summaryrefslogtreecommitdiffstats
path: root/security/device_cgroup.c
blob: 4237b19e8fb3c43a0dcb16572a02cea76e221e69 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
/*
 * dev_cgroup.c - device cgroup subsystem
 *
 * Copyright 2007 IBM Corp
 */

#include <linux/device_cgroup.h>
#include <linux/cgroup.h>
#include <linux/ctype.h>
#include <linux/list.h>
#include <linux/uaccess.h>

#define ACC_MKNOD 1
#define ACC_READ  2
#define ACC_WRITE 4
#define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)

#define DEV_BLOCK 1
#define DEV_CHAR  2
#define DEV_ALL   4  /* this represents all devices */

/*
 * whitelist locking rules:
 * cgroup_lock() cannot be taken under dev_cgroup->lock.
 * dev_cgroup->lock can be taken with or without cgroup_lock().
 *
 * modifications always require cgroup_lock
 * modifications to a list which is visible require the
 *   dev_cgroup->lock *and* cgroup_lock()
 * walking the list requires dev_cgroup->lock or cgroup_lock().
 *
 * reasoning: dev_whitelist_copy() needs to kmalloc, so needs
 *   a mutex, which the cgroup_lock() is.  Since modifying
 *   a visible list requires both locks, either lock can be
 *   taken for walking the list.
 */

struct dev_whitelist_item {
	u32 major, minor;
	short type;
	short access;
	struct list_head list;
};

struct dev_cgroup {
	struct cgroup_subsys_state css;
	struct list_head whitelist;
	spinlock_t lock;
};

static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
{
	return container_of(cgroup_subsys_state(cgroup, devices_subsys_id),
			    struct dev_cgroup, css);
}

struct cgroup_subsys devices_subsys;

static int devcgroup_can_attach(struct cgroup_subsys *ss,
		struct cgroup *new_cgroup, struct task_struct *task)
{
	if (current != task && !capable(CAP_SYS_ADMIN))
			return -EPERM;

	return 0;
}

/*
 * called under cgroup_lock()
 */
static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
{
	struct dev_whitelist_item *wh, *tmp, *new;

	list_for_each_entry(wh, orig, list) {
		new = kmalloc(sizeof(*wh), GFP_KERNEL);
		if (!new)
			goto free_and_exit;
		new->major = wh->major;
		new->minor = wh->minor;
		new->type = wh->type;
		new->access = wh->access;
		list_add_tail(&new->list, dest);
	}

	return 0;

free_and_exit:
	list_for_each_entry_safe(wh, tmp, dest, list) {
		list_del(&wh->list);
		kfree(wh);
	}
	return -ENOMEM;
}

/* Stupid prototype - don't bother combining existing entries */
/*
 * called under cgroup_lock()
 * since the list is visible to other tasks, we need the spinlock also
 */
static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
			struct dev_whitelist_item *wh)
{
	struct dev_whitelist_item *whcopy;

	whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL);
	if (!whcopy)
		return -ENOMEM;

	memcpy(whcopy, wh, sizeof(*whcopy));
	spin_lock(&dev_cgroup->lock);
	list_add_tail(&whcopy->list, &dev_cgroup->whitelist);
	spin_unlock(&dev_cgroup->lock);
	return 0;
}

/*
 * called under cgroup_lock()
 * since the list is visible to other tasks, we need the spinlock also
 */
static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
			struct dev_whitelist_item *wh)
{
	struct dev_whitelist_item *walk, *tmp;

	spin_lock(&dev_cgroup->lock);
	list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
		if (walk->type == DEV_ALL)
			goto remove;
		if (walk->type != wh->type)
			continue;
		if (walk->major != ~0 && walk->major != wh->major)
			continue;
		if (walk->minor != ~0 && walk->minor != wh->minor)
			continue;

remove:
		walk->access &= ~wh->access;
		if (!walk->access) {
			list_del(&walk->list);
			kfree(walk);
		}
	}
	spin_unlock(&dev_cgroup->lock);
}

/*
 * called from kernel/cgroup.c with cgroup_lock() held.
 */
static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
						struct cgroup *cgroup)
{
	struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
	struct cgroup *parent_cgroup;
	int ret;

	dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
	if (!dev_cgroup)
		return ERR_PTR(-ENOMEM);
	INIT_LIST_HEAD(&dev_cgroup->whitelist);
	parent_cgroup = cgroup->parent;

	if (parent_cgroup == NULL) {
		struct dev_whitelist_item *wh;
		wh = kmalloc(sizeof(*wh), GFP_KERNEL);
		if (!wh) {
			kfree(dev_cgroup);
			return ERR_PTR(-ENOMEM);
		}
		wh->minor = wh->major = ~0;
		wh->type = DEV_ALL;
		wh->access = ACC_MKNOD | ACC_READ | ACC_WRITE;
		list_add(&wh->list, &dev_cgroup->whitelist);
	} else {
		parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
		ret = dev_whitelist_copy(&dev_cgroup->whitelist,
				&parent_dev_cgroup->whitelist);
		if (ret) {
			kfree(dev_cgroup);
			return ERR_PTR(ret);
		}
	}

	spin_lock_init(&dev_cgroup->lock);
	return &dev_cgroup->css;
}

static void devcgroup_destroy(struct cgroup_subsys *ss,
			struct cgroup *cgroup)
{
	struct dev_cgroup *dev_cgroup;
	struct dev_whitelist_item *wh, *tmp;

	dev_cgroup = cgroup_to_devcgroup(cgroup);
	list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
		list_del(&wh->list);
		kfree(wh);
	}
	kfree(dev_cgroup);
}

#define DEVCG_ALLOW 1
#define DEVCG_DENY 2

static void set_access(char *acc, short access)
{
	int idx = 0;
	memset(acc, 0, 4);
	if (access & ACC_READ)
		acc[idx++] = 'r';
	if (access & ACC_WRITE)
		acc[idx++] = 'w';
	if (access & ACC_MKNOD)
		acc[idx++] = 'm';
}

static char type_to_char(short type)
{
	if (type == DEV_ALL)
		return 'a';
	if (type == DEV_CHAR)
		return 'c';
	if (type == DEV_BLOCK)
		return 'b';
	return 'X';
}

static void set_majmin(char *str, int len, unsigned m)
{
	memset(str, 0, len);
	if (m == ~0)
		sprintf(str, "*");
	else
		snprintf(str, len, "%d", m);
}

static char *print_whitelist(struct dev_cgroup *devcgroup, int *len)
{
	char *buf, *s, acc[4];
	struct dev_whitelist_item *wh;
	int ret;
	int count = 0;
	char maj[10], min[10];

	buf = kmalloc(4096, GFP_KERNEL);
	if (!buf)
		return ERR_PTR(-ENOMEM);
	s = buf;
	*s = '\0';
	*len = 0;

	spin_lock(&devcgroup->lock);
	list_for_each_entry(wh, &devcgroup->whitelist, list) {
		set_access(acc, wh->access);
		set_majmin(maj, 10, wh->major);
		set_majmin(min, 10, wh->minor);
		ret = snprintf(s, 4095-(s-buf), "%c %s:%s %s\n",
			type_to_char(wh->type), maj, min, acc);
		if (s+ret >= buf+4095) {
			kfree(buf);
			buf = ERR_PTR(-ENOMEM);
			break;
		}
		s += ret;
		*len += ret;
		count++;
	}
	spin_unlock(&devcgroup->lock);

	return buf;
}

static ssize_t devcgroup_access_read(struct cgroup *cgroup,
			struct cftype *cft, struct file *file,
			char __user *userbuf, size_t nbytes, loff_t *ppos)
{
	struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
	int filetype = cft->private;
	char *buffer;
	int uninitialized_var(len);
	int retval;

	if (filetype != DEVCG_ALLOW)
		return -EINVAL;
	buffer = print_whitelist(devcgroup, &len);
	if (IS_ERR(buffer))
		return PTR_ERR(buffer);

	retval = simple_read_from_buffer(userbuf, nbytes, ppos, buffer, len);
	kfree(buffer);
	return retval;
}

/*
 * may_access_whitelist:
 * does the access granted to dev_cgroup c contain the access
 * requested in whitelist item refwh.
 * return 1 if yes, 0 if no.
 * call with c->lock held
 */
static int may_access_whitelist(struct dev_cgroup *c,
				       struct dev_whitelist_item *refwh)
{
	struct dev_whitelist_item *whitem;

	list_for_each_entry(whitem, &c->whitelist, list) {
		if (whitem->type & DEV_ALL)
			return 1;
		if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
			continue;
		if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
			continue;
		if (whitem->major != ~0 && whitem->major != refwh->major)
			continue;
		if (whitem->minor != ~0 && whitem->minor != refwh->minor)
			continue;
		if (refwh->access & (~(whitem->access | ACC_MASK)))
			continue;
		return 1;
	}
	return 0;
}

/*
 * parent_has_perm:
 * when adding a new allow rule to a device whitelist, the rule
 * must be allowed in the parent device
 */
static int parent_has_perm(struct cgroup *childcg,
				  struct dev_whitelist_item *wh)
{
	struct cgroup *pcg = childcg->parent;
	struct dev_cgroup *parent;
	int ret;

	if (!pcg)
		return 1;
	parent = cgroup_to_devcgroup(pcg);
	spin_lock(&parent->lock);
	ret = may_access_whitelist(parent, wh);
	spin_unlock(&parent->lock);
	return ret;
}

/*
 * Modify the whitelist using allow/deny rules.
 * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 * so we can give a container CAP_MKNOD to let it create devices but not
 * modify the whitelist.
 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 * us to also grant CAP_SYS_ADMIN to containers without giving away the
 * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
 *
 * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 * new access is only allowed if you're in the top-level cgroup, or your
 * parent cgroup has the access you're asking for.
 */
static ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
				struct file *file, const char __user *userbuf,
				size_t nbytes, loff_t *ppos)
{
	struct cgroup *cur_cgroup;
	struct dev_cgroup *devcgroup, *cur_devcgroup;
	int filetype = cft->private;
	char *buffer, *b;
	int retval = 0, count;
	struct dev_whitelist_item wh;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	devcgroup = cgroup_to_devcgroup(cgroup);
	cur_cgroup = task_cgroup(current, devices_subsys.subsys_id);
	cur_devcgroup = cgroup_to_devcgroup(cur_cgroup);

	buffer = kmalloc(nbytes+1, GFP_KERNEL);
	if (!buffer)
		return -ENOMEM;

	if (copy_from_user(buffer, userbuf, nbytes)) {
		retval = -EFAULT;
		goto out1;
	}
	buffer[nbytes] = 0;	/* nul-terminate */

	cgroup_lock();
	if (cgroup_is_removed(cgroup)) {
		retval = -ENODEV;
		goto out2;
	}

	memset(&wh, 0, sizeof(wh));
	b = buffer;

	switch (*b) {
	case 'a':
		wh.type = DEV_ALL;
		wh.access = ACC_MASK;
		goto handle;
	case 'b':
		wh.type = DEV_BLOCK;
		break;
	case 'c':
		wh.type = DEV_CHAR;
		break;
	default:
		retval = -EINVAL;
		goto out2;
	}
	b++;
	if (!isspace(*b)) {
		retval = -EINVAL;
		goto out2;
	}
	b++;
	if (*b == '*') {
		wh.major = ~0;
		b++;
	} else if (isdigit(*b)) {
		wh.major = 0;
		while (isdigit(*b)) {
			wh.major = wh.major*10+(*b-'0');
			b++;
		}
	} else {
		retval = -EINVAL;
		goto out2;
	}
	if (*b != ':') {
		retval = -EINVAL;
		goto out2;
	}
	b++;

	/* read minor */
	if (*b == '*') {
		wh.minor = ~0;
		b++;
	} else if (isdigit(*b)) {
		wh.minor = 0;
		while (isdigit(*b)) {
			wh.minor = wh.minor*10+(*b-'0');
			b++;
		}
	} else {
		retval = -EINVAL;
		goto out2;
	}
	if (!isspace(*b)) {
		retval = -EINVAL;
		goto out2;
	}
	for (b++, count = 0; count < 3; count++, b++) {
		switch (*b) {
		case 'r':
			wh.access |= ACC_READ;
			break;
		case 'w':
			wh.access |= ACC_WRITE;
			break;
		case 'm':
			wh.access |= ACC_MKNOD;
			break;
		case '\n':
		case '\0':
			count = 3;
			break;
		default:
			retval = -EINVAL;
			goto out2;
		}
	}

handle:
	retval = 0;
	switch (filetype) {
	case DEVCG_ALLOW:
		if (!parent_has_perm(cgroup, &wh))
			retval = -EPERM;
		else
			retval = dev_whitelist_add(devcgroup, &wh);
		break;
	case DEVCG_DENY:
		dev_whitelist_rm(devcgroup, &wh);
		break;
	default:
		retval = -EINVAL;
		goto out2;
	}

	if (retval == 0)
		retval = nbytes;

out2:
	cgroup_unlock();
out1:
	kfree(buffer);
	return retval;
}

static struct cftype dev_cgroup_files[] = {
	{
		.name = "allow",
		.read = devcgroup_access_read,
		.write  = devcgroup_access_write,
		.private = DEVCG_ALLOW,
	},
	{
		.name = "deny",
		.write = devcgroup_access_write,
		.private = DEVCG_DENY,
	},
};

static int devcgroup_populate(struct cgroup_subsys *ss,
				struct cgroup *cgroup)
{
	return cgroup_add_files(cgroup, ss, dev_cgroup_files,
					ARRAY_SIZE(dev_cgroup_files));
}

struct cgroup_subsys devices_subsys = {
	.name = "devices",
	.can_attach = devcgroup_can_attach,
	.create = devcgroup_create,
	.destroy  = devcgroup_destroy,
	.populate = devcgroup_populate,
	.subsys_id = devices_subsys_id,
};

int devcgroup_inode_permission(struct inode *inode, int mask)
{
	struct cgroup *cgroup;
	struct dev_cgroup *dev_cgroup;
	struct dev_whitelist_item *wh;

	dev_t device = inode->i_rdev;
	if (!device)
		return 0;
	if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
		return 0;
	cgroup = task_cgroup(current, devices_subsys.subsys_id);
	dev_cgroup = cgroup_to_devcgroup(cgroup);
	if (!dev_cgroup)
		return 0;

	spin_lock(&dev_cgroup->lock);
	list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
		if (wh->type & DEV_ALL)
			goto acc_check;
		if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
			continue;
		if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
			continue;
		if (wh->major != ~0 && wh->major != imajor(inode))
			continue;
		if (wh->minor != ~0 && wh->minor != iminor(inode))
			continue;
acc_check:
		if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
			continue;
		if ((mask & MAY_READ) && !(wh->access & ACC_READ))
			continue;
		spin_unlock(&dev_cgroup->lock);
		return 0;
	}
	spin_unlock(&dev_cgroup->lock);

	return -EPERM;
}

int devcgroup_inode_mknod(int mode, dev_t dev)
{
	struct cgroup *cgroup;
	struct dev_cgroup *dev_cgroup;
	struct dev_whitelist_item *wh;

	cgroup = task_cgroup(current, devices_subsys.subsys_id);
	dev_cgroup = cgroup_to_devcgroup(cgroup);
	if (!dev_cgroup)
		return 0;

	spin_lock(&dev_cgroup->lock);
	list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
		if (wh->type & DEV_ALL)
			goto acc_check;
		if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
			continue;
		if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
			continue;
		if (wh->major != ~0 && wh->major != MAJOR(dev))
			continue;
		if (wh->minor != ~0 && wh->minor != MINOR(dev))
			continue;
acc_check:
		if (!(wh->access & ACC_MKNOD))
			continue;
		spin_unlock(&dev_cgroup->lock);
		return 0;
	}
	spin_unlock(&dev_cgroup->lock);
	return -EPERM;
}
OpenPOWER on IntegriCloud