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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 | ||
3c4ed7bd | 15 | #include <linux/lsm_hooks.h> |
2d514487 KC |
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 | { | |
b1d9e6b0 | 157 | int rc = -ENOSYS; |
2d514487 KC |
158 | struct task_struct *myself = current; |
159 | ||
2d514487 KC |
160 | switch (option) { |
161 | case PR_SET_PTRACER: | |
162 | /* Since a thread can call prctl(), find the group leader | |
163 | * before calling _add() or _del() on it, since we want | |
164 | * process-level granularity of control. The tracer group | |
165 | * leader checking is handled later when walking the ancestry | |
166 | * at the time of PTRACE_ATTACH check. | |
167 | */ | |
168 | rcu_read_lock(); | |
169 | if (!thread_group_leader(myself)) | |
170 | myself = rcu_dereference(myself->group_leader); | |
171 | get_task_struct(myself); | |
172 | rcu_read_unlock(); | |
173 | ||
174 | if (arg2 == 0) { | |
175 | yama_ptracer_del(NULL, myself); | |
176 | rc = 0; | |
2e4930eb | 177 | } else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) { |
bf06189e | 178 | rc = yama_ptracer_add(NULL, myself); |
2d514487 KC |
179 | } else { |
180 | struct task_struct *tracer; | |
181 | ||
182 | rcu_read_lock(); | |
183 | tracer = find_task_by_vpid(arg2); | |
184 | if (tracer) | |
185 | get_task_struct(tracer); | |
186 | else | |
187 | rc = -EINVAL; | |
188 | rcu_read_unlock(); | |
189 | ||
190 | if (tracer) { | |
191 | rc = yama_ptracer_add(tracer, myself); | |
192 | put_task_struct(tracer); | |
193 | } | |
194 | } | |
195 | ||
196 | put_task_struct(myself); | |
197 | break; | |
198 | } | |
199 | ||
200 | return rc; | |
201 | } | |
202 | ||
203 | /** | |
204 | * task_is_descendant - walk up a process family tree looking for a match | |
205 | * @parent: the process to compare against while walking up from child | |
206 | * @child: the process to start from while looking upwards for parent | |
207 | * | |
208 | * Returns 1 if child is a descendant of parent, 0 if not. | |
209 | */ | |
210 | static int task_is_descendant(struct task_struct *parent, | |
211 | struct task_struct *child) | |
212 | { | |
213 | int rc = 0; | |
214 | struct task_struct *walker = child; | |
215 | ||
216 | if (!parent || !child) | |
217 | return 0; | |
218 | ||
219 | rcu_read_lock(); | |
220 | if (!thread_group_leader(parent)) | |
221 | parent = rcu_dereference(parent->group_leader); | |
222 | while (walker->pid > 0) { | |
223 | if (!thread_group_leader(walker)) | |
224 | walker = rcu_dereference(walker->group_leader); | |
225 | if (walker == parent) { | |
226 | rc = 1; | |
227 | break; | |
228 | } | |
229 | walker = rcu_dereference(walker->real_parent); | |
230 | } | |
231 | rcu_read_unlock(); | |
232 | ||
233 | return rc; | |
234 | } | |
235 | ||
236 | /** | |
237 | * ptracer_exception_found - tracer registered as exception for this tracee | |
238 | * @tracer: the task_struct of the process attempting ptrace | |
239 | * @tracee: the task_struct of the process to be ptraced | |
240 | * | |
241 | * Returns 1 if tracer has is ptracer exception ancestor for tracee. | |
242 | */ | |
243 | static int ptracer_exception_found(struct task_struct *tracer, | |
244 | struct task_struct *tracee) | |
245 | { | |
246 | int rc = 0; | |
247 | struct ptrace_relation *relation; | |
248 | struct task_struct *parent = NULL; | |
bf06189e | 249 | bool found = false; |
2d514487 | 250 | |
2d514487 KC |
251 | rcu_read_lock(); |
252 | if (!thread_group_leader(tracee)) | |
253 | tracee = rcu_dereference(tracee->group_leader); | |
235e7527 KC |
254 | list_for_each_entry_rcu(relation, &ptracer_relations, node) { |
255 | if (relation->invalid) | |
256 | continue; | |
2d514487 KC |
257 | if (relation->tracee == tracee) { |
258 | parent = relation->tracer; | |
bf06189e | 259 | found = true; |
2d514487 KC |
260 | break; |
261 | } | |
235e7527 | 262 | } |
2d514487 | 263 | |
bf06189e | 264 | if (found && (parent == NULL || task_is_descendant(parent, tracer))) |
2d514487 KC |
265 | rc = 1; |
266 | rcu_read_unlock(); | |
2d514487 KC |
267 | |
268 | return rc; | |
269 | } | |
270 | ||
271 | /** | |
272 | * yama_ptrace_access_check - validate PTRACE_ATTACH calls | |
273 | * @child: task that current task is attempting to ptrace | |
274 | * @mode: ptrace attach mode | |
275 | * | |
276 | * Returns 0 if following the ptrace is allowed, -ve on error. | |
277 | */ | |
b1d9e6b0 | 278 | static int yama_ptrace_access_check(struct task_struct *child, |
2d514487 KC |
279 | unsigned int mode) |
280 | { | |
b1d9e6b0 | 281 | int rc = 0; |
2d514487 KC |
282 | |
283 | /* require ptrace target be a child of ptracer on attach */ | |
389da25f KC |
284 | if (mode == PTRACE_MODE_ATTACH) { |
285 | switch (ptrace_scope) { | |
286 | case YAMA_SCOPE_DISABLED: | |
287 | /* No additional restrictions. */ | |
288 | break; | |
289 | case YAMA_SCOPE_RELATIONAL: | |
4c44aaaf | 290 | rcu_read_lock(); |
389da25f KC |
291 | if (!task_is_descendant(current, child) && |
292 | !ptracer_exception_found(current, child) && | |
4c44aaaf | 293 | !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE)) |
389da25f | 294 | rc = -EPERM; |
4c44aaaf | 295 | rcu_read_unlock(); |
389da25f KC |
296 | break; |
297 | case YAMA_SCOPE_CAPABILITY: | |
4c44aaaf EB |
298 | rcu_read_lock(); |
299 | if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE)) | |
389da25f | 300 | rc = -EPERM; |
4c44aaaf | 301 | rcu_read_unlock(); |
389da25f KC |
302 | break; |
303 | case YAMA_SCOPE_NO_ATTACH: | |
304 | default: | |
305 | rc = -EPERM; | |
306 | break; | |
307 | } | |
308 | } | |
2d514487 KC |
309 | |
310 | if (rc) { | |
389da25f KC |
311 | printk_ratelimited(KERN_NOTICE |
312 | "ptrace of pid %d was attempted by: %s (pid %d)\n", | |
7612bfee | 313 | child->pid, current->comm, current->pid); |
2d514487 KC |
314 | } |
315 | ||
316 | return rc; | |
317 | } | |
318 | ||
9d8dad74 KC |
319 | /** |
320 | * yama_ptrace_traceme - validate PTRACE_TRACEME calls | |
321 | * @parent: task that will become the ptracer of the current task | |
322 | * | |
323 | * Returns 0 if following the ptrace is allowed, -ve on error. | |
324 | */ | |
c6993e4a | 325 | int yama_ptrace_traceme(struct task_struct *parent) |
9d8dad74 | 326 | { |
b1d9e6b0 | 327 | int rc = 0; |
9d8dad74 KC |
328 | |
329 | /* Only disallow PTRACE_TRACEME on more aggressive settings. */ | |
330 | switch (ptrace_scope) { | |
331 | case YAMA_SCOPE_CAPABILITY: | |
eddc0a3a | 332 | if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE)) |
9d8dad74 KC |
333 | rc = -EPERM; |
334 | break; | |
335 | case YAMA_SCOPE_NO_ATTACH: | |
336 | rc = -EPERM; | |
337 | break; | |
338 | } | |
339 | ||
340 | if (rc) { | |
9d8dad74 KC |
341 | printk_ratelimited(KERN_NOTICE |
342 | "ptraceme of pid %d was attempted by: %s (pid %d)\n", | |
7612bfee | 343 | current->pid, parent->comm, parent->pid); |
9d8dad74 KC |
344 | } |
345 | ||
346 | return rc; | |
347 | } | |
348 | ||
b1d9e6b0 | 349 | static struct security_hook_list yama_hooks[] = { |
e20b043a CS |
350 | LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check), |
351 | LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme), | |
352 | LSM_HOOK_INIT(task_prctl, yama_task_prctl), | |
353 | LSM_HOOK_INIT(task_free, yama_task_free), | |
2d514487 | 354 | }; |
b1d9e6b0 CS |
355 | |
356 | void __init yama_add_hooks(void) | |
357 | { | |
358 | security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks)); | |
359 | } | |
2d514487 KC |
360 | |
361 | #ifdef CONFIG_SYSCTL | |
389da25f KC |
362 | static int yama_dointvec_minmax(struct ctl_table *table, int write, |
363 | void __user *buffer, size_t *lenp, loff_t *ppos) | |
364 | { | |
41a4695c | 365 | struct ctl_table table_copy; |
389da25f KC |
366 | |
367 | if (write && !capable(CAP_SYS_PTRACE)) | |
368 | return -EPERM; | |
369 | ||
389da25f | 370 | /* Lock the max value if it ever gets set. */ |
41a4695c KC |
371 | table_copy = *table; |
372 | if (*(int *)table_copy.data == *(int *)table_copy.extra2) | |
373 | table_copy.extra1 = table_copy.extra2; | |
389da25f | 374 | |
41a4695c | 375 | return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos); |
389da25f KC |
376 | } |
377 | ||
2d514487 | 378 | static int zero; |
389da25f | 379 | static int max_scope = YAMA_SCOPE_NO_ATTACH; |
2d514487 KC |
380 | |
381 | struct ctl_path yama_sysctl_path[] = { | |
382 | { .procname = "kernel", }, | |
383 | { .procname = "yama", }, | |
384 | { } | |
385 | }; | |
386 | ||
387 | static struct ctl_table yama_sysctl_table[] = { | |
388 | { | |
389 | .procname = "ptrace_scope", | |
390 | .data = &ptrace_scope, | |
391 | .maxlen = sizeof(int), | |
392 | .mode = 0644, | |
389da25f | 393 | .proc_handler = yama_dointvec_minmax, |
2d514487 | 394 | .extra1 = &zero, |
389da25f | 395 | .extra2 = &max_scope, |
2d514487 KC |
396 | }, |
397 | { } | |
398 | }; | |
399 | #endif /* CONFIG_SYSCTL */ | |
400 | ||
401 | static __init int yama_init(void) | |
402 | { | |
c6993e4a | 403 | #ifndef CONFIG_SECURITY_YAMA_STACKED |
b1d9e6b0 CS |
404 | /* |
405 | * If yama is being stacked this is already taken care of. | |
406 | */ | |
407 | if (!security_module_enable("yama")) | |
2d514487 | 408 | return 0; |
c6993e4a | 409 | #endif |
b1d9e6b0 | 410 | pr_info("Yama: becoming mindful.\n"); |
2d514487 KC |
411 | |
412 | #ifdef CONFIG_SYSCTL | |
413 | if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table)) | |
414 | panic("Yama: sysctl registration failed.\n"); | |
415 | #endif | |
416 | ||
417 | return 0; | |
418 | } | |
419 | ||
420 | security_initcall(yama_init); |