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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 | { |
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 | /* |
129 | * called under devcgroup_mutex |
130 | */ |
131 | static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup, |
132 | struct dev_whitelist_item *wh) |
133 | { |
134 | struct dev_whitelist_item *walk, *tmp; |
135 | |
136 | list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) { |
137 | if (walk->type == DEV_ALL) |
138 | goto remove; |
139 | if (walk->type != wh->type) |
140 | continue; |
141 | if (walk->major != ~0 && walk->major != wh->major) |
142 | continue; |
143 | if (walk->minor != ~0 && walk->minor != wh->minor) |
144 | continue; |
145 | |
146 | remove: |
147 | walk->access &= ~wh->access; |
148 | if (!walk->access) { |
149 | list_del_rcu(&walk->list); |
150 | kfree_rcu(walk, rcu); |
151 | } |
152 | } |
153 | } |
154 | |
155 | /* |
156 | * called from kernel/cgroup.c with cgroup_lock() held. |
157 | */ |
158 | static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss, |
159 | struct cgroup *cgroup) |
160 | { |
161 | struct dev_cgroup *dev_cgroup, *parent_dev_cgroup; |
162 | struct cgroup *parent_cgroup; |
163 | int ret; |
164 | |
165 | dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL); |
166 | if (!dev_cgroup) |
167 | return ERR_PTR(-ENOMEM); |
168 | INIT_LIST_HEAD(&dev_cgroup->whitelist); |
169 | parent_cgroup = cgroup->parent; |
170 | |
171 | if (parent_cgroup == NULL) { |
172 | struct dev_whitelist_item *wh; |
173 | wh = kmalloc(sizeof(*wh), GFP_KERNEL); |
174 | if (!wh) { |
175 | kfree(dev_cgroup); |
176 | return ERR_PTR(-ENOMEM); |
177 | } |
178 | wh->minor = wh->major = ~0; |
179 | wh->type = DEV_ALL; |
180 | wh->access = ACC_MASK; |
181 | list_add(&wh->list, &dev_cgroup->whitelist); |
182 | } else { |
183 | parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup); |
184 | mutex_lock(&devcgroup_mutex); |
185 | ret = dev_whitelist_copy(&dev_cgroup->whitelist, |
186 | &parent_dev_cgroup->whitelist); |
187 | mutex_unlock(&devcgroup_mutex); |
188 | if (ret) { |
189 | kfree(dev_cgroup); |
190 | return ERR_PTR(ret); |
191 | } |
192 | } |
193 | |
194 | return &dev_cgroup->css; |
195 | } |
196 | |
197 | static void devcgroup_destroy(struct cgroup_subsys *ss, |
198 | struct cgroup *cgroup) |
199 | { |
200 | struct dev_cgroup *dev_cgroup; |
201 | struct dev_whitelist_item *wh, *tmp; |
202 | |
203 | dev_cgroup = cgroup_to_devcgroup(cgroup); |
204 | list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) { |
205 | list_del(&wh->list); |
206 | kfree(wh); |
207 | } |
208 | kfree(dev_cgroup); |
209 | } |
210 | |
211 | #define DEVCG_ALLOW 1 |
212 | #define DEVCG_DENY 2 |
213 | #define DEVCG_LIST 3 |
214 | |
215 | #define MAJMINLEN 13 |
216 | #define ACCLEN 4 |
217 | |
218 | static void set_access(char *acc, short access) |
219 | { |
220 | int idx = 0; |
221 | memset(acc, 0, ACCLEN); |
222 | if (access & ACC_READ) |
223 | acc[idx++] = 'r'; |
224 | if (access & ACC_WRITE) |
225 | acc[idx++] = 'w'; |
226 | if (access & ACC_MKNOD) |
227 | acc[idx++] = 'm'; |
228 | } |
229 | |
230 | static char type_to_char(short type) |
231 | { |
232 | if (type == DEV_ALL) |
233 | return 'a'; |
234 | if (type == DEV_CHAR) |
235 | return 'c'; |
236 | if (type == DEV_BLOCK) |
237 | return 'b'; |
238 | return 'X'; |
239 | } |
240 | |
241 | static void set_majmin(char *str, unsigned m) |
242 | { |
243 | if (m == ~0) |
244 | strcpy(str, "*"); |
245 | else |
246 | sprintf(str, "%u", m); |
247 | } |
248 | |
249 | static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft, |
250 | struct seq_file *m) |
251 | { |
252 | struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup); |
253 | struct dev_whitelist_item *wh; |
254 | char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN]; |
255 | |
256 | rcu_read_lock(); |
257 | list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) { |
258 | set_access(acc, wh->access); |
259 | set_majmin(maj, wh->major); |
260 | set_majmin(min, wh->minor); |
261 | seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type), |
262 | maj, min, acc); |
263 | } |
264 | rcu_read_unlock(); |
265 | |
266 | return 0; |
267 | } |
268 | |
269 | /* |
270 | * may_access_whitelist: |
271 | * does the access granted to dev_cgroup c contain the access |
272 | * requested in whitelist item refwh. |
273 | * return 1 if yes, 0 if no. |
274 | * call with devcgroup_mutex held |
275 | */ |
276 | static int may_access_whitelist(struct dev_cgroup *c, |
277 | struct dev_whitelist_item *refwh) |
278 | { |
279 | struct dev_whitelist_item *whitem; |
280 | |
281 | list_for_each_entry(whitem, &c->whitelist, list) { |
282 | if (whitem->type & DEV_ALL) |
283 | return 1; |
284 | if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK)) |
285 | continue; |
286 | if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR)) |
287 | continue; |
288 | if (whitem->major != ~0 && whitem->major != refwh->major) |
289 | continue; |
290 | if (whitem->minor != ~0 && whitem->minor != refwh->minor) |
291 | continue; |
292 | if (refwh->access & (~whitem->access)) |
293 | continue; |
294 | return 1; |
295 | } |
296 | return 0; |
297 | } |
298 | |
299 | /* |
300 | * parent_has_perm: |
301 | * when adding a new allow rule to a device whitelist, the rule |
302 | * must be allowed in the parent device |
303 | */ |
304 | static int parent_has_perm(struct dev_cgroup *childcg, |
305 | struct dev_whitelist_item *wh) |
306 | { |
307 | struct cgroup *pcg = childcg->css.cgroup->parent; |
308 | struct dev_cgroup *parent; |
309 | |
310 | if (!pcg) |
311 | return 1; |
312 | parent = cgroup_to_devcgroup(pcg); |
313 | return may_access_whitelist(parent, wh); |
314 | } |
315 | |
316 | /* |
317 | * Modify the whitelist using allow/deny rules. |
318 | * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD |
319 | * so we can give a container CAP_MKNOD to let it create devices but not |
320 | * modify the whitelist. |
321 | * It seems likely we'll want to add a CAP_CONTAINER capability to allow |
322 | * us to also grant CAP_SYS_ADMIN to containers without giving away the |
323 | * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN |
324 | * |
325 | * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting |
326 | * new access is only allowed if you're in the top-level cgroup, or your |
327 | * parent cgroup has the access you're asking for. |
328 | */ |
329 | static int devcgroup_update_access(struct dev_cgroup *devcgroup, |
330 | int filetype, const char *buffer) |
331 | { |
332 | const char *b; |
333 | char *endp; |
334 | int count; |
335 | struct dev_whitelist_item wh; |
336 | |
337 | if (!capable(CAP_SYS_ADMIN)) |
338 | return -EPERM; |
339 | |
340 | memset(&wh, 0, sizeof(wh)); |
341 | b = buffer; |
342 | |
343 | switch (*b) { |
344 | case 'a': |
345 | wh.type = DEV_ALL; |
346 | wh.access = ACC_MASK; |
347 | wh.major = ~0; |
348 | wh.minor = ~0; |
349 | goto handle; |
350 | case 'b': |
351 | wh.type = DEV_BLOCK; |
352 | break; |
353 | case 'c': |
354 | wh.type = DEV_CHAR; |
355 | break; |
356 | default: |
357 | return -EINVAL; |
358 | } |
359 | b++; |
360 | if (!isspace(*b)) |
361 | return -EINVAL; |
362 | b++; |
363 | if (*b == '*') { |
364 | wh.major = ~0; |
365 | b++; |
366 | } else if (isdigit(*b)) { |
367 | wh.major = simple_strtoul(b, &endp, 10); |
368 | b = endp; |
369 | } else { |
370 | return -EINVAL; |
371 | } |
372 | if (*b != ':') |
373 | return -EINVAL; |
374 | b++; |
375 | |
376 | /* read minor */ |
377 | if (*b == '*') { |
378 | wh.minor = ~0; |
379 | b++; |
380 | } else if (isdigit(*b)) { |
381 | wh.minor = simple_strtoul(b, &endp, 10); |
382 | b = endp; |
383 | } else { |
384 | return -EINVAL; |
385 | } |
386 | if (!isspace(*b)) |
387 | return -EINVAL; |
388 | for (b++, count = 0; count < 3; count++, b++) { |
389 | switch (*b) { |
390 | case 'r': |
391 | wh.access |= ACC_READ; |
392 | break; |
393 | case 'w': |
394 | wh.access |= ACC_WRITE; |
395 | break; |
396 | case 'm': |
397 | wh.access |= ACC_MKNOD; |
398 | break; |
399 | case '\n': |
400 | case '\0': |
401 | count = 3; |
402 | break; |
403 | default: |
404 | return -EINVAL; |
405 | } |
406 | } |
407 | |
408 | handle: |
409 | switch (filetype) { |
410 | case DEVCG_ALLOW: |
411 | if (!parent_has_perm(devcgroup, &wh)) |
412 | return -EPERM; |
413 | return dev_whitelist_add(devcgroup, &wh); |
414 | case DEVCG_DENY: |
415 | dev_whitelist_rm(devcgroup, &wh); |
416 | break; |
417 | default: |
418 | return -EINVAL; |
419 | } |
420 | return 0; |
421 | } |
422 | |
423 | static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft, |
424 | const char *buffer) |
425 | { |
426 | int retval; |
427 | |
428 | mutex_lock(&devcgroup_mutex); |
429 | retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp), |
430 | cft->private, buffer); |
431 | mutex_unlock(&devcgroup_mutex); |
432 | return retval; |
433 | } |
434 | |
435 | static struct cftype dev_cgroup_files[] = { |
436 | { |
437 | .name = "allow", |
438 | .write_string = devcgroup_access_write, |
439 | .private = DEVCG_ALLOW, |
440 | }, |
441 | { |
442 | .name = "deny", |
443 | .write_string = devcgroup_access_write, |
444 | .private = DEVCG_DENY, |
445 | }, |
446 | { |
447 | .name = "list", |
448 | .read_seq_string = devcgroup_seq_read, |
449 | .private = DEVCG_LIST, |
450 | }, |
451 | }; |
452 | |
453 | static int devcgroup_populate(struct cgroup_subsys *ss, |
454 | struct cgroup *cgroup) |
455 | { |
456 | return cgroup_add_files(cgroup, ss, dev_cgroup_files, |
457 | ARRAY_SIZE(dev_cgroup_files)); |
458 | } |
459 | |
460 | struct cgroup_subsys devices_subsys = { |
461 | .name = "devices", |
462 | .can_attach = devcgroup_can_attach, |
463 | .create = devcgroup_create, |
464 | .destroy = devcgroup_destroy, |
465 | .populate = devcgroup_populate, |
466 | .subsys_id = devices_subsys_id, |
467 | }; |
468 | |
469 | int __devcgroup_inode_permission(struct inode *inode, int mask) |
470 | { |
471 | struct dev_cgroup *dev_cgroup; |
472 | struct dev_whitelist_item *wh; |
473 | |
474 | rcu_read_lock(); |
475 | |
476 | dev_cgroup = task_devcgroup(current); |
477 | |
478 | list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) { |
479 | if (wh->type & DEV_ALL) |
480 | goto found; |
481 | if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode)) |
482 | continue; |
483 | if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode)) |
484 | continue; |
485 | if (wh->major != ~0 && wh->major != imajor(inode)) |
486 | continue; |
487 | if (wh->minor != ~0 && wh->minor != iminor(inode)) |
488 | continue; |
489 | |
490 | if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE)) |
491 | continue; |
492 | if ((mask & MAY_READ) && !(wh->access & ACC_READ)) |
493 | continue; |
494 | found: |
495 | rcu_read_unlock(); |
496 | return 0; |
497 | } |
498 | |
499 | rcu_read_unlock(); |
500 | |
501 | return -EPERM; |
502 | } |
503 | |
504 | int devcgroup_inode_mknod(int mode, dev_t dev) |
505 | { |
506 | struct dev_cgroup *dev_cgroup; |
507 | struct dev_whitelist_item *wh; |
508 | |
509 | if (!S_ISBLK(mode) && !S_ISCHR(mode)) |
510 | return 0; |
511 | |
512 | rcu_read_lock(); |
513 | |
514 | dev_cgroup = task_devcgroup(current); |
515 | |
516 | list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) { |
517 | if (wh->type & DEV_ALL) |
518 | goto found; |
519 | if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode)) |
520 | continue; |
521 | if ((wh->type & DEV_CHAR) && !S_ISCHR(mode)) |
522 | continue; |
523 | if (wh->major != ~0 && wh->major != MAJOR(dev)) |
524 | continue; |
525 | if (wh->minor != ~0 && wh->minor != MINOR(dev)) |
526 | continue; |
527 | |
528 | if (!(wh->access & ACC_MKNOD)) |
529 | continue; |
530 | found: |
531 | rcu_read_unlock(); |
532 | return 0; |
533 | } |
534 | |
535 | rcu_read_unlock(); |
536 | |
537 | return -EPERM; |
538 | } |
539 |
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