xref: /openbmc/linux/fs/binfmt_misc.c (revision 9d749629) 
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 	/* Update interp in case binfmt_script needs it. */
176 	retval = bprm_change_interp(iname, bprm);
177 	if (retval < 0)
178 		goto _error;
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 	retval = search_binary_handler(bprm);
200 	if (retval < 0)
201 		goto _error;
202 
203 _ret:
204 	return retval;
205 _error:
206 	if (fd_binary > 0)
207 		sys_close(fd_binary);
208 	bprm->interp_flags = 0;
209 	bprm->interp_data = 0;
210 	goto _ret;
211 }
212 
213 /* Command parsers */
214 
215 /*
216  * parses and copies one argument enclosed in del from *sp to *dp,
217  * recognising the \x special.
218  * returns pointer to the copied argument or NULL in case of an
219  * error (and sets err) or null argument length.
220  */
221 static char *scanarg(char *s, char del)
222 {
223 	char c;
224 
225 	while ((c = *s++) != del) {
226 		if (c == '\\' && *s == 'x') {
227 			s++;
228 			if (!isxdigit(*s++))
229 				return NULL;
230 			if (!isxdigit(*s++))
231 				return NULL;
232 		}
233 	}
234 	return s;
235 }
236 
237 static int unquote(char *from)
238 {
239 	char c = 0, *s = from, *p = from;
240 
241 	while ((c = *s++) != '\0') {
242 		if (c == '\\' && *s == 'x') {
243 			s++;
244 			c = toupper(*s++);
245 			*p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
246 			c = toupper(*s++);
247 			*p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
248 			continue;
249 		}
250 		*p++ = c;
251 	}
252 	return p - from;
253 }
254 
255 static char * check_special_flags (char * sfs, Node * e)
256 {
257 	char * p = sfs;
258 	int cont = 1;
259 
260 	/* special flags */
261 	while (cont) {
262 		switch (*p) {
263 			case 'P':
264 				p++;
265 				e->flags |= MISC_FMT_PRESERVE_ARGV0;
266 				break;
267 			case 'O':
268 				p++;
269 				e->flags |= MISC_FMT_OPEN_BINARY;
270 				break;
271 			case 'C':
272 				p++;
273 				/* this flags also implies the
274 				   open-binary flag */
275 				e->flags |= (MISC_FMT_CREDENTIALS |
276 						MISC_FMT_OPEN_BINARY);
277 				break;
278 			default:
279 				cont = 0;
280 		}
281 	}
282 
283 	return p;
284 }
285 /*
286  * This registers a new binary format, it recognises the syntax
287  * ':name:type:offset:magic:mask:interpreter:flags'
288  * where the ':' is the IFS, that can be chosen with the first char
289  */
290 static Node *create_entry(const char __user *buffer, size_t count)
291 {
292 	Node *e;
293 	int memsize, err;
294 	char *buf, *p;
295 	char del;
296 
297 	/* some sanity checks */
298 	err = -EINVAL;
299 	if ((count < 11) || (count > 256))
300 		goto out;
301 
302 	err = -ENOMEM;
303 	memsize = sizeof(Node) + count + 8;
304 	e = kmalloc(memsize, GFP_USER);
305 	if (!e)
306 		goto out;
307 
308 	p = buf = (char *)e + sizeof(Node);
309 
310 	memset(e, 0, sizeof(Node));
311 	if (copy_from_user(buf, buffer, count))
312 		goto Efault;
313 
314 	del = *p++;	/* delimeter */
315 
316 	memset(buf+count, del, 8);
317 
318 	e->name = p;
319 	p = strchr(p, del);
320 	if (!p)
321 		goto Einval;
322 	*p++ = '\0';
323 	if (!e->name[0] ||
324 	    !strcmp(e->name, ".") ||
325 	    !strcmp(e->name, "..") ||
326 	    strchr(e->name, '/'))
327 		goto Einval;
328 	switch (*p++) {
329 		case 'E': e->flags = 1<<Enabled; break;
330 		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
331 		default: goto Einval;
332 	}
333 	if (*p++ != del)
334 		goto Einval;
335 	if (test_bit(Magic, &e->flags)) {
336 		char *s = strchr(p, del);
337 		if (!s)
338 			goto Einval;
339 		*s++ = '\0';
340 		e->offset = simple_strtoul(p, &p, 10);
341 		if (*p++)
342 			goto Einval;
343 		e->magic = p;
344 		p = scanarg(p, del);
345 		if (!p)
346 			goto Einval;
347 		p[-1] = '\0';
348 		if (!e->magic[0])
349 			goto Einval;
350 		e->mask = p;
351 		p = scanarg(p, del);
352 		if (!p)
353 			goto Einval;
354 		p[-1] = '\0';
355 		if (!e->mask[0])
356 			e->mask = NULL;
357 		e->size = unquote(e->magic);
358 		if (e->mask && unquote(e->mask) != e->size)
359 			goto Einval;
360 		if (e->size + e->offset > BINPRM_BUF_SIZE)
361 			goto Einval;
362 	} else {
363 		p = strchr(p, del);
364 		if (!p)
365 			goto Einval;
366 		*p++ = '\0';
367 		e->magic = p;
368 		p = strchr(p, del);
369 		if (!p)
370 			goto Einval;
371 		*p++ = '\0';
372 		if (!e->magic[0] || strchr(e->magic, '/'))
373 			goto Einval;
374 		p = strchr(p, del);
375 		if (!p)
376 			goto Einval;
377 		*p++ = '\0';
378 	}
379 	e->interpreter = p;
380 	p = strchr(p, del);
381 	if (!p)
382 		goto Einval;
383 	*p++ = '\0';
384 	if (!e->interpreter[0])
385 		goto Einval;
386 
387 
388 	p = check_special_flags (p, e);
389 
390 	if (*p == '\n')
391 		p++;
392 	if (p != buf + count)
393 		goto Einval;
394 	return e;
395 
396 out:
397 	return ERR_PTR(err);
398 
399 Efault:
400 	kfree(e);
401 	return ERR_PTR(-EFAULT);
402 Einval:
403 	kfree(e);
404 	return ERR_PTR(-EINVAL);
405 }
406 
407 /*
408  * Set status of entry/binfmt_misc:
409  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
410  */
411 static int parse_command(const char __user *buffer, size_t count)
412 {
413 	char s[4];
414 
415 	if (!count)
416 		return 0;
417 	if (count > 3)
418 		return -EINVAL;
419 	if (copy_from_user(s, buffer, count))
420 		return -EFAULT;
421 	if (s[count-1] == '\n')
422 		count--;
423 	if (count == 1 && s[0] == '0')
424 		return 1;
425 	if (count == 1 && s[0] == '1')
426 		return 2;
427 	if (count == 2 && s[0] == '-' && s[1] == '1')
428 		return 3;
429 	return -EINVAL;
430 }
431 
432 /* generic stuff */
433 
434 static void entry_status(Node *e, char *page)
435 {
436 	char *dp;
437 	char *status = "disabled";
438 	const char * flags = "flags: ";
439 
440 	if (test_bit(Enabled, &e->flags))
441 		status = "enabled";
442 
443 	if (!VERBOSE_STATUS) {
444 		sprintf(page, "%s\n", status);
445 		return;
446 	}
447 
448 	sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
449 	dp = page + strlen(page);
450 
451 	/* print the special flags */
452 	sprintf (dp, "%s", flags);
453 	dp += strlen (flags);
454 	if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
455 		*dp ++ = 'P';
456 	}
457 	if (e->flags & MISC_FMT_OPEN_BINARY) {
458 		*dp ++ = 'O';
459 	}
460 	if (e->flags & MISC_FMT_CREDENTIALS) {
461 		*dp ++ = 'C';
462 	}
463 	*dp ++ = '\n';
464 
465 
466 	if (!test_bit(Magic, &e->flags)) {
467 		sprintf(dp, "extension .%s\n", e->magic);
468 	} else {
469 		int i;
470 
471 		sprintf(dp, "offset %i\nmagic ", e->offset);
472 		dp = page + strlen(page);
473 		for (i = 0; i < e->size; i++) {
474 			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
475 			dp += 2;
476 		}
477 		if (e->mask) {
478 			sprintf(dp, "\nmask ");
479 			dp += 6;
480 			for (i = 0; i < e->size; i++) {
481 				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
482 				dp += 2;
483 			}
484 		}
485 		*dp++ = '\n';
486 		*dp = '\0';
487 	}
488 }
489 
490 static struct inode *bm_get_inode(struct super_block *sb, int mode)
491 {
492 	struct inode * inode = new_inode(sb);
493 
494 	if (inode) {
495 		inode->i_ino = get_next_ino();
496 		inode->i_mode = mode;
497 		inode->i_atime = inode->i_mtime = inode->i_ctime =
498 			current_fs_time(inode->i_sb);
499 	}
500 	return inode;
501 }
502 
503 static void bm_evict_inode(struct inode *inode)
504 {
505 	clear_inode(inode);
506 	kfree(inode->i_private);
507 }
508 
509 static void kill_node(Node *e)
510 {
511 	struct dentry *dentry;
512 
513 	write_lock(&entries_lock);
514 	dentry = e->dentry;
515 	if (dentry) {
516 		list_del_init(&e->list);
517 		e->dentry = NULL;
518 	}
519 	write_unlock(&entries_lock);
520 
521 	if (dentry) {
522 		drop_nlink(dentry->d_inode);
523 		d_drop(dentry);
524 		dput(dentry);
525 		simple_release_fs(&bm_mnt, &entry_count);
526 	}
527 }
528 
529 /* /<entry> */
530 
531 static ssize_t
532 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
533 {
534 	Node *e = file->f_path.dentry->d_inode->i_private;
535 	ssize_t res;
536 	char *page;
537 
538 	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
539 		return -ENOMEM;
540 
541 	entry_status(e, page);
542 
543 	res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
544 
545 	free_page((unsigned long) page);
546 	return res;
547 }
548 
549 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
550 				size_t count, loff_t *ppos)
551 {
552 	struct dentry *root;
553 	Node *e = file->f_path.dentry->d_inode->i_private;
554 	int res = parse_command(buffer, count);
555 
556 	switch (res) {
557 		case 1: clear_bit(Enabled, &e->flags);
558 			break;
559 		case 2: set_bit(Enabled, &e->flags);
560 			break;
561 		case 3: root = dget(file->f_path.dentry->d_sb->s_root);
562 			mutex_lock(&root->d_inode->i_mutex);
563 
564 			kill_node(e);
565 
566 			mutex_unlock(&root->d_inode->i_mutex);
567 			dput(root);
568 			break;
569 		default: return res;
570 	}
571 	return count;
572 }
573 
574 static const struct file_operations bm_entry_operations = {
575 	.read		= bm_entry_read,
576 	.write		= bm_entry_write,
577 	.llseek		= default_llseek,
578 };
579 
580 /* /register */
581 
582 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
583 			       size_t count, loff_t *ppos)
584 {
585 	Node *e;
586 	struct inode *inode;
587 	struct dentry *root, *dentry;
588 	struct super_block *sb = file->f_path.dentry->d_sb;
589 	int err = 0;
590 
591 	e = create_entry(buffer, count);
592 
593 	if (IS_ERR(e))
594 		return PTR_ERR(e);
595 
596 	root = dget(sb->s_root);
597 	mutex_lock(&root->d_inode->i_mutex);
598 	dentry = lookup_one_len(e->name, root, strlen(e->name));
599 	err = PTR_ERR(dentry);
600 	if (IS_ERR(dentry))
601 		goto out;
602 
603 	err = -EEXIST;
604 	if (dentry->d_inode)
605 		goto out2;
606 
607 	inode = bm_get_inode(sb, S_IFREG | 0644);
608 
609 	err = -ENOMEM;
610 	if (!inode)
611 		goto out2;
612 
613 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
614 	if (err) {
615 		iput(inode);
616 		inode = NULL;
617 		goto out2;
618 	}
619 
620 	e->dentry = dget(dentry);
621 	inode->i_private = e;
622 	inode->i_fop = &bm_entry_operations;
623 
624 	d_instantiate(dentry, inode);
625 	write_lock(&entries_lock);
626 	list_add(&e->list, &entries);
627 	write_unlock(&entries_lock);
628 
629 	err = 0;
630 out2:
631 	dput(dentry);
632 out:
633 	mutex_unlock(&root->d_inode->i_mutex);
634 	dput(root);
635 
636 	if (err) {
637 		kfree(e);
638 		return -EINVAL;
639 	}
640 	return count;
641 }
642 
643 static const struct file_operations bm_register_operations = {
644 	.write		= bm_register_write,
645 	.llseek		= noop_llseek,
646 };
647 
648 /* /status */
649 
650 static ssize_t
651 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
652 {
653 	char *s = enabled ? "enabled\n" : "disabled\n";
654 
655 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
656 }
657 
658 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
659 		size_t count, loff_t *ppos)
660 {
661 	int res = parse_command(buffer, count);
662 	struct dentry *root;
663 
664 	switch (res) {
665 		case 1: enabled = 0; break;
666 		case 2: enabled = 1; break;
667 		case 3: root = dget(file->f_path.dentry->d_sb->s_root);
668 			mutex_lock(&root->d_inode->i_mutex);
669 
670 			while (!list_empty(&entries))
671 				kill_node(list_entry(entries.next, Node, list));
672 
673 			mutex_unlock(&root->d_inode->i_mutex);
674 			dput(root);
675 		default: return res;
676 	}
677 	return count;
678 }
679 
680 static const struct file_operations bm_status_operations = {
681 	.read		= bm_status_read,
682 	.write		= bm_status_write,
683 	.llseek		= default_llseek,
684 };
685 
686 /* Superblock handling */
687 
688 static const struct super_operations s_ops = {
689 	.statfs		= simple_statfs,
690 	.evict_inode	= bm_evict_inode,
691 };
692 
693 static int bm_fill_super(struct super_block * sb, void * data, int silent)
694 {
695 	static struct tree_descr bm_files[] = {
696 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
697 		[3] = {"register", &bm_register_operations, S_IWUSR},
698 		/* last one */ {""}
699 	};
700 	int err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
701 	if (!err)
702 		sb->s_op = &s_ops;
703 	return err;
704 }
705 
706 static struct dentry *bm_mount(struct file_system_type *fs_type,
707 	int flags, const char *dev_name, void *data)
708 {
709 	return mount_single(fs_type, flags, data, bm_fill_super);
710 }
711 
712 static struct linux_binfmt misc_format = {
713 	.module = THIS_MODULE,
714 	.load_binary = load_misc_binary,
715 };
716 
717 static struct file_system_type bm_fs_type = {
718 	.owner		= THIS_MODULE,
719 	.name		= "binfmt_misc",
720 	.mount		= bm_mount,
721 	.kill_sb	= kill_litter_super,
722 };
723 
724 static int __init init_misc_binfmt(void)
725 {
726 	int err = register_filesystem(&bm_fs_type);
727 	if (!err)
728 		insert_binfmt(&misc_format);
729 	return err;
730 }
731 
732 static void __exit exit_misc_binfmt(void)
733 {
734 	unregister_binfmt(&misc_format);
735 	unregister_filesystem(&bm_fs_type);
736 }
737 
738 core_initcall(init_misc_binfmt);
739 module_exit(exit_misc_binfmt);
740 MODULE_LICENSE("GPL");
741