1// SPDX-License-Identifier: GPL-2.0-only 2/* 3 * binfmt_misc.c 4 * 5 * Copyright (C) 1997 Richard G��nther 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(&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(&e->users)) { 164 if (e->flags & MISC_FMT_OPEN_FILE) 165 filp_close(e->interp_file, NULL); 166 kfree(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(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(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(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(fmt->interp_file); 252 if (!IS_ERR(interp_file)) 253 deny_write_access(interp_file); 254 } else { 255 interp_file = open_exec(fmt->interpreter); 256 } 257 retval = PTR_ERR(interp_file); 258 if (IS_ERR(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(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(e, 0, sizeof(Node)); 372 if (copy_from_user(buf, buffer, 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(buf + count, del, 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(p, 10, &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(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(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(e->magic, UNESCAPE_HEX); 463 if (e->mask && 464 string_unescape_inplace(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(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(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(err); 541 542efault: 543 kfree(e); 544 return ERR_PTR(-EFAULT); 545einval: 546 kfree(e); 547 return ERR_PTR(-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(s, buffer, 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(page, "%s\n", status); 587 return; 588 } 589 590 dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter); 591 592 /* print the special flags */ 593 dp += sprintf(dp, "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(dp, "extension .%s\n", e->magic); 606 } else { 607 dp += sprintf(dp, "offset %i\nmagic ", e->offset); 608 dp = bin2hex(dp, e->magic, e->size); 609 if (e->mask) { 610 dp += sprintf(dp, "\nmask "); 611 dp = bin2hex(dp, e->mask, 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(&e->list)) 671 list_del_init(&e->list); 672 write_unlock(&misc->entries_lock); 673 put_binfmt_handler(e); 674 } 675} 676 677/** 678 * unlink_binfmt_dentry - remove the dentry for the binary type handler 679 * @dentry: dentry associated with the binary type handler 680 * 681 * Do the actual filesystem work to remove a dentry for a registered binary 682 * type handler. Since binfmt_misc only allows simple files to be created 683 * directly under the root dentry of the filesystem we ensure that we are 684 * indeed passed a dentry directly beneath the root dentry, that the inode 685 * associated with the root dentry is locked, and that it is a regular file we 686 * are asked to remove. 687 */ 688static void unlink_binfmt_dentry(struct dentry *dentry) 689{ 690 struct dentry *parent = dentry->d_parent; 691 struct inode *inode, *parent_inode; 692 693 /* All entries are immediate descendants of the root dentry. */ 694 if (WARN_ON_ONCE(dentry->d_sb->s_root != parent)) 695 return; 696 697 /* We only expect to be called on regular files. */ 698 inode = d_inode(dentry); 699 if (WARN_ON_ONCE(!S_ISREG(inode->i_mode))) 700 return; 701 702 /* The parent inode must be locked. */ 703 parent_inode = d_inode(parent); 704 if (WARN_ON_ONCE(!inode_is_locked(parent_inode))) 705 return; 706 707 if (simple_positive(dentry)) { 708 dget(dentry); 709 simple_unlink(parent_inode, dentry); 710 d_delete(dentry); 711 dput(dentry); 712 } 713} 714 715/** 716 * remove_binfmt_handler - remove a binary type handler 717 * @misc: handle to binfmt_misc instance 718 * @e: binary type handler to remove 719 * 720 * Remove a binary type handler from the list of binary type handlers and 721 * remove its associated dentry. This is called from 722 * binfmt_{entry,status}_write(). In the future, we might want to think about 723 * adding a proper ->unlink() method to binfmt_misc instead of forcing caller's 724 * to use writes to files in order to delete binary type handlers. But it has 725 * worked for so long that it's not a pressing issue. 726 */ 727static void remove_binfmt_handler(struct binfmt_misc *misc, Node *e) 728{ 729 write_lock(&misc->entries_lock); 730 list_del_init(&e->list); 731 write_unlock(&misc->entries_lock); 732 unlink_binfmt_dentry(e->dentry); 733} 734 735/* /<entry> */ 736 737static ssize_t 738bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) 739{ 740 Node *e = file_inode(file)->i_private; 741 ssize_t res; 742 char *page; 743 744 page = (char *) __get_free_page(GFP_KERNEL); 745 if (!page) 746 return -ENOMEM; 747 748 entry_status(e, page); 749 750 res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page)); 751 752 free_page((unsigned long) page); 753 return res; 754} 755 756static ssize_t bm_entry_write(struct file *file, const char __user *buffer, 757 size_t count, loff_t *ppos) 758{ 759 struct inode *inode = file_inode(file); 760 Node *e = inode->i_private; 761 int res = parse_command(buffer, count); 762 763 switch (res) { 764 case 1: 765 /* Disable this handler. */ 766 clear_bit(Enabled, &e->flags); 767 break; 768 case 2: 769 /* Enable this handler. */ 770 set_bit(Enabled, &e->flags); 771 break; 772 case 3: 773 /* Delete this handler. */ 774 inode = d_inode(inode->i_sb->s_root); 775 inode_lock(inode); 776 777 /* 778 * In order to add new element or remove elements from the list 779 * via bm_{entry,register,status}_write() inode_lock() on the 780 * root inode must be held. 781 * The lock is exclusive ensuring that the list can't be 782 * modified. Only load_misc_binary() can access but does so 783 * read-only. So we only need to take the write lock when we 784 * actually remove the entry from the list. 785 */ 786 if (!list_empty(&e->list)) 787 remove_binfmt_handler(i_binfmt_misc(inode), e); 788 789 inode_unlock(inode); 790 break; 791 default: 792 return res; 793 } 794 795 return count; 796} 797 798static const struct file_operations bm_entry_operations = { 799 .read = bm_entry_read, 800 .write = bm_entry_write, 801 .llseek = default_llseek, 802}; 803 804/* /register */ 805 806static ssize_t bm_register_write(struct file *file, const char __user *buffer, 807 size_t count, loff_t *ppos) 808{ 809 Node *e; 810 struct inode *inode; 811 struct super_block *sb = file_inode(file)->i_sb; 812 struct dentry *root = sb->s_root, *dentry; 813 struct binfmt_misc *misc; 814 int err = 0; 815 struct file *f = NULL; 816 817 e = create_entry(buffer, count); 818 819 if (IS_ERR(e)) 820 return PTR_ERR(e); 821 822 if (e->flags & MISC_FMT_OPEN_FILE) { 823 const struct cred *old_cred; 824 825 /* 826 * Now that we support unprivileged binfmt_misc mounts make 827 * sure we use the credentials that the register @file was 828 * opened with to also open the interpreter. Before that this 829 * didn't matter much as only a privileged process could open 830 * the register file. 831 */ 832 old_cred = override_creds(file->f_cred); 833 f = open_exec(e->interpreter); 834 revert_creds(old_cred); 835 if (IS_ERR(f)) { 836 pr_notice("register: failed to install interpreter file %s\n", 837 e->interpreter); 838 kfree(e); 839 return PTR_ERR(f); 840 } 841 e->interp_file = f; 842 } 843 844 inode_lock(d_inode(root)); 845 dentry = lookup_one_len(e->name, root, strlen(e->name)); 846 err = PTR_ERR(dentry); 847 if (IS_ERR(dentry)) 848 goto out; 849 850 err = -EEXIST; 851 if (d_really_is_positive(dentry)) 852 goto out2; 853 854 inode = bm_get_inode(sb, S_IFREG | 0644); 855 856 err = -ENOMEM; 857 if (!inode) 858 goto out2; 859 860 refcount_set(&e->users, 1); 861 e->dentry = dget(dentry); 862 inode->i_private = e; 863 inode->i_fop = &bm_entry_operations; 864 865 d_instantiate(dentry, inode); 866 misc = i_binfmt_misc(inode); 867 write_lock(&misc->entries_lock); 868 list_add(&e->list, &misc->entries); 869 write_unlock(&misc->entries_lock); 870 871 err = 0; 872out2: 873 dput(dentry); 874out: 875 inode_unlock(d_inode(root)); 876 877 if (err) { 878 if (f) 879 filp_close(f, NULL); 880 kfree(e); 881 return err; 882 } 883 return count; 884} 885 886static const struct file_operations bm_register_operations = { 887 .write = bm_register_write, 888 .llseek = noop_llseek, 889}; 890 891/* /status */ 892 893static ssize_t 894bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) 895{ 896 struct binfmt_misc *misc; 897 char *s; 898 899 misc = i_binfmt_misc(file_inode(file)); 900 s = misc->enabled ? "enabled\n" : "disabled\n"; 901 return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s)); 902} 903 904static ssize_t bm_status_write(struct file *file, const char __user *buffer, 905 size_t count, loff_t *ppos) 906{ 907 struct binfmt_misc *misc; 908 int res = parse_command(buffer, count); 909 Node *e, *next; 910 struct inode *inode; 911 912 misc = i_binfmt_misc(file_inode(file)); 913 switch (res) { 914 case 1: 915 /* Disable all handlers. */ 916 misc->enabled = false; 917 break; 918 case 2: 919 /* Enable all handlers. */ 920 misc->enabled = true; 921 break; 922 case 3: 923 /* Delete all handlers. */ 924 inode = d_inode(file_inode(file)->i_sb->s_root); 925 inode_lock(inode); 926 927 /* 928 * In order to add new element or remove elements from the list 929 * via bm_{entry,register,status}_write() inode_lock() on the 930 * root inode must be held. 931 * The lock is exclusive ensuring that the list can't be 932 * modified. Only load_misc_binary() can access but does so 933 * read-only. So we only need to take the write lock when we 934 * actually remove the entry from the list. 935 */ 936 list_for_each_entry_safe(e, next, &misc->entries, list) 937 remove_binfmt_handler(misc, e); 938 939 inode_unlock(inode); 940 break; 941 default: 942 return res; 943 } 944 945 return count; 946} 947 948static const struct file_operations bm_status_operations = { 949 .read = bm_status_read, 950 .write = bm_status_write, 951 .llseek = default_llseek, 952}; 953 954/* Superblock handling */ 955 956static void bm_put_super(struct super_block *sb) 957{ 958 struct user_namespace *user_ns = sb->s_fs_info; 959 960 sb->s_fs_info = NULL; 961 put_user_ns(user_ns); 962} 963 964static const struct super_operations s_ops = { 965 .statfs = simple_statfs, 966 .evict_inode = bm_evict_inode, 967 .put_super = bm_put_super, 968}; 969 970static int bm_fill_super(struct super_block *sb, struct fs_context *fc) 971{ 972 int err; 973 struct user_namespace *user_ns = sb->s_user_ns; 974 struct binfmt_misc *misc; 975 static const struct tree_descr bm_files[] = { 976 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO}, 977 [3] = {"register", &bm_register_operations, S_IWUSR}, 978 /* last one */ {""} 979 }; 980 981 if (WARN_ON(user_ns != current_user_ns())) 982 return -EINVAL; 983 984 /* 985 * Lazily allocate a new binfmt_misc instance for this namespace, i.e. 986 * do it here during the first mount of binfmt_misc. We don't need to 987 * waste memory for every user namespace allocation. It's likely much 988 * more common to not mount a separate binfmt_misc instance than it is 989 * to mount one. 990 * 991 * While multiple superblocks can exist they are keyed by userns in 992 * s_fs_info for binfmt_misc. Hence, the vfs guarantees that 993 * bm_fill_super() is called exactly once whenever a binfmt_misc 994 * superblock for a userns is created. This in turn lets us conclude 995 * that when a binfmt_misc superblock is created for the first time for 996 * a userns there's no one racing us. Therefore we don't need any 997 * barriers when we dereference binfmt_misc. 998 */ 999 misc = user_ns->binfmt_misc; 1000 if (!misc) { 1001 /* 1002 * If it turns out that most user namespaces actually want to 1003 * register their own binary type handler and therefore all 1004 * create their own separate binfm_misc mounts we should 1005 * consider turning this into a kmem cache. 1006 */ 1007 misc = kzalloc(sizeof(struct binfmt_misc), GFP_KERNEL); 1008 if (!misc) 1009 return -ENOMEM; 1010 1011 INIT_LIST_HEAD(&misc->entries); 1012 rwlock_init(&misc->entries_lock); 1013 1014 /* Pairs with smp_load_acquire() in load_binfmt_misc(). */ 1015 smp_store_release(&user_ns->binfmt_misc, misc); 1016 } 1017 1018 /* 1019 * When the binfmt_misc superblock for this userns is shutdown 1020 * ->enabled might have been set to false and we don't reinitialize 1021 * ->enabled again in put_super() as someone might already be mounting 1022 * binfmt_misc again. It also would be pointless since by the time 1023 * ->put_super() is called we know that the binary type list for this 1024 * bintfmt_misc mount is empty making load_misc_binary() return 1025 * -ENOEXEC independent of whether ->enabled is true. Instead, if 1026 * someone mounts binfmt_misc for the first time or again we simply 1027 * reset ->enabled to true. 1028 */ 1029 misc->enabled = true; 1030 1031 err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files); 1032 if (!err) 1033 sb->s_op = &s_ops; 1034 return err; 1035} 1036 1037static void bm_free(struct fs_context *fc) 1038{ 1039 if (fc->s_fs_info) 1040 put_user_ns(fc->s_fs_info); 1041} 1042 1043static int bm_get_tree(struct fs_context *fc) 1044{ 1045 return get_tree_keyed(fc, bm_fill_super, get_user_ns(fc->user_ns)); 1046} 1047 1048static const struct fs_context_operations bm_context_ops = { 1049 .free = bm_free, 1050 .get_tree = bm_get_tree, 1051}; 1052 1053static int bm_init_fs_context(struct fs_context *fc) 1054{ 1055 fc->ops = &bm_context_ops; 1056 return 0; 1057} 1058 1059static struct linux_binfmt misc_format = { 1060 .module = THIS_MODULE, 1061 .load_binary = load_misc_binary, 1062}; 1063 1064static struct file_system_type bm_fs_type = { 1065 .owner = THIS_MODULE, 1066 .name = "binfmt_misc", 1067 .init_fs_context = bm_init_fs_context, 1068 .fs_flags = FS_USERNS_MOUNT, 1069 .kill_sb = kill_litter_super, 1070}; 1071MODULE_ALIAS_FS("binfmt_misc"); 1072 1073static int __init init_misc_binfmt(void) 1074{ 1075 int err = register_filesystem(&bm_fs_type); 1076 if (!err) 1077 insert_binfmt(&misc_format); 1078 return err; 1079} 1080 1081static void __exit exit_misc_binfmt(void) 1082{ 1083 unregister_binfmt(&misc_format); 1084 unregister_filesystem(&bm_fs_type); 1085} 1086 1087core_initcall(init_misc_binfmt); 1088module_exit(exit_misc_binfmt); 1089MODULE_LICENSE("GPL"); 1090