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