1 // SPDX-License-Identifier: GPL-2.0-only
3 * Yama Linux Security Module
5 * Author: Kees Cook <keescook@chromium.org>
7 * Copyright (C) 2010 Canonical, Ltd.
8 * Copyright (C) 2011 The Chromium OS Authors.
11 #include <linux/lsm_hooks.h>
12 #include <linux/sysctl.h>
13 #include <linux/ptrace.h>
14 #include <linux/prctl.h>
15 #include <linux/ratelimit.h>
16 #include <linux/workqueue.h>
17 #include <linux/string_helpers.h>
18 #include <linux/task_work.h>
19 #include <linux/sched.h>
20 #include <linux/spinlock.h>
21 #include <uapi/linux/lsm.h>
23 #define YAMA_SCOPE_DISABLED 0
24 #define YAMA_SCOPE_RELATIONAL 1
25 #define YAMA_SCOPE_CAPABILITY 2
26 #define YAMA_SCOPE_NO_ATTACH 3
28 static int ptrace_scope = YAMA_SCOPE_RELATIONAL;
30 /* describe a ptrace relationship for potential exception */
31 struct ptrace_relation {
32 struct task_struct *tracer;
33 struct task_struct *tracee;
35 struct list_head node;
39 static LIST_HEAD(ptracer_relations);
40 static DEFINE_SPINLOCK(ptracer_relations_lock);
42 static void yama_relation_cleanup(struct work_struct *work);
43 static DECLARE_WORK(yama_relation_work, yama_relation_cleanup);
45 struct access_report_info {
46 struct callback_head work;
48 struct task_struct *target;
49 struct task_struct *agent;
52 static void __report_access(struct callback_head *work)
54 struct access_report_info *info =
55 container_of(work, struct access_report_info, work);
56 char *target_cmd, *agent_cmd;
58 target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL);
59 agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL);
61 pr_notice_ratelimited(
62 "ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
63 info->access, target_cmd, info->target->pid, agent_cmd,
69 put_task_struct(info->agent);
70 put_task_struct(info->target);
74 /* defers execution because cmdline access can sleep */
75 static void report_access(const char *access, struct task_struct *target,
76 struct task_struct *agent)
78 struct access_report_info *info;
79 char agent_comm[sizeof(agent->comm)];
81 assert_spin_locked(&target->alloc_lock); /* for target->comm */
83 if (current->flags & PF_KTHREAD) {
84 /* I don't think kthreads call task_work_run() before exiting.
85 * Imagine angry ranting about procfs here.
87 pr_notice_ratelimited(
88 "ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
89 access, target->comm, target->pid,
90 get_task_comm(agent_comm, agent), agent->pid);
94 info = kmalloc(sizeof(*info), GFP_ATOMIC);
97 init_task_work(&info->work, __report_access);
98 get_task_struct(target);
99 get_task_struct(agent);
100 info->access = access;
101 info->target = target;
103 if (task_work_add(current, &info->work, TWA_RESUME) == 0)
104 return; /* success */
106 WARN(1, "report_access called from exiting task");
107 put_task_struct(target);
108 put_task_struct(agent);
113 * yama_relation_cleanup - remove invalid entries from the relation list
116 static void yama_relation_cleanup(struct work_struct *work)
118 struct ptrace_relation *relation;
120 spin_lock(&ptracer_relations_lock);
122 list_for_each_entry_rcu(relation, &ptracer_relations, node) {
123 if (relation->invalid) {
124 list_del_rcu(&relation->node);
125 kfree_rcu(relation, rcu);
129 spin_unlock(&ptracer_relations_lock);
133 * yama_ptracer_add - add/replace an exception for this tracer/tracee pair
134 * @tracer: the task_struct of the process doing the ptrace
135 * @tracee: the task_struct of the process to be ptraced
137 * Each tracee can have, at most, one tracer registered. Each time this
138 * is called, the prior registered tracer will be replaced for the tracee.
140 * Returns 0 if relationship was added, -ve on error.
142 static int yama_ptracer_add(struct task_struct *tracer,
143 struct task_struct *tracee)
145 struct ptrace_relation *relation, *added;
147 added = kmalloc(sizeof(*added), GFP_KERNEL);
151 added->tracee = tracee;
152 added->tracer = tracer;
153 added->invalid = false;
155 spin_lock(&ptracer_relations_lock);
157 list_for_each_entry_rcu(relation, &ptracer_relations, node) {
158 if (relation->invalid)
160 if (relation->tracee == tracee) {
161 list_replace_rcu(&relation->node, &added->node);
162 kfree_rcu(relation, rcu);
167 list_add_rcu(&added->node, &ptracer_relations);
171 spin_unlock(&ptracer_relations_lock);
176 * yama_ptracer_del - remove exceptions related to the given tasks
177 * @tracer: remove any relation where tracer task matches
178 * @tracee: remove any relation where tracee task matches
180 static void yama_ptracer_del(struct task_struct *tracer,
181 struct task_struct *tracee)
183 struct ptrace_relation *relation;
187 list_for_each_entry_rcu(relation, &ptracer_relations, node) {
188 if (relation->invalid)
190 if (relation->tracee == tracee ||
191 (tracer && relation->tracer == tracer)) {
192 relation->invalid = true;
199 schedule_work(&yama_relation_work);
203 * yama_task_free - check for task_pid to remove from exception list
204 * @task: task being removed
206 static void yama_task_free(struct task_struct *task)
208 yama_ptracer_del(task, task);
212 * yama_task_prctl - check for Yama-specific prctl operations
219 * Return 0 on success, -ve on error. -ENOSYS is returned when Yama
220 * does not handle the given option.
222 static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
223 unsigned long arg4, unsigned long arg5)
226 struct task_struct *myself = current;
230 /* Since a thread can call prctl(), find the group leader
231 * before calling _add() or _del() on it, since we want
232 * process-level granularity of control. The tracer group
233 * leader checking is handled later when walking the ancestry
234 * at the time of PTRACE_ATTACH check.
237 if (!thread_group_leader(myself))
238 myself = rcu_dereference(myself->group_leader);
239 get_task_struct(myself);
243 yama_ptracer_del(NULL, myself);
245 } else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) {
246 rc = yama_ptracer_add(NULL, myself);
248 struct task_struct *tracer;
250 tracer = find_get_task_by_vpid(arg2);
254 rc = yama_ptracer_add(tracer, myself);
255 put_task_struct(tracer);
259 put_task_struct(myself);
267 * task_is_descendant - walk up a process family tree looking for a match
268 * @parent: the process to compare against while walking up from child
269 * @child: the process to start from while looking upwards for parent
271 * Returns 1 if child is a descendant of parent, 0 if not.
273 static int task_is_descendant(struct task_struct *parent,
274 struct task_struct *child)
277 struct task_struct *walker = child;
279 if (!parent || !child)
283 if (!thread_group_leader(parent))
284 parent = rcu_dereference(parent->group_leader);
285 while (walker->pid > 0) {
286 if (!thread_group_leader(walker))
287 walker = rcu_dereference(walker->group_leader);
288 if (walker == parent) {
292 walker = rcu_dereference(walker->real_parent);
300 * ptracer_exception_found - tracer registered as exception for this tracee
301 * @tracer: the task_struct of the process attempting ptrace
302 * @tracee: the task_struct of the process to be ptraced
304 * Returns 1 if tracer has a ptracer exception ancestor for tracee.
306 static int ptracer_exception_found(struct task_struct *tracer,
307 struct task_struct *tracee)
310 struct ptrace_relation *relation;
311 struct task_struct *parent = NULL;
317 * If there's already an active tracing relationship, then make an
318 * exception for the sake of other accesses, like process_vm_rw().
320 parent = ptrace_parent(tracee);
321 if (parent != NULL && same_thread_group(parent, tracer)) {
326 /* Look for a PR_SET_PTRACER relationship. */
327 if (!thread_group_leader(tracee))
328 tracee = rcu_dereference(tracee->group_leader);
329 list_for_each_entry_rcu(relation, &ptracer_relations, node) {
330 if (relation->invalid)
332 if (relation->tracee == tracee) {
333 parent = relation->tracer;
339 if (found && (parent == NULL || task_is_descendant(parent, tracer)))
349 * yama_ptrace_access_check - validate PTRACE_ATTACH calls
350 * @child: task that current task is attempting to ptrace
351 * @mode: ptrace attach mode
353 * Returns 0 if following the ptrace is allowed, -ve on error.
355 static int yama_ptrace_access_check(struct task_struct *child,
360 /* require ptrace target be a child of ptracer on attach */
361 if (mode & PTRACE_MODE_ATTACH) {
362 switch (ptrace_scope) {
363 case YAMA_SCOPE_DISABLED:
364 /* No additional restrictions. */
366 case YAMA_SCOPE_RELATIONAL:
368 if (!pid_alive(child))
370 if (!rc && !task_is_descendant(current, child) &&
371 !ptracer_exception_found(current, child) &&
372 !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
376 case YAMA_SCOPE_CAPABILITY:
378 if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
382 case YAMA_SCOPE_NO_ATTACH:
389 if (rc && (mode & PTRACE_MODE_NOAUDIT) == 0)
390 report_access("attach", child, current);
396 * yama_ptrace_traceme - validate PTRACE_TRACEME calls
397 * @parent: task that will become the ptracer of the current task
399 * Returns 0 if following the ptrace is allowed, -ve on error.
401 static int yama_ptrace_traceme(struct task_struct *parent)
405 /* Only disallow PTRACE_TRACEME on more aggressive settings. */
406 switch (ptrace_scope) {
407 case YAMA_SCOPE_CAPABILITY:
408 if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE))
411 case YAMA_SCOPE_NO_ATTACH:
418 report_access("traceme", current, parent);
419 task_unlock(current);
425 static const struct lsm_id yama_lsmid = {
430 static struct security_hook_list yama_hooks[] __ro_after_init = {
431 LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check),
432 LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme),
433 LSM_HOOK_INIT(task_prctl, yama_task_prctl),
434 LSM_HOOK_INIT(task_free, yama_task_free),
438 static int yama_dointvec_minmax(struct ctl_table *table, int write,
439 void *buffer, size_t *lenp, loff_t *ppos)
441 struct ctl_table table_copy;
443 if (write && !capable(CAP_SYS_PTRACE))
446 /* Lock the max value if it ever gets set. */
448 if (*(int *)table_copy.data == *(int *)table_copy.extra2)
449 table_copy.extra1 = table_copy.extra2;
451 return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
454 static int max_scope = YAMA_SCOPE_NO_ATTACH;
456 static struct ctl_table yama_sysctl_table[] = {
458 .procname = "ptrace_scope",
459 .data = &ptrace_scope,
460 .maxlen = sizeof(int),
462 .proc_handler = yama_dointvec_minmax,
463 .extra1 = SYSCTL_ZERO,
464 .extra2 = &max_scope,
468 static void __init yama_init_sysctl(void)
470 if (!register_sysctl("kernel/yama", yama_sysctl_table))
471 panic("Yama: sysctl registration failed.\n");
474 static inline void yama_init_sysctl(void) { }
475 #endif /* CONFIG_SYSCTL */
477 static int __init yama_init(void)
479 pr_info("Yama: becoming mindful.\n");
480 security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), &yama_lsmid);