xref: /openbmc/linux/security/landlock/ptrace.c (revision bbaf1ff0)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Landlock LSM - Ptrace hooks
4  *
5  * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
6  * Copyright © 2019-2020 ANSSI
7  */
8 
9 #include <asm/current.h>
10 #include <linux/cred.h>
11 #include <linux/errno.h>
12 #include <linux/kernel.h>
13 #include <linux/lsm_hooks.h>
14 #include <linux/rcupdate.h>
15 #include <linux/sched.h>
16 
17 #include "common.h"
18 #include "cred.h"
19 #include "ptrace.h"
20 #include "ruleset.h"
21 #include "setup.h"
22 
23 /**
24  * domain_scope_le - Checks domain ordering for scoped ptrace
25  *
26  * @parent: Parent domain.
27  * @child: Potential child of @parent.
28  *
29  * Checks if the @parent domain is less or equal to (i.e. an ancestor, which
30  * means a subset of) the @child domain.
31  */
32 static bool domain_scope_le(const struct landlock_ruleset *const parent,
33 			    const struct landlock_ruleset *const child)
34 {
35 	const struct landlock_hierarchy *walker;
36 
37 	if (!parent)
38 		return true;
39 	if (!child)
40 		return false;
41 	for (walker = child->hierarchy; walker; walker = walker->parent) {
42 		if (walker == parent->hierarchy)
43 			/* @parent is in the scoped hierarchy of @child. */
44 			return true;
45 	}
46 	/* There is no relationship between @parent and @child. */
47 	return false;
48 }
49 
50 static bool task_is_scoped(const struct task_struct *const parent,
51 			   const struct task_struct *const child)
52 {
53 	bool is_scoped;
54 	const struct landlock_ruleset *dom_parent, *dom_child;
55 
56 	rcu_read_lock();
57 	dom_parent = landlock_get_task_domain(parent);
58 	dom_child = landlock_get_task_domain(child);
59 	is_scoped = domain_scope_le(dom_parent, dom_child);
60 	rcu_read_unlock();
61 	return is_scoped;
62 }
63 
64 static int task_ptrace(const struct task_struct *const parent,
65 		       const struct task_struct *const child)
66 {
67 	/* Quick return for non-landlocked tasks. */
68 	if (!landlocked(parent))
69 		return 0;
70 	if (task_is_scoped(parent, child))
71 		return 0;
72 	return -EPERM;
73 }
74 
75 /**
76  * hook_ptrace_access_check - Determines whether the current process may access
77  *			      another
78  *
79  * @child: Process to be accessed.
80  * @mode: Mode of attachment.
81  *
82  * If the current task has Landlock rules, then the child must have at least
83  * the same rules.  Else denied.
84  *
85  * Determines whether a process may access another, returning 0 if permission
86  * granted, -errno if denied.
87  */
88 static int hook_ptrace_access_check(struct task_struct *const child,
89 				    const unsigned int mode)
90 {
91 	return task_ptrace(current, child);
92 }
93 
94 /**
95  * hook_ptrace_traceme - Determines whether another process may trace the
96  *			 current one
97  *
98  * @parent: Task proposed to be the tracer.
99  *
100  * If the parent has Landlock rules, then the current task must have the same
101  * or more rules.  Else denied.
102  *
103  * Determines whether the nominated task is permitted to trace the current
104  * process, returning 0 if permission is granted, -errno if denied.
105  */
106 static int hook_ptrace_traceme(struct task_struct *const parent)
107 {
108 	return task_ptrace(parent, current);
109 }
110 
111 static struct security_hook_list landlock_hooks[] __ro_after_init = {
112 	LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check),
113 	LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme),
114 };
115 
116 __init void landlock_add_ptrace_hooks(void)
117 {
118 	security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
119 			   LANDLOCK_NAME);
120 }
121