xref: /openbmc/linux/fs/binfmt_misc.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 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 	struct files_struct *files = NULL;
114 
115 	retval = -ENOEXEC;
116 	if (!enabled)
117 		goto _ret;
118 
119 	/* to keep locking time low, we copy the interpreter string */
120 	read_lock(&entries_lock);
121 	fmt = check_file(bprm);
122 	if (fmt)
123 		strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
124 	read_unlock(&entries_lock);
125 	if (!fmt)
126 		goto _ret;
127 
128 	if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
129 		remove_arg_zero(bprm);
130 	}
131 
132 	if (fmt->flags & MISC_FMT_OPEN_BINARY) {
133 
134 		files = current->files;
135 		retval = unshare_files();
136 		if (retval < 0)
137 			goto _ret;
138 		if (files == current->files) {
139 			put_files_struct(files);
140 			files = NULL;
141 		}
142 		/* if the binary should be opened on behalf of the
143 		 * interpreter than keep it open and assign descriptor
144 		 * to it */
145  		fd_binary = get_unused_fd();
146  		if (fd_binary < 0) {
147  			retval = fd_binary;
148  			goto _unshare;
149  		}
150  		fd_install(fd_binary, bprm->file);
151 
152 		/* if the binary is not readable than enforce mm->dumpable=0
153 		   regardless of the interpreter's permissions */
154 		if (file_permission(bprm->file, MAY_READ))
155 			bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
156 
157 		allow_write_access(bprm->file);
158 		bprm->file = NULL;
159 
160 		/* mark the bprm that fd should be passed to interp */
161 		bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
162 		bprm->interp_data = fd_binary;
163 
164  	} else {
165  		allow_write_access(bprm->file);
166  		fput(bprm->file);
167  		bprm->file = NULL;
168  	}
169 	/* make argv[1] be the path to the binary */
170 	retval = copy_strings_kernel (1, &bprm->interp, bprm);
171 	if (retval < 0)
172 		goto _error;
173 	bprm->argc++;
174 
175 	/* add the interp as argv[0] */
176 	retval = copy_strings_kernel (1, &iname_addr, bprm);
177 	if (retval < 0)
178 		goto _error;
179 	bprm->argc ++;
180 
181 	bprm->interp = iname;	/* for binfmt_script */
182 
183 	interp_file = open_exec (iname);
184 	retval = PTR_ERR (interp_file);
185 	if (IS_ERR (interp_file))
186 		goto _error;
187 
188 	bprm->file = interp_file;
189 	if (fmt->flags & MISC_FMT_CREDENTIALS) {
190 		/*
191 		 * No need to call prepare_binprm(), it's already been
192 		 * done.  bprm->buf is stale, update from interp_file.
193 		 */
194 		memset(bprm->buf, 0, BINPRM_BUF_SIZE);
195 		retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
196 	} else
197 		retval = prepare_binprm (bprm);
198 
199 	if (retval < 0)
200 		goto _error;
201 
202 	retval = search_binary_handler (bprm, regs);
203 	if (retval < 0)
204 		goto _error;
205 
206 	if (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 		reset_files_struct(current, files);
220 	goto _ret;
221 }
222 
223 /* Command parsers */
224 
225 /*
226  * parses and copies one argument enclosed in del from *sp to *dp,
227  * recognising the \x special.
228  * returns pointer to the copied argument or NULL in case of an
229  * error (and sets err) or null argument length.
230  */
231 static char *scanarg(char *s, char del)
232 {
233 	char c;
234 
235 	while ((c = *s++) != del) {
236 		if (c == '\\' && *s == 'x') {
237 			s++;
238 			if (!isxdigit(*s++))
239 				return NULL;
240 			if (!isxdigit(*s++))
241 				return NULL;
242 		}
243 	}
244 	return s;
245 }
246 
247 static int unquote(char *from)
248 {
249 	char c = 0, *s = from, *p = from;
250 
251 	while ((c = *s++) != '\0') {
252 		if (c == '\\' && *s == 'x') {
253 			s++;
254 			c = toupper(*s++);
255 			*p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
256 			c = toupper(*s++);
257 			*p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
258 			continue;
259 		}
260 		*p++ = c;
261 	}
262 	return p - from;
263 }
264 
265 static char * check_special_flags (char * sfs, Node * e)
266 {
267 	char * p = sfs;
268 	int cont = 1;
269 
270 	/* special flags */
271 	while (cont) {
272 		switch (*p) {
273 			case 'P':
274 				p++;
275 				e->flags |= MISC_FMT_PRESERVE_ARGV0;
276 				break;
277 			case 'O':
278 				p++;
279 				e->flags |= MISC_FMT_OPEN_BINARY;
280 				break;
281 			case 'C':
282 				p++;
283 				/* this flags also implies the
284 				   open-binary flag */
285 				e->flags |= (MISC_FMT_CREDENTIALS |
286 						MISC_FMT_OPEN_BINARY);
287 				break;
288 			default:
289 				cont = 0;
290 		}
291 	}
292 
293 	return p;
294 }
295 /*
296  * This registers a new binary format, it recognises the syntax
297  * ':name:type:offset:magic:mask:interpreter:flags'
298  * where the ':' is the IFS, that can be chosen with the first char
299  */
300 static Node *create_entry(const char __user *buffer, size_t count)
301 {
302 	Node *e;
303 	int memsize, err;
304 	char *buf, *p;
305 	char del;
306 
307 	/* some sanity checks */
308 	err = -EINVAL;
309 	if ((count < 11) || (count > 256))
310 		goto out;
311 
312 	err = -ENOMEM;
313 	memsize = sizeof(Node) + count + 8;
314 	e = kmalloc(memsize, GFP_USER);
315 	if (!e)
316 		goto out;
317 
318 	p = buf = (char *)e + sizeof(Node);
319 
320 	memset(e, 0, sizeof(Node));
321 	if (copy_from_user(buf, buffer, count))
322 		goto Efault;
323 
324 	del = *p++;	/* delimeter */
325 
326 	memset(buf+count, del, 8);
327 
328 	e->name = p;
329 	p = strchr(p, del);
330 	if (!p)
331 		goto Einval;
332 	*p++ = '\0';
333 	if (!e->name[0] ||
334 	    !strcmp(e->name, ".") ||
335 	    !strcmp(e->name, "..") ||
336 	    strchr(e->name, '/'))
337 		goto Einval;
338 	switch (*p++) {
339 		case 'E': e->flags = 1<<Enabled; break;
340 		case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
341 		default: goto Einval;
342 	}
343 	if (*p++ != del)
344 		goto Einval;
345 	if (test_bit(Magic, &e->flags)) {
346 		char *s = strchr(p, del);
347 		if (!s)
348 			goto Einval;
349 		*s++ = '\0';
350 		e->offset = simple_strtoul(p, &p, 10);
351 		if (*p++)
352 			goto Einval;
353 		e->magic = p;
354 		p = scanarg(p, del);
355 		if (!p)
356 			goto Einval;
357 		p[-1] = '\0';
358 		if (!e->magic[0])
359 			goto Einval;
360 		e->mask = p;
361 		p = scanarg(p, del);
362 		if (!p)
363 			goto Einval;
364 		p[-1] = '\0';
365 		if (!e->mask[0])
366 			e->mask = NULL;
367 		e->size = unquote(e->magic);
368 		if (e->mask && unquote(e->mask) != e->size)
369 			goto Einval;
370 		if (e->size + e->offset > BINPRM_BUF_SIZE)
371 			goto Einval;
372 	} else {
373 		p = strchr(p, del);
374 		if (!p)
375 			goto Einval;
376 		*p++ = '\0';
377 		e->magic = p;
378 		p = strchr(p, del);
379 		if (!p)
380 			goto Einval;
381 		*p++ = '\0';
382 		if (!e->magic[0] || strchr(e->magic, '/'))
383 			goto Einval;
384 		p = strchr(p, del);
385 		if (!p)
386 			goto Einval;
387 		*p++ = '\0';
388 	}
389 	e->interpreter = p;
390 	p = strchr(p, del);
391 	if (!p)
392 		goto Einval;
393 	*p++ = '\0';
394 	if (!e->interpreter[0])
395 		goto Einval;
396 
397 
398 	p = check_special_flags (p, e);
399 
400 	if (*p == '\n')
401 		p++;
402 	if (p != buf + count)
403 		goto Einval;
404 	return e;
405 
406 out:
407 	return ERR_PTR(err);
408 
409 Efault:
410 	kfree(e);
411 	return ERR_PTR(-EFAULT);
412 Einval:
413 	kfree(e);
414 	return ERR_PTR(-EINVAL);
415 }
416 
417 /*
418  * Set status of entry/binfmt_misc:
419  * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
420  */
421 static int parse_command(const char __user *buffer, size_t count)
422 {
423 	char s[4];
424 
425 	if (!count)
426 		return 0;
427 	if (count > 3)
428 		return -EINVAL;
429 	if (copy_from_user(s, buffer, count))
430 		return -EFAULT;
431 	if (s[count-1] == '\n')
432 		count--;
433 	if (count == 1 && s[0] == '0')
434 		return 1;
435 	if (count == 1 && s[0] == '1')
436 		return 2;
437 	if (count == 2 && s[0] == '-' && s[1] == '1')
438 		return 3;
439 	return -EINVAL;
440 }
441 
442 /* generic stuff */
443 
444 static void entry_status(Node *e, char *page)
445 {
446 	char *dp;
447 	char *status = "disabled";
448 	const char * flags = "flags: ";
449 
450 	if (test_bit(Enabled, &e->flags))
451 		status = "enabled";
452 
453 	if (!VERBOSE_STATUS) {
454 		sprintf(page, "%s\n", status);
455 		return;
456 	}
457 
458 	sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
459 	dp = page + strlen(page);
460 
461 	/* print the special flags */
462 	sprintf (dp, "%s", flags);
463 	dp += strlen (flags);
464 	if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
465 		*dp ++ = 'P';
466 	}
467 	if (e->flags & MISC_FMT_OPEN_BINARY) {
468 		*dp ++ = 'O';
469 	}
470 	if (e->flags & MISC_FMT_CREDENTIALS) {
471 		*dp ++ = 'C';
472 	}
473 	*dp ++ = '\n';
474 
475 
476 	if (!test_bit(Magic, &e->flags)) {
477 		sprintf(dp, "extension .%s\n", e->magic);
478 	} else {
479 		int i;
480 
481 		sprintf(dp, "offset %i\nmagic ", e->offset);
482 		dp = page + strlen(page);
483 		for (i = 0; i < e->size; i++) {
484 			sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
485 			dp += 2;
486 		}
487 		if (e->mask) {
488 			sprintf(dp, "\nmask ");
489 			dp += 6;
490 			for (i = 0; i < e->size; i++) {
491 				sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
492 				dp += 2;
493 			}
494 		}
495 		*dp++ = '\n';
496 		*dp = '\0';
497 	}
498 }
499 
500 static struct inode *bm_get_inode(struct super_block *sb, int mode)
501 {
502 	struct inode * inode = new_inode(sb);
503 
504 	if (inode) {
505 		inode->i_mode = mode;
506 		inode->i_uid = 0;
507 		inode->i_gid = 0;
508 		inode->i_blocks = 0;
509 		inode->i_atime = inode->i_mtime = inode->i_ctime =
510 			current_fs_time(inode->i_sb);
511 	}
512 	return inode;
513 }
514 
515 static void bm_clear_inode(struct inode *inode)
516 {
517 	kfree(inode->i_private);
518 }
519 
520 static void kill_node(Node *e)
521 {
522 	struct dentry *dentry;
523 
524 	write_lock(&entries_lock);
525 	dentry = e->dentry;
526 	if (dentry) {
527 		list_del_init(&e->list);
528 		e->dentry = NULL;
529 	}
530 	write_unlock(&entries_lock);
531 
532 	if (dentry) {
533 		dentry->d_inode->i_nlink--;
534 		d_drop(dentry);
535 		dput(dentry);
536 		simple_release_fs(&bm_mnt, &entry_count);
537 	}
538 }
539 
540 /* /<entry> */
541 
542 static ssize_t
543 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
544 {
545 	Node *e = file->f_path.dentry->d_inode->i_private;
546 	loff_t pos = *ppos;
547 	ssize_t res;
548 	char *page;
549 	int len;
550 
551 	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
552 		return -ENOMEM;
553 
554 	entry_status(e, page);
555 	len = strlen(page);
556 
557 	res = -EINVAL;
558 	if (pos < 0)
559 		goto out;
560 	res = 0;
561 	if (pos >= len)
562 		goto out;
563 	if (len < pos + nbytes)
564 		nbytes = len - pos;
565 	res = -EFAULT;
566 	if (copy_to_user(buf, page + pos, nbytes))
567 		goto out;
568 	*ppos = pos + nbytes;
569 	res = nbytes;
570 out:
571 	free_page((unsigned long) page);
572 	return res;
573 }
574 
575 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
576 				size_t count, loff_t *ppos)
577 {
578 	struct dentry *root;
579 	Node *e = file->f_path.dentry->d_inode->i_private;
580 	int res = parse_command(buffer, count);
581 
582 	switch (res) {
583 		case 1: clear_bit(Enabled, &e->flags);
584 			break;
585 		case 2: set_bit(Enabled, &e->flags);
586 			break;
587 		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
588 			mutex_lock(&root->d_inode->i_mutex);
589 
590 			kill_node(e);
591 
592 			mutex_unlock(&root->d_inode->i_mutex);
593 			dput(root);
594 			break;
595 		default: return res;
596 	}
597 	return count;
598 }
599 
600 static const struct file_operations bm_entry_operations = {
601 	.read		= bm_entry_read,
602 	.write		= bm_entry_write,
603 };
604 
605 /* /register */
606 
607 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
608 			       size_t count, loff_t *ppos)
609 {
610 	Node *e;
611 	struct inode *inode;
612 	struct dentry *root, *dentry;
613 	struct super_block *sb = file->f_path.mnt->mnt_sb;
614 	int err = 0;
615 
616 	e = create_entry(buffer, count);
617 
618 	if (IS_ERR(e))
619 		return PTR_ERR(e);
620 
621 	root = dget(sb->s_root);
622 	mutex_lock(&root->d_inode->i_mutex);
623 	dentry = lookup_one_len(e->name, root, strlen(e->name));
624 	err = PTR_ERR(dentry);
625 	if (IS_ERR(dentry))
626 		goto out;
627 
628 	err = -EEXIST;
629 	if (dentry->d_inode)
630 		goto out2;
631 
632 	inode = bm_get_inode(sb, S_IFREG | 0644);
633 
634 	err = -ENOMEM;
635 	if (!inode)
636 		goto out2;
637 
638 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
639 	if (err) {
640 		iput(inode);
641 		inode = NULL;
642 		goto out2;
643 	}
644 
645 	e->dentry = dget(dentry);
646 	inode->i_private = e;
647 	inode->i_fop = &bm_entry_operations;
648 
649 	d_instantiate(dentry, inode);
650 	write_lock(&entries_lock);
651 	list_add(&e->list, &entries);
652 	write_unlock(&entries_lock);
653 
654 	err = 0;
655 out2:
656 	dput(dentry);
657 out:
658 	mutex_unlock(&root->d_inode->i_mutex);
659 	dput(root);
660 
661 	if (err) {
662 		kfree(e);
663 		return -EINVAL;
664 	}
665 	return count;
666 }
667 
668 static const struct file_operations bm_register_operations = {
669 	.write		= bm_register_write,
670 };
671 
672 /* /status */
673 
674 static ssize_t
675 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
676 {
677 	char *s = enabled ? "enabled" : "disabled";
678 
679 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
680 }
681 
682 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
683 		size_t count, loff_t *ppos)
684 {
685 	int res = parse_command(buffer, count);
686 	struct dentry *root;
687 
688 	switch (res) {
689 		case 1: enabled = 0; break;
690 		case 2: enabled = 1; break;
691 		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
692 			mutex_lock(&root->d_inode->i_mutex);
693 
694 			while (!list_empty(&entries))
695 				kill_node(list_entry(entries.next, Node, list));
696 
697 			mutex_unlock(&root->d_inode->i_mutex);
698 			dput(root);
699 		default: return res;
700 	}
701 	return count;
702 }
703 
704 static const struct file_operations bm_status_operations = {
705 	.read		= bm_status_read,
706 	.write		= bm_status_write,
707 };
708 
709 /* Superblock handling */
710 
711 static const struct super_operations s_ops = {
712 	.statfs		= simple_statfs,
713 	.clear_inode	= bm_clear_inode,
714 };
715 
716 static int bm_fill_super(struct super_block * sb, void * data, int silent)
717 {
718 	static struct tree_descr bm_files[] = {
719 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
720 		[3] = {"register", &bm_register_operations, S_IWUSR},
721 		/* last one */ {""}
722 	};
723 	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
724 	if (!err)
725 		sb->s_op = &s_ops;
726 	return err;
727 }
728 
729 static int bm_get_sb(struct file_system_type *fs_type,
730 	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
731 {
732 	return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
733 }
734 
735 static struct linux_binfmt misc_format = {
736 	.module = THIS_MODULE,
737 	.load_binary = load_misc_binary,
738 };
739 
740 static struct file_system_type bm_fs_type = {
741 	.owner		= THIS_MODULE,
742 	.name		= "binfmt_misc",
743 	.get_sb		= bm_get_sb,
744 	.kill_sb	= kill_litter_super,
745 };
746 
747 static int __init init_misc_binfmt(void)
748 {
749 	int err = register_filesystem(&bm_fs_type);
750 	if (!err) {
751 		err = register_binfmt(&misc_format);
752 		if (err)
753 			unregister_filesystem(&bm_fs_type);
754 	}
755 	return err;
756 }
757 
758 static void __exit exit_misc_binfmt(void)
759 {
760 	unregister_binfmt(&misc_format);
761 	unregister_filesystem(&bm_fs_type);
762 }
763 
764 core_initcall(init_misc_binfmt);
765 module_exit(exit_misc_binfmt);
766 MODULE_LICENSE("GPL");
767