1 /* -*- linux-c -*- --------------------------------------------------------- * 2 * 3 * linux/fs/devpts/inode.c 4 * 5 * Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved 6 * 7 * This file is part of the Linux kernel and is made available under 8 * the terms of the GNU General Public License, version 2, or at your 9 * option, any later version, incorporated herein by reference. 10 * 11 * ------------------------------------------------------------------------- */ 12 13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 14 15 #include <linux/module.h> 16 #include <linux/init.h> 17 #include <linux/fs.h> 18 #include <linux/sched.h> 19 #include <linux/namei.h> 20 #include <linux/slab.h> 21 #include <linux/mount.h> 22 #include <linux/tty.h> 23 #include <linux/mutex.h> 24 #include <linux/magic.h> 25 #include <linux/idr.h> 26 #include <linux/devpts_fs.h> 27 #include <linux/parser.h> 28 #include <linux/fsnotify.h> 29 #include <linux/seq_file.h> 30 31 #define DEVPTS_DEFAULT_MODE 0600 32 /* 33 * ptmx is a new node in /dev/pts and will be unused in legacy (single- 34 * instance) mode. To prevent surprises in user space, set permissions of 35 * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful 36 * permissions. 37 */ 38 #define DEVPTS_DEFAULT_PTMX_MODE 0000 39 #define PTMX_MINOR 2 40 41 /* 42 * sysctl support for setting limits on the number of Unix98 ptys allocated. 43 * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly. 44 */ 45 static int pty_limit = NR_UNIX98_PTY_DEFAULT; 46 static int pty_reserve = NR_UNIX98_PTY_RESERVE; 47 static int pty_limit_min; 48 static int pty_limit_max = INT_MAX; 49 static int pty_count; 50 51 static struct ctl_table pty_table[] = { 52 { 53 .procname = "max", 54 .maxlen = sizeof(int), 55 .mode = 0644, 56 .data = &pty_limit, 57 .proc_handler = proc_dointvec_minmax, 58 .extra1 = &pty_limit_min, 59 .extra2 = &pty_limit_max, 60 }, { 61 .procname = "reserve", 62 .maxlen = sizeof(int), 63 .mode = 0644, 64 .data = &pty_reserve, 65 .proc_handler = proc_dointvec_minmax, 66 .extra1 = &pty_limit_min, 67 .extra2 = &pty_limit_max, 68 }, { 69 .procname = "nr", 70 .maxlen = sizeof(int), 71 .mode = 0444, 72 .data = &pty_count, 73 .proc_handler = proc_dointvec, 74 }, 75 {} 76 }; 77 78 static struct ctl_table pty_kern_table[] = { 79 { 80 .procname = "pty", 81 .mode = 0555, 82 .child = pty_table, 83 }, 84 {} 85 }; 86 87 static struct ctl_table pty_root_table[] = { 88 { 89 .procname = "kernel", 90 .mode = 0555, 91 .child = pty_kern_table, 92 }, 93 {} 94 }; 95 96 static DEFINE_MUTEX(allocated_ptys_lock); 97 98 static struct vfsmount *devpts_mnt; 99 100 struct pts_mount_opts { 101 int setuid; 102 int setgid; 103 kuid_t uid; 104 kgid_t gid; 105 umode_t mode; 106 umode_t ptmxmode; 107 int newinstance; 108 int max; 109 }; 110 111 enum { 112 Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max, 113 Opt_err 114 }; 115 116 static const match_table_t tokens = { 117 {Opt_uid, "uid=%u"}, 118 {Opt_gid, "gid=%u"}, 119 {Opt_mode, "mode=%o"}, 120 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 121 {Opt_ptmxmode, "ptmxmode=%o"}, 122 {Opt_newinstance, "newinstance"}, 123 {Opt_max, "max=%d"}, 124 #endif 125 {Opt_err, NULL} 126 }; 127 128 struct pts_fs_info { 129 struct ida allocated_ptys; 130 struct pts_mount_opts mount_opts; 131 struct dentry *ptmx_dentry; 132 }; 133 134 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb) 135 { 136 return sb->s_fs_info; 137 } 138 139 static inline struct super_block *pts_sb_from_inode(struct inode *inode) 140 { 141 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 142 if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC) 143 return inode->i_sb; 144 #endif 145 if (!devpts_mnt) 146 return NULL; 147 return devpts_mnt->mnt_sb; 148 } 149 150 #define PARSE_MOUNT 0 151 #define PARSE_REMOUNT 1 152 153 /* 154 * parse_mount_options(): 155 * Set @opts to mount options specified in @data. If an option is not 156 * specified in @data, set it to its default value. The exception is 157 * 'newinstance' option which can only be set/cleared on a mount (i.e. 158 * cannot be changed during remount). 159 * 160 * Note: @data may be NULL (in which case all options are set to default). 161 */ 162 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts) 163 { 164 char *p; 165 kuid_t uid; 166 kgid_t gid; 167 168 opts->setuid = 0; 169 opts->setgid = 0; 170 opts->uid = GLOBAL_ROOT_UID; 171 opts->gid = GLOBAL_ROOT_GID; 172 opts->mode = DEVPTS_DEFAULT_MODE; 173 opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE; 174 opts->max = NR_UNIX98_PTY_MAX; 175 176 /* newinstance makes sense only on initial mount */ 177 if (op == PARSE_MOUNT) 178 opts->newinstance = 0; 179 180 while ((p = strsep(&data, ",")) != NULL) { 181 substring_t args[MAX_OPT_ARGS]; 182 int token; 183 int option; 184 185 if (!*p) 186 continue; 187 188 token = match_token(p, tokens, args); 189 switch (token) { 190 case Opt_uid: 191 if (match_int(&args[0], &option)) 192 return -EINVAL; 193 uid = make_kuid(current_user_ns(), option); 194 if (!uid_valid(uid)) 195 return -EINVAL; 196 opts->uid = uid; 197 opts->setuid = 1; 198 break; 199 case Opt_gid: 200 if (match_int(&args[0], &option)) 201 return -EINVAL; 202 gid = make_kgid(current_user_ns(), option); 203 if (!gid_valid(gid)) 204 return -EINVAL; 205 opts->gid = gid; 206 opts->setgid = 1; 207 break; 208 case Opt_mode: 209 if (match_octal(&args[0], &option)) 210 return -EINVAL; 211 opts->mode = option & S_IALLUGO; 212 break; 213 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 214 case Opt_ptmxmode: 215 if (match_octal(&args[0], &option)) 216 return -EINVAL; 217 opts->ptmxmode = option & S_IALLUGO; 218 break; 219 case Opt_newinstance: 220 /* newinstance makes sense only on initial mount */ 221 if (op == PARSE_MOUNT) 222 opts->newinstance = 1; 223 break; 224 case Opt_max: 225 if (match_int(&args[0], &option) || 226 option < 0 || option > NR_UNIX98_PTY_MAX) 227 return -EINVAL; 228 opts->max = option; 229 break; 230 #endif 231 default: 232 pr_err("called with bogus options\n"); 233 return -EINVAL; 234 } 235 } 236 237 return 0; 238 } 239 240 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 241 static int mknod_ptmx(struct super_block *sb) 242 { 243 int mode; 244 int rc = -ENOMEM; 245 struct dentry *dentry; 246 struct inode *inode; 247 struct dentry *root = sb->s_root; 248 struct pts_fs_info *fsi = DEVPTS_SB(sb); 249 struct pts_mount_opts *opts = &fsi->mount_opts; 250 kuid_t root_uid; 251 kgid_t root_gid; 252 253 root_uid = make_kuid(current_user_ns(), 0); 254 root_gid = make_kgid(current_user_ns(), 0); 255 if (!uid_valid(root_uid) || !gid_valid(root_gid)) 256 return -EINVAL; 257 258 mutex_lock(&d_inode(root)->i_mutex); 259 260 /* If we have already created ptmx node, return */ 261 if (fsi->ptmx_dentry) { 262 rc = 0; 263 goto out; 264 } 265 266 dentry = d_alloc_name(root, "ptmx"); 267 if (!dentry) { 268 pr_err("Unable to alloc dentry for ptmx node\n"); 269 goto out; 270 } 271 272 /* 273 * Create a new 'ptmx' node in this mount of devpts. 274 */ 275 inode = new_inode(sb); 276 if (!inode) { 277 pr_err("Unable to alloc inode for ptmx node\n"); 278 dput(dentry); 279 goto out; 280 } 281 282 inode->i_ino = 2; 283 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; 284 285 mode = S_IFCHR|opts->ptmxmode; 286 init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2)); 287 inode->i_uid = root_uid; 288 inode->i_gid = root_gid; 289 290 d_add(dentry, inode); 291 292 fsi->ptmx_dentry = dentry; 293 rc = 0; 294 out: 295 mutex_unlock(&d_inode(root)->i_mutex); 296 return rc; 297 } 298 299 static void update_ptmx_mode(struct pts_fs_info *fsi) 300 { 301 struct inode *inode; 302 if (fsi->ptmx_dentry) { 303 inode = d_inode(fsi->ptmx_dentry); 304 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode; 305 } 306 } 307 #else 308 static inline void update_ptmx_mode(struct pts_fs_info *fsi) 309 { 310 return; 311 } 312 #endif 313 314 static int devpts_remount(struct super_block *sb, int *flags, char *data) 315 { 316 int err; 317 struct pts_fs_info *fsi = DEVPTS_SB(sb); 318 struct pts_mount_opts *opts = &fsi->mount_opts; 319 320 sync_filesystem(sb); 321 err = parse_mount_options(data, PARSE_REMOUNT, opts); 322 323 /* 324 * parse_mount_options() restores options to default values 325 * before parsing and may have changed ptmxmode. So, update the 326 * mode in the inode too. Bogus options don't fail the remount, 327 * so do this even on error return. 328 */ 329 update_ptmx_mode(fsi); 330 331 return err; 332 } 333 334 static int devpts_show_options(struct seq_file *seq, struct dentry *root) 335 { 336 struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb); 337 struct pts_mount_opts *opts = &fsi->mount_opts; 338 339 if (opts->setuid) 340 seq_printf(seq, ",uid=%u", 341 from_kuid_munged(&init_user_ns, opts->uid)); 342 if (opts->setgid) 343 seq_printf(seq, ",gid=%u", 344 from_kgid_munged(&init_user_ns, opts->gid)); 345 seq_printf(seq, ",mode=%03o", opts->mode); 346 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 347 seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode); 348 if (opts->max < NR_UNIX98_PTY_MAX) 349 seq_printf(seq, ",max=%d", opts->max); 350 #endif 351 352 return 0; 353 } 354 355 static const struct super_operations devpts_sops = { 356 .statfs = simple_statfs, 357 .remount_fs = devpts_remount, 358 .show_options = devpts_show_options, 359 }; 360 361 static void *new_pts_fs_info(void) 362 { 363 struct pts_fs_info *fsi; 364 365 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL); 366 if (!fsi) 367 return NULL; 368 369 ida_init(&fsi->allocated_ptys); 370 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE; 371 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE; 372 373 return fsi; 374 } 375 376 static int 377 devpts_fill_super(struct super_block *s, void *data, int silent) 378 { 379 struct inode *inode; 380 381 s->s_blocksize = 1024; 382 s->s_blocksize_bits = 10; 383 s->s_magic = DEVPTS_SUPER_MAGIC; 384 s->s_op = &devpts_sops; 385 s->s_time_gran = 1; 386 387 s->s_fs_info = new_pts_fs_info(); 388 if (!s->s_fs_info) 389 goto fail; 390 391 inode = new_inode(s); 392 if (!inode) 393 goto fail; 394 inode->i_ino = 1; 395 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; 396 inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR; 397 inode->i_op = &simple_dir_inode_operations; 398 inode->i_fop = &simple_dir_operations; 399 set_nlink(inode, 2); 400 401 s->s_root = d_make_root(inode); 402 if (s->s_root) 403 return 0; 404 405 pr_err("get root dentry failed\n"); 406 407 fail: 408 return -ENOMEM; 409 } 410 411 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 412 static int compare_init_pts_sb(struct super_block *s, void *p) 413 { 414 if (devpts_mnt) 415 return devpts_mnt->mnt_sb == s; 416 return 0; 417 } 418 419 /* 420 * devpts_mount() 421 * 422 * If the '-o newinstance' mount option was specified, mount a new 423 * (private) instance of devpts. PTYs created in this instance are 424 * independent of the PTYs in other devpts instances. 425 * 426 * If the '-o newinstance' option was not specified, mount/remount the 427 * initial kernel mount of devpts. This type of mount gives the 428 * legacy, single-instance semantics. 429 * 430 * The 'newinstance' option is needed to support multiple namespace 431 * semantics in devpts while preserving backward compatibility of the 432 * current 'single-namespace' semantics. i.e all mounts of devpts 433 * without the 'newinstance' mount option should bind to the initial 434 * kernel mount, like mount_single(). 435 * 436 * Mounts with 'newinstance' option create a new, private namespace. 437 * 438 * NOTE: 439 * 440 * For single-mount semantics, devpts cannot use mount_single(), 441 * because mount_single()/sget() find and use the super-block from 442 * the most recent mount of devpts. But that recent mount may be a 443 * 'newinstance' mount and mount_single() would pick the newinstance 444 * super-block instead of the initial super-block. 445 */ 446 static struct dentry *devpts_mount(struct file_system_type *fs_type, 447 int flags, const char *dev_name, void *data) 448 { 449 int error; 450 struct pts_mount_opts opts; 451 struct super_block *s; 452 453 error = parse_mount_options(data, PARSE_MOUNT, &opts); 454 if (error) 455 return ERR_PTR(error); 456 457 /* Require newinstance for all user namespace mounts to ensure 458 * the mount options are not changed. 459 */ 460 if ((current_user_ns() != &init_user_ns) && !opts.newinstance) 461 return ERR_PTR(-EINVAL); 462 463 if (opts.newinstance) 464 s = sget(fs_type, NULL, set_anon_super, flags, NULL); 465 else 466 s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags, 467 NULL); 468 469 if (IS_ERR(s)) 470 return ERR_CAST(s); 471 472 if (!s->s_root) { 473 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0); 474 if (error) 475 goto out_undo_sget; 476 s->s_flags |= MS_ACTIVE; 477 } 478 479 memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts)); 480 481 error = mknod_ptmx(s); 482 if (error) 483 goto out_undo_sget; 484 485 return dget(s->s_root); 486 487 out_undo_sget: 488 deactivate_locked_super(s); 489 return ERR_PTR(error); 490 } 491 492 #else 493 /* 494 * This supports only the legacy single-instance semantics (no 495 * multiple-instance semantics) 496 */ 497 static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags, 498 const char *dev_name, void *data) 499 { 500 return mount_single(fs_type, flags, data, devpts_fill_super); 501 } 502 #endif 503 504 static void devpts_kill_sb(struct super_block *sb) 505 { 506 struct pts_fs_info *fsi = DEVPTS_SB(sb); 507 508 ida_destroy(&fsi->allocated_ptys); 509 kfree(fsi); 510 kill_litter_super(sb); 511 } 512 513 static struct file_system_type devpts_fs_type = { 514 .name = "devpts", 515 .mount = devpts_mount, 516 .kill_sb = devpts_kill_sb, 517 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 518 .fs_flags = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT, 519 #endif 520 }; 521 522 /* 523 * The normal naming convention is simply /dev/pts/<number>; this conforms 524 * to the System V naming convention 525 */ 526 527 int devpts_new_index(struct inode *ptmx_inode) 528 { 529 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 530 struct pts_fs_info *fsi; 531 int index; 532 int ida_ret; 533 534 if (!sb) 535 return -ENODEV; 536 537 fsi = DEVPTS_SB(sb); 538 retry: 539 if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL)) 540 return -ENOMEM; 541 542 mutex_lock(&allocated_ptys_lock); 543 if (pty_count >= pty_limit - 544 (fsi->mount_opts.newinstance ? pty_reserve : 0)) { 545 mutex_unlock(&allocated_ptys_lock); 546 return -ENOSPC; 547 } 548 549 ida_ret = ida_get_new(&fsi->allocated_ptys, &index); 550 if (ida_ret < 0) { 551 mutex_unlock(&allocated_ptys_lock); 552 if (ida_ret == -EAGAIN) 553 goto retry; 554 return -EIO; 555 } 556 557 if (index >= fsi->mount_opts.max) { 558 ida_remove(&fsi->allocated_ptys, index); 559 mutex_unlock(&allocated_ptys_lock); 560 return -ENOSPC; 561 } 562 pty_count++; 563 mutex_unlock(&allocated_ptys_lock); 564 return index; 565 } 566 567 void devpts_kill_index(struct inode *ptmx_inode, int idx) 568 { 569 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 570 struct pts_fs_info *fsi = DEVPTS_SB(sb); 571 572 mutex_lock(&allocated_ptys_lock); 573 ida_remove(&fsi->allocated_ptys, idx); 574 pty_count--; 575 mutex_unlock(&allocated_ptys_lock); 576 } 577 578 /** 579 * devpts_pty_new -- create a new inode in /dev/pts/ 580 * @ptmx_inode: inode of the master 581 * @device: major+minor of the node to be created 582 * @index: used as a name of the node 583 * @priv: what's given back by devpts_get_priv 584 * 585 * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill. 586 */ 587 struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index, 588 void *priv) 589 { 590 struct dentry *dentry; 591 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 592 struct inode *inode; 593 struct dentry *root; 594 struct pts_fs_info *fsi; 595 struct pts_mount_opts *opts; 596 char s[12]; 597 598 if (!sb) 599 return ERR_PTR(-ENODEV); 600 601 root = sb->s_root; 602 fsi = DEVPTS_SB(sb); 603 opts = &fsi->mount_opts; 604 605 inode = new_inode(sb); 606 if (!inode) 607 return ERR_PTR(-ENOMEM); 608 609 inode->i_ino = index + 3; 610 inode->i_uid = opts->setuid ? opts->uid : current_fsuid(); 611 inode->i_gid = opts->setgid ? opts->gid : current_fsgid(); 612 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; 613 init_special_inode(inode, S_IFCHR|opts->mode, device); 614 inode->i_private = priv; 615 616 sprintf(s, "%d", index); 617 618 mutex_lock(&d_inode(root)->i_mutex); 619 620 dentry = d_alloc_name(root, s); 621 if (dentry) { 622 d_add(dentry, inode); 623 fsnotify_create(d_inode(root), dentry); 624 } else { 625 iput(inode); 626 inode = ERR_PTR(-ENOMEM); 627 } 628 629 mutex_unlock(&d_inode(root)->i_mutex); 630 631 return inode; 632 } 633 634 /** 635 * devpts_get_priv -- get private data for a slave 636 * @pts_inode: inode of the slave 637 * 638 * Returns whatever was passed as priv in devpts_pty_new for a given inode. 639 */ 640 void *devpts_get_priv(struct inode *pts_inode) 641 { 642 struct dentry *dentry; 643 void *priv = NULL; 644 645 BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR)); 646 647 /* Ensure dentry has not been deleted by devpts_pty_kill() */ 648 dentry = d_find_alias(pts_inode); 649 if (!dentry) 650 return NULL; 651 652 if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC) 653 priv = pts_inode->i_private; 654 655 dput(dentry); 656 657 return priv; 658 } 659 660 /** 661 * devpts_pty_kill -- remove inode form /dev/pts/ 662 * @inode: inode of the slave to be removed 663 * 664 * This is an inverse operation of devpts_pty_new. 665 */ 666 void devpts_pty_kill(struct inode *inode) 667 { 668 struct super_block *sb = pts_sb_from_inode(inode); 669 struct dentry *root = sb->s_root; 670 struct dentry *dentry; 671 672 BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR)); 673 674 mutex_lock(&d_inode(root)->i_mutex); 675 676 dentry = d_find_alias(inode); 677 678 drop_nlink(inode); 679 d_delete(dentry); 680 dput(dentry); /* d_alloc_name() in devpts_pty_new() */ 681 dput(dentry); /* d_find_alias above */ 682 683 mutex_unlock(&d_inode(root)->i_mutex); 684 } 685 686 static int __init init_devpts_fs(void) 687 { 688 int err = register_filesystem(&devpts_fs_type); 689 struct ctl_table_header *table; 690 691 if (!err) { 692 struct vfsmount *mnt; 693 694 table = register_sysctl_table(pty_root_table); 695 mnt = kern_mount(&devpts_fs_type); 696 if (IS_ERR(mnt)) { 697 err = PTR_ERR(mnt); 698 unregister_filesystem(&devpts_fs_type); 699 unregister_sysctl_table(table); 700 } else { 701 devpts_mnt = mnt; 702 } 703 } 704 return err; 705 } 706 module_init(init_devpts_fs) 707