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