devcgroup: fix permission check when adding entry to child cgroup
[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 };
45
46 struct dev_cgroup {
47         struct cgroup_subsys_state css;
48         struct list_head whitelist;
49         spinlock_t lock;
50 };
51
52 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
53 {
54         return container_of(s, struct dev_cgroup, css);
55 }
56
57 static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
58 {
59         return css_to_devcgroup(cgroup_subsys_state(cgroup, 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 cgroup_lock()
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 = kmalloc(sizeof(*wh), GFP_KERNEL);
82                 if (!new)
83                         goto free_and_exit;
84                 new->major = wh->major;
85                 new->minor = wh->minor;
86                 new->type = wh->type;
87                 new->access = wh->access;
88                 list_add_tail(&new->list, dest);
89         }
90
91         return 0;
92
93 free_and_exit:
94         list_for_each_entry_safe(wh, tmp, dest, list) {
95                 list_del(&wh->list);
96                 kfree(wh);
97         }
98         return -ENOMEM;
99 }
100
101 /* Stupid prototype - don't bother combining existing entries */
102 /*
103  * called under cgroup_lock()
104  * since the list is visible to other tasks, we need the spinlock also
105  */
106 static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
107                         struct dev_whitelist_item *wh)
108 {
109         struct dev_whitelist_item *whcopy, *walk;
110
111         whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL);
112         if (!whcopy)
113                 return -ENOMEM;
114
115         memcpy(whcopy, wh, sizeof(*whcopy));
116         spin_lock(&dev_cgroup->lock);
117         list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
118                 if (walk->type != wh->type)
119                         continue;
120                 if (walk->major != wh->major)
121                         continue;
122                 if (walk->minor != wh->minor)
123                         continue;
124
125                 walk->access |= wh->access;
126                 kfree(whcopy);
127                 whcopy = NULL;
128         }
129
130         if (whcopy != NULL)
131                 list_add_tail(&whcopy->list, &dev_cgroup->whitelist);
132         spin_unlock(&dev_cgroup->lock);
133         return 0;
134 }
135
136 /*
137  * called under cgroup_lock()
138  * since the list is visible to other tasks, we need the spinlock also
139  */
140 static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
141                         struct dev_whitelist_item *wh)
142 {
143         struct dev_whitelist_item *walk, *tmp;
144
145         spin_lock(&dev_cgroup->lock);
146         list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
147                 if (walk->type == DEV_ALL)
148                         goto remove;
149                 if (walk->type != wh->type)
150                         continue;
151                 if (walk->major != ~0 && walk->major != wh->major)
152                         continue;
153                 if (walk->minor != ~0 && walk->minor != wh->minor)
154                         continue;
155
156 remove:
157                 walk->access &= ~wh->access;
158                 if (!walk->access) {
159                         list_del(&walk->list);
160                         kfree(walk);
161                 }
162         }
163         spin_unlock(&dev_cgroup->lock);
164 }
165
166 /*
167  * called from kernel/cgroup.c with cgroup_lock() held.
168  */
169 static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
170                                                 struct cgroup *cgroup)
171 {
172         struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
173         struct cgroup *parent_cgroup;
174         int ret;
175
176         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
177         if (!dev_cgroup)
178                 return ERR_PTR(-ENOMEM);
179         INIT_LIST_HEAD(&dev_cgroup->whitelist);
180         parent_cgroup = cgroup->parent;
181
182         if (parent_cgroup == NULL) {
183                 struct dev_whitelist_item *wh;
184                 wh = kmalloc(sizeof(*wh), GFP_KERNEL);
185                 if (!wh) {
186                         kfree(dev_cgroup);
187                         return ERR_PTR(-ENOMEM);
188                 }
189                 wh->minor = wh->major = ~0;
190                 wh->type = DEV_ALL;
191                 wh->access = ACC_MKNOD | ACC_READ | ACC_WRITE;
192                 list_add(&wh->list, &dev_cgroup->whitelist);
193         } else {
194                 parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
195                 ret = dev_whitelist_copy(&dev_cgroup->whitelist,
196                                 &parent_dev_cgroup->whitelist);
197                 if (ret) {
198                         kfree(dev_cgroup);
199                         return ERR_PTR(ret);
200                 }
201         }
202
203         spin_lock_init(&dev_cgroup->lock);
204         return &dev_cgroup->css;
205 }
206
207 static void devcgroup_destroy(struct cgroup_subsys *ss,
208                         struct cgroup *cgroup)
209 {
210         struct dev_cgroup *dev_cgroup;
211         struct dev_whitelist_item *wh, *tmp;
212
213         dev_cgroup = cgroup_to_devcgroup(cgroup);
214         list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
215                 list_del(&wh->list);
216                 kfree(wh);
217         }
218         kfree(dev_cgroup);
219 }
220
221 #define DEVCG_ALLOW 1
222 #define DEVCG_DENY 2
223 #define DEVCG_LIST 3
224
225 #define MAJMINLEN 13
226 #define ACCLEN 4
227
228 static void set_access(char *acc, short access)
229 {
230         int idx = 0;
231         memset(acc, 0, ACCLEN);
232         if (access & ACC_READ)
233                 acc[idx++] = 'r';
234         if (access & ACC_WRITE)
235                 acc[idx++] = 'w';
236         if (access & ACC_MKNOD)
237                 acc[idx++] = 'm';
238 }
239
240 static char type_to_char(short type)
241 {
242         if (type == DEV_ALL)
243                 return 'a';
244         if (type == DEV_CHAR)
245                 return 'c';
246         if (type == DEV_BLOCK)
247                 return 'b';
248         return 'X';
249 }
250
251 static void set_majmin(char *str, unsigned m)
252 {
253         memset(str, 0, MAJMINLEN);
254         if (m == ~0)
255                 sprintf(str, "*");
256         else
257                 snprintf(str, MAJMINLEN, "%u", m);
258 }
259
260 static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
261                                 struct seq_file *m)
262 {
263         struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
264         struct dev_whitelist_item *wh;
265         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
266
267         spin_lock(&devcgroup->lock);
268         list_for_each_entry(wh, &devcgroup->whitelist, list) {
269                 set_access(acc, wh->access);
270                 set_majmin(maj, wh->major);
271                 set_majmin(min, wh->minor);
272                 seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
273                            maj, min, acc);
274         }
275         spin_unlock(&devcgroup->lock);
276
277         return 0;
278 }
279
280 /*
281  * may_access_whitelist:
282  * does the access granted to dev_cgroup c contain the access
283  * requested in whitelist item refwh.
284  * return 1 if yes, 0 if no.
285  * call with c->lock held
286  */
287 static int may_access_whitelist(struct dev_cgroup *c,
288                                        struct dev_whitelist_item *refwh)
289 {
290         struct dev_whitelist_item *whitem;
291
292         list_for_each_entry(whitem, &c->whitelist, list) {
293                 if (whitem->type & DEV_ALL)
294                         return 1;
295                 if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
296                         continue;
297                 if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
298                         continue;
299                 if (whitem->major != ~0 && whitem->major != refwh->major)
300                         continue;
301                 if (whitem->minor != ~0 && whitem->minor != refwh->minor)
302                         continue;
303                 if (refwh->access & (~whitem->access))
304                         continue;
305                 return 1;
306         }
307         return 0;
308 }
309
310 /*
311  * parent_has_perm:
312  * when adding a new allow rule to a device whitelist, the rule
313  * must be allowed in the parent device
314  */
315 static int parent_has_perm(struct cgroup *childcg,
316                                   struct dev_whitelist_item *wh)
317 {
318         struct cgroup *pcg = childcg->parent;
319         struct dev_cgroup *parent;
320         int ret;
321
322         if (!pcg)
323                 return 1;
324         parent = cgroup_to_devcgroup(pcg);
325         spin_lock(&parent->lock);
326         ret = may_access_whitelist(parent, wh);
327         spin_unlock(&parent->lock);
328         return ret;
329 }
330
331 /*
332  * Modify the whitelist using allow/deny rules.
333  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
334  * so we can give a container CAP_MKNOD to let it create devices but not
335  * modify the whitelist.
336  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
337  * us to also grant CAP_SYS_ADMIN to containers without giving away the
338  * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
339  *
340  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
341  * new access is only allowed if you're in the top-level cgroup, or your
342  * parent cgroup has the access you're asking for.
343  */
344 static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
345                                 struct file *file, const char __user *userbuf,
346                                 size_t nbytes, loff_t *ppos)
347 {
348         struct cgroup *cur_cgroup;
349         struct dev_cgroup *devcgroup, *cur_devcgroup;
350         int filetype = cft->private;
351         char *buffer, *b;
352         int retval = 0, count;
353         struct dev_whitelist_item wh;
354
355         if (!capable(CAP_SYS_ADMIN))
356                 return -EPERM;
357
358         devcgroup = cgroup_to_devcgroup(cgroup);
359         cur_cgroup = task_cgroup(current, devices_subsys.subsys_id);
360         cur_devcgroup = cgroup_to_devcgroup(cur_cgroup);
361
362         buffer = kmalloc(nbytes+1, GFP_KERNEL);
363         if (!buffer)
364                 return -ENOMEM;
365
366         if (copy_from_user(buffer, userbuf, nbytes)) {
367                 retval = -EFAULT;
368                 goto out1;
369         }
370         buffer[nbytes] = 0;     /* nul-terminate */
371
372         cgroup_lock();
373         if (cgroup_is_removed(cgroup)) {
374                 retval = -ENODEV;
375                 goto out2;
376         }
377
378         memset(&wh, 0, sizeof(wh));
379         b = buffer;
380
381         switch (*b) {
382         case 'a':
383                 wh.type = DEV_ALL;
384                 wh.access = ACC_MASK;
385                 wh.major = ~0;
386                 wh.minor = ~0;
387                 goto handle;
388         case 'b':
389                 wh.type = DEV_BLOCK;
390                 break;
391         case 'c':
392                 wh.type = DEV_CHAR;
393                 break;
394         default:
395                 retval = -EINVAL;
396                 goto out2;
397         }
398         b++;
399         if (!isspace(*b)) {
400                 retval = -EINVAL;
401                 goto out2;
402         }
403         b++;
404         if (*b == '*') {
405                 wh.major = ~0;
406                 b++;
407         } else if (isdigit(*b)) {
408                 wh.major = 0;
409                 while (isdigit(*b)) {
410                         wh.major = wh.major*10+(*b-'0');
411                         b++;
412                 }
413         } else {
414                 retval = -EINVAL;
415                 goto out2;
416         }
417         if (*b != ':') {
418                 retval = -EINVAL;
419                 goto out2;
420         }
421         b++;
422
423         /* read minor */
424         if (*b == '*') {
425                 wh.minor = ~0;
426                 b++;
427         } else if (isdigit(*b)) {
428                 wh.minor = 0;
429                 while (isdigit(*b)) {
430                         wh.minor = wh.minor*10+(*b-'0');
431                         b++;
432                 }
433         } else {
434                 retval = -EINVAL;
435                 goto out2;
436         }
437         if (!isspace(*b)) {
438                 retval = -EINVAL;
439                 goto out2;
440         }
441         for (b++, count = 0; count < 3; count++, b++) {
442                 switch (*b) {
443                 case 'r':
444                         wh.access |= ACC_READ;
445                         break;
446                 case 'w':
447                         wh.access |= ACC_WRITE;
448                         break;
449                 case 'm':
450                         wh.access |= ACC_MKNOD;
451                         break;
452                 case '\n':
453                 case '\0':
454                         count = 3;
455                         break;
456                 default:
457                         retval = -EINVAL;
458                         goto out2;
459                 }
460         }
461
462 handle:
463         retval = 0;
464         switch (filetype) {
465         case DEVCG_ALLOW:
466                 if (!parent_has_perm(cgroup, &wh))
467                         retval = -EPERM;
468                 else
469                         retval = dev_whitelist_add(devcgroup, &wh);
470                 break;
471         case DEVCG_DENY:
472                 dev_whitelist_rm(devcgroup, &wh);
473                 break;
474         default:
475                 retval = -EINVAL;
476                 goto out2;
477         }
478
479         if (retval == 0)
480                 retval = nbytes;
481
482 out2:
483         cgroup_unlock();
484 out1:
485         kfree(buffer);
486         return retval;
487 }
488
489 static struct cftype dev_cgroup_files[] = {
490         {
491                 .name = "allow",
492                 .write  = devcgroup_access_write,
493                 .private = DEVCG_ALLOW,
494         },
495         {
496                 .name = "deny",
497                 .write = devcgroup_access_write,
498                 .private = DEVCG_DENY,
499         },
500         {
501                 .name = "list",
502                 .read_seq_string = devcgroup_seq_read,
503                 .private = DEVCG_LIST,
504         },
505 };
506
507 static int devcgroup_populate(struct cgroup_subsys *ss,
508                                 struct cgroup *cgroup)
509 {
510         return cgroup_add_files(cgroup, ss, dev_cgroup_files,
511                                         ARRAY_SIZE(dev_cgroup_files));
512 }
513
514 struct cgroup_subsys devices_subsys = {
515         .name = "devices",
516         .can_attach = devcgroup_can_attach,
517         .create = devcgroup_create,
518         .destroy  = devcgroup_destroy,
519         .populate = devcgroup_populate,
520         .subsys_id = devices_subsys_id,
521 };
522
523 int devcgroup_inode_permission(struct inode *inode, int mask)
524 {
525         struct dev_cgroup *dev_cgroup;
526         struct dev_whitelist_item *wh;
527
528         dev_t device = inode->i_rdev;
529         if (!device)
530                 return 0;
531         if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
532                 return 0;
533         dev_cgroup = css_to_devcgroup(task_subsys_state(current,
534                                 devices_subsys_id));
535         if (!dev_cgroup)
536                 return 0;
537
538         spin_lock(&dev_cgroup->lock);
539         list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
540                 if (wh->type & DEV_ALL)
541                         goto acc_check;
542                 if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
543                         continue;
544                 if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
545                         continue;
546                 if (wh->major != ~0 && wh->major != imajor(inode))
547                         continue;
548                 if (wh->minor != ~0 && wh->minor != iminor(inode))
549                         continue;
550 acc_check:
551                 if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
552                         continue;
553                 if ((mask & MAY_READ) && !(wh->access & ACC_READ))
554                         continue;
555                 spin_unlock(&dev_cgroup->lock);
556                 return 0;
557         }
558         spin_unlock(&dev_cgroup->lock);
559
560         return -EPERM;
561 }
562
563 int devcgroup_inode_mknod(int mode, dev_t dev)
564 {
565         struct dev_cgroup *dev_cgroup;
566         struct dev_whitelist_item *wh;
567
568         dev_cgroup = css_to_devcgroup(task_subsys_state(current,
569                                 devices_subsys_id));
570         if (!dev_cgroup)
571                 return 0;
572
573         spin_lock(&dev_cgroup->lock);
574         list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
575                 if (wh->type & DEV_ALL)
576                         goto acc_check;
577                 if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
578                         continue;
579                 if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
580                         continue;
581                 if (wh->major != ~0 && wh->major != MAJOR(dev))
582                         continue;
583                 if (wh->minor != ~0 && wh->minor != MINOR(dev))
584                         continue;
585 acc_check:
586                 if (!(wh->access & ACC_MKNOD))
587                         continue;
588                 spin_unlock(&dev_cgroup->lock);
589                 return 0;
590         }
591         spin_unlock(&dev_cgroup->lock);
592         return -EPERM;
593 }