cred.h

  1/* SPDX-License-Identifier: GPL-2.0-only */
  2/*
  3 * Landlock - Credential hooks
  4 *
  5 * Copyright © 2019-2020 Mickaël Salaün <mic@digikod.net>
  6 * Copyright © 2019-2020 ANSSI
  7 * Copyright © 2021-2025 Microsoft Corporation
  8 */
  9
 10#ifndef _SECURITY_LANDLOCK_CRED_H
 11#define _SECURITY_LANDLOCK_CRED_H
 12
 13#include <linux/container_of.h>
 14#include <linux/cred.h>
 15#include <linux/init.h>
 16#include <linux/rcupdate.h>
 17
 18#include "access.h"
 19#include "limits.h"
 20#include "ruleset.h"
 21#include "setup.h"
 22
 23/**
 24 * struct landlock_cred_security - Credential security blob
 25 *
 26 * This structure is packed to minimize the size of struct
 27 * landlock_file_security.  However, it is always aligned in the LSM cred blob,
 28 * see lsm_set_blob_size().
 29 */
 30struct landlock_cred_security {
 31	/**
 32	 * @domain: Immutable ruleset enforced on a task.
 33	 */
 34	struct landlock_ruleset *domain;
 35
 36#ifdef CONFIG_AUDIT
 37	/**
 38	 * @domain_exec: Bitmask identifying the domain layers that were enforced by
 39	 * the current task's executed file (i.e. no new execve(2) since
 40	 * landlock_restrict_self(2)).
 41	 */
 42	u16 domain_exec;
 43	/**
 44	 * @log_subdomains_off: Set if the domain descendants's log_status should be
 45	 * set to %LANDLOCK_LOG_DISABLED.  This is not a landlock_hierarchy
 46	 * configuration because it applies to future descendant domains and it does
 47	 * not require a current domain.
 48	 */
 49	u8 log_subdomains_off : 1;
 50#endif /* CONFIG_AUDIT */
 51} __packed;
 52
 53#ifdef CONFIG_AUDIT
 54
 55/* Makes sure all layer executions can be stored. */
 56static_assert(BITS_PER_TYPE(typeof_member(struct landlock_cred_security,
 57					  domain_exec)) >=
 58	      LANDLOCK_MAX_NUM_LAYERS);
 59
 60#endif /* CONFIG_AUDIT */
 61
 62static inline struct landlock_cred_security *
 63landlock_cred(const struct cred *cred)
 64{
 65	return cred->security + landlock_blob_sizes.lbs_cred;
 66}
 67
 68static inline struct landlock_ruleset *landlock_get_current_domain(void)
 69{
 70	return landlock_cred(current_cred())->domain;
 71}
 72
 73/*
 74 * The call needs to come from an RCU read-side critical section.
 75 */
 76static inline const struct landlock_ruleset *
 77landlock_get_task_domain(const struct task_struct *const task)
 78{
 79	return landlock_cred(__task_cred(task))->domain;
 80}
 81
 82static inline bool landlocked(const struct task_struct *const task)
 83{
 84	bool has_dom;
 85
 86	if (task == current)
 87		return !!landlock_get_current_domain();
 88
 89	rcu_read_lock();
 90	has_dom = !!landlock_get_task_domain(task);
 91	rcu_read_unlock();
 92	return has_dom;
 93}
 94
 95/**
 96 * landlock_get_applicable_subject - Return the subject's Landlock credential
 97 *                                   if its enforced domain applies to (i.e.
 98 *                                   handles) at least one of the access rights
 99 *                                   specified in @masks
100 *
101 * @cred: credential
102 * @masks: access masks
103 * @handle_layer: returned youngest layer handling a subset of @masks.  Not set
104 *                if the function returns NULL.
105 *
106 * Returns: landlock_cred(@cred) if any access rights specified in @masks is
107 * handled, or NULL otherwise.
108 */
109static inline const struct landlock_cred_security *
110landlock_get_applicable_subject(const struct cred *const cred,
111				const struct access_masks masks,
112				size_t *const handle_layer)
113{
114	const union access_masks_all masks_all = {
115		.masks = masks,
116	};
117	const struct landlock_ruleset *domain;
118	ssize_t layer_level;
119
120	if (!cred)
121		return NULL;
122
123	domain = landlock_cred(cred)->domain;
124	if (!domain)
125		return NULL;
126
127	for (layer_level = domain->num_layers - 1; layer_level >= 0;
128	     layer_level--) {
129		union access_masks_all layer = {
130			.masks = domain->access_masks[layer_level],
131		};
132
133		if (layer.all & masks_all.all) {
134			if (handle_layer)
135				*handle_layer = layer_level;
136
137			return landlock_cred(cred);
138		}
139	}
140
141	return NULL;
142}
143
144__init void landlock_add_cred_hooks(void);
145
146#endif /* _SECURITY_LANDLOCK_CRED_H */