xref: /openbmc/linux/fs/binfmt_misc.c (revision bc2bf338) 
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 		retval = remove_arg_zero(bprm);
158 		if (retval)
159 			goto ret;
160 	}
161 
162 	if (fmt->flags & MISC_FMT_OPEN_BINARY)
163 		bprm->have_execfd = 1;
164 
165 	/* make argv[1] be the path to the binary */
166 	retval = copy_strings_kernel(1, &bprm->interp, bprm);
167 	if (retval < 0)
168 		goto ret;
169 	bprm->argc++;
170 
171 	/* add the interp as argv[0] */
172 	retval = copy_strings_kernel(1, &fmt->interpreter, bprm);
173 	if (retval < 0)
174 		goto ret;
175 	bprm->argc++;
176 
177 	/* Update interp in case binfmt_script needs it. */
178 	retval = bprm_change_interp(fmt->interpreter, bprm);
179 	if (retval < 0)
180 		goto ret;
181 
182 	if (fmt->flags & MISC_FMT_OPEN_FILE) {
183 		interp_file = file_clone_open(fmt->interp_file);
184 		if (!IS_ERR(interp_file))
185 			deny_write_access(interp_file);
186 	} else {
187 		interp_file = open_exec(fmt->interpreter);
188 	}
189 	retval = PTR_ERR(interp_file);
190 	if (IS_ERR(interp_file))
191 		goto ret;
192 
193 	bprm->interpreter = interp_file;
194 	if (fmt->flags & MISC_FMT_CREDENTIALS)
195 		bprm->preserve_creds = 1;
196 
197 	retval = 0;
198 ret:
199 	dput(fmt->dentry);
200 	return retval;
201 }
202 
203 /* Command parsers */
204 
205 /*
206  * parses and copies one argument enclosed in del from *sp to *dp,
207  * recognising the \x special.
208  * returns pointer to the copied argument or NULL in case of an
209  * error (and sets err) or null argument length.
210  */
211 static char *scanarg(char *s, char del)
212 {
213 	char c;
214 
215 	while ((c = *s++) != del) {
216 		if (c == '\\' && *s == 'x') {
217 			s++;
218 			if (!isxdigit(*s++))
219 				return NULL;
220 			if (!isxdigit(*s++))
221 				return NULL;
222 		}
223 	}
224 	s[-1] ='\0';
225 	return s;
226 }
227 
228 static char *check_special_flags(char *sfs, Node *e)
229 {
230 	char *p = sfs;
231 	int cont = 1;
232 
233 	/* special flags */
234 	while (cont) {
235 		switch (*p) {
236 		case 'P':
237 			pr_debug("register: flag: P (preserve argv0)\n");
238 			p++;
239 			e->flags |= MISC_FMT_PRESERVE_ARGV0;
240 			break;
241 		case 'O':
242 			pr_debug("register: flag: O (open binary)\n");
243 			p++;
244 			e->flags |= MISC_FMT_OPEN_BINARY;
245 			break;
246 		case 'C':
247 			pr_debug("register: flag: C (preserve creds)\n");
248 			p++;
249 			/* this flags also implies the
250 			   open-binary flag */
251 			e->flags |= (MISC_FMT_CREDENTIALS |
252 					MISC_FMT_OPEN_BINARY);
253 			break;
254 		case 'F':
255 			pr_debug("register: flag: F: open interpreter file now\n");
256 			p++;
257 			e->flags |= MISC_FMT_OPEN_FILE;
258 			break;
259 		default:
260 			cont = 0;
261 		}
262 	}
263 
264 	return p;
265 }
266 
267 /*
268  * This registers a new binary format, it recognises the syntax
269  * ':name:type:offset:magic:mask:interpreter:flags'
270  * where the ':' is the IFS, that can be chosen with the first char
271  */
272 static Node *create_entry(const char __user *buffer, size_t count)
273 {
274 	Node *e;
275 	int memsize, err;
276 	char *buf, *p;
277 	char del;
278 
279 	pr_debug("register: received %zu bytes\n", count);
280 
281 	/* some sanity checks */
282 	err = -EINVAL;
283 	if ((count < 11) || (count > MAX_REGISTER_LENGTH))
284 		goto out;
285 
286 	err = -ENOMEM;
287 	memsize = sizeof(Node) + count + 8;
288 	e = kmalloc(memsize, GFP_KERNEL);
289 	if (!e)
290 		goto out;
291 
292 	p = buf = (char *)e + sizeof(Node);
293 
294 	memset(e, 0, sizeof(Node));
295 	if (copy_from_user(buf, buffer, count))
296 		goto efault;
297 
298 	del = *p++;	/* delimeter */
299 
300 	pr_debug("register: delim: %#x {%c}\n", del, del);
301 
302 	/* Pad the buffer with the delim to simplify parsing below. */
303 	memset(buf + count, del, 8);
304 
305 	/* Parse the 'name' field. */
306 	e->name = p;
307 	p = strchr(p, del);
308 	if (!p)
309 		goto einval;
310 	*p++ = '\0';
311 	if (!e->name[0] ||
312 	    !strcmp(e->name, ".") ||
313 	    !strcmp(e->name, "..") ||
314 	    strchr(e->name, '/'))
315 		goto einval;
316 
317 	pr_debug("register: name: {%s}\n", e->name);
318 
319 	/* Parse the 'type' field. */
320 	switch (*p++) {
321 	case 'E':
322 		pr_debug("register: type: E (extension)\n");
323 		e->flags = 1 << Enabled;
324 		break;
325 	case 'M':
326 		pr_debug("register: type: M (magic)\n");
327 		e->flags = (1 << Enabled) | (1 << Magic);
328 		break;
329 	default:
330 		goto einval;
331 	}
332 	if (*p++ != del)
333 		goto einval;
334 
335 	if (test_bit(Magic, &e->flags)) {
336 		/* Handle the 'M' (magic) format. */
337 		char *s;
338 
339 		/* Parse the 'offset' field. */
340 		s = strchr(p, del);
341 		if (!s)
342 			goto einval;
343 		*s = '\0';
344 		if (p != s) {
345 			int r = kstrtoint(p, 10, &e->offset);
346 			if (r != 0 || e->offset < 0)
347 				goto einval;
348 		}
349 		p = s;
350 		if (*p++)
351 			goto einval;
352 		pr_debug("register: offset: %#x\n", e->offset);
353 
354 		/* Parse the 'magic' field. */
355 		e->magic = p;
356 		p = scanarg(p, del);
357 		if (!p)
358 			goto einval;
359 		if (!e->magic[0])
360 			goto einval;
361 		if (USE_DEBUG)
362 			print_hex_dump_bytes(
363 				KBUILD_MODNAME ": register: magic[raw]: ",
364 				DUMP_PREFIX_NONE, e->magic, p - e->magic);
365 
366 		/* Parse the 'mask' field. */
367 		e->mask = p;
368 		p = scanarg(p, del);
369 		if (!p)
370 			goto einval;
371 		if (!e->mask[0]) {
372 			e->mask = NULL;
373 			pr_debug("register:  mask[raw]: none\n");
374 		} else if (USE_DEBUG)
375 			print_hex_dump_bytes(
376 				KBUILD_MODNAME ": register:  mask[raw]: ",
377 				DUMP_PREFIX_NONE, e->mask, p - e->mask);
378 
379 		/*
380 		 * Decode the magic & mask fields.
381 		 * Note: while we might have accepted embedded NUL bytes from
382 		 * above, the unescape helpers here will stop at the first one
383 		 * it encounters.
384 		 */
385 		e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
386 		if (e->mask &&
387 		    string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
388 			goto einval;
389 		if (e->size > BINPRM_BUF_SIZE ||
390 		    BINPRM_BUF_SIZE - e->size < e->offset)
391 			goto einval;
392 		pr_debug("register: magic/mask length: %i\n", e->size);
393 		if (USE_DEBUG) {
394 			print_hex_dump_bytes(
395 				KBUILD_MODNAME ": register: magic[decoded]: ",
396 				DUMP_PREFIX_NONE, e->magic, e->size);
397 
398 			if (e->mask) {
399 				int i;
400 				char *masked = kmalloc(e->size, GFP_KERNEL);
401 
402 				print_hex_dump_bytes(
403 					KBUILD_MODNAME ": register:  mask[decoded]: ",
404 					DUMP_PREFIX_NONE, e->mask, e->size);
405 
406 				if (masked) {
407 					for (i = 0; i < e->size; ++i)
408 						masked[i] = e->magic[i] & e->mask[i];
409 					print_hex_dump_bytes(
410 						KBUILD_MODNAME ": register:  magic[masked]: ",
411 						DUMP_PREFIX_NONE, masked, e->size);
412 
413 					kfree(masked);
414 				}
415 			}
416 		}
417 	} else {
418 		/* Handle the 'E' (extension) format. */
419 
420 		/* Skip the 'offset' field. */
421 		p = strchr(p, del);
422 		if (!p)
423 			goto einval;
424 		*p++ = '\0';
425 
426 		/* Parse the 'magic' field. */
427 		e->magic = p;
428 		p = strchr(p, del);
429 		if (!p)
430 			goto einval;
431 		*p++ = '\0';
432 		if (!e->magic[0] || strchr(e->magic, '/'))
433 			goto einval;
434 		pr_debug("register: extension: {%s}\n", e->magic);
435 
436 		/* Skip the 'mask' field. */
437 		p = strchr(p, del);
438 		if (!p)
439 			goto einval;
440 		*p++ = '\0';
441 	}
442 
443 	/* Parse the 'interpreter' field. */
444 	e->interpreter = p;
445 	p = strchr(p, del);
446 	if (!p)
447 		goto einval;
448 	*p++ = '\0';
449 	if (!e->interpreter[0])
450 		goto einval;
451 	pr_debug("register: interpreter: {%s}\n", e->interpreter);
452 
453 	/* Parse the 'flags' field. */
454 	p = check_special_flags(p, e);
455 	if (*p == '\n')
456 		p++;
457 	if (p != buf + count)
458 		goto einval;
459 
460 	return e;
461 
462 out:
463 	return ERR_PTR(err);
464 
465 efault:
466 	kfree(e);
467 	return ERR_PTR(-EFAULT);
468 einval:
469 	kfree(e);
470 	return ERR_PTR(-EINVAL);
471 }
472 
473 /*
474  * Set status of entry/binfmt_misc:
475  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
476  */
477 static int parse_command(const char __user *buffer, size_t count)
478 {
479 	char s[4];
480 
481 	if (count > 3)
482 		return -EINVAL;
483 	if (copy_from_user(s, buffer, count))
484 		return -EFAULT;
485 	if (!count)
486 		return 0;
487 	if (s[count - 1] == '\n')
488 		count--;
489 	if (count == 1 && s[0] == '0')
490 		return 1;
491 	if (count == 1 && s[0] == '1')
492 		return 2;
493 	if (count == 2 && s[0] == '-' && s[1] == '1')
494 		return 3;
495 	return -EINVAL;
496 }
497 
498 /* generic stuff */
499 
500 static void entry_status(Node *e, char *page)
501 {
502 	char *dp = page;
503 	const char *status = "disabled";
504 
505 	if (test_bit(Enabled, &e->flags))
506 		status = "enabled";
507 
508 	if (!VERBOSE_STATUS) {
509 		sprintf(page, "%s\n", status);
510 		return;
511 	}
512 
513 	dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
514 
515 	/* print the special flags */
516 	dp += sprintf(dp, "flags: ");
517 	if (e->flags & MISC_FMT_PRESERVE_ARGV0)
518 		*dp++ = 'P';
519 	if (e->flags & MISC_FMT_OPEN_BINARY)
520 		*dp++ = 'O';
521 	if (e->flags & MISC_FMT_CREDENTIALS)
522 		*dp++ = 'C';
523 	if (e->flags & MISC_FMT_OPEN_FILE)
524 		*dp++ = 'F';
525 	*dp++ = '\n';
526 
527 	if (!test_bit(Magic, &e->flags)) {
528 		sprintf(dp, "extension .%s\n", e->magic);
529 	} else {
530 		dp += sprintf(dp, "offset %i\nmagic ", e->offset);
531 		dp = bin2hex(dp, e->magic, e->size);
532 		if (e->mask) {
533 			dp += sprintf(dp, "\nmask ");
534 			dp = bin2hex(dp, e->mask, e->size);
535 		}
536 		*dp++ = '\n';
537 		*dp = '\0';
538 	}
539 }
540 
541 static struct inode *bm_get_inode(struct super_block *sb, int mode)
542 {
543 	struct inode *inode = new_inode(sb);
544 
545 	if (inode) {
546 		inode->i_ino = get_next_ino();
547 		inode->i_mode = mode;
548 		inode->i_atime = inode->i_mtime = inode->i_ctime =
549 			current_time(inode);
550 	}
551 	return inode;
552 }
553 
554 static void bm_evict_inode(struct inode *inode)
555 {
556 	Node *e = inode->i_private;
557 
558 	if (e && e->flags & MISC_FMT_OPEN_FILE)
559 		filp_close(e->interp_file, NULL);
560 
561 	clear_inode(inode);
562 	kfree(e);
563 }
564 
565 static void kill_node(Node *e)
566 {
567 	struct dentry *dentry;
568 
569 	write_lock(&entries_lock);
570 	list_del_init(&e->list);
571 	write_unlock(&entries_lock);
572 
573 	dentry = e->dentry;
574 	drop_nlink(d_inode(dentry));
575 	d_drop(dentry);
576 	dput(dentry);
577 	simple_release_fs(&bm_mnt, &entry_count);
578 }
579 
580 /* /<entry> */
581 
582 static ssize_t
583 bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
584 {
585 	Node *e = file_inode(file)->i_private;
586 	ssize_t res;
587 	char *page;
588 
589 	page = (char *) __get_free_page(GFP_KERNEL);
590 	if (!page)
591 		return -ENOMEM;
592 
593 	entry_status(e, page);
594 
595 	res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
596 
597 	free_page((unsigned long) page);
598 	return res;
599 }
600 
601 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
602 				size_t count, loff_t *ppos)
603 {
604 	struct dentry *root;
605 	Node *e = file_inode(file)->i_private;
606 	int res = parse_command(buffer, count);
607 
608 	switch (res) {
609 	case 1:
610 		/* Disable this handler. */
611 		clear_bit(Enabled, &e->flags);
612 		break;
613 	case 2:
614 		/* Enable this handler. */
615 		set_bit(Enabled, &e->flags);
616 		break;
617 	case 3:
618 		/* Delete this handler. */
619 		root = file_inode(file)->i_sb->s_root;
620 		inode_lock(d_inode(root));
621 
622 		if (!list_empty(&e->list))
623 			kill_node(e);
624 
625 		inode_unlock(d_inode(root));
626 		break;
627 	default:
628 		return res;
629 	}
630 
631 	return count;
632 }
633 
634 static const struct file_operations bm_entry_operations = {
635 	.read		= bm_entry_read,
636 	.write		= bm_entry_write,
637 	.llseek		= default_llseek,
638 };
639 
640 /* /register */
641 
642 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
643 			       size_t count, loff_t *ppos)
644 {
645 	Node *e;
646 	struct inode *inode;
647 	struct super_block *sb = file_inode(file)->i_sb;
648 	struct dentry *root = sb->s_root, *dentry;
649 	int err = 0;
650 
651 	e = create_entry(buffer, count);
652 
653 	if (IS_ERR(e))
654 		return PTR_ERR(e);
655 
656 	inode_lock(d_inode(root));
657 	dentry = lookup_one_len(e->name, root, strlen(e->name));
658 	err = PTR_ERR(dentry);
659 	if (IS_ERR(dentry))
660 		goto out;
661 
662 	err = -EEXIST;
663 	if (d_really_is_positive(dentry))
664 		goto out2;
665 
666 	inode = bm_get_inode(sb, S_IFREG | 0644);
667 
668 	err = -ENOMEM;
669 	if (!inode)
670 		goto out2;
671 
672 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
673 	if (err) {
674 		iput(inode);
675 		inode = NULL;
676 		goto out2;
677 	}
678 
679 	if (e->flags & MISC_FMT_OPEN_FILE) {
680 		struct file *f;
681 
682 		f = open_exec(e->interpreter);
683 		if (IS_ERR(f)) {
684 			err = PTR_ERR(f);
685 			pr_notice("register: failed to install interpreter file %s\n", e->interpreter);
686 			simple_release_fs(&bm_mnt, &entry_count);
687 			iput(inode);
688 			inode = NULL;
689 			goto out2;
690 		}
691 		e->interp_file = f;
692 	}
693 
694 	e->dentry = dget(dentry);
695 	inode->i_private = e;
696 	inode->i_fop = &bm_entry_operations;
697 
698 	d_instantiate(dentry, inode);
699 	write_lock(&entries_lock);
700 	list_add(&e->list, &entries);
701 	write_unlock(&entries_lock);
702 
703 	err = 0;
704 out2:
705 	dput(dentry);
706 out:
707 	inode_unlock(d_inode(root));
708 
709 	if (err) {
710 		kfree(e);
711 		return err;
712 	}
713 	return count;
714 }
715 
716 static const struct file_operations bm_register_operations = {
717 	.write		= bm_register_write,
718 	.llseek		= noop_llseek,
719 };
720 
721 /* /status */
722 
723 static ssize_t
724 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
725 {
726 	char *s = enabled ? "enabled\n" : "disabled\n";
727 
728 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
729 }
730 
731 static ssize_t bm_status_write(struct file *file, const char __user *buffer,
732 		size_t count, loff_t *ppos)
733 {
734 	int res = parse_command(buffer, count);
735 	struct dentry *root;
736 
737 	switch (res) {
738 	case 1:
739 		/* Disable all handlers. */
740 		enabled = 0;
741 		break;
742 	case 2:
743 		/* Enable all handlers. */
744 		enabled = 1;
745 		break;
746 	case 3:
747 		/* Delete all handlers. */
748 		root = file_inode(file)->i_sb->s_root;
749 		inode_lock(d_inode(root));
750 
751 		while (!list_empty(&entries))
752 			kill_node(list_first_entry(&entries, Node, list));
753 
754 		inode_unlock(d_inode(root));
755 		break;
756 	default:
757 		return res;
758 	}
759 
760 	return count;
761 }
762 
763 static const struct file_operations bm_status_operations = {
764 	.read		= bm_status_read,
765 	.write		= bm_status_write,
766 	.llseek		= default_llseek,
767 };
768 
769 /* Superblock handling */
770 
771 static const struct super_operations s_ops = {
772 	.statfs		= simple_statfs,
773 	.evict_inode	= bm_evict_inode,
774 };
775 
776 static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
777 {
778 	int err;
779 	static const struct tree_descr bm_files[] = {
780 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
781 		[3] = {"register", &bm_register_operations, S_IWUSR},
782 		/* last one */ {""}
783 	};
784 
785 	err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
786 	if (!err)
787 		sb->s_op = &s_ops;
788 	return err;
789 }
790 
791 static int bm_get_tree(struct fs_context *fc)
792 {
793 	return get_tree_single(fc, bm_fill_super);
794 }
795 
796 static const struct fs_context_operations bm_context_ops = {
797 	.get_tree	= bm_get_tree,
798 };
799 
800 static int bm_init_fs_context(struct fs_context *fc)
801 {
802 	fc->ops = &bm_context_ops;
803 	return 0;
804 }
805 
806 static struct linux_binfmt misc_format = {
807 	.module = THIS_MODULE,
808 	.load_binary = load_misc_binary,
809 };
810 
811 static struct file_system_type bm_fs_type = {
812 	.owner		= THIS_MODULE,
813 	.name		= "binfmt_misc",
814 	.init_fs_context = bm_init_fs_context,
815 	.kill_sb	= kill_litter_super,
816 };
817 MODULE_ALIAS_FS("binfmt_misc");
818 
819 static int __init init_misc_binfmt(void)
820 {
821 	int err = register_filesystem(&bm_fs_type);
822 	if (!err)
823 		insert_binfmt(&misc_format);
824 	return err;
825 }
826 
827 static void __exit exit_misc_binfmt(void)
828 {
829 	unregister_binfmt(&misc_format);
830 	unregister_filesystem(&bm_fs_type);
831 }
832 
833 core_initcall(init_misc_binfmt);
834 module_exit(exit_misc_binfmt);
835 MODULE_LICENSE("GPL");
836