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/export.h>
13#include <linux/uaccess.h>
14
15/**
16 * fsverity_ioctl_measure() - get a verity file's digest
17 * @filp: file to get digest of
18 * @_uarg: user pointer to fsverity_digest
19 *
20 * Retrieve the file digest that the kernel is enforcing for reads from a verity
21 * file. See the "FS_IOC_MEASURE_VERITY" section of
22 * Documentation/filesystems/fsverity.rst for the documentation.
23 *
24 * Return: 0 on success, -errno on failure
25 */
26int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
27{
28 const struct inode *inode = file_inode(f: filp);
29 struct fsverity_digest __user *uarg = _uarg;
30 const struct fsverity_info *vi;
31 const struct fsverity_hash_alg *hash_alg;
32 struct fsverity_digest arg;
33
34 vi = fsverity_get_info(inode);
35 if (!vi)
36 return -ENODATA; /* not a verity file */
37 hash_alg = vi->tree_params.hash_alg;
38
39 /*
40 * The user specifies the digest_size their buffer has space for; we can
41 * return the digest if it fits in the available space. We write back
42 * the actual size, which may be shorter than the user-specified size.
43 */
44
45 if (get_user(arg.digest_size, &uarg->digest_size))
46 return -EFAULT;
47 if (arg.digest_size < hash_alg->digest_size)
48 return -EOVERFLOW;
49
50 memset(&arg, 0, sizeof(arg));
51 arg.digest_algorithm = hash_alg - fsverity_hash_algs;
52 arg.digest_size = hash_alg->digest_size;
53
54 if (copy_to_user(to: uarg, from: &arg, n: sizeof(arg)))
55 return -EFAULT;
56
57 if (copy_to_user(to: uarg->digest, from: vi->file_digest, n: hash_alg->digest_size))
58 return -EFAULT;
59
60 return 0;
61}
62EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
63
64/**
65 * fsverity_get_digest() - get a verity file's digest
66 * @inode: inode to get digest of
67 * @raw_digest: (out) the raw file digest
68 * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value
69 * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value
70 *
71 * Retrieves the fsverity digest of the given file. The file must have been
72 * opened at least once since the inode was last loaded into the inode cache;
73 * otherwise this function will not recognize when fsverity is enabled.
74 *
75 * The file's fsverity digest consists of @raw_digest in combination with either
76 * @alg or @halg. (The caller can choose which one of @alg or @halg to use.)
77 *
78 * IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since
79 * @raw_digest is meaningless without knowing which algorithm it uses! fsverity
80 * provides no security guarantee for users who ignore the algorithm ID, even if
81 * they use the digest size (since algorithms can share the same digest size).
82 *
83 * Return: The size of the raw digest in bytes, or 0 if the file doesn't have
84 * fsverity enabled.
85 */
86int fsverity_get_digest(struct inode *inode,
87 u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
88 u8 *alg, enum hash_algo *halg)
89{
90 const struct fsverity_info *vi;
91 const struct fsverity_hash_alg *hash_alg;
92
93 vi = fsverity_get_info(inode);
94 if (!vi)
95 return 0; /* not a verity file */
96
97 hash_alg = vi->tree_params.hash_alg;
98 memcpy(raw_digest, vi->file_digest, hash_alg->digest_size);
99 if (alg)
100 *alg = hash_alg - fsverity_hash_algs;
101 if (halg)
102 *halg = hash_alg->algo_id;
103 return hash_alg->digest_size;
104}
105EXPORT_SYMBOL_GPL(fsverity_get_digest);
106
107#ifdef CONFIG_BPF_SYSCALL
108
109/* bpf kfuncs */
110__bpf_kfunc_start_defs();
111
112/**
113 * bpf_get_fsverity_digest: read fsverity digest of file
114 * @file: file to get digest from
115 * @digest_p: (out) dynptr for struct fsverity_digest
116 *
117 * Read fsverity_digest of *file* into *digest_ptr*.
118 *
119 * Return: 0 on success, a negative value on error.
120 */
121__bpf_kfunc int bpf_get_fsverity_digest(struct file *file, struct bpf_dynptr *digest_p)
122{
123 struct bpf_dynptr_kern *digest_ptr = (struct bpf_dynptr_kern *)digest_p;
124 const struct inode *inode = file_inode(f: file);
125 u32 dynptr_sz = __bpf_dynptr_size(ptr: digest_ptr);
126 struct fsverity_digest *arg;
127 const struct fsverity_info *vi;
128 const struct fsverity_hash_alg *hash_alg;
129 int out_digest_sz;
130
131 if (dynptr_sz < sizeof(struct fsverity_digest))
132 return -EINVAL;
133
134 arg = __bpf_dynptr_data_rw(ptr: digest_ptr, len: dynptr_sz);
135 if (!arg)
136 return -EINVAL;
137
138 if (!IS_ALIGNED((uintptr_t)arg, __alignof__(*arg)))
139 return -EINVAL;
140
141 vi = fsverity_get_info(inode);
142 if (!vi)
143 return -ENODATA; /* not a verity file */
144
145 hash_alg = vi->tree_params.hash_alg;
146
147 arg->digest_algorithm = hash_alg - fsverity_hash_algs;
148 arg->digest_size = hash_alg->digest_size;
149
150 out_digest_sz = dynptr_sz - sizeof(struct fsverity_digest);
151
152 /* copy digest */
153 memcpy(arg->digest, vi->file_digest, min_t(int, hash_alg->digest_size, out_digest_sz));
154
155 /* fill the extra buffer with zeros */
156 if (out_digest_sz > hash_alg->digest_size)
157 memset(arg->digest + arg->digest_size, 0, out_digest_sz - hash_alg->digest_size);
158
159 return 0;
160}
161
162__bpf_kfunc_end_defs();
163
164BTF_KFUNCS_START(fsverity_set_ids)
165BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS)
166BTF_KFUNCS_END(fsverity_set_ids)
167
168static int bpf_get_fsverity_digest_filter(const struct bpf_prog *prog, u32 kfunc_id)
169{
170 if (!btf_id_set8_contains(set: &fsverity_set_ids, id: kfunc_id))
171 return 0;
172
173 /* Only allow to attach from LSM hooks, to avoid recursion */
174 return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0;
175}
176
177static const struct btf_kfunc_id_set bpf_fsverity_set = {
178 .owner = THIS_MODULE,
179 .set = &fsverity_set_ids,
180 .filter = bpf_get_fsverity_digest_filter,
181};
182
183void __init fsverity_init_bpf(void)
184{
185 register_btf_kfunc_id_set(prog_type: BPF_PROG_TYPE_LSM, s: &bpf_fsverity_set);
186}
187
188#endif /* CONFIG_BPF_SYSCALL */
189

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