projects/linux·blob master · refs

159 lines · 5.0 KiB

1/* SPDX-License-Identifier: GPL-2.0-only */
2/*
3 * Landlock - Access types and helpers
4 *
5 * Copyright © 2016-2020 Mickaël Salaün <[email protected]>
6 * Copyright © 2018-2020 ANSSI
7 * Copyright © 2024-2025 Microsoft Corporation
8 */
9
10#ifndef _SECURITY_LANDLOCK_ACCESS_H
11#define _SECURITY_LANDLOCK_ACCESS_H
12
13#include <linux/bitops.h>
14#include <linux/build_bug.h>
15#include <linux/kernel.h>
16#include <uapi/linux/landlock.h>
17
18#include "limits.h"
19
20/*
21 * All access rights that are denied by default whether they are handled or not
22 * by a ruleset/layer. This must be ORed with all domain->handled_masks[]
23 * entries when we need to get the absolute handled access masks, see
24 * landlock_upgrade_handled_access_masks().
25 */
26/* clang-format off */
27#define _LANDLOCK_ACCESS_FS_INITIALLY_DENIED ( \
28 LANDLOCK_ACCESS_FS_REFER)
29/* clang-format on */
30
31/* clang-format off */
32#define _LANDLOCK_ACCESS_FS_OPTIONAL ( \
33 LANDLOCK_ACCESS_FS_TRUNCATE | \
34 LANDLOCK_ACCESS_FS_IOCTL_DEV)
35/* clang-format on */
36
37typedef u32 access_mask_t;
38
39/* Makes sure all filesystem access rights can be stored. */
40static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
41/* Makes sure all network access rights can be stored. */
42static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_NET);
43/* Makes sure all scoped rights can be stored. */
44static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_SCOPE);
45/* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */
46static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
47
48/* Ruleset access masks. */
49struct access_masks {
50 access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
51 access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
52 access_mask_t scope : LANDLOCK_NUM_SCOPE;
53} __packed __aligned(sizeof(u32));
54
55union access_masks_all {
56 struct access_masks masks;
57 u32 all;
58};
59
60/* Makes sure all fields are covered. */
61static_assert(sizeof(typeof_member(union access_masks_all, masks)) ==
62 sizeof(typeof_member(union access_masks_all, all)));
63
64#define _LANDLOCK_LAYER_MASK_PADDING \
65 (BITS_PER_TYPE(access_mask_t) - LANDLOCK_NUM_ACCESS_MAX - \
66 IS_ENABLED(CONFIG_SECURITY_LANDLOCK_LOG))
67
68/**
69 * struct layer_mask - The access rights and rule flags for a layer.
70 *
71 * This has a bit for each access rights and rule flags. During access checks,
72 * it is used to represent the access rights for each layer which still need to
73 * be fulfilled. When all bits are 0, the access request is considered to be
74 * fulfilled.
75 */
76struct layer_mask {
77 /**
78 * @access: The unfulfilled access rights for this layer.
79 */
80 access_mask_t access : LANDLOCK_NUM_ACCESS_MAX;
81#ifdef CONFIG_SECURITY_LANDLOCK_LOG
82 /**
83 * @quiet: Whether we have encountered a rule with the quiet flag for
84 * this layer. Used to control logging.
85 */
86 access_mask_t quiet : 1;
87#endif /* CONFIG_SECURITY_LANDLOCK_LOG */
88 /**
89 * @__pad: Padding for the compiler's bitfield initialization.
90 */
91 access_mask_t __pad : _LANDLOCK_LAYER_MASK_PADDING;
92} __packed __aligned(sizeof(access_mask_t));
93
94/*
95 * Make sure that we don't increase the size of struct layer_mask when storing
96 * rule flags.
97 */
98static_assert(sizeof(struct layer_mask) == sizeof(access_mask_t));
99
100/**
101 * struct layer_masks - An array of struct layer_mask, one per layer.
102 */
103struct layer_masks {
104 /**
105 * @layers: The unfulfilled access rights for each layer.
106 */
107 struct layer_mask layers[LANDLOCK_MAX_NUM_LAYERS];
108};
109
110/*
111 * Tracks domains responsible of a denied access. This avoids storing in each
112 * object the full matrix of per-layer unfulfilled access rights, which is
113 * required by update_request().
114 *
115 * Each nibble represents the layer index of the newest layer which denied a
116 * certain access right. For file system access rights, the upper four bits are
117 * the index of the layer which denies LANDLOCK_ACCESS_FS_IOCTL_DEV and the
118 * lower nibble represents LANDLOCK_ACCESS_FS_TRUNCATE.
119 */
120typedef u8 deny_masks_t;
121
122/*
123 * Makes sure all optional access rights can be tied to a layer index (cf.
124 * get_deny_mask).
125 */
126static_assert(BITS_PER_TYPE(deny_masks_t) >=
127 (HWEIGHT(LANDLOCK_MAX_NUM_LAYERS - 1) *
128 HWEIGHT(_LANDLOCK_ACCESS_FS_OPTIONAL)));
129
130/* LANDLOCK_MAX_NUM_LAYERS must be a power of two (cf. deny_masks_t assert). */
131static_assert(HWEIGHT(LANDLOCK_MAX_NUM_LAYERS) == 1);
132
133/* Upgrades with all initially denied by default access rights. */
134static inline struct access_masks
135landlock_upgrade_handled_access_masks(struct access_masks access_masks)
136{
137 /*
138 * All access rights that are denied by default whether they are
139 * explicitly handled or not.
140 */
141 if (access_masks.fs)
142 access_masks.fs |= _LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
143
144 return access_masks;
145}
146
147/* Checks the subset relation between access masks. */
148static inline bool access_mask_subset(access_mask_t subset,
149 access_mask_t superset)
150{
151 return (subset | superset) == superset;
152}
153
154/* A bitmask that is large enough to hold set of optional accesses. */
155typedef u8 optional_access_t;
156static_assert(BITS_PER_TYPE(optional_access_t) >=
157 HWEIGHT(_LANDLOCK_ACCESS_FS_OPTIONAL));
158
159#endif /* _SECURITY_LANDLOCK_ACCESS_H */