xref: /linux/fs/binfmt_misc.c (revision b43ab901d671e3e3cad425ea5e9a3c74e266dcdd) 
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/binfmts.h>
23 #include <linux/slab.h>
24 #include <linux/ctype.h>
25 #include <linux/file.h>
26 #include <linux/pagemap.h>
27 #include <linux/namei.h>
28 #include <linux/mount.h>
29 #include <linux/syscalls.h>
30 #include <linux/fs.h>
31 
32 #include <asm/uaccess.h>
33 
34 enum {
35 	VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
36 };
37 
38 static LIST_HEAD(entries);
39 static int enabled = 1;
40 
41 enum {Enabled, Magic};
42 #define MISC_FMT_PRESERVE_ARGV0 (1<<31)
43 #define MISC_FMT_OPEN_BINARY (1<<30)
44 #define MISC_FMT_CREDENTIALS (1<<29)
45 
46 typedef struct {
47 	struct list_head list;
48 	unsigned long flags;		/* type, status, etc. */
49 	int offset;			/* offset of magic */
50 	int size;			/* size of magic/mask */
51 	char *magic;			/* magic or filename extension */
52 	char *mask;			/* mask, NULL for exact match */
53 	char *interpreter;		/* filename of interpreter */
54 	char *name;
55 	struct dentry *dentry;
56 } Node;
57 
58 static DEFINE_RWLOCK(entries_lock);
59 static struct file_system_type bm_fs_type;
60 static struct vfsmount *bm_mnt;
61 static int entry_count;
62 
63 /*
64  * Check if we support the binfmt
65  * if we do, return the node, else NULL
66  * locking is done in load_misc_binary
67  */
68 static Node *check_file(struct linux_binprm *bprm)
69 {
70 	char *p = strrchr(bprm->interp, '.');
71 	struct list_head *l;
72 
73 	list_for_each(l, &entries) {
74 		Node *e = list_entry(l, Node, list);
75 		char *s;
76 		int j;
77 
78 		if (!test_bit(Enabled, &e->flags))
79 			continue;
80 
81 		if (!test_bit(Magic, &e->flags)) {
82 			if (p && !strcmp(e->magic, p + 1))
83 				return e;
84 			continue;
85 		}
86 
87 		s = bprm->buf + e->offset;
88 		if (e->mask) {
89 			for (j = 0; j < e->size; j++)
90 				if ((*s++ ^ e->magic[j]) & e->mask[j])
91 					break;
92 		} else {
93 			for (j = 0; j < e->size; j++)
94 				if ((*s++ ^ e->magic[j]))
95 					break;
96 		}
97 		if (j == e->size)
98 			return e;
99 	}
100 	return NULL;
101 }
102 
103 /*
104  * the loader itself
105  */
106 static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
107 {
108 	Node *fmt;
109 	struct file * interp_file = NULL;
110 	char iname[BINPRM_BUF_SIZE];
111 	const char *iname_addr = iname;
112 	int retval;
113 	int fd_binary = -1;
114 
115 	retval = -ENOEXEC;
116 	if (!enabled)
117 		goto _ret;
118 
119 	retval = -ENOEXEC;
120 	if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
121 		goto _ret;
122 
123 	/* to keep locking time low, we copy the interpreter string */
124 	read_lock(&entries_lock);
125 	fmt = check_file(bprm);
126 	if (fmt)
127 		strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
128 	read_unlock(&entries_lock);
129 	if (!fmt)
130 		goto _ret;
131 
132 	if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
133 		retval = remove_arg_zero(bprm);
134 		if (retval)
135 			goto _ret;
136 	}
137 
138 	if (fmt->flags & MISC_FMT_OPEN_BINARY) {
139 
140 		/* if the binary should be opened on behalf of the
141 		 * interpreter than keep it open and assign descriptor
142 		 * to it */
143  		fd_binary = get_unused_fd();
144  		if (fd_binary < 0) {
145  			retval = fd_binary;
146  			goto _ret;
147  		}
148  		fd_install(fd_binary, bprm->file);
149 
150 		/* if the binary is not readable than enforce mm->dumpable=0
151 		   regardless of the interpreter's permissions */
152 		would_dump(bprm, bprm->file);
153 
154 		allow_write_access(bprm->file);
155 		bprm->file = NULL;
156 
157 		/* mark the bprm that fd should be passed to interp */
158 		bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
159 		bprm->interp_data = fd_binary;
160 
161  	} else {
162  		allow_write_access(bprm->file);
163  		fput(bprm->file);
164  		bprm->file = NULL;
165  	}
166 	/* make argv[1] be the path to the binary */
167 	retval = copy_strings_kernel (1, &bprm->interp, bprm);
168 	if (retval < 0)
169 		goto _error;
170 	bprm->argc++;
171 
172 	/* add the interp as argv[0] */
173 	retval = copy_strings_kernel (1, &iname_addr, bprm);
174 	if (retval < 0)
175 		goto _error;
176 	bprm->argc ++;
177 
178 	bprm->interp = iname;	/* for binfmt_script */
179 
180 	interp_file = open_exec (iname);
181 	retval = PTR_ERR (interp_file);
182 	if (IS_ERR (interp_file))
183 		goto _error;
184 
185 	bprm->file = interp_file;
186 	if (fmt->flags & MISC_FMT_CREDENTIALS) {
187 		/*
188 		 * No need to call prepare_binprm(), it's already been
189 		 * done.  bprm->buf is stale, update from interp_file.
190 		 */
191 		memset(bprm->buf, 0, BINPRM_BUF_SIZE);
192 		retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
193 	} else
194 		retval = prepare_binprm (bprm);
195 
196 	if (retval < 0)
197 		goto _error;
198 
199 	bprm->recursion_depth++;
200 
201 	retval = search_binary_handler (bprm, regs);
202 	if (retval < 0)
203 		goto _error;
204 
205 _ret:
206 	return retval;
207 _error:
208 	if (fd_binary > 0)
209 		sys_close(fd_binary);
210 	bprm->interp_flags = 0;
211 	bprm->interp_data = 0;
212 	goto _ret;
213 }
214 
215 /* Command parsers */
216 
217 /*
218  * parses and copies one argument enclosed in del from *sp to *dp,
219  * recognising the \x special.
220  * returns pointer to the copied argument or NULL in case of an
221  * error (and sets err) or null argument length.
222  */
223 static char *scanarg(char *s, char del)
224 {
225 	char c;
226 
227 	while ((c = *s++) != del) {
228 		if (c == '\\' && *s == 'x') {
229 			s++;
230 			if (!isxdigit(*s++))
231 				return NULL;
232 			if (!isxdigit(*s++))
233 				return NULL;
234 		}
235 	}
236 	return s;
237 }
238 
239 static int unquote(char *from)
240 {
241 	char c = 0, *s = from, *p = from;
242 
243 	while ((c = *s++) != '\0') {
244 		if (c == '\\' && *s == 'x') {
245 			s++;
246 			c = toupper(*s++);
247 			*p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
248 			c = toupper(*s++);
249 			*p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
250 			continue;
251 		}
252 		*p++ = c;
253 	}
254 	return p - from;
255 }
256 
257 static char * check_special_flags (char * sfs, Node * e)
258 {
259 	char * p = sfs;
260 	int cont = 1;
261 
262 	/* special flags */
263 	while (cont) {
264 		switch (*p) {
265 			case 'P':
266 				p++;
267 				e->flags |= MISC_FMT_PRESERVE_ARGV0;
268 				break;
269 			case 'O':
270 				p++;
271 				e->flags |= MISC_FMT_OPEN_BINARY;
272 				break;
273 			case 'C':
274 				p++;
275 				/* this flags also implies the
276 				   open-binary flag */
277 				e->flags |= (MISC_FMT_CREDENTIALS |
278 						MISC_FMT_OPEN_BINARY);
279 				break;
280 			default:
281 				cont = 0;
282 		}
283 	}
284 
285 	return p;
286 }
287 /*
288  * This registers a new binary format, it recognises the syntax
289  * ':name:type:offset:magic:mask:interpreter:flags'
290  * where the ':' is the IFS, that can be chosen with the first char
291  */
292 static Node *create_entry(const char __user *buffer, size_t count)
293 {
294 	Node *e;
295 	int memsize, err;
296 	char *buf, *p;
297 	char del;
298 
299 	/* some sanity checks */
300 	err = -EINVAL;
301 	if ((count < 11) || (count > 256))
302 		goto out;
303 
304 	err = -ENOMEM;
305 	memsize = sizeof(Node) + count + 8;
306 	e = kmalloc(memsize, GFP_USER);
307 	if (!e)
308 		goto out;
309 
310 	p = buf = (char *)e + sizeof(Node);
311 
312 	memset(e, 0, sizeof(Node));
313 	if (copy_from_user(buf, buffer, count))
314 		goto Efault;
315 
316 	del = *p++;	/* delimeter */
317 
318 	memset(buf+count, del, 8);
319 
320 	e->name = p;
321 	p = strchr(p, del);
322 	if (!p)
323 		goto Einval;
324 	*p++ = '\0';
325 	if (!e->name[0] ||
326 	    !strcmp(e->name, ".") ||
327 	    !strcmp(e->name, "..") ||
328 	    strchr(e->name, '/'))
329 		goto Einval;
330 	switch (*p++) {
331 		case 'E': e->flags = 1<<Enabled; break;
332 		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
333 		default: goto Einval;
334 	}
335 	if (*p++ != del)
336 		goto Einval;
337 	if (test_bit(Magic, &e->flags)) {
338 		char *s = strchr(p, del);
339 		if (!s)
340 			goto Einval;
341 		*s++ = '\0';
342 		e->offset = simple_strtoul(p, &p, 10);
343 		if (*p++)
344 			goto Einval;
345 		e->magic = p;
346 		p = scanarg(p, del);
347 		if (!p)
348 			goto Einval;
349 		p[-1] = '\0';
350 		if (!e->magic[0])
351 			goto Einval;
352 		e->mask = p;
353 		p = scanarg(p, del);
354 		if (!p)
355 			goto Einval;
356 		p[-1] = '\0';
357 		if (!e->mask[0])
358 			e->mask = NULL;
359 		e->size = unquote(e->magic);
360 		if (e->mask && unquote(e->mask) != e->size)
361 			goto Einval;
362 		if (e->size + e->offset > BINPRM_BUF_SIZE)
363 			goto Einval;
364 	} else {
365 		p = strchr(p, del);
366 		if (!p)
367 			goto Einval;
368 		*p++ = '\0';
369 		e->magic = p;
370 		p = strchr(p, del);
371 		if (!p)
372 			goto Einval;
373 		*p++ = '\0';
374 		if (!e->magic[0] || strchr(e->magic, '/'))
375 			goto Einval;
376 		p = strchr(p, del);
377 		if (!p)
378 			goto Einval;
379 		*p++ = '\0';
380 	}
381 	e->interpreter = p;
382 	p = strchr(p, del);
383 	if (!p)
384 		goto Einval;
385 	*p++ = '\0';
386 	if (!e->interpreter[0])
387 		goto Einval;
388 
389 
390 	p = check_special_flags (p, e);
391 
392 	if (*p == '\n')
393 		p++;
394 	if (p != buf + count)
395 		goto Einval;
396 	return e;
397 
398 out:
399 	return ERR_PTR(err);
400 
401 Efault:
402 	kfree(e);
403 	return ERR_PTR(-EFAULT);
404 Einval:
405 	kfree(e);
406 	return ERR_PTR(-EINVAL);
407 }
408 
409 /*
410  * Set status of entry/binfmt_misc:
411  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
412  */
413 static int parse_command(const char __user *buffer, size_t count)
414 {
415 	char s[4];
416 
417 	if (!count)
418 		return 0;
419 	if (count > 3)
420 		return -EINVAL;
421 	if (copy_from_user(s, buffer, count))
422 		return -EFAULT;
423 	if (s[count-1] == '\n')
424 		count--;
425 	if (count == 1 && s[0] == '0')
426 		return 1;
427 	if (count == 1 && s[0] == '1')
428 		return 2;
429 	if (count == 2 && s[0] == '-' && s[1] == '1')
430 		return 3;
431 	return -EINVAL;
432 }
433 
434 /* generic stuff */
435 
436 static void entry_status(Node *e, char *page)
437 {
438 	char *dp;
439 	char *status = "disabled";
440 	const char * flags = "flags: ";
441 
442 	if (test_bit(Enabled, &e->flags))
443 		status = "enabled";
444 
445 	if (!VERBOSE_STATUS) {
446 		sprintf(page, "%s\n", status);
447 		return;
448 	}
449 
450 	sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
451 	dp = page + strlen(page);
452 
453 	/* print the special flags */
454 	sprintf (dp, "%s", flags);
455 	dp += strlen (flags);
456 	if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
457 		*dp ++ = 'P';
458 	}
459 	if (e->flags & MISC_FMT_OPEN_BINARY) {
460 		*dp ++ = 'O';
461 	}
462 	if (e->flags & MISC_FMT_CREDENTIALS) {
463 		*dp ++ = 'C';
464 	}
465 	*dp ++ = '\n';
466 
467 
468 	if (!test_bit(Magic, &e->flags)) {
469 		sprintf(dp, "extension .%s\n", e->magic);
470 	} else {
471 		int i;
472 
473 		sprintf(dp, "offset %i\nmagic ", e->offset);
474 		dp = page + strlen(page);
475 		for (i = 0; i < e->size; i++) {
476 			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
477 			dp += 2;
478 		}
479 		if (e->mask) {
480 			sprintf(dp, "\nmask ");
481 			dp += 6;
482 			for (i = 0; i < e->size; i++) {
483 				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
484 				dp += 2;
485 			}
486 		}
487 		*dp++ = '\n';
488 		*dp = '\0';
489 	}
490 }
491 
492 static struct inode *bm_get_inode(struct super_block *sb, int mode)
493 {
494 	struct inode * inode = new_inode(sb);
495 
496 	if (inode) {
497 		inode->i_ino = get_next_ino();
498 		inode->i_mode = mode;
499 		inode->i_atime = inode->i_mtime = inode->i_ctime =
500 			current_fs_time(inode->i_sb);
501 	}
502 	return inode;
503 }
504 
505 static void bm_evict_inode(struct inode *inode)
506 {
507 	end_writeback(inode);
508 	kfree(inode->i_private);
509 }
510 
511 static void kill_node(Node *e)
512 {
513 	struct dentry *dentry;
514 
515 	write_lock(&entries_lock);
516 	dentry = e->dentry;
517 	if (dentry) {
518 		list_del_init(&e->list);
519 		e->dentry = NULL;
520 	}
521 	write_unlock(&entries_lock);
522 
523 	if (dentry) {
524 		drop_nlink(dentry->d_inode);
525 		d_drop(dentry);
526 		dput(dentry);
527 		simple_release_fs(&bm_mnt, &entry_count);
528 	}
529 }
530 
531 /* /<entry> */
532 
533 static ssize_t
534 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
535 {
536 	Node *e = file->f_path.dentry->d_inode->i_private;
537 	ssize_t res;
538 	char *page;
539 
540 	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
541 		return -ENOMEM;
542 
543 	entry_status(e, page);
544 
545 	res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
546 
547 	free_page((unsigned long) page);
548 	return res;
549 }
550 
551 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
552 				size_t count, loff_t *ppos)
553 {
554 	struct dentry *root;
555 	Node *e = file->f_path.dentry->d_inode->i_private;
556 	int res = parse_command(buffer, count);
557 
558 	switch (res) {
559 		case 1: clear_bit(Enabled, &e->flags);
560 			break;
561 		case 2: set_bit(Enabled, &e->flags);
562 			break;
563 		case 3: root = dget(file->f_path.dentry->d_sb->s_root);
564 			mutex_lock(&root->d_inode->i_mutex);
565 
566 			kill_node(e);
567 
568 			mutex_unlock(&root->d_inode->i_mutex);
569 			dput(root);
570 			break;
571 		default: return res;
572 	}
573 	return count;
574 }
575 
576 static const struct file_operations bm_entry_operations = {
577 	.read		= bm_entry_read,
578 	.write		= bm_entry_write,
579 	.llseek		= default_llseek,
580 };
581 
582 /* /register */
583 
584 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
585 			       size_t count, loff_t *ppos)
586 {
587 	Node *e;
588 	struct inode *inode;
589 	struct dentry *root, *dentry;
590 	struct super_block *sb = file->f_path.dentry->d_sb;
591 	int err = 0;
592 
593 	e = create_entry(buffer, count);
594 
595 	if (IS_ERR(e))
596 		return PTR_ERR(e);
597 
598 	root = dget(sb->s_root);
599 	mutex_lock(&root->d_inode->i_mutex);
600 	dentry = lookup_one_len(e->name, root, strlen(e->name));
601 	err = PTR_ERR(dentry);
602 	if (IS_ERR(dentry))
603 		goto out;
604 
605 	err = -EEXIST;
606 	if (dentry->d_inode)
607 		goto out2;
608 
609 	inode = bm_get_inode(sb, S_IFREG | 0644);
610 
611 	err = -ENOMEM;
612 	if (!inode)
613 		goto out2;
614 
615 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
616 	if (err) {
617 		iput(inode);
618 		inode = NULL;
619 		goto out2;
620 	}
621 
622 	e->dentry = dget(dentry);
623 	inode->i_private = e;
624 	inode->i_fop = &bm_entry_operations;
625 
626 	d_instantiate(dentry, inode);
627 	write_lock(&entries_lock);
628 	list_add(&e->list, &entries);
629 	write_unlock(&entries_lock);
630 
631 	err = 0;
632 out2:
633 	dput(dentry);
634 out:
635 	mutex_unlock(&root->d_inode->i_mutex);
636 	dput(root);
637 
638 	if (err) {
639 		kfree(e);
640 		return -EINVAL;
641 	}
642 	return count;
643 }
644 
645 static const struct file_operations bm_register_operations = {
646 	.write		= bm_register_write,
647 	.llseek		= noop_llseek,
648 };
649 
650 /* /status */
651 
652 static ssize_t
653 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
654 {
655 	char *s = enabled ? "enabled\n" : "disabled\n";
656 
657 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
658 }
659 
660 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
661 		size_t count, loff_t *ppos)
662 {
663 	int res = parse_command(buffer, count);
664 	struct dentry *root;
665 
666 	switch (res) {
667 		case 1: enabled = 0; break;
668 		case 2: enabled = 1; break;
669 		case 3: root = dget(file->f_path.dentry->d_sb->s_root);
670 			mutex_lock(&root->d_inode->i_mutex);
671 
672 			while (!list_empty(&entries))
673 				kill_node(list_entry(entries.next, Node, list));
674 
675 			mutex_unlock(&root->d_inode->i_mutex);
676 			dput(root);
677 		default: return res;
678 	}
679 	return count;
680 }
681 
682 static const struct file_operations bm_status_operations = {
683 	.read		= bm_status_read,
684 	.write		= bm_status_write,
685 	.llseek		= default_llseek,
686 };
687 
688 /* Superblock handling */
689 
690 static const struct super_operations s_ops = {
691 	.statfs		= simple_statfs,
692 	.evict_inode	= bm_evict_inode,
693 };
694 
695 static int bm_fill_super(struct super_block * sb, void * data, int silent)
696 {
697 	static struct tree_descr bm_files[] = {
698 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
699 		[3] = {"register", &bm_register_operations, S_IWUSR},
700 		/* last one */ {""}
701 	};
702 	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
703 	if (!err)
704 		sb->s_op = &s_ops;
705 	return err;
706 }
707 
708 static struct dentry *bm_mount(struct file_system_type *fs_type,
709 	int flags, const char *dev_name, void *data)
710 {
711 	return mount_single(fs_type, flags, data, bm_fill_super);
712 }
713 
714 static struct linux_binfmt misc_format = {
715 	.module = THIS_MODULE,
716 	.load_binary = load_misc_binary,
717 };
718 
719 static struct file_system_type bm_fs_type = {
720 	.owner		= THIS_MODULE,
721 	.name		= "binfmt_misc",
722 	.mount		= bm_mount,
723 	.kill_sb	= kill_litter_super,
724 };
725 
726 static int __init init_misc_binfmt(void)
727 {
728 	int err = register_filesystem(&bm_fs_type);
729 	if (!err) {
730 		err = insert_binfmt(&misc_format);
731 		if (err)
732 			unregister_filesystem(&bm_fs_type);
733 	}
734 	return err;
735 }
736 
737 static void __exit exit_misc_binfmt(void)
738 {
739 	unregister_binfmt(&misc_format);
740 	unregister_filesystem(&bm_fs_type);
741 }
742 
743 core_initcall(init_misc_binfmt);
744 module_exit(exit_misc_binfmt);
745 MODULE_LICENSE("GPL");
746