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1 | /* |
2 | * device_cgroup.c - device cgroup subsystem |
3 | * |
4 | * Copyright 2007 IBM Corp |
5 | */ |
6 | |
7 | #include <linux/device_cgroup.h> |
8 | #include <linux/cgroup.h> |
9 | #include <linux/ctype.h> |
10 | #include <linux/list.h> |
11 | #include <linux/uaccess.h> |
12 | #include <linux/seq_file.h> |
13 | #include <linux/slab.h> |
14 | #include <linux/rcupdate.h> |
15 | #include <linux/mutex.h> |
16 | |
17 | #define ACC_MKNOD 1 |
18 | #define ACC_READ 2 |
19 | #define ACC_WRITE 4 |
20 | #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE) |
21 | |
22 | #define DEV_BLOCK 1 |
23 | #define DEV_CHAR 2 |
24 | #define DEV_ALL 4 /* this represents all devices */ |
25 | |
26 | static DEFINE_MUTEX(devcgroup_mutex); |
27 | |
28 | /* |
29 | * whitelist locking rules: |
30 | * hold devcgroup_mutex for update/read. |
31 | * hold rcu_read_lock() for read. |
32 | */ |
33 | |
34 | struct dev_whitelist_item { |
35 | u32 major, minor; |
36 | short type; |
37 | short access; |
38 | struct list_head list; |
39 | struct rcu_head rcu; |
40 | }; |
41 | |
42 | struct dev_cgroup { |
43 | struct cgroup_subsys_state css; |
44 | struct list_head whitelist; |
45 | }; |
46 | |
47 | static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s) |
48 | { |
49 | return container_of(s, struct dev_cgroup, css); |
50 | } |
51 | |
52 | static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup) |
53 | { |
54 | return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id)); |
55 | } |
56 | |
57 | static inline struct dev_cgroup *task_devcgroup(struct task_struct *task) |
58 | { |
59 | return css_to_devcgroup(task_subsys_state(task, devices_subsys_id)); |
60 | } |
61 | |
62 | struct cgroup_subsys devices_subsys; |
63 | |
64 | static int devcgroup_can_attach(struct cgroup_subsys *ss, |
65 | struct cgroup *new_cgroup, struct task_struct *task, |
66 | bool threadgroup) |
67 | { |
68 | if (current != task && !capable(CAP_SYS_ADMIN)) |
69 | return -EPERM; |
70 | |
71 | return 0; |
72 | } |
73 | |
74 | /* |
75 | * called under devcgroup_mutex |
76 | */ |
77 | static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig) |
78 | { |
79 | struct dev_whitelist_item *wh, *tmp, *new; |
80 | |
81 | list_for_each_entry(wh, orig, list) { |
82 | new = kmemdup(wh, sizeof(*wh), GFP_KERNEL); |
83 | if (!new) |
84 | goto free_and_exit; |
85 | list_add_tail(&new->list, dest); |
86 | } |
87 | |
88 | return 0; |
89 | |
90 | free_and_exit: |
91 | list_for_each_entry_safe(wh, tmp, dest, list) { |
92 | list_del(&wh->list); |
93 | kfree(wh); |
94 | } |
95 | return -ENOMEM; |
96 | } |
97 | |
98 | /* Stupid prototype - don't bother combining existing entries */ |
99 | /* |
100 | * called under devcgroup_mutex |
101 | */ |
102 | static int dev_whitelist_add(struct dev_cgroup *dev_cgroup, |
103 | struct dev_whitelist_item *wh) |
104 | { |
105 | struct dev_whitelist_item *whcopy, *walk; |
106 | |
107 | whcopy = kmemdup(wh, sizeof(*wh), GFP_KERNEL); |
108 | if (!whcopy) |
109 | return -ENOMEM; |
110 | |
111 | list_for_each_entry(walk, &dev_cgroup->whitelist, list) { |
112 | if (walk->type != wh->type) |
113 | continue; |
114 | if (walk->major != wh->major) |
115 | continue; |
116 | if (walk->minor != wh->minor) |
117 | continue; |
118 | |
119 | walk->access |= wh->access; |
120 | kfree(whcopy); |
121 | whcopy = NULL; |
122 | } |
123 | |
124 | if (whcopy != NULL) |
125 | list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist); |
126 | return 0; |
127 | } |
128 | |
129 | static void whitelist_item_free(struct rcu_head *rcu) |
130 | { |
131 | struct dev_whitelist_item *item; |
132 | |
133 | item = container_of(rcu, struct dev_whitelist_item, rcu); |
134 | kfree(item); |
135 | } |
136 | |
137 | /* |
138 | * called under devcgroup_mutex |
139 | */ |
140 | static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup, |
141 | struct dev_whitelist_item *wh) |
142 | { |
143 | struct dev_whitelist_item *walk, *tmp; |
144 | |
145 | list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) { |
146 | if (walk->type == DEV_ALL) |
147 | goto remove; |
148 | if (walk->type != wh->type) |
149 | continue; |
150 | if (walk->major != ~0 && walk->major != wh->major) |
151 | continue; |
152 | if (walk->minor != ~0 && walk->minor != wh->minor) |
153 | continue; |
154 | |
155 | remove: |
156 | walk->access &= ~wh->access; |
157 | if (!walk->access) { |
158 | list_del_rcu(&walk->list); |
159 | call_rcu(&walk->rcu, whitelist_item_free); |
160 | } |
161 | } |
162 | } |
163 | |
164 | /* |
165 | * called from kernel/cgroup.c with cgroup_lock() held. |
166 | */ |
167 | static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss, |
168 | struct cgroup *cgroup) |
169 | { |
170 | struct dev_cgroup *dev_cgroup, *parent_dev_cgroup; |
171 | struct cgroup *parent_cgroup; |
172 | int ret; |
173 | |
174 | dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL); |
175 | if (!dev_cgroup) |
176 | return ERR_PTR(-ENOMEM); |
177 | INIT_LIST_HEAD(&dev_cgroup->whitelist); |
178 | parent_cgroup = cgroup->parent; |
179 | |
180 | if (parent_cgroup == NULL) { |
181 | struct dev_whitelist_item *wh; |
182 | wh = kmalloc(sizeof(*wh), GFP_KERNEL); |
183 | if (!wh) { |
184 | kfree(dev_cgroup); |
185 | return ERR_PTR(-ENOMEM); |
186 | } |
187 | wh->minor = wh->major = ~0; |
188 | wh->type = DEV_ALL; |
189 | wh->access = ACC_MASK; |
190 | list_add(&wh->list, &dev_cgroup->whitelist); |
191 | } else { |
192 | parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup); |
193 | mutex_lock(&devcgroup_mutex); |
194 | ret = dev_whitelist_copy(&dev_cgroup->whitelist, |
195 | &parent_dev_cgroup->whitelist); |
196 | mutex_unlock(&devcgroup_mutex); |
197 | if (ret) { |
198 | kfree(dev_cgroup); |
199 | return ERR_PTR(ret); |
200 | } |
201 | } |
202 | |
203 | return &dev_cgroup->css; |
204 | } |
205 | |
206 | static void devcgroup_destroy(struct cgroup_subsys *ss, |
207 | struct cgroup *cgroup) |
208 | { |
209 | struct dev_cgroup *dev_cgroup; |
210 | struct dev_whitelist_item *wh, *tmp; |
211 | |
212 | dev_cgroup = cgroup_to_devcgroup(cgroup); |
213 | list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) { |
214 | list_del(&wh->list); |
215 | kfree(wh); |
216 | } |
217 | kfree(dev_cgroup); |
218 | } |
219 | |
220 | #define DEVCG_ALLOW 1 |
221 | #define DEVCG_DENY 2 |
222 | #define DEVCG_LIST 3 |
223 | |
224 | #define MAJMINLEN 13 |
225 | #define ACCLEN 4 |
226 | |
227 | static void set_access(char *acc, short access) |
228 | { |
229 | int idx = 0; |
230 | memset(acc, 0, ACCLEN); |
231 | if (access & ACC_READ) |
232 | acc[idx++] = 'r'; |
233 | if (access & ACC_WRITE) |
234 | acc[idx++] = 'w'; |
235 | if (access & ACC_MKNOD) |
236 | acc[idx++] = 'm'; |
237 | } |
238 | |
239 | static char type_to_char(short type) |
240 | { |
241 | if (type == DEV_ALL) |
242 | return 'a'; |
243 | if (type == DEV_CHAR) |
244 | return 'c'; |
245 | if (type == DEV_BLOCK) |
246 | return 'b'; |
247 | return 'X'; |
248 | } |
249 | |
250 | static void set_majmin(char *str, unsigned m) |
251 | { |
252 | if (m == ~0) |
253 | strcpy(str, "*"); |
254 | else |
255 | sprintf(str, "%u", m); |
256 | } |
257 | |
258 | static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft, |
259 | struct seq_file *m) |
260 | { |
261 | struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup); |
262 | struct dev_whitelist_item *wh; |
263 | char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN]; |
264 | |
265 | rcu_read_lock(); |
266 | list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) { |
267 | set_access(acc, wh->access); |
268 | set_majmin(maj, wh->major); |
269 | set_majmin(min, wh->minor); |
270 | seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type), |
271 | maj, min, acc); |
272 | } |
273 | rcu_read_unlock(); |
274 | |
275 | return 0; |
276 | } |
277 | |
278 | /* |
279 | * may_access_whitelist: |
280 | * does the access granted to dev_cgroup c contain the access |
281 | * requested in whitelist item refwh. |
282 | * return 1 if yes, 0 if no. |
283 | * call with devcgroup_mutex held |
284 | */ |
285 | static int may_access_whitelist(struct dev_cgroup *c, |
286 | struct dev_whitelist_item *refwh) |
287 | { |
288 | struct dev_whitelist_item *whitem; |
289 | |
290 | list_for_each_entry(whitem, &c->whitelist, list) { |
291 | if (whitem->type & DEV_ALL) |
292 | return 1; |
293 | if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK)) |
294 | continue; |
295 | if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR)) |
296 | continue; |
297 | if (whitem->major != ~0 && whitem->major != refwh->major) |
298 | continue; |
299 | if (whitem->minor != ~0 && whitem->minor != refwh->minor) |
300 | continue; |
301 | if (refwh->access & (~whitem->access)) |
302 | continue; |
303 | return 1; |
304 | } |
305 | return 0; |
306 | } |
307 | |
308 | /* |
309 | * parent_has_perm: |
310 | * when adding a new allow rule to a device whitelist, the rule |
311 | * must be allowed in the parent device |
312 | */ |
313 | static int parent_has_perm(struct dev_cgroup *childcg, |
314 | struct dev_whitelist_item *wh) |
315 | { |
316 | struct cgroup *pcg = childcg->css.cgroup->parent; |
317 | struct dev_cgroup *parent; |
318 | |
319 | if (!pcg) |
320 | return 1; |
321 | parent = cgroup_to_devcgroup(pcg); |
322 | return may_access_whitelist(parent, wh); |
323 | } |
324 | |
325 | /* |
326 | * Modify the whitelist using allow/deny rules. |
327 | * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD |
328 | * so we can give a container CAP_MKNOD to let it create devices but not |
329 | * modify the whitelist. |
330 | * It seems likely we'll want to add a CAP_CONTAINER capability to allow |
331 | * us to also grant CAP_SYS_ADMIN to containers without giving away the |
332 | * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN |
333 | * |
334 | * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting |
335 | * new access is only allowed if you're in the top-level cgroup, or your |
336 | * parent cgroup has the access you're asking for. |
337 | */ |
338 | static int devcgroup_update_access(struct dev_cgroup *devcgroup, |
339 | int filetype, const char *buffer) |
340 | { |
341 | const char *b; |
342 | char *endp; |
343 | int count; |
344 | struct dev_whitelist_item wh; |
345 | |
346 | if (!capable(CAP_SYS_ADMIN)) |
347 | return -EPERM; |
348 | |
349 | memset(&wh, 0, sizeof(wh)); |
350 | b = buffer; |
351 | |
352 | switch (*b) { |
353 | case 'a': |
354 | wh.type = DEV_ALL; |
355 | wh.access = ACC_MASK; |
356 | wh.major = ~0; |
357 | wh.minor = ~0; |
358 | goto handle; |
359 | case 'b': |
360 | wh.type = DEV_BLOCK; |
361 | break; |
362 | case 'c': |
363 | wh.type = DEV_CHAR; |
364 | break; |
365 | default: |
366 | return -EINVAL; |
367 | } |
368 | b++; |
369 | if (!isspace(*b)) |
370 | return -EINVAL; |
371 | b++; |
372 | if (*b == '*') { |
373 | wh.major = ~0; |
374 | b++; |
375 | } else if (isdigit(*b)) { |
376 | wh.major = simple_strtoul(b, &endp, 10); |
377 | b = endp; |
378 | } else { |
379 | return -EINVAL; |
380 | } |
381 | if (*b != ':') |
382 | return -EINVAL; |
383 | b++; |
384 | |
385 | /* read minor */ |
386 | if (*b == '*') { |
387 | wh.minor = ~0; |
388 | b++; |
389 | } else if (isdigit(*b)) { |
390 | wh.minor = simple_strtoul(b, &endp, 10); |
391 | b = endp; |
392 | } else { |
393 | return -EINVAL; |
394 | } |
395 | if (!isspace(*b)) |
396 | return -EINVAL; |
397 | for (b++, count = 0; count < 3; count++, b++) { |
398 | switch (*b) { |
399 | case 'r': |
400 | wh.access |= ACC_READ; |
401 | break; |
402 | case 'w': |
403 | wh.access |= ACC_WRITE; |
404 | break; |
405 | case 'm': |
406 | wh.access |= ACC_MKNOD; |
407 | break; |
408 | case '\n': |
409 | case '\0': |
410 | count = 3; |
411 | break; |
412 | default: |
413 | return -EINVAL; |
414 | } |
415 | } |
416 | |
417 | handle: |
418 | switch (filetype) { |
419 | case DEVCG_ALLOW: |
420 | if (!parent_has_perm(devcgroup, &wh)) |
421 | return -EPERM; |
422 | return dev_whitelist_add(devcgroup, &wh); |
423 | case DEVCG_DENY: |
424 | dev_whitelist_rm(devcgroup, &wh); |
425 | break; |
426 | default: |
427 | return -EINVAL; |
428 | } |
429 | return 0; |
430 | } |
431 | |
432 | static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft, |
433 | const char *buffer) |
434 | { |
435 | int retval; |
436 | |
437 | mutex_lock(&devcgroup_mutex); |
438 | retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp), |
439 | cft->private, buffer); |
440 | mutex_unlock(&devcgroup_mutex); |
441 | return retval; |
442 | } |
443 | |
444 | static struct cftype dev_cgroup_files[] = { |
445 | { |
446 | .name = "allow", |
447 | .write_string = devcgroup_access_write, |
448 | .private = DEVCG_ALLOW, |
449 | }, |
450 | { |
451 | .name = "deny", |
452 | .write_string = devcgroup_access_write, |
453 | .private = DEVCG_DENY, |
454 | }, |
455 | { |
456 | .name = "list", |
457 | .read_seq_string = devcgroup_seq_read, |
458 | .private = DEVCG_LIST, |
459 | }, |
460 | }; |
461 | |
462 | static int devcgroup_populate(struct cgroup_subsys *ss, |
463 | struct cgroup *cgroup) |
464 | { |
465 | return cgroup_add_files(cgroup, ss, dev_cgroup_files, |
466 | ARRAY_SIZE(dev_cgroup_files)); |
467 | } |
468 | |
469 | struct cgroup_subsys devices_subsys = { |
470 | .name = "devices", |
471 | .can_attach = devcgroup_can_attach, |
472 | .create = devcgroup_create, |
473 | .destroy = devcgroup_destroy, |
474 | .populate = devcgroup_populate, |
475 | .subsys_id = devices_subsys_id, |
476 | }; |
477 | |
478 | int devcgroup_inode_permission(struct inode *inode, int mask) |
479 | { |
480 | struct dev_cgroup *dev_cgroup; |
481 | struct dev_whitelist_item *wh; |
482 | |
483 | dev_t device = inode->i_rdev; |
484 | if (!device) |
485 | return 0; |
486 | if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode)) |
487 | return 0; |
488 | |
489 | rcu_read_lock(); |
490 | |
491 | dev_cgroup = task_devcgroup(current); |
492 | |
493 | list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) { |
494 | if (wh->type & DEV_ALL) |
495 | goto found; |
496 | if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode)) |
497 | continue; |
498 | if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode)) |
499 | continue; |
500 | if (wh->major != ~0 && wh->major != imajor(inode)) |
501 | continue; |
502 | if (wh->minor != ~0 && wh->minor != iminor(inode)) |
503 | continue; |
504 | |
505 | if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE)) |
506 | continue; |
507 | if ((mask & MAY_READ) && !(wh->access & ACC_READ)) |
508 | continue; |
509 | found: |
510 | rcu_read_unlock(); |
511 | return 0; |
512 | } |
513 | |
514 | rcu_read_unlock(); |
515 | |
516 | return -EPERM; |
517 | } |
518 | |
519 | int devcgroup_inode_mknod(int mode, dev_t dev) |
520 | { |
521 | struct dev_cgroup *dev_cgroup; |
522 | struct dev_whitelist_item *wh; |
523 | |
524 | if (!S_ISBLK(mode) && !S_ISCHR(mode)) |
525 | return 0; |
526 | |
527 | rcu_read_lock(); |
528 | |
529 | dev_cgroup = task_devcgroup(current); |
530 | |
531 | list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) { |
532 | if (wh->type & DEV_ALL) |
533 | goto found; |
534 | if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode)) |
535 | continue; |
536 | if ((wh->type & DEV_CHAR) && !S_ISCHR(mode)) |
537 | continue; |
538 | if (wh->major != ~0 && wh->major != MAJOR(dev)) |
539 | continue; |
540 | if (wh->minor != ~0 && wh->minor != MINOR(dev)) |
541 | continue; |
542 | |
543 | if (!(wh->access & ACC_MKNOD)) |
544 | continue; |
545 | found: |
546 | rcu_read_unlock(); |
547 | return 0; |
548 | } |
549 | |
550 | rcu_read_unlock(); |
551 | |
552 | return -EPERM; |
553 | } |
554 |
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