xref: /linux/fs/binfmt_misc.c (revision 3932b9ca55b0be314a36d3e84faff3e823c081f5) 
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/string_helpers.h>
27 #include <linux/file.h>
28 #include <linux/pagemap.h>
29 #include <linux/namei.h>
30 #include <linux/mount.h>
31 #include <linux/syscalls.h>
32 #include <linux/fs.h>
33 
34 #include <asm/uaccess.h>
35 
36 enum {
37 	VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
38 };
39 
40 static LIST_HEAD(entries);
41 static int enabled = 1;
42 
43 enum {Enabled, Magic};
44 #define MISC_FMT_PRESERVE_ARGV0 (1<<31)
45 #define MISC_FMT_OPEN_BINARY (1<<30)
46 #define MISC_FMT_CREDENTIALS (1<<29)
47 
48 typedef struct {
49 	struct list_head list;
50 	unsigned long flags;		/* type, status, etc. */
51 	int offset;			/* offset of magic */
52 	int size;			/* size of magic/mask */
53 	char *magic;			/* magic or filename extension */
54 	char *mask;			/* mask, NULL for exact match */
55 	char *interpreter;		/* filename of interpreter */
56 	char *name;
57 	struct dentry *dentry;
58 } Node;
59 
60 static DEFINE_RWLOCK(entries_lock);
61 static struct file_system_type bm_fs_type;
62 static struct vfsmount *bm_mnt;
63 static int entry_count;
64 
65 /*
66  * Check if we support the binfmt
67  * if we do, return the node, else NULL
68  * locking is done in load_misc_binary
69  */
70 static Node *check_file(struct linux_binprm *bprm)
71 {
72 	char *p = strrchr(bprm->interp, '.');
73 	struct list_head *l;
74 
75 	list_for_each(l, &entries) {
76 		Node *e = list_entry(l, Node, list);
77 		char *s;
78 		int j;
79 
80 		if (!test_bit(Enabled, &e->flags))
81 			continue;
82 
83 		if (!test_bit(Magic, &e->flags)) {
84 			if (p && !strcmp(e->magic, p + 1))
85 				return e;
86 			continue;
87 		}
88 
89 		s = bprm->buf + e->offset;
90 		if (e->mask) {
91 			for (j = 0; j < e->size; j++)
92 				if ((*s++ ^ e->magic[j]) & e->mask[j])
93 					break;
94 		} else {
95 			for (j = 0; j < e->size; j++)
96 				if ((*s++ ^ e->magic[j]))
97 					break;
98 		}
99 		if (j == e->size)
100 			return e;
101 	}
102 	return NULL;
103 }
104 
105 /*
106  * the loader itself
107  */
108 static int load_misc_binary(struct linux_binprm *bprm)
109 {
110 	Node *fmt;
111 	struct file * interp_file = NULL;
112 	char iname[BINPRM_BUF_SIZE];
113 	const char *iname_addr = iname;
114 	int retval;
115 	int fd_binary = -1;
116 
117 	retval = -ENOEXEC;
118 	if (!enabled)
119 		goto _ret;
120 
121 	/* to keep locking time low, we copy the interpreter string */
122 	read_lock(&entries_lock);
123 	fmt = check_file(bprm);
124 	if (fmt)
125 		strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
126 	read_unlock(&entries_lock);
127 	if (!fmt)
128 		goto _ret;
129 
130 	if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
131 		retval = remove_arg_zero(bprm);
132 		if (retval)
133 			goto _ret;
134 	}
135 
136 	if (fmt->flags & MISC_FMT_OPEN_BINARY) {
137 
138 		/* if the binary should be opened on behalf of the
139 		 * interpreter than keep it open and assign descriptor
140 		 * to it */
141  		fd_binary = get_unused_fd();
142  		if (fd_binary < 0) {
143  			retval = fd_binary;
144  			goto _ret;
145  		}
146  		fd_install(fd_binary, bprm->file);
147 
148 		/* if the binary is not readable than enforce mm->dumpable=0
149 		   regardless of the interpreter's permissions */
150 		would_dump(bprm, bprm->file);
151 
152 		allow_write_access(bprm->file);
153 		bprm->file = NULL;
154 
155 		/* mark the bprm that fd should be passed to interp */
156 		bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
157 		bprm->interp_data = fd_binary;
158 
159  	} else {
160  		allow_write_access(bprm->file);
161  		fput(bprm->file);
162  		bprm->file = NULL;
163  	}
164 	/* make argv[1] be the path to the binary */
165 	retval = copy_strings_kernel (1, &bprm->interp, bprm);
166 	if (retval < 0)
167 		goto _error;
168 	bprm->argc++;
169 
170 	/* add the interp as argv[0] */
171 	retval = copy_strings_kernel (1, &iname_addr, bprm);
172 	if (retval < 0)
173 		goto _error;
174 	bprm->argc ++;
175 
176 	/* Update interp in case binfmt_script needs it. */
177 	retval = bprm_change_interp(iname, bprm);
178 	if (retval < 0)
179 		goto _error;
180 
181 	interp_file = open_exec (iname);
182 	retval = PTR_ERR (interp_file);
183 	if (IS_ERR (interp_file))
184 		goto _error;
185 
186 	bprm->file = interp_file;
187 	if (fmt->flags & MISC_FMT_CREDENTIALS) {
188 		/*
189 		 * No need to call prepare_binprm(), it's already been
190 		 * done.  bprm->buf is stale, update from interp_file.
191 		 */
192 		memset(bprm->buf, 0, BINPRM_BUF_SIZE);
193 		retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
194 	} else
195 		retval = prepare_binprm (bprm);
196 
197 	if (retval < 0)
198 		goto _error;
199 
200 	retval = search_binary_handler(bprm);
201 	if (retval < 0)
202 		goto _error;
203 
204 _ret:
205 	return retval;
206 _error:
207 	if (fd_binary > 0)
208 		sys_close(fd_binary);
209 	bprm->interp_flags = 0;
210 	bprm->interp_data = 0;
211 	goto _ret;
212 }
213 
214 /* Command parsers */
215 
216 /*
217  * parses and copies one argument enclosed in del from *sp to *dp,
218  * recognising the \x special.
219  * returns pointer to the copied argument or NULL in case of an
220  * error (and sets err) or null argument length.
221  */
222 static char *scanarg(char *s, char del)
223 {
224 	char c;
225 
226 	while ((c = *s++) != del) {
227 		if (c == '\\' && *s == 'x') {
228 			s++;
229 			if (!isxdigit(*s++))
230 				return NULL;
231 			if (!isxdigit(*s++))
232 				return NULL;
233 		}
234 	}
235 	return s;
236 }
237 
238 static char * check_special_flags (char * sfs, Node * e)
239 {
240 	char * p = sfs;
241 	int cont = 1;
242 
243 	/* special flags */
244 	while (cont) {
245 		switch (*p) {
246 			case 'P':
247 				p++;
248 				e->flags |= MISC_FMT_PRESERVE_ARGV0;
249 				break;
250 			case 'O':
251 				p++;
252 				e->flags |= MISC_FMT_OPEN_BINARY;
253 				break;
254 			case 'C':
255 				p++;
256 				/* this flags also implies the
257 				   open-binary flag */
258 				e->flags |= (MISC_FMT_CREDENTIALS |
259 						MISC_FMT_OPEN_BINARY);
260 				break;
261 			default:
262 				cont = 0;
263 		}
264 	}
265 
266 	return p;
267 }
268 /*
269  * This registers a new binary format, it recognises the syntax
270  * ':name:type:offset:magic:mask:interpreter:flags'
271  * where the ':' is the IFS, that can be chosen with the first char
272  */
273 static Node *create_entry(const char __user *buffer, size_t count)
274 {
275 	Node *e;
276 	int memsize, err;
277 	char *buf, *p;
278 	char del;
279 
280 	/* some sanity checks */
281 	err = -EINVAL;
282 	if ((count < 11) || (count > 256))
283 		goto out;
284 
285 	err = -ENOMEM;
286 	memsize = sizeof(Node) + count + 8;
287 	e = kmalloc(memsize, GFP_USER);
288 	if (!e)
289 		goto out;
290 
291 	p = buf = (char *)e + sizeof(Node);
292 
293 	memset(e, 0, sizeof(Node));
294 	if (copy_from_user(buf, buffer, count))
295 		goto Efault;
296 
297 	del = *p++;	/* delimeter */
298 
299 	memset(buf+count, del, 8);
300 
301 	e->name = p;
302 	p = strchr(p, del);
303 	if (!p)
304 		goto Einval;
305 	*p++ = '\0';
306 	if (!e->name[0] ||
307 	    !strcmp(e->name, ".") ||
308 	    !strcmp(e->name, "..") ||
309 	    strchr(e->name, '/'))
310 		goto Einval;
311 	switch (*p++) {
312 		case 'E': e->flags = 1<<Enabled; break;
313 		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
314 		default: goto Einval;
315 	}
316 	if (*p++ != del)
317 		goto Einval;
318 	if (test_bit(Magic, &e->flags)) {
319 		char *s = strchr(p, del);
320 		if (!s)
321 			goto Einval;
322 		*s++ = '\0';
323 		e->offset = simple_strtoul(p, &p, 10);
324 		if (*p++)
325 			goto Einval;
326 		e->magic = p;
327 		p = scanarg(p, del);
328 		if (!p)
329 			goto Einval;
330 		p[-1] = '\0';
331 		if (!e->magic[0])
332 			goto Einval;
333 		e->mask = p;
334 		p = scanarg(p, del);
335 		if (!p)
336 			goto Einval;
337 		p[-1] = '\0';
338 		if (!e->mask[0])
339 			e->mask = NULL;
340 		e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
341 		if (e->mask &&
342 		    string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
343 			goto Einval;
344 		if (e->size + e->offset > BINPRM_BUF_SIZE)
345 			goto Einval;
346 	} else {
347 		p = strchr(p, del);
348 		if (!p)
349 			goto Einval;
350 		*p++ = '\0';
351 		e->magic = p;
352 		p = strchr(p, del);
353 		if (!p)
354 			goto Einval;
355 		*p++ = '\0';
356 		if (!e->magic[0] || strchr(e->magic, '/'))
357 			goto Einval;
358 		p = strchr(p, del);
359 		if (!p)
360 			goto Einval;
361 		*p++ = '\0';
362 	}
363 	e->interpreter = p;
364 	p = strchr(p, del);
365 	if (!p)
366 		goto Einval;
367 	*p++ = '\0';
368 	if (!e->interpreter[0])
369 		goto Einval;
370 
371 
372 	p = check_special_flags (p, e);
373 
374 	if (*p == '\n')
375 		p++;
376 	if (p != buf + count)
377 		goto Einval;
378 	return e;
379 
380 out:
381 	return ERR_PTR(err);
382 
383 Efault:
384 	kfree(e);
385 	return ERR_PTR(-EFAULT);
386 Einval:
387 	kfree(e);
388 	return ERR_PTR(-EINVAL);
389 }
390 
391 /*
392  * Set status of entry/binfmt_misc:
393  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
394  */
395 static int parse_command(const char __user *buffer, size_t count)
396 {
397 	char s[4];
398 
399 	if (!count)
400 		return 0;
401 	if (count > 3)
402 		return -EINVAL;
403 	if (copy_from_user(s, buffer, count))
404 		return -EFAULT;
405 	if (s[count-1] == '\n')
406 		count--;
407 	if (count == 1 && s[0] == '0')
408 		return 1;
409 	if (count == 1 && s[0] == '1')
410 		return 2;
411 	if (count == 2 && s[0] == '-' && s[1] == '1')
412 		return 3;
413 	return -EINVAL;
414 }
415 
416 /* generic stuff */
417 
418 static void entry_status(Node *e, char *page)
419 {
420 	char *dp;
421 	char *status = "disabled";
422 	const char * flags = "flags: ";
423 
424 	if (test_bit(Enabled, &e->flags))
425 		status = "enabled";
426 
427 	if (!VERBOSE_STATUS) {
428 		sprintf(page, "%s\n", status);
429 		return;
430 	}
431 
432 	sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
433 	dp = page + strlen(page);
434 
435 	/* print the special flags */
436 	sprintf (dp, "%s", flags);
437 	dp += strlen (flags);
438 	if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
439 		*dp ++ = 'P';
440 	}
441 	if (e->flags & MISC_FMT_OPEN_BINARY) {
442 		*dp ++ = 'O';
443 	}
444 	if (e->flags & MISC_FMT_CREDENTIALS) {
445 		*dp ++ = 'C';
446 	}
447 	*dp ++ = '\n';
448 
449 
450 	if (!test_bit(Magic, &e->flags)) {
451 		sprintf(dp, "extension .%s\n", e->magic);
452 	} else {
453 		int i;
454 
455 		sprintf(dp, "offset %i\nmagic ", e->offset);
456 		dp = page + strlen(page);
457 		for (i = 0; i < e->size; i++) {
458 			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
459 			dp += 2;
460 		}
461 		if (e->mask) {
462 			sprintf(dp, "\nmask ");
463 			dp += 6;
464 			for (i = 0; i < e->size; i++) {
465 				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
466 				dp += 2;
467 			}
468 		}
469 		*dp++ = '\n';
470 		*dp = '\0';
471 	}
472 }
473 
474 static struct inode *bm_get_inode(struct super_block *sb, int mode)
475 {
476 	struct inode * inode = new_inode(sb);
477 
478 	if (inode) {
479 		inode->i_ino = get_next_ino();
480 		inode->i_mode = mode;
481 		inode->i_atime = inode->i_mtime = inode->i_ctime =
482 			current_fs_time(inode->i_sb);
483 	}
484 	return inode;
485 }
486 
487 static void bm_evict_inode(struct inode *inode)
488 {
489 	clear_inode(inode);
490 	kfree(inode->i_private);
491 }
492 
493 static void kill_node(Node *e)
494 {
495 	struct dentry *dentry;
496 
497 	write_lock(&entries_lock);
498 	dentry = e->dentry;
499 	if (dentry) {
500 		list_del_init(&e->list);
501 		e->dentry = NULL;
502 	}
503 	write_unlock(&entries_lock);
504 
505 	if (dentry) {
506 		drop_nlink(dentry->d_inode);
507 		d_drop(dentry);
508 		dput(dentry);
509 		simple_release_fs(&bm_mnt, &entry_count);
510 	}
511 }
512 
513 /* /<entry> */
514 
515 static ssize_t
516 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
517 {
518 	Node *e = file_inode(file)->i_private;
519 	ssize_t res;
520 	char *page;
521 
522 	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
523 		return -ENOMEM;
524 
525 	entry_status(e, page);
526 
527 	res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
528 
529 	free_page((unsigned long) page);
530 	return res;
531 }
532 
533 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
534 				size_t count, loff_t *ppos)
535 {
536 	struct dentry *root;
537 	Node *e = file_inode(file)->i_private;
538 	int res = parse_command(buffer, count);
539 
540 	switch (res) {
541 		case 1: clear_bit(Enabled, &e->flags);
542 			break;
543 		case 2: set_bit(Enabled, &e->flags);
544 			break;
545 		case 3: root = dget(file->f_path.dentry->d_sb->s_root);
546 			mutex_lock(&root->d_inode->i_mutex);
547 
548 			kill_node(e);
549 
550 			mutex_unlock(&root->d_inode->i_mutex);
551 			dput(root);
552 			break;
553 		default: return res;
554 	}
555 	return count;
556 }
557 
558 static const struct file_operations bm_entry_operations = {
559 	.read		= bm_entry_read,
560 	.write		= bm_entry_write,
561 	.llseek		= default_llseek,
562 };
563 
564 /* /register */
565 
566 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
567 			       size_t count, loff_t *ppos)
568 {
569 	Node *e;
570 	struct inode *inode;
571 	struct dentry *root, *dentry;
572 	struct super_block *sb = file->f_path.dentry->d_sb;
573 	int err = 0;
574 
575 	e = create_entry(buffer, count);
576 
577 	if (IS_ERR(e))
578 		return PTR_ERR(e);
579 
580 	root = dget(sb->s_root);
581 	mutex_lock(&root->d_inode->i_mutex);
582 	dentry = lookup_one_len(e->name, root, strlen(e->name));
583 	err = PTR_ERR(dentry);
584 	if (IS_ERR(dentry))
585 		goto out;
586 
587 	err = -EEXIST;
588 	if (dentry->d_inode)
589 		goto out2;
590 
591 	inode = bm_get_inode(sb, S_IFREG | 0644);
592 
593 	err = -ENOMEM;
594 	if (!inode)
595 		goto out2;
596 
597 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
598 	if (err) {
599 		iput(inode);
600 		inode = NULL;
601 		goto out2;
602 	}
603 
604 	e->dentry = dget(dentry);
605 	inode->i_private = e;
606 	inode->i_fop = &bm_entry_operations;
607 
608 	d_instantiate(dentry, inode);
609 	write_lock(&entries_lock);
610 	list_add(&e->list, &entries);
611 	write_unlock(&entries_lock);
612 
613 	err = 0;
614 out2:
615 	dput(dentry);
616 out:
617 	mutex_unlock(&root->d_inode->i_mutex);
618 	dput(root);
619 
620 	if (err) {
621 		kfree(e);
622 		return -EINVAL;
623 	}
624 	return count;
625 }
626 
627 static const struct file_operations bm_register_operations = {
628 	.write		= bm_register_write,
629 	.llseek		= noop_llseek,
630 };
631 
632 /* /status */
633 
634 static ssize_t
635 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
636 {
637 	char *s = enabled ? "enabled\n" : "disabled\n";
638 
639 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
640 }
641 
642 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
643 		size_t count, loff_t *ppos)
644 {
645 	int res = parse_command(buffer, count);
646 	struct dentry *root;
647 
648 	switch (res) {
649 		case 1: enabled = 0; break;
650 		case 2: enabled = 1; break;
651 		case 3: root = dget(file->f_path.dentry->d_sb->s_root);
652 			mutex_lock(&root->d_inode->i_mutex);
653 
654 			while (!list_empty(&entries))
655 				kill_node(list_entry(entries.next, Node, list));
656 
657 			mutex_unlock(&root->d_inode->i_mutex);
658 			dput(root);
659 			break;
660 		default: return res;
661 	}
662 	return count;
663 }
664 
665 static const struct file_operations bm_status_operations = {
666 	.read		= bm_status_read,
667 	.write		= bm_status_write,
668 	.llseek		= default_llseek,
669 };
670 
671 /* Superblock handling */
672 
673 static const struct super_operations s_ops = {
674 	.statfs		= simple_statfs,
675 	.evict_inode	= bm_evict_inode,
676 };
677 
678 static int bm_fill_super(struct super_block * sb, void * data, int silent)
679 {
680 	static struct tree_descr bm_files[] = {
681 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
682 		[3] = {"register", &bm_register_operations, S_IWUSR},
683 		/* last one */ {""}
684 	};
685 	int err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
686 	if (!err)
687 		sb->s_op = &s_ops;
688 	return err;
689 }
690 
691 static struct dentry *bm_mount(struct file_system_type *fs_type,
692 	int flags, const char *dev_name, void *data)
693 {
694 	return mount_single(fs_type, flags, data, bm_fill_super);
695 }
696 
697 static struct linux_binfmt misc_format = {
698 	.module = THIS_MODULE,
699 	.load_binary = load_misc_binary,
700 };
701 
702 static struct file_system_type bm_fs_type = {
703 	.owner		= THIS_MODULE,
704 	.name		= "binfmt_misc",
705 	.mount		= bm_mount,
706 	.kill_sb	= kill_litter_super,
707 };
708 MODULE_ALIAS_FS("binfmt_misc");
709 
710 static int __init init_misc_binfmt(void)
711 {
712 	int err = register_filesystem(&bm_fs_type);
713 	if (!err)
714 		insert_binfmt(&misc_format);
715 	return err;
716 }
717 
718 static void __exit exit_misc_binfmt(void)
719 {
720 	unregister_binfmt(&misc_format);
721 	unregister_filesystem(&bm_fs_type);
722 }
723 
724 core_initcall(init_misc_binfmt);
725 module_exit(exit_misc_binfmt);
726 MODULE_LICENSE("GPL");
727