1 // SPDX-License-Identifier: GPL-2.0-only
5 * Copyright (C) 1997 Richard Günther
7 * binfmt_misc detects binaries via a magic or filename extension and invokes
8 * a specified wrapper. See Documentation/admin-guide/binfmt-misc.rst for more details.
11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
13 #include <linux/kernel.h>
14 #include <linux/module.h>
15 #include <linux/init.h>
16 #include <linux/sched/mm.h>
17 #include <linux/magic.h>
18 #include <linux/binfmts.h>
19 #include <linux/slab.h>
20 #include <linux/ctype.h>
21 #include <linux/string_helpers.h>
22 #include <linux/file.h>
23 #include <linux/pagemap.h>
24 #include <linux/namei.h>
25 #include <linux/mount.h>
26 #include <linux/fs_context.h>
27 #include <linux/syscalls.h>
29 #include <linux/uaccess.h>
40 VERBOSE_STATUS
= 1 /* make it zero to save 400 bytes kernel memory */
43 static LIST_HEAD(entries
);
44 static int enabled
= 1;
46 enum {Enabled
, Magic
};
47 #define MISC_FMT_PRESERVE_ARGV0 (1 << 31)
48 #define MISC_FMT_OPEN_BINARY (1 << 30)
49 #define MISC_FMT_CREDENTIALS (1 << 29)
50 #define MISC_FMT_OPEN_FILE (1 << 28)
53 struct list_head list
;
54 unsigned long flags
; /* type, status, etc. */
55 int offset
; /* offset of magic */
56 int size
; /* size of magic/mask */
57 char *magic
; /* magic or filename extension */
58 char *mask
; /* mask, NULL for exact match */
59 const char *interpreter
; /* filename of interpreter */
61 struct dentry
*dentry
;
62 struct file
*interp_file
;
65 static DEFINE_RWLOCK(entries_lock
);
66 static struct file_system_type bm_fs_type
;
67 static struct vfsmount
*bm_mnt
;
68 static int entry_count
;
71 * Max length of the register string. Determined by:
75 * - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
76 * - magic: 128 bytes (512 in escaped form)
77 * - mask: 128 bytes (512 in escaped form)
80 * Round that up a bit, and then back off to hold the internal data
83 #define MAX_REGISTER_LENGTH 1920
86 * Check if we support the binfmt
87 * if we do, return the node, else NULL
88 * locking is done in load_misc_binary
90 static Node
*check_file(struct linux_binprm
*bprm
)
92 char *p
= strrchr(bprm
->interp
, '.');
95 /* Walk all the registered handlers. */
96 list_for_each(l
, &entries
) {
97 Node
*e
= list_entry(l
, Node
, list
);
101 /* Make sure this one is currently enabled. */
102 if (!test_bit(Enabled
, &e
->flags
))
105 /* Do matching based on extension if applicable. */
106 if (!test_bit(Magic
, &e
->flags
)) {
107 if (p
&& !strcmp(e
->magic
, p
+ 1))
112 /* Do matching based on magic & mask. */
113 s
= bprm
->buf
+ e
->offset
;
115 for (j
= 0; j
< e
->size
; j
++)
116 if ((*s
++ ^ e
->magic
[j
]) & e
->mask
[j
])
119 for (j
= 0; j
< e
->size
; j
++)
120 if ((*s
++ ^ e
->magic
[j
]))
132 static int load_misc_binary(struct linux_binprm
*bprm
)
135 struct file
*interp_file
= NULL
;
142 /* to keep locking time low, we copy the interpreter string */
143 read_lock(&entries_lock
);
144 fmt
= check_file(bprm
);
147 read_unlock(&entries_lock
);
151 /* Need to be able to load the file after exec */
153 if (bprm
->interp_flags
& BINPRM_FLAGS_PATH_INACCESSIBLE
)
156 if (fmt
->flags
& MISC_FMT_PRESERVE_ARGV0
) {
157 bprm
->interp_flags
|= BINPRM_FLAGS_PRESERVE_ARGV0
;
159 retval
= remove_arg_zero(bprm
);
164 if (fmt
->flags
& MISC_FMT_OPEN_BINARY
)
165 bprm
->have_execfd
= 1;
167 /* make argv[1] be the path to the binary */
168 retval
= copy_string_kernel(bprm
->interp
, bprm
);
173 /* add the interp as argv[0] */
174 retval
= copy_string_kernel(fmt
->interpreter
, bprm
);
179 /* Update interp in case binfmt_script needs it. */
180 retval
= bprm_change_interp(fmt
->interpreter
, bprm
);
184 if (fmt
->flags
& MISC_FMT_OPEN_FILE
) {
185 interp_file
= file_clone_open(fmt
->interp_file
);
186 if (!IS_ERR(interp_file
))
187 deny_write_access(interp_file
);
189 interp_file
= open_exec(fmt
->interpreter
);
191 retval
= PTR_ERR(interp_file
);
192 if (IS_ERR(interp_file
))
195 bprm
->interpreter
= interp_file
;
196 if (fmt
->flags
& MISC_FMT_CREDENTIALS
)
197 bprm
->execfd_creds
= 1;
205 /* Command parsers */
208 * parses and copies one argument enclosed in del from *sp to *dp,
209 * recognising the \x special.
210 * returns pointer to the copied argument or NULL in case of an
211 * error (and sets err) or null argument length.
213 static char *scanarg(char *s
, char del
)
217 while ((c
= *s
++) != del
) {
218 if (c
== '\\' && *s
== 'x') {
230 static char *check_special_flags(char *sfs
, Node
*e
)
239 pr_debug("register: flag: P (preserve argv0)\n");
241 e
->flags
|= MISC_FMT_PRESERVE_ARGV0
;
244 pr_debug("register: flag: O (open binary)\n");
246 e
->flags
|= MISC_FMT_OPEN_BINARY
;
249 pr_debug("register: flag: C (preserve creds)\n");
251 /* this flags also implies the
253 e
->flags
|= (MISC_FMT_CREDENTIALS
|
254 MISC_FMT_OPEN_BINARY
);
257 pr_debug("register: flag: F: open interpreter file now\n");
259 e
->flags
|= MISC_FMT_OPEN_FILE
;
270 * This registers a new binary format, it recognises the syntax
271 * ':name:type:offset:magic:mask:interpreter:flags'
272 * where the ':' is the IFS, that can be chosen with the first char
274 static Node
*create_entry(const char __user
*buffer
, size_t count
)
281 pr_debug("register: received %zu bytes\n", count
);
283 /* some sanity checks */
285 if ((count
< 11) || (count
> MAX_REGISTER_LENGTH
))
289 memsize
= sizeof(Node
) + count
+ 8;
290 e
= kmalloc(memsize
, GFP_KERNEL
);
294 p
= buf
= (char *)e
+ sizeof(Node
);
296 memset(e
, 0, sizeof(Node
));
297 if (copy_from_user(buf
, buffer
, count
))
300 del
= *p
++; /* delimeter */
302 pr_debug("register: delim: %#x {%c}\n", del
, del
);
304 /* Pad the buffer with the delim to simplify parsing below. */
305 memset(buf
+ count
, del
, 8);
307 /* Parse the 'name' field. */
314 !strcmp(e
->name
, ".") ||
315 !strcmp(e
->name
, "..") ||
316 strchr(e
->name
, '/'))
319 pr_debug("register: name: {%s}\n", e
->name
);
321 /* Parse the 'type' field. */
324 pr_debug("register: type: E (extension)\n");
325 e
->flags
= 1 << Enabled
;
328 pr_debug("register: type: M (magic)\n");
329 e
->flags
= (1 << Enabled
) | (1 << Magic
);
337 if (test_bit(Magic
, &e
->flags
)) {
338 /* Handle the 'M' (magic) format. */
341 /* Parse the 'offset' field. */
347 int r
= kstrtoint(p
, 10, &e
->offset
);
348 if (r
!= 0 || e
->offset
< 0)
354 pr_debug("register: offset: %#x\n", e
->offset
);
356 /* Parse the 'magic' field. */
364 print_hex_dump_bytes(
365 KBUILD_MODNAME
": register: magic[raw]: ",
366 DUMP_PREFIX_NONE
, e
->magic
, p
- e
->magic
);
368 /* Parse the 'mask' field. */
375 pr_debug("register: mask[raw]: none\n");
376 } else if (USE_DEBUG
)
377 print_hex_dump_bytes(
378 KBUILD_MODNAME
": register: mask[raw]: ",
379 DUMP_PREFIX_NONE
, e
->mask
, p
- e
->mask
);
382 * Decode the magic & mask fields.
383 * Note: while we might have accepted embedded NUL bytes from
384 * above, the unescape helpers here will stop at the first one
387 e
->size
= string_unescape_inplace(e
->magic
, UNESCAPE_HEX
);
389 string_unescape_inplace(e
->mask
, UNESCAPE_HEX
) != e
->size
)
391 if (e
->size
> BINPRM_BUF_SIZE
||
392 BINPRM_BUF_SIZE
- e
->size
< e
->offset
)
394 pr_debug("register: magic/mask length: %i\n", e
->size
);
396 print_hex_dump_bytes(
397 KBUILD_MODNAME
": register: magic[decoded]: ",
398 DUMP_PREFIX_NONE
, e
->magic
, e
->size
);
402 char *masked
= kmalloc(e
->size
, GFP_KERNEL
);
404 print_hex_dump_bytes(
405 KBUILD_MODNAME
": register: mask[decoded]: ",
406 DUMP_PREFIX_NONE
, e
->mask
, e
->size
);
409 for (i
= 0; i
< e
->size
; ++i
)
410 masked
[i
] = e
->magic
[i
] & e
->mask
[i
];
411 print_hex_dump_bytes(
412 KBUILD_MODNAME
": register: magic[masked]: ",
413 DUMP_PREFIX_NONE
, masked
, e
->size
);
420 /* Handle the 'E' (extension) format. */
422 /* Skip the 'offset' field. */
428 /* Parse the 'magic' field. */
434 if (!e
->magic
[0] || strchr(e
->magic
, '/'))
436 pr_debug("register: extension: {%s}\n", e
->magic
);
438 /* Skip the 'mask' field. */
445 /* Parse the 'interpreter' field. */
451 if (!e
->interpreter
[0])
453 pr_debug("register: interpreter: {%s}\n", e
->interpreter
);
455 /* Parse the 'flags' field. */
456 p
= check_special_flags(p
, e
);
459 if (p
!= buf
+ count
)
469 return ERR_PTR(-EFAULT
);
472 return ERR_PTR(-EINVAL
);
476 * Set status of entry/binfmt_misc:
477 * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
479 static int parse_command(const char __user
*buffer
, size_t count
)
485 if (copy_from_user(s
, buffer
, count
))
489 if (s
[count
- 1] == '\n')
491 if (count
== 1 && s
[0] == '0')
493 if (count
== 1 && s
[0] == '1')
495 if (count
== 2 && s
[0] == '-' && s
[1] == '1')
502 static void entry_status(Node
*e
, char *page
)
505 const char *status
= "disabled";
507 if (test_bit(Enabled
, &e
->flags
))
510 if (!VERBOSE_STATUS
) {
511 sprintf(page
, "%s\n", status
);
515 dp
+= sprintf(dp
, "%s\ninterpreter %s\n", status
, e
->interpreter
);
517 /* print the special flags */
518 dp
+= sprintf(dp
, "flags: ");
519 if (e
->flags
& MISC_FMT_PRESERVE_ARGV0
)
521 if (e
->flags
& MISC_FMT_OPEN_BINARY
)
523 if (e
->flags
& MISC_FMT_CREDENTIALS
)
525 if (e
->flags
& MISC_FMT_OPEN_FILE
)
529 if (!test_bit(Magic
, &e
->flags
)) {
530 sprintf(dp
, "extension .%s\n", e
->magic
);
532 dp
+= sprintf(dp
, "offset %i\nmagic ", e
->offset
);
533 dp
= bin2hex(dp
, e
->magic
, e
->size
);
535 dp
+= sprintf(dp
, "\nmask ");
536 dp
= bin2hex(dp
, e
->mask
, e
->size
);
543 static struct inode
*bm_get_inode(struct super_block
*sb
, int mode
)
545 struct inode
*inode
= new_inode(sb
);
548 inode
->i_ino
= get_next_ino();
549 inode
->i_mode
= mode
;
550 inode
->i_atime
= inode
->i_mtime
= inode
->i_ctime
=
556 static void bm_evict_inode(struct inode
*inode
)
558 Node
*e
= inode
->i_private
;
560 if (e
&& e
->flags
& MISC_FMT_OPEN_FILE
)
561 filp_close(e
->interp_file
, NULL
);
567 static void kill_node(Node
*e
)
569 struct dentry
*dentry
;
571 write_lock(&entries_lock
);
572 list_del_init(&e
->list
);
573 write_unlock(&entries_lock
);
576 drop_nlink(d_inode(dentry
));
579 simple_release_fs(&bm_mnt
, &entry_count
);
585 bm_entry_read(struct file
*file
, char __user
*buf
, size_t nbytes
, loff_t
*ppos
)
587 Node
*e
= file_inode(file
)->i_private
;
591 page
= (char *) __get_free_page(GFP_KERNEL
);
595 entry_status(e
, page
);
597 res
= simple_read_from_buffer(buf
, nbytes
, ppos
, page
, strlen(page
));
599 free_page((unsigned long) page
);
603 static ssize_t
bm_entry_write(struct file
*file
, const char __user
*buffer
,
604 size_t count
, loff_t
*ppos
)
607 Node
*e
= file_inode(file
)->i_private
;
608 int res
= parse_command(buffer
, count
);
612 /* Disable this handler. */
613 clear_bit(Enabled
, &e
->flags
);
616 /* Enable this handler. */
617 set_bit(Enabled
, &e
->flags
);
620 /* Delete this handler. */
621 root
= file_inode(file
)->i_sb
->s_root
;
622 inode_lock(d_inode(root
));
624 if (!list_empty(&e
->list
))
627 inode_unlock(d_inode(root
));
636 static const struct file_operations bm_entry_operations
= {
637 .read
= bm_entry_read
,
638 .write
= bm_entry_write
,
639 .llseek
= default_llseek
,
644 static ssize_t
bm_register_write(struct file
*file
, const char __user
*buffer
,
645 size_t count
, loff_t
*ppos
)
649 struct super_block
*sb
= file_inode(file
)->i_sb
;
650 struct dentry
*root
= sb
->s_root
, *dentry
;
652 struct file
*f
= NULL
;
654 e
= create_entry(buffer
, count
);
659 if (e
->flags
& MISC_FMT_OPEN_FILE
) {
660 f
= open_exec(e
->interpreter
);
662 pr_notice("register: failed to install interpreter file %s\n",
670 inode_lock(d_inode(root
));
671 dentry
= lookup_one_len(e
->name
, root
, strlen(e
->name
));
672 err
= PTR_ERR(dentry
);
677 if (d_really_is_positive(dentry
))
680 inode
= bm_get_inode(sb
, S_IFREG
| 0644);
686 err
= simple_pin_fs(&bm_fs_type
, &bm_mnt
, &entry_count
);
693 e
->dentry
= dget(dentry
);
694 inode
->i_private
= e
;
695 inode
->i_fop
= &bm_entry_operations
;
697 d_instantiate(dentry
, inode
);
698 write_lock(&entries_lock
);
699 list_add(&e
->list
, &entries
);
700 write_unlock(&entries_lock
);
706 inode_unlock(d_inode(root
));
717 static const struct file_operations bm_register_operations
= {
718 .write
= bm_register_write
,
719 .llseek
= noop_llseek
,
725 bm_status_read(struct file
*file
, char __user
*buf
, size_t nbytes
, loff_t
*ppos
)
727 char *s
= enabled
? "enabled\n" : "disabled\n";
729 return simple_read_from_buffer(buf
, nbytes
, ppos
, s
, strlen(s
));
732 static ssize_t
bm_status_write(struct file
*file
, const char __user
*buffer
,
733 size_t count
, loff_t
*ppos
)
735 int res
= parse_command(buffer
, count
);
740 /* Disable all handlers. */
744 /* Enable all handlers. */
748 /* Delete all handlers. */
749 root
= file_inode(file
)->i_sb
->s_root
;
750 inode_lock(d_inode(root
));
752 while (!list_empty(&entries
))
753 kill_node(list_first_entry(&entries
, Node
, list
));
755 inode_unlock(d_inode(root
));
764 static const struct file_operations bm_status_operations
= {
765 .read
= bm_status_read
,
766 .write
= bm_status_write
,
767 .llseek
= default_llseek
,
770 /* Superblock handling */
772 static const struct super_operations s_ops
= {
773 .statfs
= simple_statfs
,
774 .evict_inode
= bm_evict_inode
,
777 static int bm_fill_super(struct super_block
*sb
, struct fs_context
*fc
)
780 static const struct tree_descr bm_files
[] = {
781 [2] = {"status", &bm_status_operations
, S_IWUSR
|S_IRUGO
},
782 [3] = {"register", &bm_register_operations
, S_IWUSR
},
786 err
= simple_fill_super(sb
, BINFMTFS_MAGIC
, bm_files
);
792 static int bm_get_tree(struct fs_context
*fc
)
794 return get_tree_single(fc
, bm_fill_super
);
797 static const struct fs_context_operations bm_context_ops
= {
798 .get_tree
= bm_get_tree
,
801 static int bm_init_fs_context(struct fs_context
*fc
)
803 fc
->ops
= &bm_context_ops
;
807 static struct linux_binfmt misc_format
= {
808 .module
= THIS_MODULE
,
809 .load_binary
= load_misc_binary
,
812 static struct file_system_type bm_fs_type
= {
813 .owner
= THIS_MODULE
,
814 .name
= "binfmt_misc",
815 .init_fs_context
= bm_init_fs_context
,
816 .kill_sb
= kill_litter_super
,
818 MODULE_ALIAS_FS("binfmt_misc");
820 static int __init
init_misc_binfmt(void)
822 int err
= register_filesystem(&bm_fs_type
);
824 insert_binfmt(&misc_format
);
828 static void __exit
exit_misc_binfmt(void)
830 unregister_binfmt(&misc_format
);
831 unregister_filesystem(&bm_fs_type
);
834 core_initcall(init_misc_binfmt
);
835 module_exit(exit_misc_binfmt
);
836 MODULE_LICENSE("GPL");