1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * binfmt_misc.c
4 *
5 * Copyright (C) 1997 Richard Günther
6 *
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.
9 */
10
11#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
12
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>
28#include <linux/fs.h>
29#include <linux/uaccess.h>
30
31#include "internal.h"
32
33#ifdef DEBUG
34# define USE_DEBUG 1
35#else
36# define USE_DEBUG 0
37#endif
38
39enum {
40 VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
41};
42
43enum {Enabled, Magic};
44#define MISC_FMT_PRESERVE_ARGV0 (1UL << 31)
45#define MISC_FMT_OPEN_BINARY (1UL << 30)
46#define MISC_FMT_CREDENTIALS (1UL << 29)
47#define MISC_FMT_OPEN_FILE (1UL << 28)
48
49typedef struct {
50 struct list_head list;
51 unsigned long flags; /* type, status, etc. */
52 int offset; /* offset of magic */
53 int size; /* size of magic/mask */
54 char *magic; /* magic or filename extension */
55 char *mask; /* mask, NULL for exact match */
56 const char *interpreter; /* filename of interpreter */
57 char *name;
58 struct dentry *dentry;
59 struct file *interp_file;
60 refcount_t users; /* sync removal with load_misc_binary() */
61} Node;
62
63static struct file_system_type bm_fs_type;
64
65/*
66 * Max length of the register string. Determined by:
67 * - 7 delimiters
68 * - name: ~50 bytes
69 * - type: 1 byte
70 * - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
71 * - magic: 128 bytes (512 in escaped form)
72 * - mask: 128 bytes (512 in escaped form)
73 * - interp: ~50 bytes
74 * - flags: 5 bytes
75 * Round that up a bit, and then back off to hold the internal data
76 * (like struct Node).
77 */
78#define MAX_REGISTER_LENGTH 1920
79
80/**
81 * search_binfmt_handler - search for a binary handler for @bprm
82 * @misc: handle to binfmt_misc instance
83 * @bprm: binary for which we are looking for a handler
84 *
85 * Search for a binary type handler for @bprm in the list of registered binary
86 * type handlers.
87 *
88 * Return: binary type list entry on success, NULL on failure
89 */
90static Node *search_binfmt_handler(struct binfmt_misc *misc,
91 struct linux_binprm *bprm)
92{
93 char *p = strrchr(bprm->interp, '.');
94 Node *e;
95
96 /* Walk all the registered handlers. */
97 list_for_each_entry(e, &misc->entries, list) {
98 char *s;
99 int j;
100
101 /* Make sure this one is currently enabled. */
102 if (!test_bit(Enabled, &e->flags))
103 continue;
104
105 /* Do matching based on extension if applicable. */
106 if (!test_bit(Magic, &e->flags)) {
107 if (p && !strcmp(e->magic, p + 1))
108 return e;
109 continue;
110 }
111
112 /* Do matching based on magic & mask. */
113 s = bprm->buf + e->offset;
114 if (e->mask) {
115 for (j = 0; j < e->size; j++)
116 if ((*s++ ^ e->magic[j]) & e->mask[j])
117 break;
118 } else {
119 for (j = 0; j < e->size; j++)
120 if ((*s++ ^ e->magic[j]))
121 break;
122 }
123 if (j == e->size)
124 return e;
125 }
126
127 return NULL;
128}
129
130/**
131 * get_binfmt_handler - try to find a binary type handler
132 * @misc: handle to binfmt_misc instance
133 * @bprm: binary for which we are looking for a handler
134 *
135 * Try to find a binfmt handler for the binary type. If one is found take a
136 * reference to protect against removal via bm_{entry,status}_write().
137 *
138 * Return: binary type list entry on success, NULL on failure
139 */
140static Node *get_binfmt_handler(struct binfmt_misc *misc,
141 struct linux_binprm *bprm)
142{
143 Node *e;
144
145 read_lock(&misc->entries_lock);
146 e = search_binfmt_handler(misc, bprm);
147 if (e)
148 refcount_inc(r: &e->users);
149 read_unlock(&misc->entries_lock);
150 return e;
151}
152
153/**
154 * put_binfmt_handler - put binary handler node
155 * @e: node to put
156 *
157 * Free node syncing with load_misc_binary() and defer final free to
158 * load_misc_binary() in case it is using the binary type handler we were
159 * requested to remove.
160 */
161static void put_binfmt_handler(Node *e)
162{
163 if (refcount_dec_and_test(r: &e->users)) {
164 if (e->flags & MISC_FMT_OPEN_FILE)
165 filp_close(e->interp_file, NULL);
166 kfree(objp: e);
167 }
168}
169
170/**
171 * load_binfmt_misc - load the binfmt_misc of the caller's user namespace
172 *
173 * To be called in load_misc_binary() to load the relevant struct binfmt_misc.
174 * If a user namespace doesn't have its own binfmt_misc mount it can make use
175 * of its ancestor's binfmt_misc handlers. This mimicks the behavior of
176 * pre-namespaced binfmt_misc where all registered binfmt_misc handlers where
177 * available to all user and user namespaces on the system.
178 *
179 * Return: the binfmt_misc instance of the caller's user namespace
180 */
181static struct binfmt_misc *load_binfmt_misc(void)
182{
183 const struct user_namespace *user_ns;
184 struct binfmt_misc *misc;
185
186 user_ns = current_user_ns();
187 while (user_ns) {
188 /* Pairs with smp_store_release() in bm_fill_super(). */
189 misc = smp_load_acquire(&user_ns->binfmt_misc);
190 if (misc)
191 return misc;
192
193 user_ns = user_ns->parent;
194 }
195
196 return &init_binfmt_misc;
197}
198
199/*
200 * the loader itself
201 */
202static int load_misc_binary(struct linux_binprm *bprm)
203{
204 Node *fmt;
205 struct file *interp_file = NULL;
206 int retval = -ENOEXEC;
207 struct binfmt_misc *misc;
208
209 misc = load_binfmt_misc();
210 if (!misc->enabled)
211 return retval;
212
213 fmt = get_binfmt_handler(misc, bprm);
214 if (!fmt)
215 return retval;
216
217 /* Need to be able to load the file after exec */
218 retval = -ENOENT;
219 if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
220 goto ret;
221
222 if (fmt->flags & MISC_FMT_PRESERVE_ARGV0) {
223 bprm->interp_flags |= BINPRM_FLAGS_PRESERVE_ARGV0;
224 } else {
225 retval = remove_arg_zero(bprm);
226 if (retval)
227 goto ret;
228 }
229
230 if (fmt->flags & MISC_FMT_OPEN_BINARY)
231 bprm->have_execfd = 1;
232
233 /* make argv[1] be the path to the binary */
234 retval = copy_string_kernel(arg: bprm->interp, bprm);
235 if (retval < 0)
236 goto ret;
237 bprm->argc++;
238
239 /* add the interp as argv[0] */
240 retval = copy_string_kernel(arg: fmt->interpreter, bprm);
241 if (retval < 0)
242 goto ret;
243 bprm->argc++;
244
245 /* Update interp in case binfmt_script needs it. */
246 retval = bprm_change_interp(interp: fmt->interpreter, bprm);
247 if (retval < 0)
248 goto ret;
249
250 if (fmt->flags & MISC_FMT_OPEN_FILE) {
251 interp_file = file_clone_open(file: fmt->interp_file);
252 if (!IS_ERR(ptr: interp_file))
253 deny_write_access(file: interp_file);
254 } else {
255 interp_file = open_exec(fmt->interpreter);
256 }
257 retval = PTR_ERR(ptr: interp_file);
258 if (IS_ERR(ptr: interp_file))
259 goto ret;
260
261 bprm->interpreter = interp_file;
262 if (fmt->flags & MISC_FMT_CREDENTIALS)
263 bprm->execfd_creds = 1;
264
265 retval = 0;
266ret:
267
268 /*
269 * If we actually put the node here all concurrent calls to
270 * load_misc_binary() will have finished. We also know
271 * that for the refcount to be zero someone must have concurently
272 * removed the binary type handler from the list and it's our job to
273 * free it.
274 */
275 put_binfmt_handler(e: fmt);
276
277 return retval;
278}
279
280/* Command parsers */
281
282/*
283 * parses and copies one argument enclosed in del from *sp to *dp,
284 * recognising the \x special.
285 * returns pointer to the copied argument or NULL in case of an
286 * error (and sets err) or null argument length.
287 */
288static char *scanarg(char *s, char del)
289{
290 char c;
291
292 while ((c = *s++) != del) {
293 if (c == '\\' && *s == 'x') {
294 s++;
295 if (!isxdigit(*s++))
296 return NULL;
297 if (!isxdigit(*s++))
298 return NULL;
299 }
300 }
301 s[-1] ='\0';
302 return s;
303}
304
305static char *check_special_flags(char *sfs, Node *e)
306{
307 char *p = sfs;
308 int cont = 1;
309
310 /* special flags */
311 while (cont) {
312 switch (*p) {
313 case 'P':
314 pr_debug("register: flag: P (preserve argv0)\n");
315 p++;
316 e->flags |= MISC_FMT_PRESERVE_ARGV0;
317 break;
318 case 'O':
319 pr_debug("register: flag: O (open binary)\n");
320 p++;
321 e->flags |= MISC_FMT_OPEN_BINARY;
322 break;
323 case 'C':
324 pr_debug("register: flag: C (preserve creds)\n");
325 p++;
326 /* this flags also implies the
327 open-binary flag */
328 e->flags |= (MISC_FMT_CREDENTIALS |
329 MISC_FMT_OPEN_BINARY);
330 break;
331 case 'F':
332 pr_debug("register: flag: F: open interpreter file now\n");
333 p++;
334 e->flags |= MISC_FMT_OPEN_FILE;
335 break;
336 default:
337 cont = 0;
338 }
339 }
340
341 return p;
342}
343
344/*
345 * This registers a new binary format, it recognises the syntax
346 * ':name:type:offset:magic:mask:interpreter:flags'
347 * where the ':' is the IFS, that can be chosen with the first char
348 */
349static Node *create_entry(const char __user *buffer, size_t count)
350{
351 Node *e;
352 int memsize, err;
353 char *buf, *p;
354 char del;
355
356 pr_debug("register: received %zu bytes\n", count);
357
358 /* some sanity checks */
359 err = -EINVAL;
360 if ((count < 11) || (count > MAX_REGISTER_LENGTH))
361 goto out;
362
363 err = -ENOMEM;
364 memsize = sizeof(Node) + count + 8;
365 e = kmalloc(memsize, GFP_KERNEL_ACCOUNT);
366 if (!e)
367 goto out;
368
369 p = buf = (char *)e + sizeof(Node);
370
371 memset(s: e, c: 0, n: sizeof(Node));
372 if (copy_from_user(to: buf, from: buffer, n: count))
373 goto efault;
374
375 del = *p++; /* delimeter */
376
377 pr_debug("register: delim: %#x {%c}\n", del, del);
378
379 /* Pad the buffer with the delim to simplify parsing below. */
380 memset(s: buf + count, c: del, n: 8);
381
382 /* Parse the 'name' field. */
383 e->name = p;
384 p = strchr(p, del);
385 if (!p)
386 goto einval;
387 *p++ = '\0';
388 if (!e->name[0] ||
389 !strcmp(e->name, ".") ||
390 !strcmp(e->name, "..") ||
391 strchr(e->name, '/'))
392 goto einval;
393
394 pr_debug("register: name: {%s}\n", e->name);
395
396 /* Parse the 'type' field. */
397 switch (*p++) {
398 case 'E':
399 pr_debug("register: type: E (extension)\n");
400 e->flags = 1 << Enabled;
401 break;
402 case 'M':
403 pr_debug("register: type: M (magic)\n");
404 e->flags = (1 << Enabled) | (1 << Magic);
405 break;
406 default:
407 goto einval;
408 }
409 if (*p++ != del)
410 goto einval;
411
412 if (test_bit(Magic, &e->flags)) {
413 /* Handle the 'M' (magic) format. */
414 char *s;
415
416 /* Parse the 'offset' field. */
417 s = strchr(p, del);
418 if (!s)
419 goto einval;
420 *s = '\0';
421 if (p != s) {
422 int r = kstrtoint(s: p, base: 10, res: &e->offset);
423 if (r != 0 || e->offset < 0)
424 goto einval;
425 }
426 p = s;
427 if (*p++)
428 goto einval;
429 pr_debug("register: offset: %#x\n", e->offset);
430
431 /* Parse the 'magic' field. */
432 e->magic = p;
433 p = scanarg(s: p, del);
434 if (!p)
435 goto einval;
436 if (!e->magic[0])
437 goto einval;
438 if (USE_DEBUG)
439 print_hex_dump_bytes(
440 KBUILD_MODNAME ": register: magic[raw]: ",
441 DUMP_PREFIX_NONE, e->magic, p - e->magic);
442
443 /* Parse the 'mask' field. */
444 e->mask = p;
445 p = scanarg(s: p, del);
446 if (!p)
447 goto einval;
448 if (!e->mask[0]) {
449 e->mask = NULL;
450 pr_debug("register: mask[raw]: none\n");
451 } else if (USE_DEBUG)
452 print_hex_dump_bytes(
453 KBUILD_MODNAME ": register: mask[raw]: ",
454 DUMP_PREFIX_NONE, e->mask, p - e->mask);
455
456 /*
457 * Decode the magic & mask fields.
458 * Note: while we might have accepted embedded NUL bytes from
459 * above, the unescape helpers here will stop at the first one
460 * it encounters.
461 */
462 e->size = string_unescape_inplace(buf: e->magic, UNESCAPE_HEX);
463 if (e->mask &&
464 string_unescape_inplace(buf: e->mask, UNESCAPE_HEX) != e->size)
465 goto einval;
466 if (e->size > BINPRM_BUF_SIZE ||
467 BINPRM_BUF_SIZE - e->size < e->offset)
468 goto einval;
469 pr_debug("register: magic/mask length: %i\n", e->size);
470 if (USE_DEBUG) {
471 print_hex_dump_bytes(
472 KBUILD_MODNAME ": register: magic[decoded]: ",
473 DUMP_PREFIX_NONE, e->magic, e->size);
474
475 if (e->mask) {
476 int i;
477 char *masked = kmalloc(e->size, GFP_KERNEL_ACCOUNT);
478
479 print_hex_dump_bytes(
480 KBUILD_MODNAME ": register: mask[decoded]: ",
481 DUMP_PREFIX_NONE, e->mask, e->size);
482
483 if (masked) {
484 for (i = 0; i < e->size; ++i)
485 masked[i] = e->magic[i] & e->mask[i];
486 print_hex_dump_bytes(
487 KBUILD_MODNAME ": register: magic[masked]: ",
488 DUMP_PREFIX_NONE, masked, e->size);
489
490 kfree(objp: masked);
491 }
492 }
493 }
494 } else {
495 /* Handle the 'E' (extension) format. */
496
497 /* Skip the 'offset' field. */
498 p = strchr(p, del);
499 if (!p)
500 goto einval;
501 *p++ = '\0';
502
503 /* Parse the 'magic' field. */
504 e->magic = p;
505 p = strchr(p, del);
506 if (!p)
507 goto einval;
508 *p++ = '\0';
509 if (!e->magic[0] || strchr(e->magic, '/'))
510 goto einval;
511 pr_debug("register: extension: {%s}\n", e->magic);
512
513 /* Skip the 'mask' field. */
514 p = strchr(p, del);
515 if (!p)
516 goto einval;
517 *p++ = '\0';
518 }
519
520 /* Parse the 'interpreter' field. */
521 e->interpreter = p;
522 p = strchr(p, del);
523 if (!p)
524 goto einval;
525 *p++ = '\0';
526 if (!e->interpreter[0])
527 goto einval;
528 pr_debug("register: interpreter: {%s}\n", e->interpreter);
529
530 /* Parse the 'flags' field. */
531 p = check_special_flags(sfs: p, e);
532 if (*p == '\n')
533 p++;
534 if (p != buf + count)
535 goto einval;
536
537 return e;
538
539out:
540 return ERR_PTR(error: err);
541
542efault:
543 kfree(objp: e);
544 return ERR_PTR(error: -EFAULT);
545einval:
546 kfree(objp: e);
547 return ERR_PTR(error: -EINVAL);
548}
549
550/*
551 * Set status of entry/binfmt_misc:
552 * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
553 */
554static int parse_command(const char __user *buffer, size_t count)
555{
556 char s[4];
557
558 if (count > 3)
559 return -EINVAL;
560 if (copy_from_user(to: s, from: buffer, n: count))
561 return -EFAULT;
562 if (!count)
563 return 0;
564 if (s[count - 1] == '\n')
565 count--;
566 if (count == 1 && s[0] == '0')
567 return 1;
568 if (count == 1 && s[0] == '1')
569 return 2;
570 if (count == 2 && s[0] == '-' && s[1] == '1')
571 return 3;
572 return -EINVAL;
573}
574
575/* generic stuff */
576
577static void entry_status(Node *e, char *page)
578{
579 char *dp = page;
580 const char *status = "disabled";
581
582 if (test_bit(Enabled, &e->flags))
583 status = "enabled";
584
585 if (!VERBOSE_STATUS) {
586 sprintf(buf: page, fmt: "%s\n", status);
587 return;
588 }
589
590 dp += sprintf(buf: dp, fmt: "%s\ninterpreter %s\n", status, e->interpreter);
591
592 /* print the special flags */
593 dp += sprintf(buf: dp, fmt: "flags: ");
594 if (e->flags & MISC_FMT_PRESERVE_ARGV0)
595 *dp++ = 'P';
596 if (e->flags & MISC_FMT_OPEN_BINARY)
597 *dp++ = 'O';
598 if (e->flags & MISC_FMT_CREDENTIALS)
599 *dp++ = 'C';
600 if (e->flags & MISC_FMT_OPEN_FILE)
601 *dp++ = 'F';
602 *dp++ = '\n';
603
604 if (!test_bit(Magic, &e->flags)) {
605 sprintf(buf: dp, fmt: "extension .%s\n", e->magic);
606 } else {
607 dp += sprintf(buf: dp, fmt: "offset %i\nmagic ", e->offset);
608 dp = bin2hex(dst: dp, src: e->magic, count: e->size);
609 if (e->mask) {
610 dp += sprintf(buf: dp, fmt: "\nmask ");
611 dp = bin2hex(dst: dp, src: e->mask, count: e->size);
612 }
613 *dp++ = '\n';
614 *dp = '\0';
615 }
616}
617
618static struct inode *bm_get_inode(struct super_block *sb, int mode)
619{
620 struct inode *inode = new_inode(sb);
621
622 if (inode) {
623 inode->i_ino = get_next_ino();
624 inode->i_mode = mode;
625 simple_inode_init_ts(inode);
626 }
627 return inode;
628}
629
630/**
631 * i_binfmt_misc - retrieve struct binfmt_misc from a binfmt_misc inode
632 * @inode: inode of the relevant binfmt_misc instance
633 *
634 * This helper retrieves struct binfmt_misc from a binfmt_misc inode. This can
635 * be done without any memory barriers because we are guaranteed that
636 * user_ns->binfmt_misc is fully initialized. It was fully initialized when the
637 * binfmt_misc mount was first created.
638 *
639 * Return: struct binfmt_misc of the relevant binfmt_misc instance
640 */
641static struct binfmt_misc *i_binfmt_misc(struct inode *inode)
642{
643 return inode->i_sb->s_user_ns->binfmt_misc;
644}
645
646/**
647 * bm_evict_inode - cleanup data associated with @inode
648 * @inode: inode to which the data is attached
649 *
650 * Cleanup the binary type handler data associated with @inode if a binary type
651 * entry is removed or the filesystem is unmounted and the super block is
652 * shutdown.
653 *
654 * If the ->evict call was not caused by a super block shutdown but by a write
655 * to remove the entry or all entries via bm_{entry,status}_write() the entry
656 * will have already been removed from the list. We keep the list_empty() check
657 * to make that explicit.
658*/
659static void bm_evict_inode(struct inode *inode)
660{
661 Node *e = inode->i_private;
662
663 clear_inode(inode);
664
665 if (e) {
666 struct binfmt_misc *misc;
667
668 misc = i_binfmt_misc(inode);
669 write_lock(&misc->entries_lock);
670 if (!list_empty(head: &e->list))
671 list_del_init(entry: &e->list);
672 write_unlock(&misc->entries_lock);
673 put_binfmt_handler(e);
674 }
675}
676
677/**
678 * remove_binfmt_handler - remove a binary type handler
679 * @misc: handle to binfmt_misc instance
680 * @e: binary type handler to remove
681 *
682 * Remove a binary type handler from the list of binary type handlers and
683 * remove its associated dentry. This is called from
684 * binfmt_{entry,status}_write(). In the future, we might want to think about
685 * adding a proper ->unlink() method to binfmt_misc instead of forcing caller's
686 * to use writes to files in order to delete binary type handlers. But it has
687 * worked for so long that it's not a pressing issue.
688 */
689static void remove_binfmt_handler(struct binfmt_misc *misc, Node *e)
690{
691 write_lock(&misc->entries_lock);
692 list_del_init(entry: &e->list);
693 write_unlock(&misc->entries_lock);
694 locked_recursive_removal(e->dentry, NULL);
695}
696
697/* /<entry> */
698
699static ssize_t
700bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
701{
702 Node *e = file_inode(f: file)->i_private;
703 ssize_t res;
704 char *page;
705
706 page = (char *) __get_free_page(GFP_KERNEL);
707 if (!page)
708 return -ENOMEM;
709
710 entry_status(e, page);
711
712 res = simple_read_from_buffer(to: buf, count: nbytes, ppos, from: page, available: strlen(page));
713
714 free_page((unsigned long) page);
715 return res;
716}
717
718static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
719 size_t count, loff_t *ppos)
720{
721 struct inode *inode = file_inode(f: file);
722 Node *e = inode->i_private;
723 int res = parse_command(buffer, count);
724
725 switch (res) {
726 case 1:
727 /* Disable this handler. */
728 clear_bit(nr: Enabled, addr: &e->flags);
729 break;
730 case 2:
731 /* Enable this handler. */
732 set_bit(nr: Enabled, addr: &e->flags);
733 break;
734 case 3:
735 /* Delete this handler. */
736 inode = d_inode(dentry: inode->i_sb->s_root);
737 inode_lock_nested(inode, subclass: I_MUTEX_PARENT);
738
739 /*
740 * In order to add new element or remove elements from the list
741 * via bm_{entry,register,status}_write() inode_lock() on the
742 * root inode must be held.
743 * The lock is exclusive ensuring that the list can't be
744 * modified. Only load_misc_binary() can access but does so
745 * read-only. So we only need to take the write lock when we
746 * actually remove the entry from the list.
747 */
748 if (!list_empty(head: &e->list))
749 remove_binfmt_handler(misc: i_binfmt_misc(inode), e);
750
751 inode_unlock(inode);
752 break;
753 default:
754 return res;
755 }
756
757 return count;
758}
759
760static const struct file_operations bm_entry_operations = {
761 .read = bm_entry_read,
762 .write = bm_entry_write,
763 .llseek = default_llseek,
764};
765
766/* /register */
767
768static ssize_t bm_register_write(struct file *file, const char __user *buffer,
769 size_t count, loff_t *ppos)
770{
771 Node *e;
772 struct inode *inode;
773 struct super_block *sb = file_inode(f: file)->i_sb;
774 struct dentry *root = sb->s_root, *dentry;
775 struct binfmt_misc *misc;
776 int err = 0;
777 struct file *f = NULL;
778
779 e = create_entry(buffer, count);
780
781 if (IS_ERR(ptr: e))
782 return PTR_ERR(ptr: e);
783
784 if (e->flags & MISC_FMT_OPEN_FILE) {
785 const struct cred *old_cred;
786
787 /*
788 * Now that we support unprivileged binfmt_misc mounts make
789 * sure we use the credentials that the register @file was
790 * opened with to also open the interpreter. Before that this
791 * didn't matter much as only a privileged process could open
792 * the register file.
793 */
794 old_cred = override_creds(override_cred: file->f_cred);
795 f = open_exec(e->interpreter);
796 revert_creds(revert_cred: old_cred);
797 if (IS_ERR(ptr: f)) {
798 pr_notice("register: failed to install interpreter file %s\n",
799 e->interpreter);
800 kfree(objp: e);
801 return PTR_ERR(ptr: f);
802 }
803 e->interp_file = f;
804 }
805
806 inode_lock(inode: d_inode(dentry: root));
807 dentry = lookup_noperm(&QSTR(e->name), root);
808 err = PTR_ERR(ptr: dentry);
809 if (IS_ERR(ptr: dentry))
810 goto out;
811
812 err = -EEXIST;
813 if (d_really_is_positive(dentry))
814 goto out2;
815
816 inode = bm_get_inode(sb, S_IFREG | 0644);
817
818 err = -ENOMEM;
819 if (!inode)
820 goto out2;
821
822 refcount_set(r: &e->users, n: 1);
823 e->dentry = dget(dentry);
824 inode->i_private = e;
825 inode->i_fop = &bm_entry_operations;
826
827 d_instantiate(dentry, inode);
828 misc = i_binfmt_misc(inode);
829 write_lock(&misc->entries_lock);
830 list_add(new: &e->list, head: &misc->entries);
831 write_unlock(&misc->entries_lock);
832
833 err = 0;
834out2:
835 dput(dentry);
836out:
837 inode_unlock(inode: d_inode(dentry: root));
838
839 if (err) {
840 if (f)
841 filp_close(f, NULL);
842 kfree(objp: e);
843 return err;
844 }
845 return count;
846}
847
848static const struct file_operations bm_register_operations = {
849 .write = bm_register_write,
850 .llseek = noop_llseek,
851};
852
853/* /status */
854
855static ssize_t
856bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
857{
858 struct binfmt_misc *misc;
859 char *s;
860
861 misc = i_binfmt_misc(inode: file_inode(f: file));
862 s = misc->enabled ? "enabled\n" : "disabled\n";
863 return simple_read_from_buffer(to: buf, count: nbytes, ppos, from: s, available: strlen(s));
864}
865
866static ssize_t bm_status_write(struct file *file, const char __user *buffer,
867 size_t count, loff_t *ppos)
868{
869 struct binfmt_misc *misc;
870 int res = parse_command(buffer, count);
871 Node *e, *next;
872 struct inode *inode;
873
874 misc = i_binfmt_misc(inode: file_inode(f: file));
875 switch (res) {
876 case 1:
877 /* Disable all handlers. */
878 misc->enabled = false;
879 break;
880 case 2:
881 /* Enable all handlers. */
882 misc->enabled = true;
883 break;
884 case 3:
885 /* Delete all handlers. */
886 inode = d_inode(dentry: file_inode(f: file)->i_sb->s_root);
887 inode_lock_nested(inode, subclass: I_MUTEX_PARENT);
888
889 /*
890 * In order to add new element or remove elements from the list
891 * via bm_{entry,register,status}_write() inode_lock() on the
892 * root inode must be held.
893 * The lock is exclusive ensuring that the list can't be
894 * modified. Only load_misc_binary() can access but does so
895 * read-only. So we only need to take the write lock when we
896 * actually remove the entry from the list.
897 */
898 list_for_each_entry_safe(e, next, &misc->entries, list)
899 remove_binfmt_handler(misc, e);
900
901 inode_unlock(inode);
902 break;
903 default:
904 return res;
905 }
906
907 return count;
908}
909
910static const struct file_operations bm_status_operations = {
911 .read = bm_status_read,
912 .write = bm_status_write,
913 .llseek = default_llseek,
914};
915
916/* Superblock handling */
917
918static void bm_put_super(struct super_block *sb)
919{
920 struct user_namespace *user_ns = sb->s_fs_info;
921
922 sb->s_fs_info = NULL;
923 put_user_ns(ns: user_ns);
924}
925
926static const struct super_operations s_ops = {
927 .statfs = simple_statfs,
928 .evict_inode = bm_evict_inode,
929 .put_super = bm_put_super,
930};
931
932static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
933{
934 int err;
935 struct user_namespace *user_ns = sb->s_user_ns;
936 struct binfmt_misc *misc;
937 static const struct tree_descr bm_files[] = {
938 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
939 [3] = {.name: "register", .ops: &bm_register_operations, S_IWUSR},
940 /* last one */ {""}
941 };
942
943 if (WARN_ON(user_ns != current_user_ns()))
944 return -EINVAL;
945
946 /*
947 * Lazily allocate a new binfmt_misc instance for this namespace, i.e.
948 * do it here during the first mount of binfmt_misc. We don't need to
949 * waste memory for every user namespace allocation. It's likely much
950 * more common to not mount a separate binfmt_misc instance than it is
951 * to mount one.
952 *
953 * While multiple superblocks can exist they are keyed by userns in
954 * s_fs_info for binfmt_misc. Hence, the vfs guarantees that
955 * bm_fill_super() is called exactly once whenever a binfmt_misc
956 * superblock for a userns is created. This in turn lets us conclude
957 * that when a binfmt_misc superblock is created for the first time for
958 * a userns there's no one racing us. Therefore we don't need any
959 * barriers when we dereference binfmt_misc.
960 */
961 misc = user_ns->binfmt_misc;
962 if (!misc) {
963 /*
964 * If it turns out that most user namespaces actually want to
965 * register their own binary type handler and therefore all
966 * create their own separate binfmt_misc mounts we should
967 * consider turning this into a kmem cache.
968 */
969 misc = kzalloc(sizeof(struct binfmt_misc), GFP_KERNEL);
970 if (!misc)
971 return -ENOMEM;
972
973 INIT_LIST_HEAD(list: &misc->entries);
974 rwlock_init(&misc->entries_lock);
975
976 /* Pairs with smp_load_acquire() in load_binfmt_misc(). */
977 smp_store_release(&user_ns->binfmt_misc, misc);
978 }
979
980 /*
981 * When the binfmt_misc superblock for this userns is shutdown
982 * ->enabled might have been set to false and we don't reinitialize
983 * ->enabled again in put_super() as someone might already be mounting
984 * binfmt_misc again. It also would be pointless since by the time
985 * ->put_super() is called we know that the binary type list for this
986 * bintfmt_misc mount is empty making load_misc_binary() return
987 * -ENOEXEC independent of whether ->enabled is true. Instead, if
988 * someone mounts binfmt_misc for the first time or again we simply
989 * reset ->enabled to true.
990 */
991 misc->enabled = true;
992
993 err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
994 if (!err)
995 sb->s_op = &s_ops;
996 return err;
997}
998
999static void bm_free(struct fs_context *fc)
1000{
1001 if (fc->s_fs_info)
1002 put_user_ns(ns: fc->s_fs_info);
1003}
1004
1005static int bm_get_tree(struct fs_context *fc)
1006{
1007 return get_tree_keyed(fc, fill_super: bm_fill_super, key: get_user_ns(ns: fc->user_ns));
1008}
1009
1010static const struct fs_context_operations bm_context_ops = {
1011 .free = bm_free,
1012 .get_tree = bm_get_tree,
1013};
1014
1015static int bm_init_fs_context(struct fs_context *fc)
1016{
1017 fc->ops = &bm_context_ops;
1018 return 0;
1019}
1020
1021static struct linux_binfmt misc_format = {
1022 .module = THIS_MODULE,
1023 .load_binary = load_misc_binary,
1024};
1025
1026static struct file_system_type bm_fs_type = {
1027 .owner = THIS_MODULE,
1028 .name = "binfmt_misc",
1029 .init_fs_context = bm_init_fs_context,
1030 .fs_flags = FS_USERNS_MOUNT,
1031 .kill_sb = kill_litter_super,
1032};
1033MODULE_ALIAS_FS("binfmt_misc");
1034
1035static int __init init_misc_binfmt(void)
1036{
1037 int err = register_filesystem(&bm_fs_type);
1038 if (!err)
1039 insert_binfmt(fmt: &misc_format);
1040 return err;
1041}
1042
1043static void __exit exit_misc_binfmt(void)
1044{
1045 unregister_binfmt(&misc_format);
1046 unregister_filesystem(&bm_fs_type);
1047}
1048
1049core_initcall(init_misc_binfmt);
1050module_exit(exit_misc_binfmt);
1051MODULE_DESCRIPTION("Kernel support for miscellaneous binaries");
1052MODULE_LICENSE("GPL");
1053