xref: /openbmc/linux/fs/binfmt_misc.c (revision 22246614) 
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 
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 file_system_type bm_fs_type;
59 static struct vfsmount *bm_mnt;
60 static int entry_count;
61 
62 /*
63  * Check if we support the binfmt
64  * if we do, return the node, else NULL
65  * locking is done in load_misc_binary
66  */
67 static Node *check_file(struct linux_binprm *bprm)
68 {
69 	char *p = strrchr(bprm->interp, '.');
70 	struct list_head *l;
71 
72 	list_for_each(l, &entries) {
73 		Node *e = list_entry(l, Node, list);
74 		char *s;
75 		int j;
76 
77 		if (!test_bit(Enabled, &e->flags))
78 			continue;
79 
80 		if (!test_bit(Magic, &e->flags)) {
81 			if (p && !strcmp(e->magic, p + 1))
82 				return e;
83 			continue;
84 		}
85 
86 		s = bprm->buf + e->offset;
87 		if (e->mask) {
88 			for (j = 0; j < e->size; j++)
89 				if ((*s++ ^ e->magic[j]) & e->mask[j])
90 					break;
91 		} else {
92 			for (j = 0; j < e->size; j++)
93 				if ((*s++ ^ e->magic[j]))
94 					break;
95 		}
96 		if (j == e->size)
97 			return e;
98 	}
99 	return NULL;
100 }
101 
102 /*
103  * the loader itself
104  */
105 static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
106 {
107 	Node *fmt;
108 	struct file * interp_file = NULL;
109 	char iname[BINPRM_BUF_SIZE];
110 	char *iname_addr = iname;
111 	int retval;
112 	int fd_binary = -1;
113 
114 	retval = -ENOEXEC;
115 	if (!enabled)
116 		goto _ret;
117 
118 	retval = -ENOEXEC;
119 	if (bprm->misc_bang)
120 		goto _ret;
121 
122 	bprm->misc_bang = 1;
123 
124 	/* to keep locking time low, we copy the interpreter string */
125 	read_lock(&entries_lock);
126 	fmt = check_file(bprm);
127 	if (fmt)
128 		strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
129 	read_unlock(&entries_lock);
130 	if (!fmt)
131 		goto _ret;
132 
133 	if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
134 		retval = remove_arg_zero(bprm);
135 		if (retval)
136 			goto _ret;
137 	}
138 
139 	if (fmt->flags & MISC_FMT_OPEN_BINARY) {
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 _ret;
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 _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_mode = mode;
498 		inode->i_uid = 0;
499 		inode->i_gid = 0;
500 		inode->i_blocks = 0;
501 		inode->i_atime = inode->i_mtime = inode->i_ctime =
502 			current_fs_time(inode->i_sb);
503 	}
504 	return inode;
505 }
506 
507 static void bm_clear_inode(struct inode *inode)
508 {
509 	kfree(inode->i_private);
510 }
511 
512 static void kill_node(Node *e)
513 {
514 	struct dentry *dentry;
515 
516 	write_lock(&entries_lock);
517 	dentry = e->dentry;
518 	if (dentry) {
519 		list_del_init(&e->list);
520 		e->dentry = NULL;
521 	}
522 	write_unlock(&entries_lock);
523 
524 	if (dentry) {
525 		dentry->d_inode->i_nlink--;
526 		d_drop(dentry);
527 		dput(dentry);
528 		simple_release_fs(&bm_mnt, &entry_count);
529 	}
530 }
531 
532 /* /<entry> */
533 
534 static ssize_t
535 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
536 {
537 	Node *e = file->f_path.dentry->d_inode->i_private;
538 	loff_t pos = *ppos;
539 	ssize_t res;
540 	char *page;
541 	int len;
542 
543 	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
544 		return -ENOMEM;
545 
546 	entry_status(e, page);
547 	len = strlen(page);
548 
549 	res = -EINVAL;
550 	if (pos < 0)
551 		goto out;
552 	res = 0;
553 	if (pos >= len)
554 		goto out;
555 	if (len < pos + nbytes)
556 		nbytes = len - pos;
557 	res = -EFAULT;
558 	if (copy_to_user(buf, page + pos, nbytes))
559 		goto out;
560 	*ppos = pos + nbytes;
561 	res = nbytes;
562 out:
563 	free_page((unsigned long) page);
564 	return res;
565 }
566 
567 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
568 				size_t count, loff_t *ppos)
569 {
570 	struct dentry *root;
571 	Node *e = file->f_path.dentry->d_inode->i_private;
572 	int res = parse_command(buffer, count);
573 
574 	switch (res) {
575 		case 1: clear_bit(Enabled, &e->flags);
576 			break;
577 		case 2: set_bit(Enabled, &e->flags);
578 			break;
579 		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
580 			mutex_lock(&root->d_inode->i_mutex);
581 
582 			kill_node(e);
583 
584 			mutex_unlock(&root->d_inode->i_mutex);
585 			dput(root);
586 			break;
587 		default: return res;
588 	}
589 	return count;
590 }
591 
592 static const struct file_operations bm_entry_operations = {
593 	.read		= bm_entry_read,
594 	.write		= bm_entry_write,
595 };
596 
597 /* /register */
598 
599 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
600 			       size_t count, loff_t *ppos)
601 {
602 	Node *e;
603 	struct inode *inode;
604 	struct dentry *root, *dentry;
605 	struct super_block *sb = file->f_path.mnt->mnt_sb;
606 	int err = 0;
607 
608 	e = create_entry(buffer, count);
609 
610 	if (IS_ERR(e))
611 		return PTR_ERR(e);
612 
613 	root = dget(sb->s_root);
614 	mutex_lock(&root->d_inode->i_mutex);
615 	dentry = lookup_one_len(e->name, root, strlen(e->name));
616 	err = PTR_ERR(dentry);
617 	if (IS_ERR(dentry))
618 		goto out;
619 
620 	err = -EEXIST;
621 	if (dentry->d_inode)
622 		goto out2;
623 
624 	inode = bm_get_inode(sb, S_IFREG | 0644);
625 
626 	err = -ENOMEM;
627 	if (!inode)
628 		goto out2;
629 
630 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
631 	if (err) {
632 		iput(inode);
633 		inode = NULL;
634 		goto out2;
635 	}
636 
637 	e->dentry = dget(dentry);
638 	inode->i_private = e;
639 	inode->i_fop = &bm_entry_operations;
640 
641 	d_instantiate(dentry, inode);
642 	write_lock(&entries_lock);
643 	list_add(&e->list, &entries);
644 	write_unlock(&entries_lock);
645 
646 	err = 0;
647 out2:
648 	dput(dentry);
649 out:
650 	mutex_unlock(&root->d_inode->i_mutex);
651 	dput(root);
652 
653 	if (err) {
654 		kfree(e);
655 		return -EINVAL;
656 	}
657 	return count;
658 }
659 
660 static const struct file_operations bm_register_operations = {
661 	.write		= bm_register_write,
662 };
663 
664 /* /status */
665 
666 static ssize_t
667 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
668 {
669 	char *s = enabled ? "enabled" : "disabled";
670 
671 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
672 }
673 
674 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
675 		size_t count, loff_t *ppos)
676 {
677 	int res = parse_command(buffer, count);
678 	struct dentry *root;
679 
680 	switch (res) {
681 		case 1: enabled = 0; break;
682 		case 2: enabled = 1; break;
683 		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
684 			mutex_lock(&root->d_inode->i_mutex);
685 
686 			while (!list_empty(&entries))
687 				kill_node(list_entry(entries.next, Node, list));
688 
689 			mutex_unlock(&root->d_inode->i_mutex);
690 			dput(root);
691 		default: return res;
692 	}
693 	return count;
694 }
695 
696 static const struct file_operations bm_status_operations = {
697 	.read		= bm_status_read,
698 	.write		= bm_status_write,
699 };
700 
701 /* Superblock handling */
702 
703 static const struct super_operations s_ops = {
704 	.statfs		= simple_statfs,
705 	.clear_inode	= bm_clear_inode,
706 };
707 
708 static int bm_fill_super(struct super_block * sb, void * data, int silent)
709 {
710 	static struct tree_descr bm_files[] = {
711 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
712 		[3] = {"register", &bm_register_operations, S_IWUSR},
713 		/* last one */ {""}
714 	};
715 	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
716 	if (!err)
717 		sb->s_op = &s_ops;
718 	return err;
719 }
720 
721 static int bm_get_sb(struct file_system_type *fs_type,
722 	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
723 {
724 	return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
725 }
726 
727 static struct linux_binfmt misc_format = {
728 	.module = THIS_MODULE,
729 	.load_binary = load_misc_binary,
730 };
731 
732 static struct file_system_type bm_fs_type = {
733 	.owner		= THIS_MODULE,
734 	.name		= "binfmt_misc",
735 	.get_sb		= bm_get_sb,
736 	.kill_sb	= kill_litter_super,
737 };
738 
739 static int __init init_misc_binfmt(void)
740 {
741 	int err = register_filesystem(&bm_fs_type);
742 	if (!err) {
743 		err = register_binfmt(&misc_format);
744 		if (err)
745 			unregister_filesystem(&bm_fs_type);
746 	}
747 	return err;
748 }
749 
750 static void __exit exit_misc_binfmt(void)
751 {
752 	unregister_binfmt(&misc_format);
753 	unregister_filesystem(&bm_fs_type);
754 }
755 
756 core_initcall(init_misc_binfmt);
757 module_exit(exit_misc_binfmt);
758 MODULE_LICENSE("GPL");
759