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