summaryrefslogtreecommitdiffstats
path: root/drivers/android/binderfs.c
blob: 9518e2e7da05dfa4b526db52f80137d45ca69962 (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
/* SPDX-License-Identifier: GPL-2.0 */

#include <linux/compiler_types.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/fsnotify.h>
#include <linux/gfp.h>
#include <linux/idr.h>
#include <linux/init.h>
#include <linux/ipc_namespace.h>
#include <linux/kdev_t.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/magic.h>
#include <linux/major.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/mount.h>
#include <linux/parser.h>
#include <linux/radix-tree.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/spinlock_types.h>
#include <linux/stddef.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/uaccess.h>
#include <linux/user_namespace.h>
#include <linux/xarray.h>
#include <uapi/asm-generic/errno-base.h>
#include <uapi/linux/android/binder.h>
#include <uapi/linux/android/binderfs.h>

#include "binder_internal.h"

#define FIRST_INODE 1
#define SECOND_INODE 2
#define INODE_OFFSET 3
#define INTSTRLEN 21
#define BINDERFS_MAX_MINOR (1U << MINORBITS)
/* Ensure that the initial ipc namespace always has devices available. */
#define BINDERFS_MAX_MINOR_CAPPED (BINDERFS_MAX_MINOR - 4)

static dev_t binderfs_dev;
static DEFINE_MUTEX(binderfs_minors_mutex);
static DEFINE_IDA(binderfs_minors);

/**
 * binderfs_mount_opts - mount options for binderfs
 * @max: maximum number of allocatable binderfs binder devices
 */
struct binderfs_mount_opts {
	int max;
};

enum {
	Opt_max,
	Opt_err
};

static const match_table_t tokens = {
	{ Opt_max, "max=%d" },
	{ Opt_err, NULL     }
};

/**
 * binderfs_info - information about a binderfs mount
 * @ipc_ns:         The ipc namespace the binderfs mount belongs to.
 * @control_dentry: This records the dentry of this binderfs mount
 *                  binder-control device.
 * @root_uid:       uid that needs to be used when a new binder device is
 *                  created.
 * @root_gid:       gid that needs to be used when a new binder device is
 *                  created.
 * @mount_opts:     The mount options in use.
 * @device_count:   The current number of allocated binder devices.
 */
struct binderfs_info {
	struct ipc_namespace *ipc_ns;
	struct dentry *control_dentry;
	kuid_t root_uid;
	kgid_t root_gid;
	struct binderfs_mount_opts mount_opts;
	int device_count;
};

static inline struct binderfs_info *BINDERFS_I(const struct inode *inode)
{
	return inode->i_sb->s_fs_info;
}

bool is_binderfs_device(const struct inode *inode)
{
	if (inode->i_sb->s_magic == BINDERFS_SUPER_MAGIC)
		return true;

	return false;
}

/**
 * binderfs_binder_device_create - allocate inode from super block of a
 *                                 binderfs mount
 * @ref_inode: inode from wich the super block will be taken
 * @userp:     buffer to copy information about new device for userspace to
 * @req:       struct binderfs_device as copied from userspace
 *
 * This function allocated a new binder_device and reserves a new minor
 * number for it.
 * Minor numbers are limited and tracked globally in binderfs_minors. The
 * function will stash a struct binder_device for the specific binder
 * device in i_private of the inode.
 * It will go on to allocate a new inode from the super block of the
 * filesystem mount, stash a struct binder_device in its i_private field
 * and attach a dentry to that inode.
 *
 * Return: 0 on success, negative errno on failure
 */
static int binderfs_binder_device_create(struct inode *ref_inode,
					 struct binderfs_device __user *userp,
					 struct binderfs_device *req)
{
	int minor, ret;
	struct dentry *dentry, *dup, *root;
	struct binder_device *device;
	size_t name_len = BINDERFS_MAX_NAME + 1;
	char *name = NULL;
	struct inode *inode = NULL;
	struct super_block *sb = ref_inode->i_sb;
	struct binderfs_info *info = sb->s_fs_info;
#if defined(CONFIG_IPC_NS)
	bool use_reserve = (info->ipc_ns == &init_ipc_ns);
#else
	bool use_reserve = true;
#endif

	/* Reserve new minor number for the new device. */
	mutex_lock(&binderfs_minors_mutex);
	if (++info->device_count <= info->mount_opts.max)
		minor = ida_alloc_max(&binderfs_minors,
				      use_reserve ? BINDERFS_MAX_MINOR :
						    BINDERFS_MAX_MINOR_CAPPED,
				      GFP_KERNEL);
	else
		minor = -ENOSPC;
	if (minor < 0) {
		--info->device_count;
		mutex_unlock(&binderfs_minors_mutex);
		return minor;
	}
	mutex_unlock(&binderfs_minors_mutex);

	ret = -ENOMEM;
	device = kzalloc(sizeof(*device), GFP_KERNEL);
	if (!device)
		goto err;

	inode = new_inode(sb);
	if (!inode)
		goto err;

	inode->i_ino = minor + INODE_OFFSET;
	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
	init_special_inode(inode, S_IFCHR | 0600,
			   MKDEV(MAJOR(binderfs_dev), minor));
	inode->i_fop = &binder_fops;
	inode->i_uid = info->root_uid;
	inode->i_gid = info->root_gid;

	name = kmalloc(name_len, GFP_KERNEL);
	if (!name)
		goto err;

	strscpy(name, req->name, name_len);

	device->binderfs_inode = inode;
	device->context.binder_context_mgr_uid = INVALID_UID;
	device->context.name = name;
	device->miscdev.name = name;
	device->miscdev.minor = minor;
	mutex_init(&device->context.context_mgr_node_lock);

	req->major = MAJOR(binderfs_dev);
	req->minor = minor;

	ret = copy_to_user(userp, req, sizeof(*req));
	if (ret) {
		ret = -EFAULT;
		goto err;
	}

	root = sb->s_root;
	inode_lock(d_inode(root));
	dentry = d_alloc_name(root, name);
	if (!dentry) {
		inode_unlock(d_inode(root));
		ret = -ENOMEM;
		goto err;
	}

	/* Verify that the name userspace gave us is not already in use. */
	dup = d_lookup(root, &dentry->d_name);
	if (dup) {
		if (d_really_is_positive(dup)) {
			dput(dup);
			dput(dentry);
			inode_unlock(d_inode(root));
			ret = -EEXIST;
			goto err;
		}
		dput(dup);
	}

	inode->i_private = device;
	d_add(dentry, inode);
	fsnotify_create(root->d_inode, dentry);
	inode_unlock(d_inode(root));

	return 0;

err:
	kfree(name);
	kfree(device);
	mutex_lock(&binderfs_minors_mutex);
	--info->device_count;
	ida_free(&binderfs_minors, minor);
	mutex_unlock(&binderfs_minors_mutex);
	iput(inode);

	return ret;
}

/**
 * binderfs_ctl_ioctl - handle binder device node allocation requests
 *
 * The request handler for the binder-control device. All requests operate on
 * the binderfs mount the binder-control device resides in:
 * - BINDER_CTL_ADD
 *   Allocate a new binder device.
 *
 * Return: 0 on success, negative errno on failure
 */
static long binder_ctl_ioctl(struct file *file, unsigned int cmd,
			     unsigned long arg)
{
	int ret = -EINVAL;
	struct inode *inode = file_inode(file);
	struct binderfs_device __user *device = (struct binderfs_device __user *)arg;
	struct binderfs_device device_req;

	switch (cmd) {
	case BINDER_CTL_ADD:
		ret = copy_from_user(&device_req, device, sizeof(device_req));
		if (ret) {
			ret = -EFAULT;
			break;
		}

		ret = binderfs_binder_device_create(inode, device, &device_req);
		break;
	default:
		break;
	}

	return ret;
}

static void binderfs_evict_inode(struct inode *inode)
{
	struct binder_device *device = inode->i_private;
	struct binderfs_info *info = BINDERFS_I(inode);

	clear_inode(inode);

	if (!device)
		return;

	mutex_lock(&binderfs_minors_mutex);
	--info->device_count;
	ida_free(&binderfs_minors, device->miscdev.minor);
	mutex_unlock(&binderfs_minors_mutex);

	kfree(device->context.name);
	kfree(device);
}

/**
 * binderfs_parse_mount_opts - parse binderfs mount options
 * @data: options to set (can be NULL in which case defaults are used)
 */
static int binderfs_parse_mount_opts(char *data,
				     struct binderfs_mount_opts *opts)
{
	char *p;
	opts->max = BINDERFS_MAX_MINOR;

	while ((p = strsep(&data, ",")) != NULL) {
		substring_t args[MAX_OPT_ARGS];
		int token;
		int max_devices;

		if (!*p)
			continue;

		token = match_token(p, tokens, args);
		switch (token) {
		case Opt_max:
			if (match_int(&args[0], &max_devices) ||
			    (max_devices < 0 ||
			     (max_devices > BINDERFS_MAX_MINOR)))
				return -EINVAL;

			opts->max = max_devices;
			break;
		default:
			pr_err("Invalid mount options\n");
			return -EINVAL;
		}
	}

	return 0;
}

static int binderfs_remount(struct super_block *sb, int *flags, char *data)
{
	struct binderfs_info *info = sb->s_fs_info;
	return binderfs_parse_mount_opts(data, &info->mount_opts);
}

static int binderfs_show_mount_opts(struct seq_file *seq, struct dentry *root)
{
	struct binderfs_info *info;

	info = root->d_sb->s_fs_info;
	if (info->mount_opts.max <= BINDERFS_MAX_MINOR)
		seq_printf(seq, ",max=%d", info->mount_opts.max);

	return 0;
}

static const struct super_operations binderfs_super_ops = {
	.evict_inode    = binderfs_evict_inode,
	.remount_fs	= binderfs_remount,
	.show_options	= binderfs_show_mount_opts,
	.statfs         = simple_statfs,
};

static int binderfs_rename(struct inode *old_dir, struct dentry *old_dentry,
			   struct inode *new_dir, struct dentry *new_dentry,
			   unsigned int flags)
{
	struct inode *inode = d_inode(old_dentry);

	/* binderfs doesn't support directories. */
	if (d_is_dir(old_dentry))
		return -EPERM;

	if (flags & ~RENAME_NOREPLACE)
		return -EINVAL;

	if (!simple_empty(new_dentry))
		return -ENOTEMPTY;

	if (d_really_is_positive(new_dentry))
		simple_unlink(new_dir, new_dentry);

	old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
		new_dir->i_mtime = inode->i_ctime = current_time(old_dir);

	return 0;
}

static int binderfs_unlink(struct inode *dir, struct dentry *dentry)
{
	/*
	 * The control dentry is only ever touched during mount so checking it
	 * here should not require us to take lock.
	 */
	if (BINDERFS_I(dir)->control_dentry == dentry)
		return -EPERM;

	return simple_unlink(dir, dentry);
}

static const struct file_operations binder_ctl_fops = {
	.owner		= THIS_MODULE,
	.open		= nonseekable_open,
	.unlocked_ioctl	= binder_ctl_ioctl,
	.compat_ioctl	= binder_ctl_ioctl,
	.llseek		= noop_llseek,
};

/**
 * binderfs_binder_ctl_create - create a new binder-control device
 * @sb: super block of the binderfs mount
 *
 * This function creates a new binder-control device node in the binderfs mount
 * referred to by @sb.
 *
 * Return: 0 on success, negative errno on failure
 */
static int binderfs_binder_ctl_create(struct super_block *sb)
{
	int minor, ret;
	struct dentry *dentry;
	struct binder_device *device;
	struct inode *inode = NULL;
	struct dentry *root = sb->s_root;
	struct binderfs_info *info = sb->s_fs_info;

	device = kzalloc(sizeof(*device), GFP_KERNEL);
	if (!device)
		return -ENOMEM;

	inode_lock(d_inode(root));

	/* If we have already created a binder-control node, return. */
	if (info->control_dentry) {
		ret = 0;
		goto out;
	}

	ret = -ENOMEM;
	inode = new_inode(sb);
	if (!inode)
		goto out;

	/* Reserve a new minor number for the new device. */
	mutex_lock(&binderfs_minors_mutex);
	minor = ida_alloc_max(&binderfs_minors, BINDERFS_MAX_MINOR, GFP_KERNEL);
	mutex_unlock(&binderfs_minors_mutex);
	if (minor < 0) {
		ret = minor;
		goto out;
	}

	inode->i_ino = SECOND_INODE;
	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
	init_special_inode(inode, S_IFCHR | 0600,
			   MKDEV(MAJOR(binderfs_dev), minor));
	inode->i_fop = &binder_ctl_fops;
	inode->i_uid = info->root_uid;
	inode->i_gid = info->root_gid;

	device->binderfs_inode = inode;
	device->miscdev.minor = minor;

	dentry = d_alloc_name(root, "binder-control");
	if (!dentry)
		goto out;

	inode->i_private = device;
	info->control_dentry = dentry;
	d_add(dentry, inode);
	inode_unlock(d_inode(root));

	return 0;

out:
	inode_unlock(d_inode(root));
	kfree(device);
	iput(inode);

	return ret;
}

static const struct inode_operations binderfs_dir_inode_operations = {
	.lookup = simple_lookup,
	.rename = binderfs_rename,
	.unlink = binderfs_unlink,
};

static int binderfs_fill_super(struct super_block *sb, void *data, int silent)
{
	struct binderfs_info *info;
	int ret = -ENOMEM;
	struct inode *inode = NULL;
	struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;

	get_ipc_ns(ipc_ns);

	sb->s_blocksize = PAGE_SIZE;
	sb->s_blocksize_bits = PAGE_SHIFT;

	/*
	 * The binderfs filesystem can be mounted by userns root in a
	 * non-initial userns. By default such mounts have the SB_I_NODEV flag
	 * set in s_iflags to prevent security issues where userns root can
	 * just create random device nodes via mknod() since it owns the
	 * filesystem mount. But binderfs does not allow to create any files
	 * including devices nodes. The only way to create binder devices nodes
	 * is through the binder-control device which userns root is explicitly
	 * allowed to do. So removing the SB_I_NODEV flag from s_iflags is both
	 * necessary and safe.
	 */
	sb->s_iflags &= ~SB_I_NODEV;
	sb->s_iflags |= SB_I_NOEXEC;
	sb->s_magic = BINDERFS_SUPER_MAGIC;
	sb->s_op = &binderfs_super_ops;
	sb->s_time_gran = 1;

	info = kzalloc(sizeof(struct binderfs_info), GFP_KERNEL);
	if (!info)
		goto err_without_dentry;

	ret = binderfs_parse_mount_opts(data, &info->mount_opts);
	if (ret)
		goto err_without_dentry;

	info->ipc_ns = ipc_ns;
	info->root_gid = make_kgid(sb->s_user_ns, 0);
	if (!gid_valid(info->root_gid))
		info->root_gid = GLOBAL_ROOT_GID;
	info->root_uid = make_kuid(sb->s_user_ns, 0);
	if (!uid_valid(info->root_uid))
		info->root_uid = GLOBAL_ROOT_UID;

	sb->s_fs_info = info;

	inode = new_inode(sb);
	if (!inode)
		goto err_without_dentry;

	inode->i_ino = FIRST_INODE;
	inode->i_fop = &simple_dir_operations;
	inode->i_mode = S_IFDIR | 0755;
	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
	inode->i_op = &binderfs_dir_inode_operations;
	set_nlink(inode, 2);

	sb->s_root = d_make_root(inode);
	if (!sb->s_root)
		goto err_without_dentry;

	ret = binderfs_binder_ctl_create(sb);
	if (ret)
		goto err_with_dentry;

	return 0;

err_with_dentry:
	dput(sb->s_root);
	sb->s_root = NULL;

err_without_dentry:
	put_ipc_ns(ipc_ns);
	iput(inode);
	kfree(info);

	return ret;
}

static struct dentry *binderfs_mount(struct file_system_type *fs_type,
				     int flags, const char *dev_name,
				     void *data)
{
	return mount_nodev(fs_type, flags, data, binderfs_fill_super);
}

static void binderfs_kill_super(struct super_block *sb)
{
	struct binderfs_info *info = sb->s_fs_info;

	if (info && info->ipc_ns)
		put_ipc_ns(info->ipc_ns);

	kfree(info);
	kill_litter_super(sb);
}

static struct file_system_type binder_fs_type = {
	.name		= "binder",
	.mount		= binderfs_mount,
	.kill_sb	= binderfs_kill_super,
	.fs_flags	= FS_USERNS_MOUNT,
};

static int __init init_binderfs(void)
{
	int ret;

	/* Allocate new major number for binderfs. */
	ret = alloc_chrdev_region(&binderfs_dev, 0, BINDERFS_MAX_MINOR,
				  "binder");
	if (ret)
		return ret;

	ret = register_filesystem(&binder_fs_type);
	if (ret) {
		unregister_chrdev_region(binderfs_dev, BINDERFS_MAX_MINOR);
		return ret;
	}

	return ret;
}

device_initcall(init_binderfs);