xref: /linux/fs/binfmt_misc.c (revision d39d0ed196aa1685bb24771e92f78633c66ac9cb) 
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 		if (file_permission(bprm->file, MAY_READ))
153 			bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
154 
155 		allow_write_access(bprm->file);
156 		bprm->file = NULL;
157 
158 		/* mark the bprm that fd should be passed to interp */
159 		bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
160 		bprm->interp_data = fd_binary;
161 
162  	} else {
163  		allow_write_access(bprm->file);
164  		fput(bprm->file);
165  		bprm->file = NULL;
166  	}
167 	/* make argv[1] be the path to the binary */
168 	retval = copy_strings_kernel (1, &bprm->interp, bprm);
169 	if (retval < 0)
170 		goto _error;
171 	bprm->argc++;
172 
173 	/* add the interp as argv[0] */
174 	retval = copy_strings_kernel (1, &iname_addr, bprm);
175 	if (retval < 0)
176 		goto _error;
177 	bprm->argc ++;
178 
179 	bprm->interp = iname;	/* for binfmt_script */
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 	bprm->recursion_depth++;
201 
202 	retval = search_binary_handler (bprm, regs);
203 	if (retval < 0)
204 		goto _error;
205 
206 _ret:
207 	return retval;
208 _error:
209 	if (fd_binary > 0)
210 		sys_close(fd_binary);
211 	bprm->interp_flags = 0;
212 	bprm->interp_data = 0;
213 	goto _ret;
214 }
215 
216 /* Command parsers */
217 
218 /*
219  * parses and copies one argument enclosed in del from *sp to *dp,
220  * recognising the \x special.
221  * returns pointer to the copied argument or NULL in case of an
222  * error (and sets err) or null argument length.
223  */
224 static char *scanarg(char *s, char del)
225 {
226 	char c;
227 
228 	while ((c = *s++) != del) {
229 		if (c == '\\' && *s == 'x') {
230 			s++;
231 			if (!isxdigit(*s++))
232 				return NULL;
233 			if (!isxdigit(*s++))
234 				return NULL;
235 		}
236 	}
237 	return s;
238 }
239 
240 static int unquote(char *from)
241 {
242 	char c = 0, *s = from, *p = from;
243 
244 	while ((c = *s++) != '\0') {
245 		if (c == '\\' && *s == 'x') {
246 			s++;
247 			c = toupper(*s++);
248 			*p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
249 			c = toupper(*s++);
250 			*p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
251 			continue;
252 		}
253 		*p++ = c;
254 	}
255 	return p - from;
256 }
257 
258 static char * check_special_flags (char * sfs, Node * e)
259 {
260 	char * p = sfs;
261 	int cont = 1;
262 
263 	/* special flags */
264 	while (cont) {
265 		switch (*p) {
266 			case 'P':
267 				p++;
268 				e->flags |= MISC_FMT_PRESERVE_ARGV0;
269 				break;
270 			case 'O':
271 				p++;
272 				e->flags |= MISC_FMT_OPEN_BINARY;
273 				break;
274 			case 'C':
275 				p++;
276 				/* this flags also implies the
277 				   open-binary flag */
278 				e->flags |= (MISC_FMT_CREDENTIALS |
279 						MISC_FMT_OPEN_BINARY);
280 				break;
281 			default:
282 				cont = 0;
283 		}
284 	}
285 
286 	return p;
287 }
288 /*
289  * This registers a new binary format, it recognises the syntax
290  * ':name:type:offset:magic:mask:interpreter:flags'
291  * where the ':' is the IFS, that can be chosen with the first char
292  */
293 static Node *create_entry(const char __user *buffer, size_t count)
294 {
295 	Node *e;
296 	int memsize, err;
297 	char *buf, *p;
298 	char del;
299 
300 	/* some sanity checks */
301 	err = -EINVAL;
302 	if ((count < 11) || (count > 256))
303 		goto out;
304 
305 	err = -ENOMEM;
306 	memsize = sizeof(Node) + count + 8;
307 	e = kmalloc(memsize, GFP_USER);
308 	if (!e)
309 		goto out;
310 
311 	p = buf = (char *)e + sizeof(Node);
312 
313 	memset(e, 0, sizeof(Node));
314 	if (copy_from_user(buf, buffer, count))
315 		goto Efault;
316 
317 	del = *p++;	/* delimeter */
318 
319 	memset(buf+count, del, 8);
320 
321 	e->name = p;
322 	p = strchr(p, del);
323 	if (!p)
324 		goto Einval;
325 	*p++ = '\0';
326 	if (!e->name[0] ||
327 	    !strcmp(e->name, ".") ||
328 	    !strcmp(e->name, "..") ||
329 	    strchr(e->name, '/'))
330 		goto Einval;
331 	switch (*p++) {
332 		case 'E': e->flags = 1<<Enabled; break;
333 		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
334 		default: goto Einval;
335 	}
336 	if (*p++ != del)
337 		goto Einval;
338 	if (test_bit(Magic, &e->flags)) {
339 		char *s = strchr(p, del);
340 		if (!s)
341 			goto Einval;
342 		*s++ = '\0';
343 		e->offset = simple_strtoul(p, &p, 10);
344 		if (*p++)
345 			goto Einval;
346 		e->magic = p;
347 		p = scanarg(p, del);
348 		if (!p)
349 			goto Einval;
350 		p[-1] = '\0';
351 		if (!e->magic[0])
352 			goto Einval;
353 		e->mask = p;
354 		p = scanarg(p, del);
355 		if (!p)
356 			goto Einval;
357 		p[-1] = '\0';
358 		if (!e->mask[0])
359 			e->mask = NULL;
360 		e->size = unquote(e->magic);
361 		if (e->mask && unquote(e->mask) != e->size)
362 			goto Einval;
363 		if (e->size + e->offset > BINPRM_BUF_SIZE)
364 			goto Einval;
365 	} else {
366 		p = strchr(p, del);
367 		if (!p)
368 			goto Einval;
369 		*p++ = '\0';
370 		e->magic = p;
371 		p = strchr(p, del);
372 		if (!p)
373 			goto Einval;
374 		*p++ = '\0';
375 		if (!e->magic[0] || strchr(e->magic, '/'))
376 			goto Einval;
377 		p = strchr(p, del);
378 		if (!p)
379 			goto Einval;
380 		*p++ = '\0';
381 	}
382 	e->interpreter = p;
383 	p = strchr(p, del);
384 	if (!p)
385 		goto Einval;
386 	*p++ = '\0';
387 	if (!e->interpreter[0])
388 		goto Einval;
389 
390 
391 	p = check_special_flags (p, e);
392 
393 	if (*p == '\n')
394 		p++;
395 	if (p != buf + count)
396 		goto Einval;
397 	return e;
398 
399 out:
400 	return ERR_PTR(err);
401 
402 Efault:
403 	kfree(e);
404 	return ERR_PTR(-EFAULT);
405 Einval:
406 	kfree(e);
407 	return ERR_PTR(-EINVAL);
408 }
409 
410 /*
411  * Set status of entry/binfmt_misc:
412  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
413  */
414 static int parse_command(const char __user *buffer, size_t count)
415 {
416 	char s[4];
417 
418 	if (!count)
419 		return 0;
420 	if (count > 3)
421 		return -EINVAL;
422 	if (copy_from_user(s, buffer, count))
423 		return -EFAULT;
424 	if (s[count-1] == '\n')
425 		count--;
426 	if (count == 1 && s[0] == '0')
427 		return 1;
428 	if (count == 1 && s[0] == '1')
429 		return 2;
430 	if (count == 2 && s[0] == '-' && s[1] == '1')
431 		return 3;
432 	return -EINVAL;
433 }
434 
435 /* generic stuff */
436 
437 static void entry_status(Node *e, char *page)
438 {
439 	char *dp;
440 	char *status = "disabled";
441 	const char * flags = "flags: ";
442 
443 	if (test_bit(Enabled, &e->flags))
444 		status = "enabled";
445 
446 	if (!VERBOSE_STATUS) {
447 		sprintf(page, "%s\n", status);
448 		return;
449 	}
450 
451 	sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
452 	dp = page + strlen(page);
453 
454 	/* print the special flags */
455 	sprintf (dp, "%s", flags);
456 	dp += strlen (flags);
457 	if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
458 		*dp ++ = 'P';
459 	}
460 	if (e->flags & MISC_FMT_OPEN_BINARY) {
461 		*dp ++ = 'O';
462 	}
463 	if (e->flags & MISC_FMT_CREDENTIALS) {
464 		*dp ++ = 'C';
465 	}
466 	*dp ++ = '\n';
467 
468 
469 	if (!test_bit(Magic, &e->flags)) {
470 		sprintf(dp, "extension .%s\n", e->magic);
471 	} else {
472 		int i;
473 
474 		sprintf(dp, "offset %i\nmagic ", e->offset);
475 		dp = page + strlen(page);
476 		for (i = 0; i < e->size; i++) {
477 			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
478 			dp += 2;
479 		}
480 		if (e->mask) {
481 			sprintf(dp, "\nmask ");
482 			dp += 6;
483 			for (i = 0; i < e->size; i++) {
484 				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
485 				dp += 2;
486 			}
487 		}
488 		*dp++ = '\n';
489 		*dp = '\0';
490 	}
491 }
492 
493 static struct inode *bm_get_inode(struct super_block *sb, int mode)
494 {
495 	struct inode * inode = new_inode(sb);
496 
497 	if (inode) {
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 		dentry->d_inode->i_nlink--;
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.mnt->mnt_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 };
580 
581 /* /register */
582 
583 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
584 			       size_t count, loff_t *ppos)
585 {
586 	Node *e;
587 	struct inode *inode;
588 	struct dentry *root, *dentry;
589 	struct super_block *sb = file->f_path.mnt->mnt_sb;
590 	int err = 0;
591 
592 	e = create_entry(buffer, count);
593 
594 	if (IS_ERR(e))
595 		return PTR_ERR(e);
596 
597 	root = dget(sb->s_root);
598 	mutex_lock(&root->d_inode->i_mutex);
599 	dentry = lookup_one_len(e->name, root, strlen(e->name));
600 	err = PTR_ERR(dentry);
601 	if (IS_ERR(dentry))
602 		goto out;
603 
604 	err = -EEXIST;
605 	if (dentry->d_inode)
606 		goto out2;
607 
608 	inode = bm_get_inode(sb, S_IFREG | 0644);
609 
610 	err = -ENOMEM;
611 	if (!inode)
612 		goto out2;
613 
614 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
615 	if (err) {
616 		iput(inode);
617 		inode = NULL;
618 		goto out2;
619 	}
620 
621 	e->dentry = dget(dentry);
622 	inode->i_private = e;
623 	inode->i_fop = &bm_entry_operations;
624 
625 	d_instantiate(dentry, inode);
626 	write_lock(&entries_lock);
627 	list_add(&e->list, &entries);
628 	write_unlock(&entries_lock);
629 
630 	err = 0;
631 out2:
632 	dput(dentry);
633 out:
634 	mutex_unlock(&root->d_inode->i_mutex);
635 	dput(root);
636 
637 	if (err) {
638 		kfree(e);
639 		return -EINVAL;
640 	}
641 	return count;
642 }
643 
644 static const struct file_operations bm_register_operations = {
645 	.write		= bm_register_write,
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.mnt->mnt_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 };
684 
685 /* Superblock handling */
686 
687 static const struct super_operations s_ops = {
688 	.statfs		= simple_statfs,
689 	.evict_inode	= bm_evict_inode,
690 };
691 
692 static int bm_fill_super(struct super_block * sb, void * data, int silent)
693 {
694 	static struct tree_descr bm_files[] = {
695 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
696 		[3] = {"register", &bm_register_operations, S_IWUSR},
697 		/* last one */ {""}
698 	};
699 	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
700 	if (!err)
701 		sb->s_op = &s_ops;
702 	return err;
703 }
704 
705 static int bm_get_sb(struct file_system_type *fs_type,
706 	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
707 {
708 	return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
709 }
710 
711 static struct linux_binfmt misc_format = {
712 	.module = THIS_MODULE,
713 	.load_binary = load_misc_binary,
714 };
715 
716 static struct file_system_type bm_fs_type = {
717 	.owner		= THIS_MODULE,
718 	.name		= "binfmt_misc",
719 	.get_sb		= bm_get_sb,
720 	.kill_sb	= kill_litter_super,
721 };
722 
723 static int __init init_misc_binfmt(void)
724 {
725 	int err = register_filesystem(&bm_fs_type);
726 	if (!err) {
727 		err = register_binfmt(&misc_format);
728 		if (err)
729 			unregister_filesystem(&bm_fs_type);
730 	}
731 	return err;
732 }
733 
734 static void __exit exit_misc_binfmt(void)
735 {
736 	unregister_binfmt(&misc_format);
737 	unregister_filesystem(&bm_fs_type);
738 }
739 
740 core_initcall(init_misc_binfmt);
741 module_exit(exit_misc_binfmt);
742 MODULE_LICENSE("GPL");
743