blob: 23414b93771f30ec82ccf76b6cfb49fbed27edef [file] [log] [blame]
Kees Cook2d514482011-12-21 12:17:04 -08001/*
2 * Yama Linux Security Module
3 *
4 * Author: Kees Cook <keescook@chromium.org>
5 *
6 * Copyright (C) 2010 Canonical, Ltd.
7 * Copyright (C) 2011 The Chromium OS Authors.
8 *
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License version 2, as
11 * published by the Free Software Foundation.
12 *
13 */
14
15#include <linux/security.h>
16#include <linux/sysctl.h>
17#include <linux/ptrace.h>
18#include <linux/prctl.h>
19#include <linux/ratelimit.h>
Kees Cook235e7522012-11-19 15:21:26 -080020#include <linux/workqueue.h>
Kees Cook2d514482011-12-21 12:17:04 -080021
Kees Cook389da252012-04-16 11:56:45 -070022#define YAMA_SCOPE_DISABLED 0
23#define YAMA_SCOPE_RELATIONAL 1
24#define YAMA_SCOPE_CAPABILITY 2
25#define YAMA_SCOPE_NO_ATTACH 3
26
27static int ptrace_scope = YAMA_SCOPE_RELATIONAL;
Kees Cook2d514482011-12-21 12:17:04 -080028
29/* describe a ptrace relationship for potential exception */
30struct ptrace_relation {
31 struct task_struct *tracer;
32 struct task_struct *tracee;
Kees Cook235e7522012-11-19 15:21:26 -080033 bool invalid;
Kees Cook2d514482011-12-21 12:17:04 -080034 struct list_head node;
Kees Cook93b69d42012-10-18 14:53:58 -070035 struct rcu_head rcu;
Kees Cook2d514482011-12-21 12:17:04 -080036};
37
38static LIST_HEAD(ptracer_relations);
39static DEFINE_SPINLOCK(ptracer_relations_lock);
40
Kees Cook235e7522012-11-19 15:21:26 -080041static void yama_relation_cleanup(struct work_struct *work);
42static DECLARE_WORK(yama_relation_work, yama_relation_cleanup);
43
44/**
45 * yama_relation_cleanup - remove invalid entries from the relation list
46 *
47 */
48static void yama_relation_cleanup(struct work_struct *work)
49{
50 struct ptrace_relation *relation;
51
52 spin_lock(&ptracer_relations_lock);
53 rcu_read_lock();
54 list_for_each_entry_rcu(relation, &ptracer_relations, node) {
55 if (relation->invalid) {
56 list_del_rcu(&relation->node);
57 kfree_rcu(relation, rcu);
58 }
59 }
60 rcu_read_unlock();
61 spin_unlock(&ptracer_relations_lock);
62}
63
Kees Cook2d514482011-12-21 12:17:04 -080064/**
65 * yama_ptracer_add - add/replace an exception for this tracer/tracee pair
66 * @tracer: the task_struct of the process doing the ptrace
67 * @tracee: the task_struct of the process to be ptraced
68 *
69 * Each tracee can have, at most, one tracer registered. Each time this
70 * is called, the prior registered tracer will be replaced for the tracee.
71 *
72 * Returns 0 if relationship was added, -ve on error.
73 */
74static int yama_ptracer_add(struct task_struct *tracer,
75 struct task_struct *tracee)
76{
Kees Cook93b69d42012-10-18 14:53:58 -070077 struct ptrace_relation *relation, *added;
Kees Cook2d514482011-12-21 12:17:04 -080078
79 added = kmalloc(sizeof(*added), GFP_KERNEL);
80 if (!added)
81 return -ENOMEM;
82
Kees Cook93b69d42012-10-18 14:53:58 -070083 added->tracee = tracee;
84 added->tracer = tracer;
Kees Cook235e7522012-11-19 15:21:26 -080085 added->invalid = false;
Kees Cook93b69d42012-10-18 14:53:58 -070086
Kees Cook235e7522012-11-19 15:21:26 -080087 spin_lock(&ptracer_relations_lock);
Kees Cook93b69d42012-10-18 14:53:58 -070088 rcu_read_lock();
89 list_for_each_entry_rcu(relation, &ptracer_relations, node) {
Kees Cook235e7522012-11-19 15:21:26 -080090 if (relation->invalid)
91 continue;
Kees Cook93b69d42012-10-18 14:53:58 -070092 if (relation->tracee == tracee) {
93 list_replace_rcu(&relation->node, &added->node);
94 kfree_rcu(relation, rcu);
95 goto out;
Kees Cook2d514482011-12-21 12:17:04 -080096 }
Kees Cook2d514482011-12-21 12:17:04 -080097 }
Kees Cook2d514482011-12-21 12:17:04 -080098
Kees Cook93b69d42012-10-18 14:53:58 -070099 list_add_rcu(&added->node, &ptracer_relations);
100
101out:
102 rcu_read_unlock();
Kees Cook235e7522012-11-19 15:21:26 -0800103 spin_unlock(&ptracer_relations_lock);
Kees Cook93b69d42012-10-18 14:53:58 -0700104 return 0;
Kees Cook2d514482011-12-21 12:17:04 -0800105}
106
107/**
108 * yama_ptracer_del - remove exceptions related to the given tasks
109 * @tracer: remove any relation where tracer task matches
110 * @tracee: remove any relation where tracee task matches
111 */
112static void yama_ptracer_del(struct task_struct *tracer,
113 struct task_struct *tracee)
114{
Kees Cook93b69d42012-10-18 14:53:58 -0700115 struct ptrace_relation *relation;
Kees Cook235e7522012-11-19 15:21:26 -0800116 bool marked = false;
Kees Cook2d514482011-12-21 12:17:04 -0800117
Kees Cook93b69d42012-10-18 14:53:58 -0700118 rcu_read_lock();
119 list_for_each_entry_rcu(relation, &ptracer_relations, node) {
Kees Cook235e7522012-11-19 15:21:26 -0800120 if (relation->invalid)
121 continue;
Kees Cook2d514482011-12-21 12:17:04 -0800122 if (relation->tracee == tracee ||
Kees Cookbf061892012-02-14 16:48:09 -0800123 (tracer && relation->tracer == tracer)) {
Kees Cook235e7522012-11-19 15:21:26 -0800124 relation->invalid = true;
125 marked = true;
Kees Cook2d514482011-12-21 12:17:04 -0800126 }
Kees Cook93b69d42012-10-18 14:53:58 -0700127 }
128 rcu_read_unlock();
Kees Cook235e7522012-11-19 15:21:26 -0800129
130 if (marked)
131 schedule_work(&yama_relation_work);
Kees Cook2d514482011-12-21 12:17:04 -0800132}
133
134/**
135 * yama_task_free - check for task_pid to remove from exception list
136 * @task: task being removed
137 */
Kees Cookc6993e42012-09-04 13:32:13 -0700138void yama_task_free(struct task_struct *task)
Kees Cook2d514482011-12-21 12:17:04 -0800139{
140 yama_ptracer_del(task, task);
141}
142
143/**
144 * yama_task_prctl - check for Yama-specific prctl operations
145 * @option: operation
146 * @arg2: argument
147 * @arg3: argument
148 * @arg4: argument
149 * @arg5: argument
150 *
151 * Return 0 on success, -ve on error. -ENOSYS is returned when Yama
152 * does not handle the given option.
153 */
Kees Cookc6993e42012-09-04 13:32:13 -0700154int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
Kees Cook2d514482011-12-21 12:17:04 -0800155 unsigned long arg4, unsigned long arg5)
156{
157 int rc;
158 struct task_struct *myself = current;
159
160 rc = cap_task_prctl(option, arg2, arg3, arg4, arg5);
161 if (rc != -ENOSYS)
162 return rc;
163
164 switch (option) {
165 case PR_SET_PTRACER:
166 /* Since a thread can call prctl(), find the group leader
167 * before calling _add() or _del() on it, since we want
168 * process-level granularity of control. The tracer group
169 * leader checking is handled later when walking the ancestry
170 * at the time of PTRACE_ATTACH check.
171 */
172 rcu_read_lock();
173 if (!thread_group_leader(myself))
174 myself = rcu_dereference(myself->group_leader);
175 get_task_struct(myself);
176 rcu_read_unlock();
177
178 if (arg2 == 0) {
179 yama_ptracer_del(NULL, myself);
180 rc = 0;
Kees Cook2e4930e2012-08-27 11:38:13 -0700181 } else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) {
Kees Cookbf061892012-02-14 16:48:09 -0800182 rc = yama_ptracer_add(NULL, myself);
Kees Cook2d514482011-12-21 12:17:04 -0800183 } else {
184 struct task_struct *tracer;
185
186 rcu_read_lock();
187 tracer = find_task_by_vpid(arg2);
188 if (tracer)
189 get_task_struct(tracer);
190 else
191 rc = -EINVAL;
192 rcu_read_unlock();
193
194 if (tracer) {
195 rc = yama_ptracer_add(tracer, myself);
196 put_task_struct(tracer);
197 }
198 }
199
200 put_task_struct(myself);
201 break;
202 }
203
204 return rc;
205}
206
207/**
208 * task_is_descendant - walk up a process family tree looking for a match
209 * @parent: the process to compare against while walking up from child
210 * @child: the process to start from while looking upwards for parent
211 *
212 * Returns 1 if child is a descendant of parent, 0 if not.
213 */
214static int task_is_descendant(struct task_struct *parent,
215 struct task_struct *child)
216{
217 int rc = 0;
218 struct task_struct *walker = child;
219
220 if (!parent || !child)
221 return 0;
222
223 rcu_read_lock();
224 if (!thread_group_leader(parent))
225 parent = rcu_dereference(parent->group_leader);
226 while (walker->pid > 0) {
227 if (!thread_group_leader(walker))
228 walker = rcu_dereference(walker->group_leader);
229 if (walker == parent) {
230 rc = 1;
231 break;
232 }
233 walker = rcu_dereference(walker->real_parent);
234 }
235 rcu_read_unlock();
236
237 return rc;
238}
239
240/**
241 * ptracer_exception_found - tracer registered as exception for this tracee
242 * @tracer: the task_struct of the process attempting ptrace
243 * @tracee: the task_struct of the process to be ptraced
244 *
245 * Returns 1 if tracer has is ptracer exception ancestor for tracee.
246 */
247static int ptracer_exception_found(struct task_struct *tracer,
248 struct task_struct *tracee)
249{
250 int rc = 0;
251 struct ptrace_relation *relation;
252 struct task_struct *parent = NULL;
Kees Cookbf061892012-02-14 16:48:09 -0800253 bool found = false;
Kees Cook2d514482011-12-21 12:17:04 -0800254
Kees Cook2d514482011-12-21 12:17:04 -0800255 rcu_read_lock();
256 if (!thread_group_leader(tracee))
257 tracee = rcu_dereference(tracee->group_leader);
Kees Cook235e7522012-11-19 15:21:26 -0800258 list_for_each_entry_rcu(relation, &ptracer_relations, node) {
259 if (relation->invalid)
260 continue;
Kees Cook2d514482011-12-21 12:17:04 -0800261 if (relation->tracee == tracee) {
262 parent = relation->tracer;
Kees Cookbf061892012-02-14 16:48:09 -0800263 found = true;
Kees Cook2d514482011-12-21 12:17:04 -0800264 break;
265 }
Kees Cook235e7522012-11-19 15:21:26 -0800266 }
Kees Cook2d514482011-12-21 12:17:04 -0800267
Kees Cookbf061892012-02-14 16:48:09 -0800268 if (found && (parent == NULL || task_is_descendant(parent, tracer)))
Kees Cook2d514482011-12-21 12:17:04 -0800269 rc = 1;
270 rcu_read_unlock();
Kees Cook2d514482011-12-21 12:17:04 -0800271
272 return rc;
273}
274
275/**
276 * yama_ptrace_access_check - validate PTRACE_ATTACH calls
277 * @child: task that current task is attempting to ptrace
278 * @mode: ptrace attach mode
279 *
280 * Returns 0 if following the ptrace is allowed, -ve on error.
281 */
Kees Cookc6993e42012-09-04 13:32:13 -0700282int yama_ptrace_access_check(struct task_struct *child,
Kees Cook2d514482011-12-21 12:17:04 -0800283 unsigned int mode)
284{
285 int rc;
286
287 /* If standard caps disallows it, so does Yama. We should
288 * only tighten restrictions further.
289 */
290 rc = cap_ptrace_access_check(child, mode);
291 if (rc)
292 return rc;
293
294 /* require ptrace target be a child of ptracer on attach */
Kees Cook389da252012-04-16 11:56:45 -0700295 if (mode == PTRACE_MODE_ATTACH) {
296 switch (ptrace_scope) {
297 case YAMA_SCOPE_DISABLED:
298 /* No additional restrictions. */
299 break;
300 case YAMA_SCOPE_RELATIONAL:
Eric W. Biederman4c44aaa2012-07-26 05:05:21 -0700301 rcu_read_lock();
Kees Cook389da252012-04-16 11:56:45 -0700302 if (!task_is_descendant(current, child) &&
303 !ptracer_exception_found(current, child) &&
Eric W. Biederman4c44aaa2012-07-26 05:05:21 -0700304 !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
Kees Cook389da252012-04-16 11:56:45 -0700305 rc = -EPERM;
Eric W. Biederman4c44aaa2012-07-26 05:05:21 -0700306 rcu_read_unlock();
Kees Cook389da252012-04-16 11:56:45 -0700307 break;
308 case YAMA_SCOPE_CAPABILITY:
Eric W. Biederman4c44aaa2012-07-26 05:05:21 -0700309 rcu_read_lock();
310 if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
Kees Cook389da252012-04-16 11:56:45 -0700311 rc = -EPERM;
Eric W. Biederman4c44aaa2012-07-26 05:05:21 -0700312 rcu_read_unlock();
Kees Cook389da252012-04-16 11:56:45 -0700313 break;
314 case YAMA_SCOPE_NO_ATTACH:
315 default:
316 rc = -EPERM;
317 break;
318 }
319 }
Kees Cook2d514482011-12-21 12:17:04 -0800320
321 if (rc) {
Kees Cook389da252012-04-16 11:56:45 -0700322 printk_ratelimited(KERN_NOTICE
323 "ptrace of pid %d was attempted by: %s (pid %d)\n",
Kees Cook7612bfe2012-08-15 11:41:55 -0700324 child->pid, current->comm, current->pid);
Kees Cook2d514482011-12-21 12:17:04 -0800325 }
326
327 return rc;
328}
329
Kees Cook9d8dad72012-08-09 19:01:26 -0700330/**
331 * yama_ptrace_traceme - validate PTRACE_TRACEME calls
332 * @parent: task that will become the ptracer of the current task
333 *
334 * Returns 0 if following the ptrace is allowed, -ve on error.
335 */
Kees Cookc6993e42012-09-04 13:32:13 -0700336int yama_ptrace_traceme(struct task_struct *parent)
Kees Cook9d8dad72012-08-09 19:01:26 -0700337{
338 int rc;
339
340 /* If standard caps disallows it, so does Yama. We should
341 * only tighten restrictions further.
342 */
343 rc = cap_ptrace_traceme(parent);
344 if (rc)
345 return rc;
346
347 /* Only disallow PTRACE_TRACEME on more aggressive settings. */
348 switch (ptrace_scope) {
349 case YAMA_SCOPE_CAPABILITY:
Eric W. Biederman4c44aaa2012-07-26 05:05:21 -0700350 rcu_read_lock();
351 if (!ns_capable(__task_cred(parent)->user_ns, CAP_SYS_PTRACE))
Kees Cook9d8dad72012-08-09 19:01:26 -0700352 rc = -EPERM;
Eric W. Biederman4c44aaa2012-07-26 05:05:21 -0700353 rcu_read_unlock();
Kees Cook9d8dad72012-08-09 19:01:26 -0700354 break;
355 case YAMA_SCOPE_NO_ATTACH:
356 rc = -EPERM;
357 break;
358 }
359
360 if (rc) {
Kees Cook9d8dad72012-08-09 19:01:26 -0700361 printk_ratelimited(KERN_NOTICE
362 "ptraceme of pid %d was attempted by: %s (pid %d)\n",
Kees Cook7612bfe2012-08-15 11:41:55 -0700363 current->pid, parent->comm, parent->pid);
Kees Cook9d8dad72012-08-09 19:01:26 -0700364 }
365
366 return rc;
367}
368
Kees Cookc6993e42012-09-04 13:32:13 -0700369#ifndef CONFIG_SECURITY_YAMA_STACKED
Kees Cook2d514482011-12-21 12:17:04 -0800370static struct security_operations yama_ops = {
371 .name = "yama",
372
373 .ptrace_access_check = yama_ptrace_access_check,
Kees Cook9d8dad72012-08-09 19:01:26 -0700374 .ptrace_traceme = yama_ptrace_traceme,
Kees Cook2d514482011-12-21 12:17:04 -0800375 .task_prctl = yama_task_prctl,
376 .task_free = yama_task_free,
377};
Kees Cookc6993e42012-09-04 13:32:13 -0700378#endif
Kees Cook2d514482011-12-21 12:17:04 -0800379
380#ifdef CONFIG_SYSCTL
Kees Cook389da252012-04-16 11:56:45 -0700381static int yama_dointvec_minmax(struct ctl_table *table, int write,
382 void __user *buffer, size_t *lenp, loff_t *ppos)
383{
384 int rc;
385
386 if (write && !capable(CAP_SYS_PTRACE))
387 return -EPERM;
388
389 rc = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
390 if (rc)
391 return rc;
392
393 /* Lock the max value if it ever gets set. */
394 if (write && *(int *)table->data == *(int *)table->extra2)
395 table->extra1 = table->extra2;
396
397 return rc;
398}
399
Kees Cook2d514482011-12-21 12:17:04 -0800400static int zero;
Kees Cook389da252012-04-16 11:56:45 -0700401static int max_scope = YAMA_SCOPE_NO_ATTACH;
Kees Cook2d514482011-12-21 12:17:04 -0800402
403struct ctl_path yama_sysctl_path[] = {
404 { .procname = "kernel", },
405 { .procname = "yama", },
406 { }
407};
408
409static struct ctl_table yama_sysctl_table[] = {
410 {
411 .procname = "ptrace_scope",
412 .data = &ptrace_scope,
413 .maxlen = sizeof(int),
414 .mode = 0644,
Kees Cook389da252012-04-16 11:56:45 -0700415 .proc_handler = yama_dointvec_minmax,
Kees Cook2d514482011-12-21 12:17:04 -0800416 .extra1 = &zero,
Kees Cook389da252012-04-16 11:56:45 -0700417 .extra2 = &max_scope,
Kees Cook2d514482011-12-21 12:17:04 -0800418 },
419 { }
420};
421#endif /* CONFIG_SYSCTL */
422
423static __init int yama_init(void)
424{
Kees Cookc6993e42012-09-04 13:32:13 -0700425#ifndef CONFIG_SECURITY_YAMA_STACKED
Kees Cook2d514482011-12-21 12:17:04 -0800426 if (!security_module_enable(&yama_ops))
427 return 0;
Kees Cookc6993e42012-09-04 13:32:13 -0700428#endif
Kees Cook2d514482011-12-21 12:17:04 -0800429
430 printk(KERN_INFO "Yama: becoming mindful.\n");
431
Kees Cookc6993e42012-09-04 13:32:13 -0700432#ifndef CONFIG_SECURITY_YAMA_STACKED
Kees Cook2d514482011-12-21 12:17:04 -0800433 if (register_security(&yama_ops))
434 panic("Yama: kernel registration failed.\n");
Kees Cookc6993e42012-09-04 13:32:13 -0700435#endif
Kees Cook2d514482011-12-21 12:17:04 -0800436
437#ifdef CONFIG_SYSCTL
438 if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
439 panic("Yama: sysctl registration failed.\n");
440#endif
441
442 return 0;
443}
444
445security_initcall(yama_init);