Domain transition handler.
[linux-2.6.git] / security / device_cgroup.c
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
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
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
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
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  */
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  */
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
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  */
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  */
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
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
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
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
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
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  */
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  */
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  */
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
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
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
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
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 }