xref: /linux/fs/binfmt_misc.c (revision 0d456bad36d42d16022be045c8a53ddbb59ee478) 
1 /*
2  *  binfmt_misc.c
3  *
4  *  Copyright (C) 1997 Richard Günther
5  *
6  *  binfmt_misc detects binaries via a magic or filename extension and invokes
7  *  a specified wrapper. This should obsolete binfmt_java, binfmt_em86 and
8  *  binfmt_mz.
9  *
10  *  1997-04-25 first version
11  *  [...]
12  *  1997-05-19 cleanup
13  *  1997-06-26 hpa: pass the real filename rather than argv[0]
14  *  1997-06-30 minor cleanup
15  *  1997-08-09 removed extension stripping, locking cleanup
16  *  2001-02-28 AV: rewritten into something that resembles C. Original didn't.
17  */
18 
19 #include <linux/module.h>
20 #include <linux/init.h>
21 #include <linux/sched.h>
22 #include <linux/magic.h>
23 #include <linux/binfmts.h>
24 #include <linux/slab.h>
25 #include <linux/ctype.h>
26 #include <linux/file.h>
27 #include <linux/pagemap.h>
28 #include <linux/namei.h>
29 #include <linux/mount.h>
30 #include <linux/syscalls.h>
31 #include <linux/fs.h>
32 
33 #include <asm/uaccess.h>
34 
35 enum {
36 	VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
37 };
38 
39 static LIST_HEAD(entries);
40 static int enabled = 1;
41 
42 enum {Enabled, Magic};
43 #define MISC_FMT_PRESERVE_ARGV0 (1<<31)
44 #define MISC_FMT_OPEN_BINARY (1<<30)
45 #define MISC_FMT_CREDENTIALS (1<<29)
46 
47 typedef struct {
48 	struct list_head list;
49 	unsigned long flags;		/* type, status, etc. */
50 	int offset;			/* offset of magic */
51 	int size;			/* size of magic/mask */
52 	char *magic;			/* magic or filename extension */
53 	char *mask;			/* mask, NULL for exact match */
54 	char *interpreter;		/* filename of interpreter */
55 	char *name;
56 	struct dentry *dentry;
57 } Node;
58 
59 static DEFINE_RWLOCK(entries_lock);
60 static struct file_system_type bm_fs_type;
61 static struct vfsmount *bm_mnt;
62 static int entry_count;
63 
64 /*
65  * Check if we support the binfmt
66  * if we do, return the node, else NULL
67  * locking is done in load_misc_binary
68  */
69 static Node *check_file(struct linux_binprm *bprm)
70 {
71 	char *p = strrchr(bprm->interp, '.');
72 	struct list_head *l;
73 
74 	list_for_each(l, &entries) {
75 		Node *e = list_entry(l, Node, list);
76 		char *s;
77 		int j;
78 
79 		if (!test_bit(Enabled, &e->flags))
80 			continue;
81 
82 		if (!test_bit(Magic, &e->flags)) {
83 			if (p && !strcmp(e->magic, p + 1))
84 				return e;
85 			continue;
86 		}
87 
88 		s = bprm->buf + e->offset;
89 		if (e->mask) {
90 			for (j = 0; j < e->size; j++)
91 				if ((*s++ ^ e->magic[j]) & e->mask[j])
92 					break;
93 		} else {
94 			for (j = 0; j < e->size; j++)
95 				if ((*s++ ^ e->magic[j]))
96 					break;
97 		}
98 		if (j == e->size)
99 			return e;
100 	}
101 	return NULL;
102 }
103 
104 /*
105  * the loader itself
106  */
107 static int load_misc_binary(struct linux_binprm *bprm)
108 {
109 	Node *fmt;
110 	struct file * interp_file = NULL;
111 	char iname[BINPRM_BUF_SIZE];
112 	const char *iname_addr = iname;
113 	int retval;
114 	int fd_binary = -1;
115 
116 	retval = -ENOEXEC;
117 	if (!enabled)
118 		goto _ret;
119 
120 	/* to keep locking time low, we copy the interpreter string */
121 	read_lock(&entries_lock);
122 	fmt = check_file(bprm);
123 	if (fmt)
124 		strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
125 	read_unlock(&entries_lock);
126 	if (!fmt)
127 		goto _ret;
128 
129 	if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
130 		retval = remove_arg_zero(bprm);
131 		if (retval)
132 			goto _ret;
133 	}
134 
135 	if (fmt->flags & MISC_FMT_OPEN_BINARY) {
136 
137 		/* if the binary should be opened on behalf of the
138 		 * interpreter than keep it open and assign descriptor
139 		 * to it */
140  		fd_binary = get_unused_fd();
141  		if (fd_binary < 0) {
142  			retval = fd_binary;
143  			goto _ret;
144  		}
145  		fd_install(fd_binary, bprm->file);
146 
147 		/* if the binary is not readable than enforce mm->dumpable=0
148 		   regardless of the interpreter's permissions */
149 		would_dump(bprm, bprm->file);
150 
151 		allow_write_access(bprm->file);
152 		bprm->file = NULL;
153 
154 		/* mark the bprm that fd should be passed to interp */
155 		bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
156 		bprm->interp_data = fd_binary;
157 
158  	} else {
159  		allow_write_access(bprm->file);
160  		fput(bprm->file);
161  		bprm->file = NULL;
162  	}
163 	/* make argv[1] be the path to the binary */
164 	retval = copy_strings_kernel (1, &bprm->interp, bprm);
165 	if (retval < 0)
166 		goto _error;
167 	bprm->argc++;
168 
169 	/* add the interp as argv[0] */
170 	retval = copy_strings_kernel (1, &iname_addr, bprm);
171 	if (retval < 0)
172 		goto _error;
173 	bprm->argc ++;
174 
175 	bprm->interp = iname;	/* for binfmt_script */
176 
177 	interp_file = open_exec (iname);
178 	retval = PTR_ERR (interp_file);
179 	if (IS_ERR (interp_file))
180 		goto _error;
181 
182 	bprm->file = interp_file;
183 	if (fmt->flags & MISC_FMT_CREDENTIALS) {
184 		/*
185 		 * No need to call prepare_binprm(), it's already been
186 		 * done.  bprm->buf is stale, update from interp_file.
187 		 */
188 		memset(bprm->buf, 0, BINPRM_BUF_SIZE);
189 		retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
190 	} else
191 		retval = prepare_binprm (bprm);
192 
193 	if (retval < 0)
194 		goto _error;
195 
196 	retval = search_binary_handler(bprm);
197 	if (retval < 0)
198 		goto _error;
199 
200 _ret:
201 	return retval;
202 _error:
203 	if (fd_binary > 0)
204 		sys_close(fd_binary);
205 	bprm->interp_flags = 0;
206 	bprm->interp_data = 0;
207 	goto _ret;
208 }
209 
210 /* Command parsers */
211 
212 /*
213  * parses and copies one argument enclosed in del from *sp to *dp,
214  * recognising the \x special.
215  * returns pointer to the copied argument or NULL in case of an
216  * error (and sets err) or null argument length.
217  */
218 static char *scanarg(char *s, char del)
219 {
220 	char c;
221 
222 	while ((c = *s++) != del) {
223 		if (c == '\\' && *s == 'x') {
224 			s++;
225 			if (!isxdigit(*s++))
226 				return NULL;
227 			if (!isxdigit(*s++))
228 				return NULL;
229 		}
230 	}
231 	return s;
232 }
233 
234 static int unquote(char *from)
235 {
236 	char c = 0, *s = from, *p = from;
237 
238 	while ((c = *s++) != '\0') {
239 		if (c == '\\' && *s == 'x') {
240 			s++;
241 			c = toupper(*s++);
242 			*p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
243 			c = toupper(*s++);
244 			*p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
245 			continue;
246 		}
247 		*p++ = c;
248 	}
249 	return p - from;
250 }
251 
252 static char * check_special_flags (char * sfs, Node * e)
253 {
254 	char * p = sfs;
255 	int cont = 1;
256 
257 	/* special flags */
258 	while (cont) {
259 		switch (*p) {
260 			case 'P':
261 				p++;
262 				e->flags |= MISC_FMT_PRESERVE_ARGV0;
263 				break;
264 			case 'O':
265 				p++;
266 				e->flags |= MISC_FMT_OPEN_BINARY;
267 				break;
268 			case 'C':
269 				p++;
270 				/* this flags also implies the
271 				   open-binary flag */
272 				e->flags |= (MISC_FMT_CREDENTIALS |
273 						MISC_FMT_OPEN_BINARY);
274 				break;
275 			default:
276 				cont = 0;
277 		}
278 	}
279 
280 	return p;
281 }
282 /*
283  * This registers a new binary format, it recognises the syntax
284  * ':name:type:offset:magic:mask:interpreter:flags'
285  * where the ':' is the IFS, that can be chosen with the first char
286  */
287 static Node *create_entry(const char __user *buffer, size_t count)
288 {
289 	Node *e;
290 	int memsize, err;
291 	char *buf, *p;
292 	char del;
293 
294 	/* some sanity checks */
295 	err = -EINVAL;
296 	if ((count < 11) || (count > 256))
297 		goto out;
298 
299 	err = -ENOMEM;
300 	memsize = sizeof(Node) + count + 8;
301 	e = kmalloc(memsize, GFP_USER);
302 	if (!e)
303 		goto out;
304 
305 	p = buf = (char *)e + sizeof(Node);
306 
307 	memset(e, 0, sizeof(Node));
308 	if (copy_from_user(buf, buffer, count))
309 		goto Efault;
310 
311 	del = *p++;	/* delimeter */
312 
313 	memset(buf+count, del, 8);
314 
315 	e->name = p;
316 	p = strchr(p, del);
317 	if (!p)
318 		goto Einval;
319 	*p++ = '\0';
320 	if (!e->name[0] ||
321 	    !strcmp(e->name, ".") ||
322 	    !strcmp(e->name, "..") ||
323 	    strchr(e->name, '/'))
324 		goto Einval;
325 	switch (*p++) {
326 		case 'E': e->flags = 1<<Enabled; break;
327 		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
328 		default: goto Einval;
329 	}
330 	if (*p++ != del)
331 		goto Einval;
332 	if (test_bit(Magic, &e->flags)) {
333 		char *s = strchr(p, del);
334 		if (!s)
335 			goto Einval;
336 		*s++ = '\0';
337 		e->offset = simple_strtoul(p, &p, 10);
338 		if (*p++)
339 			goto Einval;
340 		e->magic = p;
341 		p = scanarg(p, del);
342 		if (!p)
343 			goto Einval;
344 		p[-1] = '\0';
345 		if (!e->magic[0])
346 			goto Einval;
347 		e->mask = p;
348 		p = scanarg(p, del);
349 		if (!p)
350 			goto Einval;
351 		p[-1] = '\0';
352 		if (!e->mask[0])
353 			e->mask = NULL;
354 		e->size = unquote(e->magic);
355 		if (e->mask && unquote(e->mask) != e->size)
356 			goto Einval;
357 		if (e->size + e->offset > BINPRM_BUF_SIZE)
358 			goto Einval;
359 	} else {
360 		p = strchr(p, del);
361 		if (!p)
362 			goto Einval;
363 		*p++ = '\0';
364 		e->magic = p;
365 		p = strchr(p, del);
366 		if (!p)
367 			goto Einval;
368 		*p++ = '\0';
369 		if (!e->magic[0] || strchr(e->magic, '/'))
370 			goto Einval;
371 		p = strchr(p, del);
372 		if (!p)
373 			goto Einval;
374 		*p++ = '\0';
375 	}
376 	e->interpreter = p;
377 	p = strchr(p, del);
378 	if (!p)
379 		goto Einval;
380 	*p++ = '\0';
381 	if (!e->interpreter[0])
382 		goto Einval;
383 
384 
385 	p = check_special_flags (p, e);
386 
387 	if (*p == '\n')
388 		p++;
389 	if (p != buf + count)
390 		goto Einval;
391 	return e;
392 
393 out:
394 	return ERR_PTR(err);
395 
396 Efault:
397 	kfree(e);
398 	return ERR_PTR(-EFAULT);
399 Einval:
400 	kfree(e);
401 	return ERR_PTR(-EINVAL);
402 }
403 
404 /*
405  * Set status of entry/binfmt_misc:
406  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
407  */
408 static int parse_command(const char __user *buffer, size_t count)
409 {
410 	char s[4];
411 
412 	if (!count)
413 		return 0;
414 	if (count > 3)
415 		return -EINVAL;
416 	if (copy_from_user(s, buffer, count))
417 		return -EFAULT;
418 	if (s[count-1] == '\n')
419 		count--;
420 	if (count == 1 && s[0] == '0')
421 		return 1;
422 	if (count == 1 && s[0] == '1')
423 		return 2;
424 	if (count == 2 && s[0] == '-' && s[1] == '1')
425 		return 3;
426 	return -EINVAL;
427 }
428 
429 /* generic stuff */
430 
431 static void entry_status(Node *e, char *page)
432 {
433 	char *dp;
434 	char *status = "disabled";
435 	const char * flags = "flags: ";
436 
437 	if (test_bit(Enabled, &e->flags))
438 		status = "enabled";
439 
440 	if (!VERBOSE_STATUS) {
441 		sprintf(page, "%s\n", status);
442 		return;
443 	}
444 
445 	sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
446 	dp = page + strlen(page);
447 
448 	/* print the special flags */
449 	sprintf (dp, "%s", flags);
450 	dp += strlen (flags);
451 	if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
452 		*dp ++ = 'P';
453 	}
454 	if (e->flags & MISC_FMT_OPEN_BINARY) {
455 		*dp ++ = 'O';
456 	}
457 	if (e->flags & MISC_FMT_CREDENTIALS) {
458 		*dp ++ = 'C';
459 	}
460 	*dp ++ = '\n';
461 
462 
463 	if (!test_bit(Magic, &e->flags)) {
464 		sprintf(dp, "extension .%s\n", e->magic);
465 	} else {
466 		int i;
467 
468 		sprintf(dp, "offset %i\nmagic ", e->offset);
469 		dp = page + strlen(page);
470 		for (i = 0; i < e->size; i++) {
471 			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
472 			dp += 2;
473 		}
474 		if (e->mask) {
475 			sprintf(dp, "\nmask ");
476 			dp += 6;
477 			for (i = 0; i < e->size; i++) {
478 				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
479 				dp += 2;
480 			}
481 		}
482 		*dp++ = '\n';
483 		*dp = '\0';
484 	}
485 }
486 
487 static struct inode *bm_get_inode(struct super_block *sb, int mode)
488 {
489 	struct inode * inode = new_inode(sb);
490 
491 	if (inode) {
492 		inode->i_ino = get_next_ino();
493 		inode->i_mode = mode;
494 		inode->i_atime = inode->i_mtime = inode->i_ctime =
495 			current_fs_time(inode->i_sb);
496 	}
497 	return inode;
498 }
499 
500 static void bm_evict_inode(struct inode *inode)
501 {
502 	clear_inode(inode);
503 	kfree(inode->i_private);
504 }
505 
506 static void kill_node(Node *e)
507 {
508 	struct dentry *dentry;
509 
510 	write_lock(&entries_lock);
511 	dentry = e->dentry;
512 	if (dentry) {
513 		list_del_init(&e->list);
514 		e->dentry = NULL;
515 	}
516 	write_unlock(&entries_lock);
517 
518 	if (dentry) {
519 		drop_nlink(dentry->d_inode);
520 		d_drop(dentry);
521 		dput(dentry);
522 		simple_release_fs(&bm_mnt, &entry_count);
523 	}
524 }
525 
526 /* /<entry> */
527 
528 static ssize_t
529 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
530 {
531 	Node *e = file->f_path.dentry->d_inode->i_private;
532 	ssize_t res;
533 	char *page;
534 
535 	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
536 		return -ENOMEM;
537 
538 	entry_status(e, page);
539 
540 	res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
541 
542 	free_page((unsigned long) page);
543 	return res;
544 }
545 
546 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
547 				size_t count, loff_t *ppos)
548 {
549 	struct dentry *root;
550 	Node *e = file->f_path.dentry->d_inode->i_private;
551 	int res = parse_command(buffer, count);
552 
553 	switch (res) {
554 		case 1: clear_bit(Enabled, &e->flags);
555 			break;
556 		case 2: set_bit(Enabled, &e->flags);
557 			break;
558 		case 3: root = dget(file->f_path.dentry->d_sb->s_root);
559 			mutex_lock(&root->d_inode->i_mutex);
560 
561 			kill_node(e);
562 
563 			mutex_unlock(&root->d_inode->i_mutex);
564 			dput(root);
565 			break;
566 		default: return res;
567 	}
568 	return count;
569 }
570 
571 static const struct file_operations bm_entry_operations = {
572 	.read		= bm_entry_read,
573 	.write		= bm_entry_write,
574 	.llseek		= default_llseek,
575 };
576 
577 /* /register */
578 
579 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
580 			       size_t count, loff_t *ppos)
581 {
582 	Node *e;
583 	struct inode *inode;
584 	struct dentry *root, *dentry;
585 	struct super_block *sb = file->f_path.dentry->d_sb;
586 	int err = 0;
587 
588 	e = create_entry(buffer, count);
589 
590 	if (IS_ERR(e))
591 		return PTR_ERR(e);
592 
593 	root = dget(sb->s_root);
594 	mutex_lock(&root->d_inode->i_mutex);
595 	dentry = lookup_one_len(e->name, root, strlen(e->name));
596 	err = PTR_ERR(dentry);
597 	if (IS_ERR(dentry))
598 		goto out;
599 
600 	err = -EEXIST;
601 	if (dentry->d_inode)
602 		goto out2;
603 
604 	inode = bm_get_inode(sb, S_IFREG | 0644);
605 
606 	err = -ENOMEM;
607 	if (!inode)
608 		goto out2;
609 
610 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
611 	if (err) {
612 		iput(inode);
613 		inode = NULL;
614 		goto out2;
615 	}
616 
617 	e->dentry = dget(dentry);
618 	inode->i_private = e;
619 	inode->i_fop = &bm_entry_operations;
620 
621 	d_instantiate(dentry, inode);
622 	write_lock(&entries_lock);
623 	list_add(&e->list, &entries);
624 	write_unlock(&entries_lock);
625 
626 	err = 0;
627 out2:
628 	dput(dentry);
629 out:
630 	mutex_unlock(&root->d_inode->i_mutex);
631 	dput(root);
632 
633 	if (err) {
634 		kfree(e);
635 		return -EINVAL;
636 	}
637 	return count;
638 }
639 
640 static const struct file_operations bm_register_operations = {
641 	.write		= bm_register_write,
642 	.llseek		= noop_llseek,
643 };
644 
645 /* /status */
646 
647 static ssize_t
648 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
649 {
650 	char *s = enabled ? "enabled\n" : "disabled\n";
651 
652 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
653 }
654 
655 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
656 		size_t count, loff_t *ppos)
657 {
658 	int res = parse_command(buffer, count);
659 	struct dentry *root;
660 
661 	switch (res) {
662 		case 1: enabled = 0; break;
663 		case 2: enabled = 1; break;
664 		case 3: root = dget(file->f_path.dentry->d_sb->s_root);
665 			mutex_lock(&root->d_inode->i_mutex);
666 
667 			while (!list_empty(&entries))
668 				kill_node(list_entry(entries.next, Node, list));
669 
670 			mutex_unlock(&root->d_inode->i_mutex);
671 			dput(root);
672 		default: return res;
673 	}
674 	return count;
675 }
676 
677 static const struct file_operations bm_status_operations = {
678 	.read		= bm_status_read,
679 	.write		= bm_status_write,
680 	.llseek		= default_llseek,
681 };
682 
683 /* Superblock handling */
684 
685 static const struct super_operations s_ops = {
686 	.statfs		= simple_statfs,
687 	.evict_inode	= bm_evict_inode,
688 };
689 
690 static int bm_fill_super(struct super_block * sb, void * data, int silent)
691 {
692 	static struct tree_descr bm_files[] = {
693 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
694 		[3] = {"register", &bm_register_operations, S_IWUSR},
695 		/* last one */ {""}
696 	};
697 	int err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
698 	if (!err)
699 		sb->s_op = &s_ops;
700 	return err;
701 }
702 
703 static struct dentry *bm_mount(struct file_system_type *fs_type,
704 	int flags, const char *dev_name, void *data)
705 {
706 	return mount_single(fs_type, flags, data, bm_fill_super);
707 }
708 
709 static struct linux_binfmt misc_format = {
710 	.module = THIS_MODULE,
711 	.load_binary = load_misc_binary,
712 };
713 
714 static struct file_system_type bm_fs_type = {
715 	.owner		= THIS_MODULE,
716 	.name		= "binfmt_misc",
717 	.mount		= bm_mount,
718 	.kill_sb	= kill_litter_super,
719 };
720 
721 static int __init init_misc_binfmt(void)
722 {
723 	int err = register_filesystem(&bm_fs_type);
724 	if (!err)
725 		insert_binfmt(&misc_format);
726 	return err;
727 }
728 
729 static void __exit exit_misc_binfmt(void)
730 {
731 	unregister_binfmt(&misc_format);
732 	unregister_filesystem(&bm_fs_type);
733 }
734 
735 core_initcall(init_misc_binfmt);
736 module_exit(exit_misc_binfmt);
737 MODULE_LICENSE("GPL");
738