devcgroup: relax white-list protection down to RCU
[linux-2.6.git] / security / device_cgroup.c
1 /*
2  * dev_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
14 #define ACC_MKNOD 1
15 #define ACC_READ  2
16 #define ACC_WRITE 4
17 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
18
19 #define DEV_BLOCK 1
20 #define DEV_CHAR  2
21 #define DEV_ALL   4  /* this represents all devices */
22
23 /*
24  * whitelist locking rules:
25  * cgroup_lock() cannot be taken under dev_cgroup->lock.
26  * dev_cgroup->lock can be taken with or without cgroup_lock().
27  *
28  * modifications always require cgroup_lock
29  * modifications to a list which is visible require the
30  *   dev_cgroup->lock *and* cgroup_lock()
31  * walking the list requires dev_cgroup->lock or cgroup_lock().
32  *
33  * reasoning: dev_whitelist_copy() needs to kmalloc, so needs
34  *   a mutex, which the cgroup_lock() is.  Since modifying
35  *   a visible list requires both locks, either lock can be
36  *   taken for walking the list.
37  */
38
39 struct dev_whitelist_item {
40         u32 major, minor;
41         short type;
42         short access;
43         struct list_head list;
44         struct rcu_head rcu;
45 };
46
47 struct dev_cgroup {
48         struct cgroup_subsys_state css;
49         struct list_head whitelist;
50         spinlock_t lock;
51 };
52
53 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
54 {
55         return container_of(s, struct dev_cgroup, css);
56 }
57
58 static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
59 {
60         return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
61 }
62
63 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
64 {
65         return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
66 }
67
68 struct cgroup_subsys devices_subsys;
69
70 static int devcgroup_can_attach(struct cgroup_subsys *ss,
71                 struct cgroup *new_cgroup, struct task_struct *task)
72 {
73         if (current != task && !capable(CAP_SYS_ADMIN))
74                         return -EPERM;
75
76         return 0;
77 }
78
79 /*
80  * called under cgroup_lock()
81  */
82 static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
83 {
84         struct dev_whitelist_item *wh, *tmp, *new;
85
86         list_for_each_entry(wh, orig, list) {
87                 new = kmalloc(sizeof(*wh), GFP_KERNEL);
88                 if (!new)
89                         goto free_and_exit;
90                 new->major = wh->major;
91                 new->minor = wh->minor;
92                 new->type = wh->type;
93                 new->access = wh->access;
94                 list_add_tail(&new->list, dest);
95         }
96
97         return 0;
98
99 free_and_exit:
100         list_for_each_entry_safe(wh, tmp, dest, list) {
101                 list_del(&wh->list);
102                 kfree(wh);
103         }
104         return -ENOMEM;
105 }
106
107 /* Stupid prototype - don't bother combining existing entries */
108 /*
109  * called under cgroup_lock()
110  * since the list is visible to other tasks, we need the spinlock also
111  */
112 static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
113                         struct dev_whitelist_item *wh)
114 {
115         struct dev_whitelist_item *whcopy, *walk;
116
117         whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL);
118         if (!whcopy)
119                 return -ENOMEM;
120
121         memcpy(whcopy, wh, sizeof(*whcopy));
122         spin_lock(&dev_cgroup->lock);
123         list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
124                 if (walk->type != wh->type)
125                         continue;
126                 if (walk->major != wh->major)
127                         continue;
128                 if (walk->minor != wh->minor)
129                         continue;
130
131                 walk->access |= wh->access;
132                 kfree(whcopy);
133                 whcopy = NULL;
134         }
135
136         if (whcopy != NULL)
137                 list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
138         spin_unlock(&dev_cgroup->lock);
139         return 0;
140 }
141
142 static void whitelist_item_free(struct rcu_head *rcu)
143 {
144         struct dev_whitelist_item *item;
145
146         item = container_of(rcu, struct dev_whitelist_item, rcu);
147         kfree(item);
148 }
149
150 /*
151  * called under cgroup_lock()
152  * since the list is visible to other tasks, we need the spinlock also
153  */
154 static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
155                         struct dev_whitelist_item *wh)
156 {
157         struct dev_whitelist_item *walk, *tmp;
158
159         spin_lock(&dev_cgroup->lock);
160         list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
161                 if (walk->type == DEV_ALL)
162                         goto remove;
163                 if (walk->type != wh->type)
164                         continue;
165                 if (walk->major != ~0 && walk->major != wh->major)
166                         continue;
167                 if (walk->minor != ~0 && walk->minor != wh->minor)
168                         continue;
169
170 remove:
171                 walk->access &= ~wh->access;
172                 if (!walk->access) {
173                         list_del_rcu(&walk->list);
174                         call_rcu(&walk->rcu, whitelist_item_free);
175                 }
176         }
177         spin_unlock(&dev_cgroup->lock);
178 }
179
180 /*
181  * called from kernel/cgroup.c with cgroup_lock() held.
182  */
183 static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
184                                                 struct cgroup *cgroup)
185 {
186         struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
187         struct cgroup *parent_cgroup;
188         int ret;
189
190         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
191         if (!dev_cgroup)
192                 return ERR_PTR(-ENOMEM);
193         INIT_LIST_HEAD(&dev_cgroup->whitelist);
194         parent_cgroup = cgroup->parent;
195
196         if (parent_cgroup == NULL) {
197                 struct dev_whitelist_item *wh;
198                 wh = kmalloc(sizeof(*wh), GFP_KERNEL);
199                 if (!wh) {
200                         kfree(dev_cgroup);
201                         return ERR_PTR(-ENOMEM);
202                 }
203                 wh->minor = wh->major = ~0;
204                 wh->type = DEV_ALL;
205                 wh->access = ACC_MKNOD | ACC_READ | ACC_WRITE;
206                 list_add(&wh->list, &dev_cgroup->whitelist);
207         } else {
208                 parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
209                 ret = dev_whitelist_copy(&dev_cgroup->whitelist,
210                                 &parent_dev_cgroup->whitelist);
211                 if (ret) {
212                         kfree(dev_cgroup);
213                         return ERR_PTR(ret);
214                 }
215         }
216
217         spin_lock_init(&dev_cgroup->lock);
218         return &dev_cgroup->css;
219 }
220
221 static void devcgroup_destroy(struct cgroup_subsys *ss,
222                         struct cgroup *cgroup)
223 {
224         struct dev_cgroup *dev_cgroup;
225         struct dev_whitelist_item *wh, *tmp;
226
227         dev_cgroup = cgroup_to_devcgroup(cgroup);
228         list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
229                 list_del(&wh->list);
230                 kfree(wh);
231         }
232         kfree(dev_cgroup);
233 }
234
235 #define DEVCG_ALLOW 1
236 #define DEVCG_DENY 2
237 #define DEVCG_LIST 3
238
239 #define MAJMINLEN 13
240 #define ACCLEN 4
241
242 static void set_access(char *acc, short access)
243 {
244         int idx = 0;
245         memset(acc, 0, ACCLEN);
246         if (access & ACC_READ)
247                 acc[idx++] = 'r';
248         if (access & ACC_WRITE)
249                 acc[idx++] = 'w';
250         if (access & ACC_MKNOD)
251                 acc[idx++] = 'm';
252 }
253
254 static char type_to_char(short type)
255 {
256         if (type == DEV_ALL)
257                 return 'a';
258         if (type == DEV_CHAR)
259                 return 'c';
260         if (type == DEV_BLOCK)
261                 return 'b';
262         return 'X';
263 }
264
265 static void set_majmin(char *str, unsigned m)
266 {
267         memset(str, 0, MAJMINLEN);
268         if (m == ~0)
269                 sprintf(str, "*");
270         else
271                 snprintf(str, MAJMINLEN, "%u", m);
272 }
273
274 static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
275                                 struct seq_file *m)
276 {
277         struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
278         struct dev_whitelist_item *wh;
279         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
280
281         rcu_read_lock();
282         list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
283                 set_access(acc, wh->access);
284                 set_majmin(maj, wh->major);
285                 set_majmin(min, wh->minor);
286                 seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
287                            maj, min, acc);
288         }
289         rcu_read_unlock();
290
291         return 0;
292 }
293
294 /*
295  * may_access_whitelist:
296  * does the access granted to dev_cgroup c contain the access
297  * requested in whitelist item refwh.
298  * return 1 if yes, 0 if no.
299  * call with c->lock held
300  */
301 static int may_access_whitelist(struct dev_cgroup *c,
302                                        struct dev_whitelist_item *refwh)
303 {
304         struct dev_whitelist_item *whitem;
305
306         list_for_each_entry(whitem, &c->whitelist, list) {
307                 if (whitem->type & DEV_ALL)
308                         return 1;
309                 if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
310                         continue;
311                 if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
312                         continue;
313                 if (whitem->major != ~0 && whitem->major != refwh->major)
314                         continue;
315                 if (whitem->minor != ~0 && whitem->minor != refwh->minor)
316                         continue;
317                 if (refwh->access & (~whitem->access))
318                         continue;
319                 return 1;
320         }
321         return 0;
322 }
323
324 /*
325  * parent_has_perm:
326  * when adding a new allow rule to a device whitelist, the rule
327  * must be allowed in the parent device
328  */
329 static int parent_has_perm(struct dev_cgroup *childcg,
330                                   struct dev_whitelist_item *wh)
331 {
332         struct cgroup *pcg = childcg->css.cgroup->parent;
333         struct dev_cgroup *parent;
334         int ret;
335
336         if (!pcg)
337                 return 1;
338         parent = cgroup_to_devcgroup(pcg);
339         spin_lock(&parent->lock);
340         ret = may_access_whitelist(parent, wh);
341         spin_unlock(&parent->lock);
342         return ret;
343 }
344
345 /*
346  * Modify the whitelist using allow/deny rules.
347  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
348  * so we can give a container CAP_MKNOD to let it create devices but not
349  * modify the whitelist.
350  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
351  * us to also grant CAP_SYS_ADMIN to containers without giving away the
352  * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
353  *
354  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
355  * new access is only allowed if you're in the top-level cgroup, or your
356  * parent cgroup has the access you're asking for.
357  */
358 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
359                                    int filetype, const char *buffer)
360 {
361         struct dev_cgroup *cur_devcgroup;
362         const char *b;
363         int retval = 0, count;
364         struct dev_whitelist_item wh;
365
366         if (!capable(CAP_SYS_ADMIN))
367                 return -EPERM;
368
369         cur_devcgroup = task_devcgroup(current);
370
371         memset(&wh, 0, sizeof(wh));
372         b = buffer;
373
374         switch (*b) {
375         case 'a':
376                 wh.type = DEV_ALL;
377                 wh.access = ACC_MASK;
378                 wh.major = ~0;
379                 wh.minor = ~0;
380                 goto handle;
381         case 'b':
382                 wh.type = DEV_BLOCK;
383                 break;
384         case 'c':
385                 wh.type = DEV_CHAR;
386                 break;
387         default:
388                 return -EINVAL;
389         }
390         b++;
391         if (!isspace(*b))
392                 return -EINVAL;
393         b++;
394         if (*b == '*') {
395                 wh.major = ~0;
396                 b++;
397         } else if (isdigit(*b)) {
398                 wh.major = 0;
399                 while (isdigit(*b)) {
400                         wh.major = wh.major*10+(*b-'0');
401                         b++;
402                 }
403         } else {
404                 return -EINVAL;
405         }
406         if (*b != ':')
407                 return -EINVAL;
408         b++;
409
410         /* read minor */
411         if (*b == '*') {
412                 wh.minor = ~0;
413                 b++;
414         } else if (isdigit(*b)) {
415                 wh.minor = 0;
416                 while (isdigit(*b)) {
417                         wh.minor = wh.minor*10+(*b-'0');
418                         b++;
419                 }
420         } else {
421                 return -EINVAL;
422         }
423         if (!isspace(*b))
424                 return -EINVAL;
425         for (b++, count = 0; count < 3; count++, b++) {
426                 switch (*b) {
427                 case 'r':
428                         wh.access |= ACC_READ;
429                         break;
430                 case 'w':
431                         wh.access |= ACC_WRITE;
432                         break;
433                 case 'm':
434                         wh.access |= ACC_MKNOD;
435                         break;
436                 case '\n':
437                 case '\0':
438                         count = 3;
439                         break;
440                 default:
441                         return -EINVAL;
442                 }
443         }
444
445 handle:
446         retval = 0;
447         switch (filetype) {
448         case DEVCG_ALLOW:
449                 if (!parent_has_perm(devcgroup, &wh))
450                         return -EPERM;
451                 return dev_whitelist_add(devcgroup, &wh);
452         case DEVCG_DENY:
453                 dev_whitelist_rm(devcgroup, &wh);
454                 break;
455         default:
456                 return -EINVAL;
457         }
458         return 0;
459 }
460
461 static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
462                                   const char *buffer)
463 {
464         int retval;
465         if (!cgroup_lock_live_group(cgrp))
466                 return -ENODEV;
467         retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
468                                          cft->private, buffer);
469         cgroup_unlock();
470         return retval;
471 }
472
473 static struct cftype dev_cgroup_files[] = {
474         {
475                 .name = "allow",
476                 .write_string  = devcgroup_access_write,
477                 .private = DEVCG_ALLOW,
478         },
479         {
480                 .name = "deny",
481                 .write_string = devcgroup_access_write,
482                 .private = DEVCG_DENY,
483         },
484         {
485                 .name = "list",
486                 .read_seq_string = devcgroup_seq_read,
487                 .private = DEVCG_LIST,
488         },
489 };
490
491 static int devcgroup_populate(struct cgroup_subsys *ss,
492                                 struct cgroup *cgroup)
493 {
494         return cgroup_add_files(cgroup, ss, dev_cgroup_files,
495                                         ARRAY_SIZE(dev_cgroup_files));
496 }
497
498 struct cgroup_subsys devices_subsys = {
499         .name = "devices",
500         .can_attach = devcgroup_can_attach,
501         .create = devcgroup_create,
502         .destroy  = devcgroup_destroy,
503         .populate = devcgroup_populate,
504         .subsys_id = devices_subsys_id,
505 };
506
507 int devcgroup_inode_permission(struct inode *inode, int mask)
508 {
509         struct dev_cgroup *dev_cgroup;
510         struct dev_whitelist_item *wh;
511
512         dev_t device = inode->i_rdev;
513         if (!device)
514                 return 0;
515         if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
516                 return 0;
517         dev_cgroup = css_to_devcgroup(task_subsys_state(current,
518                                 devices_subsys_id));
519         if (!dev_cgroup)
520                 return 0;
521
522         rcu_read_lock();
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(inode->i_mode))
527                         continue;
528                 if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
529                         continue;
530                 if (wh->major != ~0 && wh->major != imajor(inode))
531                         continue;
532                 if (wh->minor != ~0 && wh->minor != iminor(inode))
533                         continue;
534 acc_check:
535                 if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
536                         continue;
537                 if ((mask & MAY_READ) && !(wh->access & ACC_READ))
538                         continue;
539                 rcu_read_unlock();
540                 return 0;
541         }
542         rcu_read_unlock();
543
544         return -EPERM;
545 }
546
547 int devcgroup_inode_mknod(int mode, dev_t dev)
548 {
549         struct dev_cgroup *dev_cgroup;
550         struct dev_whitelist_item *wh;
551
552         dev_cgroup = css_to_devcgroup(task_subsys_state(current,
553                                 devices_subsys_id));
554         if (!dev_cgroup)
555                 return 0;
556
557         rcu_read_lock();
558         list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
559                 if (wh->type & DEV_ALL)
560                         goto acc_check;
561                 if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
562                         continue;
563                 if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
564                         continue;
565                 if (wh->major != ~0 && wh->major != MAJOR(dev))
566                         continue;
567                 if (wh->minor != ~0 && wh->minor != MINOR(dev))
568                         continue;
569 acc_check:
570                 if (!(wh->access & ACC_MKNOD))
571                         continue;
572                 rcu_read_unlock();
573                 return 0;
574         }
575         rcu_read_unlock();
576         return -EPERM;
577 }