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2d514487 KC |
1 | /* |
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> | |
235e7527 | 20 | #include <linux/workqueue.h> |
2d514487 | 21 | |
389da25f KC |
22 | #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 | ||
27 | static int ptrace_scope = YAMA_SCOPE_RELATIONAL; | |
2d514487 KC |
28 | |
29 | /* describe a ptrace relationship for potential exception */ | |
30 | struct ptrace_relation { | |
31 | struct task_struct *tracer; | |
32 | struct task_struct *tracee; | |
235e7527 | 33 | bool invalid; |
2d514487 | 34 | struct list_head node; |
93b69d43 | 35 | struct rcu_head rcu; |
2d514487 KC |
36 | }; |
37 | ||
38 | static LIST_HEAD(ptracer_relations); | |
39 | static DEFINE_SPINLOCK(ptracer_relations_lock); | |
40 | ||
235e7527 KC |
41 | static void yama_relation_cleanup(struct work_struct *work); |
42 | static DECLARE_WORK(yama_relation_work, yama_relation_cleanup); | |
43 | ||
44 | /** | |
45 | * yama_relation_cleanup - remove invalid entries from the relation list | |
46 | * | |
47 | */ | |
48 | static 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 | ||
2d514487 KC |
64 | /** |
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 | */ | |
74 | static int yama_ptracer_add(struct task_struct *tracer, | |
75 | struct task_struct *tracee) | |
76 | { | |
93b69d43 | 77 | struct ptrace_relation *relation, *added; |
2d514487 KC |
78 | |
79 | added = kmalloc(sizeof(*added), GFP_KERNEL); | |
80 | if (!added) | |
81 | return -ENOMEM; | |
82 | ||
93b69d43 KC |
83 | added->tracee = tracee; |
84 | added->tracer = tracer; | |
235e7527 | 85 | added->invalid = false; |
93b69d43 | 86 | |
235e7527 | 87 | spin_lock(&ptracer_relations_lock); |
93b69d43 KC |
88 | rcu_read_lock(); |
89 | list_for_each_entry_rcu(relation, &ptracer_relations, node) { | |
235e7527 KC |
90 | if (relation->invalid) |
91 | continue; | |
93b69d43 KC |
92 | if (relation->tracee == tracee) { |
93 | list_replace_rcu(&relation->node, &added->node); | |
94 | kfree_rcu(relation, rcu); | |
95 | goto out; | |
2d514487 | 96 | } |
2d514487 | 97 | } |
2d514487 | 98 | |
93b69d43 | 99 | list_add_rcu(&added->node, &ptracer_relations); |
2d514487 | 100 | |
93b69d43 KC |
101 | out: |
102 | rcu_read_unlock(); | |
235e7527 | 103 | spin_unlock(&ptracer_relations_lock); |
93b69d43 | 104 | return 0; |
2d514487 KC |
105 | } |
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 | */ | |
112 | static void yama_ptracer_del(struct task_struct *tracer, | |
113 | struct task_struct *tracee) | |
114 | { | |
93b69d43 | 115 | struct ptrace_relation *relation; |
235e7527 | 116 | bool marked = false; |
2d514487 | 117 | |
93b69d43 KC |
118 | rcu_read_lock(); |
119 | list_for_each_entry_rcu(relation, &ptracer_relations, node) { | |
235e7527 KC |
120 | if (relation->invalid) |
121 | continue; | |
2d514487 | 122 | if (relation->tracee == tracee || |
bf06189e | 123 | (tracer && relation->tracer == tracer)) { |
235e7527 KC |
124 | relation->invalid = true; |
125 | marked = true; | |
2d514487 | 126 | } |
93b69d43 KC |
127 | } |
128 | rcu_read_unlock(); | |
235e7527 KC |
129 | |
130 | if (marked) | |
131 | schedule_work(&yama_relation_work); | |
2d514487 KC |
132 | } |
133 | ||
134 | /** | |
135 | * yama_task_free - check for task_pid to remove from exception list | |
136 | * @task: task being removed | |
137 | */ | |
c6993e4a | 138 | void yama_task_free(struct task_struct *task) |
2d514487 KC |
139 | { |
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 | */ | |
c6993e4a | 154 | int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3, |
2d514487 KC |
155 | 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; | |
2e4930eb | 181 | } else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) { |
bf06189e | 182 | rc = yama_ptracer_add(NULL, myself); |
2d514487 KC |
183 | } 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 | */ | |
214 | static 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 | */ | |
247 | static 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; | |
bf06189e | 253 | bool found = false; |
2d514487 | 254 | |
2d514487 KC |
255 | rcu_read_lock(); |
256 | if (!thread_group_leader(tracee)) | |
257 | tracee = rcu_dereference(tracee->group_leader); | |
235e7527 KC |
258 | list_for_each_entry_rcu(relation, &ptracer_relations, node) { |
259 | if (relation->invalid) | |
260 | continue; | |
2d514487 KC |
261 | if (relation->tracee == tracee) { |
262 | parent = relation->tracer; | |
bf06189e | 263 | found = true; |
2d514487 KC |
264 | break; |
265 | } | |
235e7527 | 266 | } |
2d514487 | 267 | |
bf06189e | 268 | if (found && (parent == NULL || task_is_descendant(parent, tracer))) |
2d514487 KC |
269 | rc = 1; |
270 | rcu_read_unlock(); | |
2d514487 KC |
271 | |
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 | */ | |
c6993e4a | 282 | int yama_ptrace_access_check(struct task_struct *child, |
2d514487 KC |
283 | 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 */ | |
389da25f KC |
295 | 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: | |
4c44aaaf | 301 | rcu_read_lock(); |
389da25f KC |
302 | if (!task_is_descendant(current, child) && |
303 | !ptracer_exception_found(current, child) && | |
4c44aaaf | 304 | !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE)) |
389da25f | 305 | rc = -EPERM; |
4c44aaaf | 306 | rcu_read_unlock(); |
389da25f KC |
307 | break; |
308 | case YAMA_SCOPE_CAPABILITY: | |
4c44aaaf EB |
309 | rcu_read_lock(); |
310 | if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE)) | |
389da25f | 311 | rc = -EPERM; |
4c44aaaf | 312 | rcu_read_unlock(); |
389da25f KC |
313 | break; |
314 | case YAMA_SCOPE_NO_ATTACH: | |
315 | default: | |
316 | rc = -EPERM; | |
317 | break; | |
318 | } | |
319 | } | |
2d514487 KC |
320 | |
321 | if (rc) { | |
389da25f KC |
322 | printk_ratelimited(KERN_NOTICE |
323 | "ptrace of pid %d was attempted by: %s (pid %d)\n", | |
7612bfee | 324 | child->pid, current->comm, current->pid); |
2d514487 KC |
325 | } |
326 | ||
327 | return rc; | |
328 | } | |
329 | ||
9d8dad74 KC |
330 | /** |
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 | */ | |
c6993e4a | 336 | int yama_ptrace_traceme(struct task_struct *parent) |
9d8dad74 KC |
337 | { |
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: | |
eddc0a3a | 350 | if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE)) |
9d8dad74 KC |
351 | rc = -EPERM; |
352 | break; | |
353 | case YAMA_SCOPE_NO_ATTACH: | |
354 | rc = -EPERM; | |
355 | break; | |
356 | } | |
357 | ||
358 | if (rc) { | |
9d8dad74 KC |
359 | printk_ratelimited(KERN_NOTICE |
360 | "ptraceme of pid %d was attempted by: %s (pid %d)\n", | |
7612bfee | 361 | current->pid, parent->comm, parent->pid); |
9d8dad74 KC |
362 | } |
363 | ||
364 | return rc; | |
365 | } | |
366 | ||
c6993e4a | 367 | #ifndef CONFIG_SECURITY_YAMA_STACKED |
2d514487 KC |
368 | static struct security_operations yama_ops = { |
369 | .name = "yama", | |
370 | ||
371 | .ptrace_access_check = yama_ptrace_access_check, | |
9d8dad74 | 372 | .ptrace_traceme = yama_ptrace_traceme, |
2d514487 KC |
373 | .task_prctl = yama_task_prctl, |
374 | .task_free = yama_task_free, | |
375 | }; | |
c6993e4a | 376 | #endif |
2d514487 KC |
377 | |
378 | #ifdef CONFIG_SYSCTL | |
389da25f KC |
379 | static int yama_dointvec_minmax(struct ctl_table *table, int write, |
380 | void __user *buffer, size_t *lenp, loff_t *ppos) | |
381 | { | |
382 | int rc; | |
383 | ||
384 | if (write && !capable(CAP_SYS_PTRACE)) | |
385 | return -EPERM; | |
386 | ||
387 | rc = proc_dointvec_minmax(table, write, buffer, lenp, ppos); | |
388 | if (rc) | |
389 | return rc; | |
390 | ||
391 | /* Lock the max value if it ever gets set. */ | |
392 | if (write && *(int *)table->data == *(int *)table->extra2) | |
393 | table->extra1 = table->extra2; | |
394 | ||
395 | return rc; | |
396 | } | |
397 | ||
2d514487 | 398 | static int zero; |
389da25f | 399 | static int max_scope = YAMA_SCOPE_NO_ATTACH; |
2d514487 KC |
400 | |
401 | struct ctl_path yama_sysctl_path[] = { | |
402 | { .procname = "kernel", }, | |
403 | { .procname = "yama", }, | |
404 | { } | |
405 | }; | |
406 | ||
407 | static struct ctl_table yama_sysctl_table[] = { | |
408 | { | |
409 | .procname = "ptrace_scope", | |
410 | .data = &ptrace_scope, | |
411 | .maxlen = sizeof(int), | |
412 | .mode = 0644, | |
389da25f | 413 | .proc_handler = yama_dointvec_minmax, |
2d514487 | 414 | .extra1 = &zero, |
389da25f | 415 | .extra2 = &max_scope, |
2d514487 KC |
416 | }, |
417 | { } | |
418 | }; | |
419 | #endif /* CONFIG_SYSCTL */ | |
420 | ||
421 | static __init int yama_init(void) | |
422 | { | |
c6993e4a | 423 | #ifndef CONFIG_SECURITY_YAMA_STACKED |
2d514487 KC |
424 | if (!security_module_enable(&yama_ops)) |
425 | return 0; | |
c6993e4a | 426 | #endif |
2d514487 KC |
427 | |
428 | printk(KERN_INFO "Yama: becoming mindful.\n"); | |
429 | ||
c6993e4a | 430 | #ifndef CONFIG_SECURITY_YAMA_STACKED |
2d514487 KC |
431 | if (register_security(&yama_ops)) |
432 | panic("Yama: kernel registration failed.\n"); | |
c6993e4a | 433 | #endif |
2d514487 KC |
434 | |
435 | #ifdef CONFIG_SYSCTL | |
436 | if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table)) | |
437 | panic("Yama: sysctl registration failed.\n"); | |
438 | #endif | |
439 | ||
440 | return 0; | |
441 | } | |
442 | ||
443 | security_initcall(yama_init); |