xref: /linux/fs/binfmt_misc.c (revision 4f3865fb57a04db7cca068fed1c15badc064a302) 
1 /*
2  *  binfmt_misc.c
3  *
4  *  Copyright (C) 1997 Richard G�nther
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 
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 
31 #include <asm/uaccess.h>
32 
33 enum {
34 	VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
35 };
36 
37 static LIST_HEAD(entries);
38 static int enabled = 1;
39 
40 enum {Enabled, Magic};
41 #define MISC_FMT_PRESERVE_ARGV0 (1<<31)
42 #define MISC_FMT_OPEN_BINARY (1<<30)
43 #define MISC_FMT_CREDENTIALS (1<<29)
44 
45 typedef struct {
46 	struct list_head list;
47 	unsigned long flags;		/* type, status, etc. */
48 	int offset;			/* offset of magic */
49 	int size;			/* size of magic/mask */
50 	char *magic;			/* magic or filename extension */
51 	char *mask;			/* mask, NULL for exact match */
52 	char *interpreter;		/* filename of interpreter */
53 	char *name;
54 	struct dentry *dentry;
55 } Node;
56 
57 static DEFINE_RWLOCK(entries_lock);
58 static struct vfsmount *bm_mnt;
59 static int entry_count;
60 
61 /*
62  * Check if we support the binfmt
63  * if we do, return the node, else NULL
64  * locking is done in load_misc_binary
65  */
66 static Node *check_file(struct linux_binprm *bprm)
67 {
68 	char *p = strrchr(bprm->interp, '.');
69 	struct list_head *l;
70 
71 	list_for_each(l, &entries) {
72 		Node *e = list_entry(l, Node, list);
73 		char *s;
74 		int j;
75 
76 		if (!test_bit(Enabled, &e->flags))
77 			continue;
78 
79 		if (!test_bit(Magic, &e->flags)) {
80 			if (p && !strcmp(e->magic, p + 1))
81 				return e;
82 			continue;
83 		}
84 
85 		s = bprm->buf + e->offset;
86 		if (e->mask) {
87 			for (j = 0; j < e->size; j++)
88 				if ((*s++ ^ e->magic[j]) & e->mask[j])
89 					break;
90 		} else {
91 			for (j = 0; j < e->size; j++)
92 				if ((*s++ ^ e->magic[j]))
93 					break;
94 		}
95 		if (j == e->size)
96 			return e;
97 	}
98 	return NULL;
99 }
100 
101 /*
102  * the loader itself
103  */
104 static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
105 {
106 	Node *fmt;
107 	struct file * interp_file = NULL;
108 	char iname[BINPRM_BUF_SIZE];
109 	char *iname_addr = iname;
110 	int retval;
111 	int fd_binary = -1;
112 	struct files_struct *files = NULL;
113 
114 	retval = -ENOEXEC;
115 	if (!enabled)
116 		goto _ret;
117 
118 	/* to keep locking time low, we copy the interpreter string */
119 	read_lock(&entries_lock);
120 	fmt = check_file(bprm);
121 	if (fmt)
122 		strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
123 	read_unlock(&entries_lock);
124 	if (!fmt)
125 		goto _ret;
126 
127 	if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
128 		remove_arg_zero(bprm);
129 	}
130 
131 	if (fmt->flags & MISC_FMT_OPEN_BINARY) {
132 
133 		files = current->files;
134 		retval = unshare_files();
135 		if (retval < 0)
136 			goto _ret;
137 		if (files == current->files) {
138 			put_files_struct(files);
139 			files = NULL;
140 		}
141 		/* if the binary should be opened on behalf of the
142 		 * interpreter than keep it open and assign descriptor
143 		 * to it */
144  		fd_binary = get_unused_fd();
145  		if (fd_binary < 0) {
146  			retval = fd_binary;
147  			goto _unshare;
148  		}
149  		fd_install(fd_binary, bprm->file);
150 
151 		/* if the binary is not readable than enforce mm->dumpable=0
152 		   regardless of the interpreter's permissions */
153 		if (file_permission(bprm->file, MAY_READ))
154 			bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
155 
156 		allow_write_access(bprm->file);
157 		bprm->file = NULL;
158 
159 		/* mark the bprm that fd should be passed to interp */
160 		bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
161 		bprm->interp_data = fd_binary;
162 
163  	} else {
164  		allow_write_access(bprm->file);
165  		fput(bprm->file);
166  		bprm->file = NULL;
167  	}
168 	/* make argv[1] be the path to the binary */
169 	retval = copy_strings_kernel (1, &bprm->interp, bprm);
170 	if (retval < 0)
171 		goto _error;
172 	bprm->argc++;
173 
174 	/* add the interp as argv[0] */
175 	retval = copy_strings_kernel (1, &iname_addr, bprm);
176 	if (retval < 0)
177 		goto _error;
178 	bprm->argc ++;
179 
180 	bprm->interp = iname;	/* for binfmt_script */
181 
182 	interp_file = open_exec (iname);
183 	retval = PTR_ERR (interp_file);
184 	if (IS_ERR (interp_file))
185 		goto _error;
186 
187 	bprm->file = interp_file;
188 	if (fmt->flags & MISC_FMT_CREDENTIALS) {
189 		/*
190 		 * No need to call prepare_binprm(), it's already been
191 		 * done.  bprm->buf is stale, update from interp_file.
192 		 */
193 		memset(bprm->buf, 0, BINPRM_BUF_SIZE);
194 		retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
195 	} else
196 		retval = prepare_binprm (bprm);
197 
198 	if (retval < 0)
199 		goto _error;
200 
201 	retval = search_binary_handler (bprm, regs);
202 	if (retval < 0)
203 		goto _error;
204 
205 	if (files) {
206 		put_files_struct(files);
207 		files = NULL;
208 	}
209 _ret:
210 	return retval;
211 _error:
212 	if (fd_binary > 0)
213 		sys_close(fd_binary);
214 	bprm->interp_flags = 0;
215 	bprm->interp_data = 0;
216 _unshare:
217 	if (files) {
218 		put_files_struct(current->files);
219 		current->files = files;
220 	}
221 	goto _ret;
222 }
223 
224 /* Command parsers */
225 
226 /*
227  * parses and copies one argument enclosed in del from *sp to *dp,
228  * recognising the \x special.
229  * returns pointer to the copied argument or NULL in case of an
230  * error (and sets err) or null argument length.
231  */
232 static char *scanarg(char *s, char del)
233 {
234 	char c;
235 
236 	while ((c = *s++) != del) {
237 		if (c == '\\' && *s == 'x') {
238 			s++;
239 			if (!isxdigit(*s++))
240 				return NULL;
241 			if (!isxdigit(*s++))
242 				return NULL;
243 		}
244 	}
245 	return s;
246 }
247 
248 static int unquote(char *from)
249 {
250 	char c = 0, *s = from, *p = from;
251 
252 	while ((c = *s++) != '\0') {
253 		if (c == '\\' && *s == 'x') {
254 			s++;
255 			c = toupper(*s++);
256 			*p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
257 			c = toupper(*s++);
258 			*p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
259 			continue;
260 		}
261 		*p++ = c;
262 	}
263 	return p - from;
264 }
265 
266 static char * check_special_flags (char * sfs, Node * e)
267 {
268 	char * p = sfs;
269 	int cont = 1;
270 
271 	/* special flags */
272 	while (cont) {
273 		switch (*p) {
274 			case 'P':
275 				p++;
276 				e->flags |= MISC_FMT_PRESERVE_ARGV0;
277 				break;
278 			case 'O':
279 				p++;
280 				e->flags |= MISC_FMT_OPEN_BINARY;
281 				break;
282 			case 'C':
283 				p++;
284 				/* this flags also implies the
285 				   open-binary flag */
286 				e->flags |= (MISC_FMT_CREDENTIALS |
287 						MISC_FMT_OPEN_BINARY);
288 				break;
289 			default:
290 				cont = 0;
291 		}
292 	}
293 
294 	return p;
295 }
296 /*
297  * This registers a new binary format, it recognises the syntax
298  * ':name:type:offset:magic:mask:interpreter:flags'
299  * where the ':' is the IFS, that can be chosen with the first char
300  */
301 static Node *create_entry(const char __user *buffer, size_t count)
302 {
303 	Node *e;
304 	int memsize, err;
305 	char *buf, *p;
306 	char del;
307 
308 	/* some sanity checks */
309 	err = -EINVAL;
310 	if ((count < 11) || (count > 256))
311 		goto out;
312 
313 	err = -ENOMEM;
314 	memsize = sizeof(Node) + count + 8;
315 	e = (Node *) kmalloc(memsize, GFP_USER);
316 	if (!e)
317 		goto out;
318 
319 	p = buf = (char *)e + sizeof(Node);
320 
321 	memset(e, 0, sizeof(Node));
322 	if (copy_from_user(buf, buffer, count))
323 		goto Efault;
324 
325 	del = *p++;	/* delimeter */
326 
327 	memset(buf+count, del, 8);
328 
329 	e->name = p;
330 	p = strchr(p, del);
331 	if (!p)
332 		goto Einval;
333 	*p++ = '\0';
334 	if (!e->name[0] ||
335 	    !strcmp(e->name, ".") ||
336 	    !strcmp(e->name, "..") ||
337 	    strchr(e->name, '/'))
338 		goto Einval;
339 	switch (*p++) {
340 		case 'E': e->flags = 1<<Enabled; break;
341 		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
342 		default: goto Einval;
343 	}
344 	if (*p++ != del)
345 		goto Einval;
346 	if (test_bit(Magic, &e->flags)) {
347 		char *s = strchr(p, del);
348 		if (!s)
349 			goto Einval;
350 		*s++ = '\0';
351 		e->offset = simple_strtoul(p, &p, 10);
352 		if (*p++)
353 			goto Einval;
354 		e->magic = p;
355 		p = scanarg(p, del);
356 		if (!p)
357 			goto Einval;
358 		p[-1] = '\0';
359 		if (!e->magic[0])
360 			goto Einval;
361 		e->mask = p;
362 		p = scanarg(p, del);
363 		if (!p)
364 			goto Einval;
365 		p[-1] = '\0';
366 		if (!e->mask[0])
367 			e->mask = NULL;
368 		e->size = unquote(e->magic);
369 		if (e->mask && unquote(e->mask) != e->size)
370 			goto Einval;
371 		if (e->size + e->offset > BINPRM_BUF_SIZE)
372 			goto Einval;
373 	} else {
374 		p = strchr(p, del);
375 		if (!p)
376 			goto Einval;
377 		*p++ = '\0';
378 		e->magic = p;
379 		p = strchr(p, del);
380 		if (!p)
381 			goto Einval;
382 		*p++ = '\0';
383 		if (!e->magic[0] || strchr(e->magic, '/'))
384 			goto Einval;
385 		p = strchr(p, del);
386 		if (!p)
387 			goto Einval;
388 		*p++ = '\0';
389 	}
390 	e->interpreter = p;
391 	p = strchr(p, del);
392 	if (!p)
393 		goto Einval;
394 	*p++ = '\0';
395 	if (!e->interpreter[0])
396 		goto Einval;
397 
398 
399 	p = check_special_flags (p, e);
400 
401 	if (*p == '\n')
402 		p++;
403 	if (p != buf + count)
404 		goto Einval;
405 	return e;
406 
407 out:
408 	return ERR_PTR(err);
409 
410 Efault:
411 	kfree(e);
412 	return ERR_PTR(-EFAULT);
413 Einval:
414 	kfree(e);
415 	return ERR_PTR(-EINVAL);
416 }
417 
418 /*
419  * Set status of entry/binfmt_misc:
420  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
421  */
422 static int parse_command(const char __user *buffer, size_t count)
423 {
424 	char s[4];
425 
426 	if (!count)
427 		return 0;
428 	if (count > 3)
429 		return -EINVAL;
430 	if (copy_from_user(s, buffer, count))
431 		return -EFAULT;
432 	if (s[count-1] == '\n')
433 		count--;
434 	if (count == 1 && s[0] == '0')
435 		return 1;
436 	if (count == 1 && s[0] == '1')
437 		return 2;
438 	if (count == 2 && s[0] == '-' && s[1] == '1')
439 		return 3;
440 	return -EINVAL;
441 }
442 
443 /* generic stuff */
444 
445 static void entry_status(Node *e, char *page)
446 {
447 	char *dp;
448 	char *status = "disabled";
449 	const char * flags = "flags: ";
450 
451 	if (test_bit(Enabled, &e->flags))
452 		status = "enabled";
453 
454 	if (!VERBOSE_STATUS) {
455 		sprintf(page, "%s\n", status);
456 		return;
457 	}
458 
459 	sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
460 	dp = page + strlen(page);
461 
462 	/* print the special flags */
463 	sprintf (dp, "%s", flags);
464 	dp += strlen (flags);
465 	if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
466 		*dp ++ = 'P';
467 	}
468 	if (e->flags & MISC_FMT_OPEN_BINARY) {
469 		*dp ++ = 'O';
470 	}
471 	if (e->flags & MISC_FMT_CREDENTIALS) {
472 		*dp ++ = 'C';
473 	}
474 	*dp ++ = '\n';
475 
476 
477 	if (!test_bit(Magic, &e->flags)) {
478 		sprintf(dp, "extension .%s\n", e->magic);
479 	} else {
480 		int i;
481 
482 		sprintf(dp, "offset %i\nmagic ", e->offset);
483 		dp = page + strlen(page);
484 		for (i = 0; i < e->size; i++) {
485 			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
486 			dp += 2;
487 		}
488 		if (e->mask) {
489 			sprintf(dp, "\nmask ");
490 			dp += 6;
491 			for (i = 0; i < e->size; i++) {
492 				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
493 				dp += 2;
494 			}
495 		}
496 		*dp++ = '\n';
497 		*dp = '\0';
498 	}
499 }
500 
501 static struct inode *bm_get_inode(struct super_block *sb, int mode)
502 {
503 	struct inode * inode = new_inode(sb);
504 
505 	if (inode) {
506 		inode->i_mode = mode;
507 		inode->i_uid = 0;
508 		inode->i_gid = 0;
509 		inode->i_blksize = PAGE_CACHE_SIZE;
510 		inode->i_blocks = 0;
511 		inode->i_atime = inode->i_mtime = inode->i_ctime =
512 			current_fs_time(inode->i_sb);
513 	}
514 	return inode;
515 }
516 
517 static void bm_clear_inode(struct inode *inode)
518 {
519 	kfree(inode->u.generic_ip);
520 }
521 
522 static void kill_node(Node *e)
523 {
524 	struct dentry *dentry;
525 
526 	write_lock(&entries_lock);
527 	dentry = e->dentry;
528 	if (dentry) {
529 		list_del_init(&e->list);
530 		e->dentry = NULL;
531 	}
532 	write_unlock(&entries_lock);
533 
534 	if (dentry) {
535 		dentry->d_inode->i_nlink--;
536 		d_drop(dentry);
537 		dput(dentry);
538 		simple_release_fs(&bm_mnt, &entry_count);
539 	}
540 }
541 
542 /* /<entry> */
543 
544 static ssize_t
545 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
546 {
547 	Node *e = file->f_dentry->d_inode->u.generic_ip;
548 	loff_t pos = *ppos;
549 	ssize_t res;
550 	char *page;
551 	int len;
552 
553 	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
554 		return -ENOMEM;
555 
556 	entry_status(e, page);
557 	len = strlen(page);
558 
559 	res = -EINVAL;
560 	if (pos < 0)
561 		goto out;
562 	res = 0;
563 	if (pos >= len)
564 		goto out;
565 	if (len < pos + nbytes)
566 		nbytes = len - pos;
567 	res = -EFAULT;
568 	if (copy_to_user(buf, page + pos, nbytes))
569 		goto out;
570 	*ppos = pos + nbytes;
571 	res = nbytes;
572 out:
573 	free_page((unsigned long) page);
574 	return res;
575 }
576 
577 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
578 				size_t count, loff_t *ppos)
579 {
580 	struct dentry *root;
581 	Node *e = file->f_dentry->d_inode->u.generic_ip;
582 	int res = parse_command(buffer, count);
583 
584 	switch (res) {
585 		case 1: clear_bit(Enabled, &e->flags);
586 			break;
587 		case 2: set_bit(Enabled, &e->flags);
588 			break;
589 		case 3: root = dget(file->f_vfsmnt->mnt_sb->s_root);
590 			mutex_lock(&root->d_inode->i_mutex);
591 
592 			kill_node(e);
593 
594 			mutex_unlock(&root->d_inode->i_mutex);
595 			dput(root);
596 			break;
597 		default: return res;
598 	}
599 	return count;
600 }
601 
602 static const struct file_operations bm_entry_operations = {
603 	.read		= bm_entry_read,
604 	.write		= bm_entry_write,
605 };
606 
607 /* /register */
608 
609 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
610 			       size_t count, loff_t *ppos)
611 {
612 	Node *e;
613 	struct inode *inode;
614 	struct dentry *root, *dentry;
615 	struct super_block *sb = file->f_vfsmnt->mnt_sb;
616 	int err = 0;
617 
618 	e = create_entry(buffer, count);
619 
620 	if (IS_ERR(e))
621 		return PTR_ERR(e);
622 
623 	root = dget(sb->s_root);
624 	mutex_lock(&root->d_inode->i_mutex);
625 	dentry = lookup_one_len(e->name, root, strlen(e->name));
626 	err = PTR_ERR(dentry);
627 	if (IS_ERR(dentry))
628 		goto out;
629 
630 	err = -EEXIST;
631 	if (dentry->d_inode)
632 		goto out2;
633 
634 	inode = bm_get_inode(sb, S_IFREG | 0644);
635 
636 	err = -ENOMEM;
637 	if (!inode)
638 		goto out2;
639 
640 	err = simple_pin_fs("binfmt_misc", &bm_mnt, &entry_count);
641 	if (err) {
642 		iput(inode);
643 		inode = NULL;
644 		goto out2;
645 	}
646 
647 	e->dentry = dget(dentry);
648 	inode->u.generic_ip = e;
649 	inode->i_fop = &bm_entry_operations;
650 
651 	d_instantiate(dentry, inode);
652 	write_lock(&entries_lock);
653 	list_add(&e->list, &entries);
654 	write_unlock(&entries_lock);
655 
656 	err = 0;
657 out2:
658 	dput(dentry);
659 out:
660 	mutex_unlock(&root->d_inode->i_mutex);
661 	dput(root);
662 
663 	if (err) {
664 		kfree(e);
665 		return -EINVAL;
666 	}
667 	return count;
668 }
669 
670 static const struct file_operations bm_register_operations = {
671 	.write		= bm_register_write,
672 };
673 
674 /* /status */
675 
676 static ssize_t
677 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
678 {
679 	char *s = enabled ? "enabled" : "disabled";
680 	int len = strlen(s);
681 	loff_t pos = *ppos;
682 
683 	if (pos < 0)
684 		return -EINVAL;
685 	if (pos >= len)
686 		return 0;
687 	if (len < pos + nbytes)
688 		nbytes = len - pos;
689 	if (copy_to_user(buf, s + pos, nbytes))
690 		return -EFAULT;
691 	*ppos = pos + nbytes;
692 	return nbytes;
693 }
694 
695 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
696 		size_t count, loff_t *ppos)
697 {
698 	int res = parse_command(buffer, count);
699 	struct dentry *root;
700 
701 	switch (res) {
702 		case 1: enabled = 0; break;
703 		case 2: enabled = 1; break;
704 		case 3: root = dget(file->f_vfsmnt->mnt_sb->s_root);
705 			mutex_lock(&root->d_inode->i_mutex);
706 
707 			while (!list_empty(&entries))
708 				kill_node(list_entry(entries.next, Node, list));
709 
710 			mutex_unlock(&root->d_inode->i_mutex);
711 			dput(root);
712 		default: return res;
713 	}
714 	return count;
715 }
716 
717 static const struct file_operations bm_status_operations = {
718 	.read		= bm_status_read,
719 	.write		= bm_status_write,
720 };
721 
722 /* Superblock handling */
723 
724 static struct super_operations s_ops = {
725 	.statfs		= simple_statfs,
726 	.clear_inode	= bm_clear_inode,
727 };
728 
729 static int bm_fill_super(struct super_block * sb, void * data, int silent)
730 {
731 	static struct tree_descr bm_files[] = {
732 		[1] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
733 		[2] = {"register", &bm_register_operations, S_IWUSR},
734 		/* last one */ {""}
735 	};
736 	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
737 	if (!err)
738 		sb->s_op = &s_ops;
739 	return err;
740 }
741 
742 static struct super_block *bm_get_sb(struct file_system_type *fs_type,
743 	int flags, const char *dev_name, void *data)
744 {
745 	return get_sb_single(fs_type, flags, data, bm_fill_super);
746 }
747 
748 static struct linux_binfmt misc_format = {
749 	.module = THIS_MODULE,
750 	.load_binary = load_misc_binary,
751 };
752 
753 static struct file_system_type bm_fs_type = {
754 	.owner		= THIS_MODULE,
755 	.name		= "binfmt_misc",
756 	.get_sb		= bm_get_sb,
757 	.kill_sb	= kill_litter_super,
758 };
759 
760 static int __init init_misc_binfmt(void)
761 {
762 	int err = register_filesystem(&bm_fs_type);
763 	if (!err) {
764 		err = register_binfmt(&misc_format);
765 		if (err)
766 			unregister_filesystem(&bm_fs_type);
767 	}
768 	return err;
769 }
770 
771 static void __exit exit_misc_binfmt(void)
772 {
773 	unregister_binfmt(&misc_format);
774 	unregister_filesystem(&bm_fs_type);
775 }
776 
777 core_initcall(init_misc_binfmt);
778 module_exit(exit_misc_binfmt);
779 MODULE_LICENSE("GPL");
780