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