aboutsummaryrefslogtreecommitdiffstats
path: root/fs/binfmt_misc.c
blob: f2744ab4e5b35c415724034f3f5a3a328997cf99 (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
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
/*
 *  binfmt_misc.c
 *
 *  Copyright (C) 1997 Richard Günther
 *
 *  binfmt_misc detects binaries via a magic or filename extension and invokes
 *  a specified wrapper. This should obsolete binfmt_java, binfmt_em86 and
 *  binfmt_mz.
 *
 *  1997-04-25 first version
 *  [...]
 *  1997-05-19 cleanup
 *  1997-06-26 hpa: pass the real filename rather than argv[0]
 *  1997-06-30 minor cleanup
 *  1997-08-09 removed extension stripping, locking cleanup
 *  2001-02-28 AV: rewritten into something that resembles C. Original didn't.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/binfmts.h>
#include <linux/slab.h>
#include <linux/ctype.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/syscalls.h>
#include <linux/fs.h>

#include <asm/uaccess.h>

enum {
	VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
};

static LIST_HEAD(entries);
static int enabled = 1;

enum {Enabled, Magic};
#define MISC_FMT_PRESERVE_ARGV0 (1<<31)
#define MISC_FMT_OPEN_BINARY (1<<30)
#define MISC_FMT_CREDENTIALS (1<<29)

typedef struct {
	struct list_head list;
	unsigned long flags;		/* type, status, etc. */
	int offset;			/* offset of magic */
	int size;			/* size of magic/mask */
	char *magic;			/* magic or filename extension */
	char *mask;			/* mask, NULL for exact match */
	char *interpreter;		/* filename of interpreter */
	char *name;
	struct dentry *dentry;
} Node;

static DEFINE_RWLOCK(entries_lock);
static struct file_system_type bm_fs_type;
static struct vfsmount *bm_mnt;
static int entry_count;

/* 
 * Check if we support the binfmt
 * if we do, return the node, else NULL
 * locking is done in load_misc_binary
 */
static Node *check_file(struct linux_binprm *bprm)
{
	char *p = strrchr(bprm->interp, '.');
	struct list_head *l;

	list_for_each(l, &entries) {
		Node *e = list_entry(l, Node, list);
		char *s;
		int j;

		if (!test_bit(Enabled, &e->flags))
			continue;

		if (!test_bit(Magic, &e->flags)) {
			if (p && !strcmp(e->magic, p + 1))
				return e;
			continue;
		}

		s = bprm->buf + e->offset;
		if (e->mask) {
			for (j = 0; j < e->size; j++)
				if ((*s++ ^ e->magic[j]) & e->mask[j])
					break;
		} else {
			for (j = 0; j < e->size; j++)
				if ((*s++ ^ e->magic[j]))
					break;
		}
		if (j == e->size)
			return e;
	}
	return NULL;
}

/*
 * the loader itself
 */
static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
{
	Node *fmt;
	struct file * interp_file = NULL;
	char iname[BINPRM_BUF_SIZE];
	char *iname_addr = iname;
	int retval;
	int fd_binary = -1;

	retval = -ENOEXEC;
	if (!enabled)
		goto _ret;

	retval = -ENOEXEC;
	if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
		goto _ret;

	/* to keep locking time low, we copy the interpreter string */
	read_lock(&entries_lock);
	fmt = check_file(bprm);
	if (fmt)
		strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
	read_unlock(&entries_lock);
	if (!fmt)
		goto _ret;

	if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
		retval = remove_arg_zero(bprm);
		if (retval)
			goto _ret;
	}

	if (fmt->flags & MISC_FMT_OPEN_BINARY) {

		/* if the binary should be opened on behalf of the
		 * interpreter than keep it open and assign descriptor
		 * to it */
 		fd_binary = get_unused_fd();
 		if (fd_binary < 0) {
 			retval = fd_binary;
 			goto _ret;
 		}
 		fd_install(fd_binary, bprm->file);

		/* if the binary is not readable than enforce mm->dumpable=0
		   regardless of the interpreter's permissions */
		if (file_permission(bprm->file, MAY_READ))
			bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;

		allow_write_access(bprm->file);
		bprm->file = NULL;

		/* mark the bprm that fd should be passed to interp */
		bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
		bprm->interp_data = fd_binary;

 	} else {
 		allow_write_access(bprm->file);
 		fput(bprm->file);
 		bprm->file = NULL;
 	}
	/* make argv[1] be the path to the binary */
	retval = copy_strings_kernel (1, &bprm->interp, bprm);
	if (retval < 0)
		goto _error;
	bprm->argc++;

	/* add the interp as argv[0] */
	retval = copy_strings_kernel (1, &iname_addr, bprm);
	if (retval < 0)
		goto _error;
	bprm->argc ++;

	bprm->interp = iname;	/* for binfmt_script */

	interp_file = open_exec (iname);
	retval = PTR_ERR (interp_file);
	if (IS_ERR (interp_file))
		goto _error;

	bprm->file = interp_file;
	if (fmt->flags & MISC_FMT_CREDENTIALS) {
		/*
		 * No need to call prepare_binprm(), it's already been
		 * done.  bprm->buf is stale, update from interp_file.
		 */
		memset(bprm->buf, 0, BINPRM_BUF_SIZE);
		retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
	} else
		retval = prepare_binprm (bprm);

	if (retval < 0)
		goto _error;

	bprm->recursion_depth++;

	retval = search_binary_handler (bprm, regs);
	if (retval < 0)
		goto _error;

_ret:
	return retval;
_error:
	if (fd_binary > 0)
		sys_close(fd_binary);
	bprm->interp_flags = 0;
	bprm->interp_data = 0;
	goto _ret;
}

/* Command parsers */

/*
 * parses and copies one argument enclosed in del from *sp to *dp,
 * recognising the \x special.
 * returns pointer to the copied argument or NULL in case of an
 * error (and sets err) or null argument length.
 */
static char *scanarg(char *s, char del)
{
	char c;

	while ((c = *s++) != del) {
		if (c == '\\' && *s == 'x') {
			s++;
			if (!isxdigit(*s++))
				return NULL;
			if (!isxdigit(*s++))
				return NULL;
		}
	}
	return s;
}

static int unquote(char *from)
{
	char c = 0, *s = from, *p = from;

	while ((c = *s++) != '\0') {
		if (c == '\\' && *s == 'x') {
			s++;
			c = toupper(*s++);
			*p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
			c = toupper(*s++);
			*p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
			continue;
		}
		*p++ = c;
	}
	return p - from;
}

static char * check_special_flags (char * sfs, Node * e)
{
	char * p = sfs;
	int cont = 1;

	/* special flags */
	while (cont) {
		switch (*p) {
			case 'P':
				p++;
				e->flags |= MISC_FMT_PRESERVE_ARGV0;
				break;
			case 'O':
				p++;
				e->flags |= MISC_FMT_OPEN_BINARY;
				break;
			case 'C':
				p++;
				/* this flags also implies the
				   open-binary flag */
				e->flags |= (MISC_FMT_CREDENTIALS |
						MISC_FMT_OPEN_BINARY);
				break;
			default:
				cont = 0;
		}
	}

	return p;
}
/*
 * This registers a new binary format, it recognises the syntax
 * ':name:type:offset:magic:mask:interpreter:flags'
 * where the ':' is the IFS, that can be chosen with the first char
 */
static Node *create_entry(const char __user *buffer, size_t count)
{
	Node *e;
	int memsize, err;
	char *buf, *p;
	char del;

	/* some sanity checks */
	err = -EINVAL;
	if ((count < 11) || (count > 256))
		goto out;

	err = -ENOMEM;
	memsize = sizeof(Node) + count + 8;
	e = kmalloc(memsize, GFP_USER);
	if (!e)
		goto out;

	p = buf = (char *)e + sizeof(Node);

	memset(e, 0, sizeof(Node));
	if (copy_from_user(buf, buffer, count))
		goto Efault;

	del = *p++;	/* delimeter */

	memset(buf+count, del, 8);

	e->name = p;
	p = strchr(p, del);
	if (!p)
		goto Einval;
	*p++ = '\0';
	if (!e->name[0] ||
	    !strcmp(e->name, ".") ||
	    !strcmp(e->name, "..") ||
	    strchr(e->name, '/'))
		goto Einval;
	switch (*p++) {
		case 'E': e->flags = 1<<Enabled; break;
		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
		default: goto Einval;
	}
	if (*p++ != del)
		goto Einval;
	if (test_bit(Magic, &e->flags)) {
		char *s = strchr(p, del);
		if (!s)
			goto Einval;
		*s++ = '\0';
		e->offset = simple_strtoul(p, &p, 10);
		if (*p++)
			goto Einval;
		e->magic = p;
		p = scanarg(p, del);
		if (!p)
			goto Einval;
		p[-1] = '\0';
		if (!e->magic[0])
			goto Einval;
		e->mask = p;
		p = scanarg(p, del);
		if (!p)
			goto Einval;
		p[-1] = '\0';
		if (!e->mask[0])
			e->mask = NULL;
		e->size = unquote(e->magic);
		if (e->mask && unquote(e->mask) != e->size)
			goto Einval;
		if (e->size + e->offset > BINPRM_BUF_SIZE)
			goto Einval;
	} else {
		p = strchr(p, del);
		if (!p)
			goto Einval;
		*p++ = '\0';
		e->magic = p;
		p = strchr(p, del);
		if (!p)
			goto Einval;
		*p++ = '\0';
		if (!e->magic[0] || strchr(e->magic, '/'))
			goto Einval;
		p = strchr(p, del);
		if (!p)
			goto Einval;
		*p++ = '\0';
	}
	e->interpreter = p;
	p = strchr(p, del);
	if (!p)
		goto Einval;
	*p++ = '\0';
	if (!e->interpreter[0])
		goto Einval;


	p = check_special_flags (p, e);

	if (*p == '\n')
		p++;
	if (p != buf + count)
		goto Einval;
	return e;

out:
	return ERR_PTR(err);

Efault:
	kfree(e);
	return ERR_PTR(-EFAULT);
Einval:
	kfree(e);
	return ERR_PTR(-EINVAL);
}

/*
 * Set status of entry/binfmt_misc:
 * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 */
static int parse_command(const char __user *buffer, size_t count)
{
	char s[4];

	if (!count)
		return 0;
	if (count > 3)
		return -EINVAL;
	if (copy_from_user(s, buffer, count))
		return -EFAULT;
	if (s[count-1] == '\n')
		count--;
	if (count == 1 && s[0] == '0')
		return 1;
	if (count == 1 && s[0] == '1')
		return 2;
	if (count == 2 && s[0] == '-' && s[1] == '1')
		return 3;
	return -EINVAL;
}

/* generic stuff */

static void entry_status(Node *e, char *page)
{
	char *dp;
	char *status = "disabled";
	const char * flags = "flags: ";

	if (test_bit(Enabled, &e->flags))
		status = "enabled";

	if (!VERBOSE_STATUS) {
		sprintf(page, "%s\n", status);
		return;
	}

	sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
	dp = page + strlen(page);

	/* print the special flags */
	sprintf (dp, "%s", flags);
	dp += strlen (flags);
	if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
		*dp ++ = 'P';
	}
	if (e->flags & MISC_FMT_OPEN_BINARY) {
		*dp ++ = 'O';
	}
	if (e->flags & MISC_FMT_CREDENTIALS) {
		*dp ++ = 'C';
	}
	*dp ++ = '\n';


	if (!test_bit(Magic, &e->flags)) {
		sprintf(dp, "extension .%s\n", e->magic);
	} else {
		int i;

		sprintf(dp, "offset %i\nmagic ", e->offset);
		dp = page + strlen(page);
		for (i = 0; i < e->size; i++) {
			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
			dp += 2;
		}
		if (e->mask) {
			sprintf(dp, "\nmask ");
			dp += 6;
			for (i = 0; i < e->size; i++) {
				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
				dp += 2;
			}
		}
		*dp++ = '\n';
		*dp = '\0';
	}
}

static struct inode *bm_get_inode(struct super_block *sb, int mode)
{
	struct inode * inode = new_inode(sb);

	if (inode) {
		inode->i_mode = mode;
		inode->i_uid = 0;
		inode->i_gid = 0;
		inode->i_blocks = 0;
		inode->i_atime = inode->i_mtime = inode->i_ctime =
			current_fs_time(inode->i_sb);
	}
	return inode;
}

static void bm_clear_inode(struct inode *inode)
{
	kfree(inode->i_private);
}

static void kill_node(Node *e)
{
	struct dentry *dentry;

	write_lock(&entries_lock);
	dentry = e->dentry;
	if (dentry) {
		list_del_init(&e->list);
		e->dentry = NULL;
	}
	write_unlock(&entries_lock);

	if (dentry) {
		dentry->d_inode->i_nlink--;
		d_drop(dentry);
		dput(dentry);
		simple_release_fs(&bm_mnt, &entry_count);
	}
}

/* /<entry> */

static ssize_t
bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
{
	Node *e = file->f_path.dentry->d_inode->i_private;
	ssize_t res;
	char *page;

	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
		return -ENOMEM;

	entry_status(e, page);

	res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));

	free_page((unsigned long) page);
	return res;
}

static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
				size_t count, loff_t *ppos)
{
	struct dentry *root;
	Node *e = file->f_path.dentry->d_inode->i_private;
	int res = parse_command(buffer, count);

	switch (res) {
		case 1: clear_bit(Enabled, &e->flags);
			break;
		case 2: set_bit(Enabled, &e->flags);
			break;
		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
			mutex_lock(&root->d_inode->i_mutex);

			kill_node(e);

			mutex_unlock(&root->d_inode->i_mutex);
			dput(root);
			break;
		default: return res;
	}
	return count;
}

static const struct file_operations bm_entry_operations = {
	.read		= bm_entry_read,
	.write		= bm_entry_write,
};

/* /register */

static ssize_t bm_register_write(struct file *file, const char __user *buffer,
			       size_t count, loff_t *ppos)
{
	Node *e;
	struct inode *inode;
	struct dentry *root, *dentry;
	struct super_block *sb = file->f_path.mnt->mnt_sb;
	int err = 0;

	e = create_entry(buffer, count);

	if (IS_ERR(e))
		return PTR_ERR(e);

	root = dget(sb->s_root);
	mutex_lock(&root->d_inode->i_mutex);
	dentry = lookup_one_len(e->name, root, strlen(e->name));
	err = PTR_ERR(dentry);
	if (IS_ERR(dentry))
		goto out;

	err = -EEXIST;
	if (dentry->d_inode)
		goto out2;

	inode = bm_get_inode(sb, S_IFREG | 0644);

	err = -ENOMEM;
	if (!inode)
		goto out2;

	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
	if (err) {
		iput(inode);
		inode = NULL;
		goto out2;
	}

	e->dentry = dget(dentry);
	inode->i_private = e;
	inode->i_fop = &bm_entry_operations;

	d_instantiate(dentry, inode);
	write_lock(&entries_lock);
	list_add(&e->list, &entries);
	write_unlock(&entries_lock);

	err = 0;
out2:
	dput(dentry);
out:
	mutex_unlock(&root->d_inode->i_mutex);
	dput(root);

	if (err) {
		kfree(e);
		return -EINVAL;
	}
	return count;
}

static const struct file_operations bm_register_operations = {
	.write		= bm_register_write,
};

/* /status */

static ssize_t
bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
	char *s = enabled ? "enabled" : "disabled";

	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
}

static ssize_t bm_status_write(struct file * file, const char __user * buffer,
		size_t count, loff_t *ppos)
{
	int res = parse_command(buffer, count);
	struct dentry *root;

	switch (res) {
		case 1: enabled = 0; break;
		case 2: enabled = 1; break;
		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
			mutex_lock(&root->d_inode->i_mutex);

			while (!list_empty(&entries))
				kill_node(list_entry(entries.next, Node, list));

			mutex_unlock(&root->d_inode->i_mutex);
			dput(root);
		default: return res;
	}
	return count;
}

static const struct file_operations bm_status_operations = {
	.read		= bm_status_read,
	.write		= bm_status_write,
};

/* Superblock handling */

static const struct super_operations s_ops = {
	.statfs		= simple_statfs,
	.clear_inode	= bm_clear_inode,
};

static int bm_fill_super(struct super_block * sb, void * data, int silent)
{
	static struct tree_descr bm_files[] = {
		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
		[3] = {"register", &bm_register_operations, S_IWUSR},
		/* last one */ {""}
	};
	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
	if (!err)
		sb->s_op = &s_ops;
	return err;
}

static int bm_get_sb(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
	return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
}

static struct linux_binfmt misc_format = {
	.module = THIS_MODULE,
	.load_binary = load_misc_binary,
};

static struct file_system_type bm_fs_type = {
	.owner		= THIS_MODULE,
	.name		= "binfmt_misc",
	.get_sb		= bm_get_sb,
	.kill_sb	= kill_litter_super,
};

static int __init init_misc_binfmt(void)
{
	int err = register_filesystem(&bm_fs_type);
	if (!err) {
		err = register_binfmt(&misc_format);
		if (err)
			unregister_filesystem(&bm_fs_type);
	}
	return err;
}

static void __exit exit_misc_binfmt(void)
{
	unregister_binfmt(&misc_format);
	unregister_filesystem(&bm_fs_type);
}

core_initcall(init_misc_binfmt);
module_exit(exit_misc_binfmt);
MODULE_LICENSE("GPL");