xref: /openbmc/linux/fs/binfmt_misc.c (revision 96de0e252cedffad61b3cb5e05662c591898e69a) 
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 	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 		retval = remove_arg_zero(bprm);
130 		if (retval)
131 			goto _ret;
132 	}
133 
134 	if (fmt->flags & MISC_FMT_OPEN_BINARY) {
135 
136 		files = current->files;
137 		retval = unshare_files();
138 		if (retval < 0)
139 			goto _ret;
140 		if (files == current->files) {
141 			put_files_struct(files);
142 			files = NULL;
143 		}
144 		/* if the binary should be opened on behalf of the
145 		 * interpreter than keep it open and assign descriptor
146 		 * to it */
147  		fd_binary = get_unused_fd();
148  		if (fd_binary < 0) {
149  			retval = fd_binary;
150  			goto _unshare;
151  		}
152  		fd_install(fd_binary, bprm->file);
153 
154 		/* if the binary is not readable than enforce mm->dumpable=0
155 		   regardless of the interpreter's permissions */
156 		if (file_permission(bprm->file, MAY_READ))
157 			bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
158 
159 		allow_write_access(bprm->file);
160 		bprm->file = NULL;
161 
162 		/* mark the bprm that fd should be passed to interp */
163 		bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
164 		bprm->interp_data = fd_binary;
165 
166  	} else {
167  		allow_write_access(bprm->file);
168  		fput(bprm->file);
169  		bprm->file = NULL;
170  	}
171 	/* make argv[1] be the path to the binary */
172 	retval = copy_strings_kernel (1, &bprm->interp, bprm);
173 	if (retval < 0)
174 		goto _error;
175 	bprm->argc++;
176 
177 	/* add the interp as argv[0] */
178 	retval = copy_strings_kernel (1, &iname_addr, bprm);
179 	if (retval < 0)
180 		goto _error;
181 	bprm->argc ++;
182 
183 	bprm->interp = iname;	/* for binfmt_script */
184 
185 	interp_file = open_exec (iname);
186 	retval = PTR_ERR (interp_file);
187 	if (IS_ERR (interp_file))
188 		goto _error;
189 
190 	bprm->file = interp_file;
191 	if (fmt->flags & MISC_FMT_CREDENTIALS) {
192 		/*
193 		 * No need to call prepare_binprm(), it's already been
194 		 * done.  bprm->buf is stale, update from interp_file.
195 		 */
196 		memset(bprm->buf, 0, BINPRM_BUF_SIZE);
197 		retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
198 	} else
199 		retval = prepare_binprm (bprm);
200 
201 	if (retval < 0)
202 		goto _error;
203 
204 	retval = search_binary_handler (bprm, regs);
205 	if (retval < 0)
206 		goto _error;
207 
208 	if (files) {
209 		put_files_struct(files);
210 		files = NULL;
211 	}
212 _ret:
213 	return retval;
214 _error:
215 	if (fd_binary > 0)
216 		sys_close(fd_binary);
217 	bprm->interp_flags = 0;
218 	bprm->interp_data = 0;
219 _unshare:
220 	if (files)
221 		reset_files_struct(current, files);
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 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 = 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_blocks = 0;
511 		inode->i_atime = inode->i_mtime = inode->i_ctime =
512 			current_fs_time(inode->i_sb);
513 	}
514 	return inode;
515 }
516 
517 static void bm_clear_inode(struct inode *inode)
518 {
519 	kfree(inode->i_private);
520 }
521 
522 static void kill_node(Node *e)
523 {
524 	struct dentry *dentry;
525 
526 	write_lock(&entries_lock);
527 	dentry = e->dentry;
528 	if (dentry) {
529 		list_del_init(&e->list);
530 		e->dentry = NULL;
531 	}
532 	write_unlock(&entries_lock);
533 
534 	if (dentry) {
535 		dentry->d_inode->i_nlink--;
536 		d_drop(dentry);
537 		dput(dentry);
538 		simple_release_fs(&bm_mnt, &entry_count);
539 	}
540 }
541 
542 /* /<entry> */
543 
544 static ssize_t
545 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
546 {
547 	Node *e = file->f_path.dentry->d_inode->i_private;
548 	loff_t pos = *ppos;
549 	ssize_t res;
550 	char *page;
551 	int len;
552 
553 	if (!(page = (char*) __get_free_page(GFP_KERNEL)))
554 		return -ENOMEM;
555 
556 	entry_status(e, page);
557 	len = strlen(page);
558 
559 	res = -EINVAL;
560 	if (pos < 0)
561 		goto out;
562 	res = 0;
563 	if (pos >= len)
564 		goto out;
565 	if (len < pos + nbytes)
566 		nbytes = len - pos;
567 	res = -EFAULT;
568 	if (copy_to_user(buf, page + pos, nbytes))
569 		goto out;
570 	*ppos = pos + nbytes;
571 	res = nbytes;
572 out:
573 	free_page((unsigned long) page);
574 	return res;
575 }
576 
577 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
578 				size_t count, loff_t *ppos)
579 {
580 	struct dentry *root;
581 	Node *e = file->f_path.dentry->d_inode->i_private;
582 	int res = parse_command(buffer, count);
583 
584 	switch (res) {
585 		case 1: clear_bit(Enabled, &e->flags);
586 			break;
587 		case 2: set_bit(Enabled, &e->flags);
588 			break;
589 		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
590 			mutex_lock(&root->d_inode->i_mutex);
591 
592 			kill_node(e);
593 
594 			mutex_unlock(&root->d_inode->i_mutex);
595 			dput(root);
596 			break;
597 		default: return res;
598 	}
599 	return count;
600 }
601 
602 static const struct file_operations bm_entry_operations = {
603 	.read		= bm_entry_read,
604 	.write		= bm_entry_write,
605 };
606 
607 /* /register */
608 
609 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
610 			       size_t count, loff_t *ppos)
611 {
612 	Node *e;
613 	struct inode *inode;
614 	struct dentry *root, *dentry;
615 	struct super_block *sb = file->f_path.mnt->mnt_sb;
616 	int err = 0;
617 
618 	e = create_entry(buffer, count);
619 
620 	if (IS_ERR(e))
621 		return PTR_ERR(e);
622 
623 	root = dget(sb->s_root);
624 	mutex_lock(&root->d_inode->i_mutex);
625 	dentry = lookup_one_len(e->name, root, strlen(e->name));
626 	err = PTR_ERR(dentry);
627 	if (IS_ERR(dentry))
628 		goto out;
629 
630 	err = -EEXIST;
631 	if (dentry->d_inode)
632 		goto out2;
633 
634 	inode = bm_get_inode(sb, S_IFREG | 0644);
635 
636 	err = -ENOMEM;
637 	if (!inode)
638 		goto out2;
639 
640 	err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
641 	if (err) {
642 		iput(inode);
643 		inode = NULL;
644 		goto out2;
645 	}
646 
647 	e->dentry = dget(dentry);
648 	inode->i_private = e;
649 	inode->i_fop = &bm_entry_operations;
650 
651 	d_instantiate(dentry, inode);
652 	write_lock(&entries_lock);
653 	list_add(&e->list, &entries);
654 	write_unlock(&entries_lock);
655 
656 	err = 0;
657 out2:
658 	dput(dentry);
659 out:
660 	mutex_unlock(&root->d_inode->i_mutex);
661 	dput(root);
662 
663 	if (err) {
664 		kfree(e);
665 		return -EINVAL;
666 	}
667 	return count;
668 }
669 
670 static const struct file_operations bm_register_operations = {
671 	.write		= bm_register_write,
672 };
673 
674 /* /status */
675 
676 static ssize_t
677 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
678 {
679 	char *s = enabled ? "enabled" : "disabled";
680 
681 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
682 }
683 
684 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
685 		size_t count, loff_t *ppos)
686 {
687 	int res = parse_command(buffer, count);
688 	struct dentry *root;
689 
690 	switch (res) {
691 		case 1: enabled = 0; break;
692 		case 2: enabled = 1; break;
693 		case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
694 			mutex_lock(&root->d_inode->i_mutex);
695 
696 			while (!list_empty(&entries))
697 				kill_node(list_entry(entries.next, Node, list));
698 
699 			mutex_unlock(&root->d_inode->i_mutex);
700 			dput(root);
701 		default: return res;
702 	}
703 	return count;
704 }
705 
706 static const struct file_operations bm_status_operations = {
707 	.read		= bm_status_read,
708 	.write		= bm_status_write,
709 };
710 
711 /* Superblock handling */
712 
713 static const struct super_operations s_ops = {
714 	.statfs		= simple_statfs,
715 	.clear_inode	= bm_clear_inode,
716 };
717 
718 static int bm_fill_super(struct super_block * sb, void * data, int silent)
719 {
720 	static struct tree_descr bm_files[] = {
721 		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
722 		[3] = {"register", &bm_register_operations, S_IWUSR},
723 		/* last one */ {""}
724 	};
725 	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
726 	if (!err)
727 		sb->s_op = &s_ops;
728 	return err;
729 }
730 
731 static int bm_get_sb(struct file_system_type *fs_type,
732 	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
733 {
734 	return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
735 }
736 
737 static struct linux_binfmt misc_format = {
738 	.module = THIS_MODULE,
739 	.load_binary = load_misc_binary,
740 };
741 
742 static struct file_system_type bm_fs_type = {
743 	.owner		= THIS_MODULE,
744 	.name		= "binfmt_misc",
745 	.get_sb		= bm_get_sb,
746 	.kill_sb	= kill_litter_super,
747 };
748 
749 static int __init init_misc_binfmt(void)
750 {
751 	int err = register_filesystem(&bm_fs_type);
752 	if (!err) {
753 		err = register_binfmt(&misc_format);
754 		if (err)
755 			unregister_filesystem(&bm_fs_type);
756 	}
757 	return err;
758 }
759 
760 static void __exit exit_misc_binfmt(void)
761 {
762 	unregister_binfmt(&misc_format);
763 	unregister_filesystem(&bm_fs_type);
764 }
765 
766 core_initcall(init_misc_binfmt);
767 module_exit(exit_misc_binfmt);
768 MODULE_LICENSE("GPL");
769