xref: /openbmc/linux/fs/binfmt_misc.c (revision bf3608f3) 
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * binfmt_misc.c
4  *
5  * Copyright (C) 1997 Richard Günther
6  *
7  * binfmt_misc detects binaries via a magic or filename extension and invokes
8  * a specified wrapper. See Documentation/admin-guide/binfmt-misc.rst for more details.
9  */
10 
11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
12 
13 #include <linux/kernel.h>
14 #include <linux/module.h>
15 #include <linux/init.h>
16 #include <linux/sched/mm.h>
17 #include <linux/magic.h>
18 #include <linux/binfmts.h>
19 #include <linux/slab.h>
20 #include <linux/ctype.h>
21 #include <linux/string_helpers.h>
22 #include <linux/file.h>
23 #include <linux/pagemap.h>
24 #include <linux/namei.h>
25 #include <linux/mount.h>
26 #include <linux/fs_context.h>
27 #include <linux/syscalls.h>
28 #include <linux/fs.h>
29 #include <linux/uaccess.h>
30 
31 #include "internal.h"
32 
33 #ifdef DEBUG
34 # define USE_DEBUG 1
35 #else
36 # define USE_DEBUG 0
37 #endif
38 
39 enum {
40 	VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
41 };
42 
43 static LIST_HEAD(entries);
44 static int enabled = 1;
45 
46 enum {Enabled, Magic};
47 #define MISC_FMT_PRESERVE_ARGV0 (1 << 31)
48 #define MISC_FMT_OPEN_BINARY (1 << 30)
49 #define MISC_FMT_CREDENTIALS (1 << 29)
50 #define MISC_FMT_OPEN_FILE (1 << 28)
51 
52 typedef struct {
53 	struct list_head list;
54 	unsigned long flags;		/* type, status, etc. */
55 	int offset;			/* offset of magic */
56 	int size;			/* size of magic/mask */
57 	char *magic;			/* magic or filename extension */
58 	char *mask;			/* mask, NULL for exact match */
59 	const char *interpreter;	/* filename of interpreter */
60 	char *name;
61 	struct dentry *dentry;
62 	struct file *interp_file;
63 } Node;
64 
65 static DEFINE_RWLOCK(entries_lock);
66 static struct file_system_type bm_fs_type;
67 static struct vfsmount *bm_mnt;
68 static int entry_count;
69 
70 /*
71  * Max length of the register string.  Determined by:
72  *  - 7 delimiters
73  *  - name:   ~50 bytes
74  *  - type:   1 byte
75  *  - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
76  *  - magic:  128 bytes (512 in escaped form)
77  *  - mask:   128 bytes (512 in escaped form)
78  *  - interp: ~50 bytes
79  *  - flags:  5 bytes
80  * Round that up a bit, and then back off to hold the internal data
81  * (like struct Node).
82  */
83 #define MAX_REGISTER_LENGTH 1920
84 
85 /*
86  * Check if we support the binfmt
87  * if we do, return the node, else NULL
88  * locking is done in load_misc_binary
89  */
90 static Node *check_file(struct linux_binprm *bprm)
91 {
92 	char *p = strrchr(bprm->interp, '.');
93 	struct list_head *l;
94 
95 	/* Walk all the registered handlers. */
96 	list_for_each(l, &entries) {
97 		Node *e = list_entry(l, Node, list);
98 		char *s;
99 		int j;
100 
101 		/* Make sure this one is currently enabled. */
102 		if (!test_bit(Enabled, &e->flags))
103 			continue;
104 
105 		/* Do matching based on extension if applicable. */
106 		if (!test_bit(Magic, &e->flags)) {
107 			if (p && !strcmp(e->magic, p + 1))
108 				return e;
109 			continue;
110 		}
111 
112 		/* Do matching based on magic & mask. */
113 		s = bprm->buf + e->offset;
114 		if (e->mask) {
115 			for (j = 0; j < e->size; j++)
116 				if ((*s++ ^ e->magic[j]) & e->mask[j])
117 					break;
118 		} else {
119 			for (j = 0; j < e->size; j++)
120 				if ((*s++ ^ e->magic[j]))
121 					break;
122 		}
123 		if (j == e->size)
124 			return e;
125 	}
126 	return NULL;
127 }
128 
129 /*
130  * the loader itself
131  */
132 static int load_misc_binary(struct linux_binprm *bprm)
133 {
134 	Node *fmt;
135 	struct file *interp_file = NULL;
136 	int retval;
137 
138 	retval = -ENOEXEC;
139 	if (!enabled)
140 		return retval;
141 
142 	/* to keep locking time low, we copy the interpreter string */
143 	read_lock(&entries_lock);
144 	fmt = check_file(bprm);
145 	if (fmt)
146 		dget(fmt->dentry);
147 	read_unlock(&entries_lock);
148 	if (!fmt)
149 		return retval;
150 
151 	/* Need to be able to load the file after exec */
152 	retval = -ENOENT;
153 	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
154 		goto ret;
155 
156 	if (fmt->flags & MISC_FMT_PRESERVE_ARGV0) {
157 		bprm->interp_flags |= BINPRM_FLAGS_PRESERVE_ARGV0;
158 	} else {
159 		retval = remove_arg_zero(bprm);
160 		if (retval)
161 			goto ret;
162 	}
163 
164 	if (fmt->flags & MISC_FMT_OPEN_BINARY)
165 		bprm->have_execfd = 1;
166 
167 	/* make argv[1] be the path to the binary */
168 	retval = copy_string_kernel(bprm->interp, bprm);
169 	if (retval < 0)
170 		goto ret;
171 	bprm->argc++;
172 
173 	/* add the interp as argv[0] */
174 	retval = copy_string_kernel(fmt->interpreter, bprm);
175 	if (retval < 0)
176 		goto ret;
177 	bprm->argc++;
178 
179 	/* Update interp in case binfmt_script needs it. */
180 	retval = bprm_change_interp(fmt->interpreter, bprm);
181 	if (retval < 0)
182 		goto ret;
183 
184 	if (fmt->flags & MISC_FMT_OPEN_FILE) {
185 		interp_file = file_clone_open(fmt->interp_file);
186 		if (!IS_ERR(interp_file))
187 			deny_write_access(interp_file);
188 	} else {
189 		interp_file = open_exec(fmt->interpreter);
190 	}
191 	retval = PTR_ERR(interp_file);
192 	if (IS_ERR(interp_file))
193 		goto ret;
194 
195 	bprm->interpreter = interp_file;
196 	if (fmt->flags & MISC_FMT_CREDENTIALS)
197 		bprm->execfd_creds = 1;
198 
199 	retval = 0;
200 ret:
201 	dput(fmt->dentry);
202 	return retval;
203 }
204 
205 /* Command parsers */
206 
207 /*
208  * parses and copies one argument enclosed in del from *sp to *dp,
209  * recognising the \x special.
210  * returns pointer to the copied argument or NULL in case of an
211  * error (and sets err) or null argument length.
212  */
213 static char *scanarg(char *s, char del)
214 {
215 	char c;
216 
217 	while ((c = *s++) != del) {
218 		if (c == '\\' && *s == 'x') {
219 			s++;
220 			if (!isxdigit(*s++))
221 				return NULL;
222 			if (!isxdigit(*s++))
223 				return NULL;
224 		}
225 	}
226 	s[-1] ='\0';
227 	return s;
228 }
229 
230 static char *check_special_flags(char *sfs, Node *e)
231 {
232 	char *p = sfs;
233 	int cont = 1;
234 
235 	/* special flags */
236 	while (cont) {
237 		switch (*p) {
238 		case 'P':
239 			pr_debug("register: flag: P (preserve argv0)\n");
240 			p++;
241 			e->flags |= MISC_FMT_PRESERVE_ARGV0;
242 			break;
243 		case 'O':
244 			pr_debug("register: flag: O (open binary)\n");
245 			p++;
246 			e->flags |= MISC_FMT_OPEN_BINARY;
247 			break;
248 		case 'C':
249 			pr_debug("register: flag: C (preserve creds)\n");
250 			p++;
251 			/* this flags also implies the
252 			   open-binary flag */
253 			e->flags |= (MISC_FMT_CREDENTIALS |
254 					MISC_FMT_OPEN_BINARY);
255 			break;
256 		case 'F':
257 			pr_debug("register: flag: F: open interpreter file now\n");
258 			p++;
259 			e->flags |= MISC_FMT_OPEN_FILE;
260 			break;
261 		default:
262 			cont = 0;
263 		}
264 	}
265 
266 	return p;
267 }
268 
269 /*
270  * This registers a new binary format, it recognises the syntax
271  * ':name:type:offset:magic:mask:interpreter:flags'
272  * where the ':' is the IFS, that can be chosen with the first char
273  */
274 static Node *create_entry(const char __user *buffer, size_t count)
275 {
276 	Node *e;
277 	int memsize, err;
278 	char *buf, *p;
279 	char del;
280 
281 	pr_debug("register: received %zu bytes\n", count);
282 
283 	/* some sanity checks */
284 	err = -EINVAL;
285 	if ((count < 11) || (count > MAX_REGISTER_LENGTH))
286 		goto out;
287 
288 	err = -ENOMEM;
289 	memsize = sizeof(Node) + count + 8;
290 	e = kmalloc(memsize, GFP_KERNEL);
291 	if (!e)
292 		goto out;
293 
294 	p = buf = (char *)e + sizeof(Node);
295 
296 	memset(e, 0, sizeof(Node));
297 	if (copy_from_user(buf, buffer, count))
298 		goto efault;
299 
300 	del = *p++;	/* delimeter */
301 
302 	pr_debug("register: delim: %#x {%c}\n", del, del);
303 
304 	/* Pad the buffer with the delim to simplify parsing below. */
305 	memset(buf + count, del, 8);
306 
307 	/* Parse the 'name' field. */
308 	e->name = p;
309 	p = strchr(p, del);
310 	if (!p)
311 		goto einval;
312 	*p++ = '\0';
313 	if (!e->name[0] ||
314 	    !strcmp(e->name, ".") ||
315 	    !strcmp(e->name, "..") ||
316 	    strchr(e->name, '/'))
317 		goto einval;
318 
319 	pr_debug("register: name: {%s}\n", e->name);
320 
321 	/* Parse the 'type' field. */
322 	switch (*p++) {
323 	case 'E':
324 		pr_debug("register: type: E (extension)\n");
325 		e->flags = 1 << Enabled;
326 		break;
327 	case 'M':
328 		pr_debug("register: type: M (magic)\n");
329 		e->flags = (1 << Enabled) | (1 << Magic);
330 		break;
331 	default:
332 		goto einval;
333 	}
334 	if (*p++ != del)
335 		goto einval;
336 
337 	if (test_bit(Magic, &e->flags)) {
338 		/* Handle the 'M' (magic) format. */
339 		char *s;
340 
341 		/* Parse the 'offset' field. */
342 		s = strchr(p, del);
343 		if (!s)
344 			goto einval;
345 		*s = '\0';
346 		if (p != s) {
347 			int r = kstrtoint(p, 10, &e->offset);
348 			if (r != 0 || e->offset < 0)
349 				goto einval;
350 		}
351 		p = s;
352 		if (*p++)
353 			goto einval;
354 		pr_debug("register: offset: %#x\n", e->offset);
355 
356 		/* Parse the 'magic' field. */
357 		e->magic = p;
358 		p = scanarg(p, del);
359 		if (!p)
360 			goto einval;
361 		if (!e->magic[0])
362 			goto einval;
363 		if (USE_DEBUG)
364 			print_hex_dump_bytes(
365 				KBUILD_MODNAME ": register: magic[raw]: ",
366 				DUMP_PREFIX_NONE, e->magic, p - e->magic);
367 
368 		/* Parse the 'mask' field. */
369 		e->mask = p;
370 		p = scanarg(p, del);
371 		if (!p)
372 			goto einval;
373 		if (!e->mask[0]) {
374 			e->mask = NULL;
375 			pr_debug("register:  mask[raw]: none\n");
376 		} else if (USE_DEBUG)
377 			print_hex_dump_bytes(
378 				KBUILD_MODNAME ": register:  mask[raw]: ",
379 				DUMP_PREFIX_NONE, e->mask, p - e->mask);
380 
381 		/*
382 		 * Decode the magic & mask fields.
383 		 * Note: while we might have accepted embedded NUL bytes from
384 		 * above, the unescape helpers here will stop at the first one
385 		 * it encounters.
386 		 */
387 		e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
388 		if (e->mask &&
389 		    string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
390 			goto einval;
391 		if (e->size > BINPRM_BUF_SIZE ||
392 		    BINPRM_BUF_SIZE - e->size < e->offset)
393 			goto einval;
394 		pr_debug("register: magic/mask length: %i\n", e->size);
395 		if (USE_DEBUG) {
396 			print_hex_dump_bytes(
397 				KBUILD_MODNAME ": register: magic[decoded]: ",
398 				DUMP_PREFIX_NONE, e->magic, e->size);
399 
400 			if (e->mask) {
401 				int i;
402 				char *masked = kmalloc(e->size, GFP_KERNEL);
403 
404 				print_hex_dump_bytes(
405 					KBUILD_MODNAME ": register:  mask[decoded]: ",
406 					DUMP_PREFIX_NONE, e->mask, e->size);
407 
408 				if (masked) {
409 					for (i = 0; i < e->size; ++i)
410 						masked[i] = e->magic[i] & e->mask[i];
411 					print_hex_dump_bytes(
412 						KBUILD_MODNAME ": register:  magic[masked]: ",
413 						DUMP_PREFIX_NONE, masked, e->size);
414 
415 					kfree(masked);
416 				}
417 			}
418 		}
419 	} else {
420 		/* Handle the 'E' (extension) format. */
421 
422 		/* Skip the 'offset' field. */
423 		p = strchr(p, del);
424 		if (!p)
425 			goto einval;
426 		*p++ = '\0';
427 
428 		/* Parse the 'magic' field. */
429 		e->magic = p;
430 		p = strchr(p, del);
431 		if (!p)
432 			goto einval;
433 		*p++ = '\0';
434 		if (!e->magic[0] || strchr(e->magic, '/'))
435 			goto einval;
436 		pr_debug("register: extension: {%s}\n", e->magic);
437 
438 		/* Skip the 'mask' field. */
439 		p = strchr(p, del);
440 		if (!p)
441 			goto einval;
442 		*p++ = '\0';
443 	}
444 
445 	/* Parse the 'interpreter' field. */
446 	e->interpreter = p;
447 	p = strchr(p, del);
448 	if (!p)
449 		goto einval;
450 	*p++ = '\0';
451 	if (!e->interpreter[0])
452 		goto einval;
453 	pr_debug("register: interpreter: {%s}\n", e->interpreter);
454 
455 	/* Parse the 'flags' field. */
456 	p = check_special_flags(p, e);
457 	if (*p == '\n')
458 		p++;
459 	if (p != buf + count)
460 		goto einval;
461 
462 	return e;
463 
464 out:
465 	return ERR_PTR(err);
466 
467 efault:
468 	kfree(e);
469 	return ERR_PTR(-EFAULT);
470 einval:
471 	kfree(e);
472 	return ERR_PTR(-EINVAL);
473 }
474 
475 /*
476  * Set status of entry/binfmt_misc:
477  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
478  */
479 static int parse_command(const char __user *buffer, size_t count)
480 {
481 	char s[4];
482 
483 	if (count > 3)
484 		return -EINVAL;
485 	if (copy_from_user(s, buffer, count))
486 		return -EFAULT;
487 	if (!count)
488 		return 0;
489 	if (s[count - 1] == '\n')
490 		count--;
491 	if (count == 1 && s[0] == '0')
492 		return 1;
493 	if (count == 1 && s[0] == '1')
494 		return 2;
495 	if (count == 2 && s[0] == '-' && s[1] == '1')
496 		return 3;
497 	return -EINVAL;
498 }
499 
500 /* generic stuff */
501 
502 static void entry_status(Node *e, char *page)
503 {
504 	char *dp = page;
505 	const char *status = "disabled";
506 
507 	if (test_bit(Enabled, &e->flags))
508 		status = "enabled";
509 
510 	if (!VERBOSE_STATUS) {
511 		sprintf(page, "%s\n", status);
512 		return;
513 	}
514 
515 	dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
516 
517 	/* print the special flags */
518 	dp += sprintf(dp, "flags: ");
519 	if (e->flags & MISC_FMT_PRESERVE_ARGV0)
520 		*dp++ = 'P';
521 	if (e->flags & MISC_FMT_OPEN_BINARY)
522 		*dp++ = 'O';
523 	if (e->flags & MISC_FMT_CREDENTIALS)
524 		*dp++ = 'C';
525 	if (e->flags & MISC_FMT_OPEN_FILE)
526 		*dp++ = 'F';
527 	*dp++ = '\n';
528 
529 	if (!test_bit(Magic, &e->flags)) {
530 		sprintf(dp, "extension .%s\n", e->magic);
531 	} else {
532 		dp += sprintf(dp, "offset %i\nmagic ", e->offset);
533 		dp = bin2hex(dp, e->magic, e->size);
534 		if (e->mask) {
535 			dp += sprintf(dp, "\nmask ");
536 			dp = bin2hex(dp, e->mask, e->size);
537 		}
538 		*dp++ = '\n';
539 		*dp = '\0';
540 	}
541 }
542 
543 static struct inode *bm_get_inode(struct super_block *sb, int mode)
544 {
545 	struct inode *inode = new_inode(sb);
546 
547 	if (inode) {
548 		inode->i_ino = get_next_ino();
549 		inode->i_mode = mode;
550 		inode->i_atime = inode->i_mtime = inode->i_ctime =
551 			current_time(inode);
552 	}
553 	return inode;
554 }
555 
556 static void bm_evict_inode(struct inode *inode)
557 {
558 	Node *e = inode->i_private;
559 
560 	if (e && e->flags & MISC_FMT_OPEN_FILE)
561 		filp_close(e->interp_file, NULL);
562 
563 	clear_inode(inode);
564 	kfree(e);
565 }
566 
567 static void kill_node(Node *e)
568 {
569 	struct dentry *dentry;
570 
571 	write_lock(&entries_lock);
572 	list_del_init(&e->list);
573 	write_unlock(&entries_lock);
574 
575 	dentry = e->dentry;
576 	drop_nlink(d_inode(dentry));
577 	d_drop(dentry);
578 	dput(dentry);
579 	simple_release_fs(&bm_mnt, &entry_count);
580 }
581 
582 /* /<entry> */
583 
584 static ssize_t
585 bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
586 {
587 	Node *e = file_inode(file)->i_private;
588 	ssize_t res;
589 	char *page;
590 
591 	page = (char *) __get_free_page(GFP_KERNEL);
592 	if (!page)
593 		return -ENOMEM;
594 
595 	entry_status(e, page);
596 
597 	res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
598 
599 	free_page((unsigned long) page);
600 	return res;
601 }
602 
603 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
604 				size_t count, loff_t *ppos)
605 {
606 	struct dentry *root;
607 	Node *e = file_inode(file)->i_private;
608 	int res = parse_command(buffer, count);
609 
610 	switch (res) {
611 	case 1:
612 		/* Disable this handler. */
613 		clear_bit(Enabled, &e->flags);
614 		break;
615 	case 2:
616 		/* Enable this handler. */
617 		set_bit(Enabled, &e->flags);
618 		break;
619 	case 3:
620 		/* Delete this handler. */
621 		root = file_inode(file)->i_sb->s_root;
622 		inode_lock(d_inode(root));
623 
624 		if (!list_empty(&e->list))
625 			kill_node(e);
626 
627 		inode_unlock(d_inode(root));
628 		break;
629 	default:
630 		return res;
631 	}
632 
633 	return count;
634 }
635 
636 static const struct file_operations bm_entry_operations = {
637 	.read		= bm_entry_read,
638 	.write		= bm_entry_write,
639 	.llseek		= default_llseek,
640 };
641 
642 /* /register */
643 
644 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
645 			       size_t count, loff_t *ppos)
646 {
647 	Node *e;
648 	struct inode *inode;
649 	struct super_block *sb = file_inode(file)->i_sb;
650 	struct dentry *root = sb->s_root, *dentry;
651 	int err = 0;
652 	struct file *f = NULL;
653 
654 	e = create_entry(buffer, count);
655 
656 	if (IS_ERR(e))
657 		return PTR_ERR(e);
658 
659 	if (e->flags & MISC_FMT_OPEN_FILE) {
660 		f = open_exec(e->interpreter);
661 		if (IS_ERR(f)) {
662 			pr_notice("register: failed to install interpreter file %s\n",
663 				 e->interpreter);
664 			kfree(e);
665 			return PTR_ERR(f);
666 		}
667 		e->interp_file = f;
668 	}
669 
670 	inode_lock(d_inode(root));
671 	dentry = lookup_one_len(e->name, root, strlen(e->name));
672 	err = PTR_ERR(dentry);
673 	if (IS_ERR(dentry))
674 		goto out;
675 
676 	err = -EEXIST;
677 	if (d_really_is_positive(dentry))
678 		goto out2;
679 
680 	inode = bm_get_inode(sb, S_IFREG | 0644);
681 
682 	err = -ENOMEM;
683 	if (!inode)
684 		goto out2;
685 
686 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
687 	if (err) {
688 		iput(inode);
689 		inode = NULL;
690 		goto out2;
691 	}
692 
693 	e->dentry = dget(dentry);
694 	inode->i_private = e;
695 	inode->i_fop = &bm_entry_operations;
696 
697 	d_instantiate(dentry, inode);
698 	write_lock(&entries_lock);
699 	list_add(&e->list, &entries);
700 	write_unlock(&entries_lock);
701 
702 	err = 0;
703 out2:
704 	dput(dentry);
705 out:
706 	inode_unlock(d_inode(root));
707 
708 	if (err) {
709 		if (f)
710 			filp_close(f, NULL);
711 		kfree(e);
712 		return err;
713 	}
714 	return count;
715 }
716 
717 static const struct file_operations bm_register_operations = {
718 	.write		= bm_register_write,
719 	.llseek		= noop_llseek,
720 };
721 
722 /* /status */
723 
724 static ssize_t
725 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
726 {
727 	char *s = enabled ? "enabled\n" : "disabled\n";
728 
729 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
730 }
731 
732 static ssize_t bm_status_write(struct file *file, const char __user *buffer,
733 		size_t count, loff_t *ppos)
734 {
735 	int res = parse_command(buffer, count);
736 	struct dentry *root;
737 
738 	switch (res) {
739 	case 1:
740 		/* Disable all handlers. */
741 		enabled = 0;
742 		break;
743 	case 2:
744 		/* Enable all handlers. */
745 		enabled = 1;
746 		break;
747 	case 3:
748 		/* Delete all handlers. */
749 		root = file_inode(file)->i_sb->s_root;
750 		inode_lock(d_inode(root));
751 
752 		while (!list_empty(&entries))
753 			kill_node(list_first_entry(&entries, Node, list));
754 
755 		inode_unlock(d_inode(root));
756 		break;
757 	default:
758 		return res;
759 	}
760 
761 	return count;
762 }
763 
764 static const struct file_operations bm_status_operations = {
765 	.read		= bm_status_read,
766 	.write		= bm_status_write,
767 	.llseek		= default_llseek,
768 };
769 
770 /* Superblock handling */
771 
772 static const struct super_operations s_ops = {
773 	.statfs		= simple_statfs,
774 	.evict_inode	= bm_evict_inode,
775 };
776 
777 static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
778 {
779 	int err;
780 	static const struct tree_descr bm_files[] = {
781 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
782 		[3] = {"register", &bm_register_operations, S_IWUSR},
783 		/* last one */ {""}
784 	};
785 
786 	err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
787 	if (!err)
788 		sb->s_op = &s_ops;
789 	return err;
790 }
791 
792 static int bm_get_tree(struct fs_context *fc)
793 {
794 	return get_tree_single(fc, bm_fill_super);
795 }
796 
797 static const struct fs_context_operations bm_context_ops = {
798 	.get_tree	= bm_get_tree,
799 };
800 
801 static int bm_init_fs_context(struct fs_context *fc)
802 {
803 	fc->ops = &bm_context_ops;
804 	return 0;
805 }
806 
807 static struct linux_binfmt misc_format = {
808 	.module = THIS_MODULE,
809 	.load_binary = load_misc_binary,
810 };
811 
812 static struct file_system_type bm_fs_type = {
813 	.owner		= THIS_MODULE,
814 	.name		= "binfmt_misc",
815 	.init_fs_context = bm_init_fs_context,
816 	.kill_sb	= kill_litter_super,
817 };
818 MODULE_ALIAS_FS("binfmt_misc");
819 
820 static struct ctl_table_header *binfmt_misc_header;
821 
822 static int __init init_misc_binfmt(void)
823 {
824 	int err = register_filesystem(&bm_fs_type);
825 	if (!err)
826 		insert_binfmt(&misc_format);
827 	binfmt_misc_header = register_sysctl_mount_point("fs/binfmt_misc");
828 	return 0;
829 }
830 
831 static void __exit exit_misc_binfmt(void)
832 {
833 	unregister_sysctl_table(binfmt_misc_header);
834 	unregister_binfmt(&misc_format);
835 	unregister_filesystem(&bm_fs_type);
836 }
837 
838 core_initcall(init_misc_binfmt);
839 module_exit(exit_misc_binfmt);
840 MODULE_LICENSE("GPL");
841