity_set); |
184 | } |
185 | |
186 | #endif /* CONFIG_BPF_SYSCALL */ |
187 | |