xref: /openbmc/linux/fs/binfmt_misc.c (revision 87c2ce3b) 
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 		steal_locks(files);
207 		put_files_struct(files);
208 		files = NULL;
209 	}
210 _ret:
211 	return retval;
212 _error:
213 	if (fd_binary > 0)
214 		sys_close(fd_binary);
215 	bprm->interp_flags = 0;
216 	bprm->interp_data = 0;
217 _unshare:
218 	if (files) {
219 		put_files_struct(current->files);
220 		current->files = files;
221 	}
222 	goto _ret;
223 }
224 
225 /* Command parsers */
226 
227 /*
228  * parses and copies one argument enclosed in del from *sp to *dp,
229  * recognising the \x special.
230  * returns pointer to the copied argument or NULL in case of an
231  * error (and sets err) or null argument length.
232  */
233 static char *scanarg(char *s, char del)
234 {
235 	char c;
236 
237 	while ((c = *s++) != del) {
238 		if (c == '\\' && *s == 'x') {
239 			s++;
240 			if (!isxdigit(*s++))
241 				return NULL;
242 			if (!isxdigit(*s++))
243 				return NULL;
244 		}
245 	}
246 	return s;
247 }
248 
249 static int unquote(char *from)
250 {
251 	char c = 0, *s = from, *p = from;
252 
253 	while ((c = *s++) != '\0') {
254 		if (c == '\\' && *s == 'x') {
255 			s++;
256 			c = toupper(*s++);
257 			*p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
258 			c = toupper(*s++);
259 			*p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
260 			continue;
261 		}
262 		*p++ = c;
263 	}
264 	return p - from;
265 }
266 
267 static inline char * check_special_flags (char * sfs, Node * e)
268 {
269 	char * p = sfs;
270 	int cont = 1;
271 
272 	/* special flags */
273 	while (cont) {
274 		switch (*p) {
275 			case 'P':
276 				p++;
277 				e->flags |= MISC_FMT_PRESERVE_ARGV0;
278 				break;
279 			case 'O':
280 				p++;
281 				e->flags |= MISC_FMT_OPEN_BINARY;
282 				break;
283 			case 'C':
284 				p++;
285 				/* this flags also implies the
286 				   open-binary flag */
287 				e->flags |= (MISC_FMT_CREDENTIALS |
288 						MISC_FMT_OPEN_BINARY);
289 				break;
290 			default:
291 				cont = 0;
292 		}
293 	}
294 
295 	return p;
296 }
297 /*
298  * This registers a new binary format, it recognises the syntax
299  * ':name:type:offset:magic:mask:interpreter:flags'
300  * where the ':' is the IFS, that can be chosen with the first char
301  */
302 static Node *create_entry(const char __user *buffer, size_t count)
303 {
304 	Node *e;
305 	int memsize, err;
306 	char *buf, *p;
307 	char del;
308 
309 	/* some sanity checks */
310 	err = -EINVAL;
311 	if ((count < 11) || (count > 256))
312 		goto out;
313 
314 	err = -ENOMEM;
315 	memsize = sizeof(Node) + count + 8;
316 	e = (Node *) kmalloc(memsize, GFP_USER);
317 	if (!e)
318 		goto out;
319 
320 	p = buf = (char *)e + sizeof(Node);
321 
322 	memset(e, 0, sizeof(Node));
323 	if (copy_from_user(buf, buffer, count))
324 		goto Efault;
325 
326 	del = *p++;	/* delimeter */
327 
328 	memset(buf+count, del, 8);
329 
330 	e->name = p;
331 	p = strchr(p, del);
332 	if (!p)
333 		goto Einval;
334 	*p++ = '\0';
335 	if (!e->name[0] ||
336 	    !strcmp(e->name, ".") ||
337 	    !strcmp(e->name, "..") ||
338 	    strchr(e->name, '/'))
339 		goto Einval;
340 	switch (*p++) {
341 		case 'E': e->flags = 1<<Enabled; break;
342 		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
343 		default: goto Einval;
344 	}
345 	if (*p++ != del)
346 		goto Einval;
347 	if (test_bit(Magic, &e->flags)) {
348 		char *s = strchr(p, del);
349 		if (!s)
350 			goto Einval;
351 		*s++ = '\0';
352 		e->offset = simple_strtoul(p, &p, 10);
353 		if (*p++)
354 			goto Einval;
355 		e->magic = p;
356 		p = scanarg(p, del);
357 		if (!p)
358 			goto Einval;
359 		p[-1] = '\0';
360 		if (!e->magic[0])
361 			goto Einval;
362 		e->mask = p;
363 		p = scanarg(p, del);
364 		if (!p)
365 			goto Einval;
366 		p[-1] = '\0';
367 		if (!e->mask[0])
368 			e->mask = NULL;
369 		e->size = unquote(e->magic);
370 		if (e->mask && unquote(e->mask) != e->size)
371 			goto Einval;
372 		if (e->size + e->offset > BINPRM_BUF_SIZE)
373 			goto Einval;
374 	} else {
375 		p = strchr(p, del);
376 		if (!p)
377 			goto Einval;
378 		*p++ = '\0';
379 		e->magic = p;
380 		p = strchr(p, del);
381 		if (!p)
382 			goto Einval;
383 		*p++ = '\0';
384 		if (!e->magic[0] || strchr(e->magic, '/'))
385 			goto Einval;
386 		p = strchr(p, del);
387 		if (!p)
388 			goto Einval;
389 		*p++ = '\0';
390 	}
391 	e->interpreter = p;
392 	p = strchr(p, del);
393 	if (!p)
394 		goto Einval;
395 	*p++ = '\0';
396 	if (!e->interpreter[0])
397 		goto Einval;
398 
399 
400 	p = check_special_flags (p, e);
401 
402 	if (*p == '\n')
403 		p++;
404 	if (p != buf + count)
405 		goto Einval;
406 	return e;
407 
408 out:
409 	return ERR_PTR(err);
410 
411 Efault:
412 	kfree(e);
413 	return ERR_PTR(-EFAULT);
414 Einval:
415 	kfree(e);
416 	return ERR_PTR(-EINVAL);
417 }
418 
419 /*
420  * Set status of entry/binfmt_misc:
421  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
422  */
423 static int parse_command(const char __user *buffer, size_t count)
424 {
425 	char s[4];
426 
427 	if (!count)
428 		return 0;
429 	if (count > 3)
430 		return -EINVAL;
431 	if (copy_from_user(s, buffer, count))
432 		return -EFAULT;
433 	if (s[count-1] == '\n')
434 		count--;
435 	if (count == 1 && s[0] == '0')
436 		return 1;
437 	if (count == 1 && s[0] == '1')
438 		return 2;
439 	if (count == 2 && s[0] == '-' && s[1] == '1')
440 		return 3;
441 	return -EINVAL;
442 }
443 
444 /* generic stuff */
445 
446 static void entry_status(Node *e, char *page)
447 {
448 	char *dp;
449 	char *status = "disabled";
450 	const char * flags = "flags: ";
451 
452 	if (test_bit(Enabled, &e->flags))
453 		status = "enabled";
454 
455 	if (!VERBOSE_STATUS) {
456 		sprintf(page, "%s\n", status);
457 		return;
458 	}
459 
460 	sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
461 	dp = page + strlen(page);
462 
463 	/* print the special flags */
464 	sprintf (dp, "%s", flags);
465 	dp += strlen (flags);
466 	if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
467 		*dp ++ = 'P';
468 	}
469 	if (e->flags & MISC_FMT_OPEN_BINARY) {
470 		*dp ++ = 'O';
471 	}
472 	if (e->flags & MISC_FMT_CREDENTIALS) {
473 		*dp ++ = 'C';
474 	}
475 	*dp ++ = '\n';
476 
477 
478 	if (!test_bit(Magic, &e->flags)) {
479 		sprintf(dp, "extension .%s\n", e->magic);
480 	} else {
481 		int i;
482 
483 		sprintf(dp, "offset %i\nmagic ", e->offset);
484 		dp = page + strlen(page);
485 		for (i = 0; i < e->size; i++) {
486 			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
487 			dp += 2;
488 		}
489 		if (e->mask) {
490 			sprintf(dp, "\nmask ");
491 			dp += 6;
492 			for (i = 0; i < e->size; i++) {
493 				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
494 				dp += 2;
495 			}
496 		}
497 		*dp++ = '\n';
498 		*dp = '\0';
499 	}
500 }
501 
502 static struct inode *bm_get_inode(struct super_block *sb, int mode)
503 {
504 	struct inode * inode = new_inode(sb);
505 
506 	if (inode) {
507 		inode->i_mode = mode;
508 		inode->i_uid = 0;
509 		inode->i_gid = 0;
510 		inode->i_blksize = PAGE_CACHE_SIZE;
511 		inode->i_blocks = 0;
512 		inode->i_atime = inode->i_mtime = inode->i_ctime =
513 			current_fs_time(inode->i_sb);
514 	}
515 	return inode;
516 }
517 
518 static void bm_clear_inode(struct inode *inode)
519 {
520 	kfree(inode->u.generic_ip);
521 }
522 
523 static void kill_node(Node *e)
524 {
525 	struct dentry *dentry;
526 
527 	write_lock(&entries_lock);
528 	dentry = e->dentry;
529 	if (dentry) {
530 		list_del_init(&e->list);
531 		e->dentry = NULL;
532 	}
533 	write_unlock(&entries_lock);
534 
535 	if (dentry) {
536 		dentry->d_inode->i_nlink--;
537 		d_drop(dentry);
538 		dput(dentry);
539 		simple_release_fs(&bm_mnt, &entry_count);
540 	}
541 }
542 
543 /* /<entry> */
544 
545 static ssize_t
546 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
547 {
548 	Node *e = file->f_dentry->d_inode->u.generic_ip;
549 	loff_t pos = *ppos;
550 	ssize_t res;
551 	char *page;
552 	int len;
553 
554 	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
555 		return -ENOMEM;
556 
557 	entry_status(e, page);
558 	len = strlen(page);
559 
560 	res = -EINVAL;
561 	if (pos < 0)
562 		goto out;
563 	res = 0;
564 	if (pos >= len)
565 		goto out;
566 	if (len < pos + nbytes)
567 		nbytes = len - pos;
568 	res = -EFAULT;
569 	if (copy_to_user(buf, page + pos, nbytes))
570 		goto out;
571 	*ppos = pos + nbytes;
572 	res = nbytes;
573 out:
574 	free_page((unsigned long) page);
575 	return res;
576 }
577 
578 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
579 				size_t count, loff_t *ppos)
580 {
581 	struct dentry *root;
582 	Node *e = file->f_dentry->d_inode->u.generic_ip;
583 	int res = parse_command(buffer, count);
584 
585 	switch (res) {
586 		case 1: clear_bit(Enabled, &e->flags);
587 			break;
588 		case 2: set_bit(Enabled, &e->flags);
589 			break;
590 		case 3: root = dget(file->f_vfsmnt->mnt_sb->s_root);
591 			mutex_lock(&root->d_inode->i_mutex);
592 
593 			kill_node(e);
594 
595 			mutex_unlock(&root->d_inode->i_mutex);
596 			dput(root);
597 			break;
598 		default: return res;
599 	}
600 	return count;
601 }
602 
603 static struct file_operations bm_entry_operations = {
604 	.read		= bm_entry_read,
605 	.write		= bm_entry_write,
606 };
607 
608 /* /register */
609 
610 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
611 			       size_t count, loff_t *ppos)
612 {
613 	Node *e;
614 	struct inode *inode;
615 	struct dentry *root, *dentry;
616 	struct super_block *sb = file->f_vfsmnt->mnt_sb;
617 	int err = 0;
618 
619 	e = create_entry(buffer, count);
620 
621 	if (IS_ERR(e))
622 		return PTR_ERR(e);
623 
624 	root = dget(sb->s_root);
625 	mutex_lock(&root->d_inode->i_mutex);
626 	dentry = lookup_one_len(e->name, root, strlen(e->name));
627 	err = PTR_ERR(dentry);
628 	if (IS_ERR(dentry))
629 		goto out;
630 
631 	err = -EEXIST;
632 	if (dentry->d_inode)
633 		goto out2;
634 
635 	inode = bm_get_inode(sb, S_IFREG | 0644);
636 
637 	err = -ENOMEM;
638 	if (!inode)
639 		goto out2;
640 
641 	err = simple_pin_fs("binfmt_misc", &bm_mnt, &entry_count);
642 	if (err) {
643 		iput(inode);
644 		inode = NULL;
645 		goto out2;
646 	}
647 
648 	e->dentry = dget(dentry);
649 	inode->u.generic_ip = e;
650 	inode->i_fop = &bm_entry_operations;
651 
652 	d_instantiate(dentry, inode);
653 	write_lock(&entries_lock);
654 	list_add(&e->list, &entries);
655 	write_unlock(&entries_lock);
656 
657 	err = 0;
658 out2:
659 	dput(dentry);
660 out:
661 	mutex_unlock(&root->d_inode->i_mutex);
662 	dput(root);
663 
664 	if (err) {
665 		kfree(e);
666 		return -EINVAL;
667 	}
668 	return count;
669 }
670 
671 static struct file_operations bm_register_operations = {
672 	.write		= bm_register_write,
673 };
674 
675 /* /status */
676 
677 static ssize_t
678 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
679 {
680 	char *s = enabled ? "enabled" : "disabled";
681 	int len = strlen(s);
682 	loff_t pos = *ppos;
683 
684 	if (pos < 0)
685 		return -EINVAL;
686 	if (pos >= len)
687 		return 0;
688 	if (len < pos + nbytes)
689 		nbytes = len - pos;
690 	if (copy_to_user(buf, s + pos, nbytes))
691 		return -EFAULT;
692 	*ppos = pos + nbytes;
693 	return nbytes;
694 }
695 
696 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
697 		size_t count, loff_t *ppos)
698 {
699 	int res = parse_command(buffer, count);
700 	struct dentry *root;
701 
702 	switch (res) {
703 		case 1: enabled = 0; break;
704 		case 2: enabled = 1; break;
705 		case 3: root = dget(file->f_vfsmnt->mnt_sb->s_root);
706 			mutex_lock(&root->d_inode->i_mutex);
707 
708 			while (!list_empty(&entries))
709 				kill_node(list_entry(entries.next, Node, list));
710 
711 			mutex_unlock(&root->d_inode->i_mutex);
712 			dput(root);
713 		default: return res;
714 	}
715 	return count;
716 }
717 
718 static struct file_operations bm_status_operations = {
719 	.read		= bm_status_read,
720 	.write		= bm_status_write,
721 };
722 
723 /* Superblock handling */
724 
725 static struct super_operations s_ops = {
726 	.statfs		= simple_statfs,
727 	.clear_inode	= bm_clear_inode,
728 };
729 
730 static int bm_fill_super(struct super_block * sb, void * data, int silent)
731 {
732 	static struct tree_descr bm_files[] = {
733 		[1] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
734 		[2] = {"register", &bm_register_operations, S_IWUSR},
735 		/* last one */ {""}
736 	};
737 	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
738 	if (!err)
739 		sb->s_op = &s_ops;
740 	return err;
741 }
742 
743 static struct super_block *bm_get_sb(struct file_system_type *fs_type,
744 	int flags, const char *dev_name, void *data)
745 {
746 	return get_sb_single(fs_type, flags, data, bm_fill_super);
747 }
748 
749 static struct linux_binfmt misc_format = {
750 	.module = THIS_MODULE,
751 	.load_binary = load_misc_binary,
752 };
753 
754 static struct file_system_type bm_fs_type = {
755 	.owner		= THIS_MODULE,
756 	.name		= "binfmt_misc",
757 	.get_sb		= bm_get_sb,
758 	.kill_sb	= kill_litter_super,
759 };
760 
761 static int __init init_misc_binfmt(void)
762 {
763 	int err = register_filesystem(&bm_fs_type);
764 	if (!err) {
765 		err = register_binfmt(&misc_format);
766 		if (err)
767 			unregister_filesystem(&bm_fs_type);
768 	}
769 	return err;
770 }
771 
772 static void __exit exit_misc_binfmt(void)
773 {
774 	unregister_binfmt(&misc_format);
775 	unregister_filesystem(&bm_fs_type);
776 }
777 
778 core_initcall(init_misc_binfmt);
779 module_exit(exit_misc_binfmt);
780 MODULE_LICENSE("GPL");
781