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 */ 45static int pty_limit = NR_UNIX98_PTY_DEFAULT; 46static int pty_reserve = NR_UNIX98_PTY_RESERVE; 47static int pty_limit_min; 48static int pty_limit_max = INT_MAX; 49static int pty_count; 50 51static 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 78static struct ctl_table pty_kern_table[] = { 79 { 80 .procname = "pty", 81 .mode = 0555, 82 .child = pty_table, 83 }, 84 {} 85}; 86 87static struct ctl_table pty_root_table[] = { 88 { 89 .procname = "kernel", 90 .mode = 0555, 91 .child = pty_kern_table, 92 }, 93 {} 94}; 95 96static DEFINE_MUTEX(allocated_ptys_lock); 97 98static struct vfsmount *devpts_mnt; 99 100struct 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 111enum { 112 Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max, 113 Opt_err 114}; 115 116static 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 128struct pts_fs_info { 129 struct ida allocated_ptys; 130 struct pts_mount_opts mount_opts; 131 struct dentry *ptmx_dentry; 132}; 133 134static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb) 135{ 136 return sb->s_fs_info; 137} 138 139static 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 return devpts_mnt->mnt_sb; 146} 147 148#define PARSE_MOUNT 0 149#define PARSE_REMOUNT 1 150 151/* 152 * parse_mount_options(): 153 * Set @opts to mount options specified in @data. If an option is not 154 * specified in @data, set it to its default value. The exception is 155 * 'newinstance' option which can only be set/cleared on a mount (i.e. 156 * cannot be changed during remount). 157 * 158 * Note: @data may be NULL (in which case all options are set to default). 159 */ 160static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts) 161{ 162 char *p; 163 kuid_t uid; 164 kgid_t gid; 165 166 opts->setuid = 0; 167 opts->setgid = 0; 168 opts->uid = GLOBAL_ROOT_UID; 169 opts->gid = GLOBAL_ROOT_GID; 170 opts->mode = DEVPTS_DEFAULT_MODE; 171 opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE; 172 opts->max = NR_UNIX98_PTY_MAX; 173 174 /* newinstance makes sense only on initial mount */ 175 if (op == PARSE_MOUNT) 176 opts->newinstance = 0; 177 178 while ((p = strsep(&data, ",")) != NULL) { 179 substring_t args[MAX_OPT_ARGS]; 180 int token; 181 int option; 182 183 if (!*p) 184 continue; 185 186 token = match_token(p, tokens, args); 187 switch (token) { 188 case Opt_uid: 189 if (match_int(&args[0], &option)) 190 return -EINVAL; 191 uid = make_kuid(current_user_ns(), option); 192 if (!uid_valid(uid)) 193 return -EINVAL; 194 opts->uid = uid; 195 opts->setuid = 1; 196 break; 197 case Opt_gid: 198 if (match_int(&args[0], &option)) 199 return -EINVAL; 200 gid = make_kgid(current_user_ns(), option); 201 if (!gid_valid(gid)) 202 return -EINVAL; 203 opts->gid = gid; 204 opts->setgid = 1; 205 break; 206 case Opt_mode: 207 if (match_octal(&args[0], &option)) 208 return -EINVAL; 209 opts->mode = option & S_IALLUGO; 210 break; 211#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 212 case Opt_ptmxmode: 213 if (match_octal(&args[0], &option)) 214 return -EINVAL; 215 opts->ptmxmode = option & S_IALLUGO; 216 break; 217 case Opt_newinstance: 218 /* newinstance makes sense only on initial mount */ 219 if (op == PARSE_MOUNT) 220 opts->newinstance = 1; 221 break; 222 case Opt_max: 223 if (match_int(&args[0], &option) || 224 option < 0 || option > NR_UNIX98_PTY_MAX) 225 return -EINVAL; 226 opts->max = option; 227 break; 228#endif 229 default: 230 pr_err("called with bogus options\n"); 231 return -EINVAL; 232 } 233 } 234 235 return 0; 236} 237 238#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 239static int mknod_ptmx(struct super_block *sb) 240{ 241 int mode; 242 int rc = -ENOMEM; 243 struct dentry *dentry; 244 struct inode *inode; 245 struct dentry *root = sb->s_root; 246 struct pts_fs_info *fsi = DEVPTS_SB(sb); 247 struct pts_mount_opts *opts = &fsi->mount_opts; 248 kuid_t root_uid; 249 kgid_t root_gid; 250 251 root_uid = make_kuid(current_user_ns(), 0); 252 root_gid = make_kgid(current_user_ns(), 0); 253 if (!uid_valid(root_uid) || !gid_valid(root_gid)) 254 return -EINVAL; 255 256 mutex_lock(&d_inode(root)->i_mutex); 257 258 /* If we have already created ptmx node, return */ 259 if (fsi->ptmx_dentry) { 260 rc = 0; 261 goto out; 262 } 263 264 dentry = d_alloc_name(root, "ptmx"); 265 if (!dentry) { 266 pr_err("Unable to alloc dentry for ptmx node\n"); 267 goto out; 268 } 269 270 /* 271 * Create a new 'ptmx' node in this mount of devpts. 272 */ 273 inode = new_inode(sb); 274 if (!inode) { 275 pr_err("Unable to alloc inode for ptmx node\n"); 276 dput(dentry); 277 goto out; 278 } 279 280 inode->i_ino = 2; 281 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; 282 283 mode = S_IFCHR|opts->ptmxmode; 284 init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2)); 285 inode->i_uid = root_uid; 286 inode->i_gid = root_gid; 287 288 d_add(dentry, inode); 289 290 fsi->ptmx_dentry = dentry; 291 rc = 0; 292out: 293 mutex_unlock(&d_inode(root)->i_mutex); 294 return rc; 295} 296 297static void update_ptmx_mode(struct pts_fs_info *fsi) 298{ 299 struct inode *inode; 300 if (fsi->ptmx_dentry) { 301 inode = d_inode(fsi->ptmx_dentry); 302 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode; 303 } 304} 305#else 306static inline void update_ptmx_mode(struct pts_fs_info *fsi) 307{ 308 return; 309} 310#endif 311 312static int devpts_remount(struct super_block *sb, int *flags, char *data) 313{ 314 int err; 315 struct pts_fs_info *fsi = DEVPTS_SB(sb); 316 struct pts_mount_opts *opts = &fsi->mount_opts; 317 318 sync_filesystem(sb); 319 err = parse_mount_options(data, PARSE_REMOUNT, opts); 320 321 /* 322 * parse_mount_options() restores options to default values 323 * before parsing and may have changed ptmxmode. So, update the 324 * mode in the inode too. Bogus options don't fail the remount, 325 * so do this even on error return. 326 */ 327 update_ptmx_mode(fsi); 328 329 return err; 330} 331 332static int devpts_show_options(struct seq_file *seq, struct dentry *root) 333{ 334 struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb); 335 struct pts_mount_opts *opts = &fsi->mount_opts; 336 337 if (opts->setuid) 338 seq_printf(seq, ",uid=%u", 339 from_kuid_munged(&init_user_ns, opts->uid)); 340 if (opts->setgid) 341 seq_printf(seq, ",gid=%u", 342 from_kgid_munged(&init_user_ns, opts->gid)); 343 seq_printf(seq, ",mode=%03o", opts->mode); 344#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 345 seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode); 346 if (opts->max < NR_UNIX98_PTY_MAX) 347 seq_printf(seq, ",max=%d", opts->max); 348#endif 349 350 return 0; 351} 352 353static const struct super_operations devpts_sops = { 354 .statfs = simple_statfs, 355 .remount_fs = devpts_remount, 356 .show_options = devpts_show_options, 357}; 358 359static void *new_pts_fs_info(void) 360{ 361 struct pts_fs_info *fsi; 362 363 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL); 364 if (!fsi) 365 return NULL; 366 367 ida_init(&fsi->allocated_ptys); 368 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE; 369 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE; 370 371 return fsi; 372} 373 374static int 375devpts_fill_super(struct super_block *s, void *data, int silent) 376{ 377 struct inode *inode; 378 379 s->s_blocksize = 1024; 380 s->s_blocksize_bits = 10; 381 s->s_magic = DEVPTS_SUPER_MAGIC; 382 s->s_op = &devpts_sops; 383 s->s_time_gran = 1; 384 385 s->s_fs_info = new_pts_fs_info(); 386 if (!s->s_fs_info) 387 goto fail; 388 389 inode = new_inode(s); 390 if (!inode) 391 goto fail; 392 inode->i_ino = 1; 393 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; 394 inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR; 395 inode->i_op = &simple_dir_inode_operations; 396 inode->i_fop = &simple_dir_operations; 397 set_nlink(inode, 2); 398 399 s->s_root = d_make_root(inode); 400 if (s->s_root) 401 return 0; 402 403 pr_err("get root dentry failed\n"); 404 405fail: 406 return -ENOMEM; 407} 408 409#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 410static int compare_init_pts_sb(struct super_block *s, void *p) 411{ 412 if (devpts_mnt) 413 return devpts_mnt->mnt_sb == s; 414 return 0; 415} 416 417/* 418 * devpts_mount() 419 * 420 * If the '-o newinstance' mount option was specified, mount a new 421 * (private) instance of devpts. PTYs created in this instance are 422 * independent of the PTYs in other devpts instances. 423 * 424 * If the '-o newinstance' option was not specified, mount/remount the 425 * initial kernel mount of devpts. This type of mount gives the 426 * legacy, single-instance semantics. 427 * 428 * The 'newinstance' option is needed to support multiple namespace 429 * semantics in devpts while preserving backward compatibility of the 430 * current 'single-namespace' semantics. i.e all mounts of devpts 431 * without the 'newinstance' mount option should bind to the initial 432 * kernel mount, like mount_single(). 433 * 434 * Mounts with 'newinstance' option create a new, private namespace. 435 * 436 * NOTE: 437 * 438 * For single-mount semantics, devpts cannot use mount_single(), 439 * because mount_single()/sget() find and use the super-block from 440 * the most recent mount of devpts. But that recent mount may be a 441 * 'newinstance' mount and mount_single() would pick the newinstance 442 * super-block instead of the initial super-block. 443 */ 444static struct dentry *devpts_mount(struct file_system_type *fs_type, 445 int flags, const char *dev_name, void *data) 446{ 447 int error; 448 struct pts_mount_opts opts; 449 struct super_block *s; 450 451 error = parse_mount_options(data, PARSE_MOUNT, &opts); 452 if (error) 453 return ERR_PTR(error); 454 455 /* Require newinstance for all user namespace mounts to ensure 456 * the mount options are not changed. 457 */ 458 if ((current_user_ns() != &init_user_ns) && !opts.newinstance) 459 return ERR_PTR(-EINVAL); 460 461 if (opts.newinstance) 462 s = sget(fs_type, NULL, set_anon_super, flags, NULL); 463 else 464 s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags, 465 NULL); 466 467 if (IS_ERR(s)) 468 return ERR_CAST(s); 469 470 if (!s->s_root) { 471 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0); 472 if (error) 473 goto out_undo_sget; 474 s->s_flags |= MS_ACTIVE; 475 } 476 477 memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts)); 478 479 error = mknod_ptmx(s); 480 if (error) 481 goto out_undo_sget; 482 483 return dget(s->s_root); 484 485out_undo_sget: 486 deactivate_locked_super(s); 487 return ERR_PTR(error); 488} 489 490#else 491/* 492 * This supports only the legacy single-instance semantics (no 493 * multiple-instance semantics) 494 */ 495static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags, 496 const char *dev_name, void *data) 497{ 498 return mount_single(fs_type, flags, data, devpts_fill_super); 499} 500#endif 501 502static void devpts_kill_sb(struct super_block *sb) 503{ 504 struct pts_fs_info *fsi = DEVPTS_SB(sb); 505 506 ida_destroy(&fsi->allocated_ptys); 507 kfree(fsi); 508 kill_litter_super(sb); 509} 510 511static struct file_system_type devpts_fs_type = { 512 .name = "devpts", 513 .mount = devpts_mount, 514 .kill_sb = devpts_kill_sb, 515#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 516 .fs_flags = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT, 517#endif 518}; 519 520/* 521 * The normal naming convention is simply /dev/pts/<number>; this conforms 522 * to the System V naming convention 523 */ 524 525int devpts_new_index(struct inode *ptmx_inode) 526{ 527 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 528 struct pts_fs_info *fsi = DEVPTS_SB(sb); 529 int index; 530 int ida_ret; 531 532retry: 533 if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL)) 534 return -ENOMEM; 535 536 mutex_lock(&allocated_ptys_lock); 537 if (pty_count >= pty_limit - 538 (fsi->mount_opts.newinstance ? pty_reserve : 0)) { 539 mutex_unlock(&allocated_ptys_lock); 540 return -ENOSPC; 541 } 542 543 ida_ret = ida_get_new(&fsi->allocated_ptys, &index); 544 if (ida_ret < 0) { 545 mutex_unlock(&allocated_ptys_lock); 546 if (ida_ret == -EAGAIN) 547 goto retry; 548 return -EIO; 549 } 550 551 if (index >= fsi->mount_opts.max) { 552 ida_remove(&fsi->allocated_ptys, index); 553 mutex_unlock(&allocated_ptys_lock); 554 return -ENOSPC; 555 } 556 pty_count++; 557 mutex_unlock(&allocated_ptys_lock); 558 return index; 559} 560 561void devpts_kill_index(struct inode *ptmx_inode, int idx) 562{ 563 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 564 struct pts_fs_info *fsi = DEVPTS_SB(sb); 565 566 mutex_lock(&allocated_ptys_lock); 567 ida_remove(&fsi->allocated_ptys, idx); 568 pty_count--; 569 mutex_unlock(&allocated_ptys_lock); 570} 571 572/* 573 * pty code needs to hold extra references in case of last /dev/tty close 574 */ 575 576void devpts_add_ref(struct inode *ptmx_inode) 577{ 578 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 579 580 atomic_inc(&sb->s_active); 581 ihold(ptmx_inode); 582} 583 584void devpts_del_ref(struct inode *ptmx_inode) 585{ 586 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 587 588 iput(ptmx_inode); 589 deactivate_super(sb); 590} 591 592/** 593 * devpts_pty_new -- create a new inode in /dev/pts/ 594 * @ptmx_inode: inode of the master 595 * @device: major+minor of the node to be created 596 * @index: used as a name of the node 597 * @priv: what's given back by devpts_get_priv 598 * 599 * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill. 600 */ 601struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index, 602 void *priv) 603{ 604 struct dentry *dentry; 605 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 606 struct inode *inode; 607 struct dentry *root = sb->s_root; 608 struct pts_fs_info *fsi = DEVPTS_SB(sb); 609 struct pts_mount_opts *opts = &fsi->mount_opts; 610 char s[12]; 611 612 inode = new_inode(sb); 613 if (!inode) 614 return ERR_PTR(-ENOMEM); 615 616 inode->i_ino = index + 3; 617 inode->i_uid = opts->setuid ? opts->uid : current_fsuid(); 618 inode->i_gid = opts->setgid ? opts->gid : current_fsgid(); 619 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; 620 init_special_inode(inode, S_IFCHR|opts->mode, device); 621 inode->i_private = priv; 622 623 sprintf(s, "%d", index); 624 625 mutex_lock(&d_inode(root)->i_mutex); 626 627 dentry = d_alloc_name(root, s); 628 if (dentry) { 629 d_add(dentry, inode); 630 fsnotify_create(d_inode(root), dentry); 631 } else { 632 iput(inode); 633 inode = ERR_PTR(-ENOMEM); 634 } 635 636 mutex_unlock(&d_inode(root)->i_mutex); 637 638 return inode; 639} 640 641/** 642 * devpts_get_priv -- get private data for a slave 643 * @pts_inode: inode of the slave 644 * 645 * Returns whatever was passed as priv in devpts_pty_new for a given inode. 646 */ 647void *devpts_get_priv(struct inode *pts_inode) 648{ 649 struct dentry *dentry; 650 void *priv = NULL; 651 652 BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR)); 653 654 /* Ensure dentry has not been deleted by devpts_pty_kill() */ 655 dentry = d_find_alias(pts_inode); 656 if (!dentry) 657 return NULL; 658 659 if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC) 660 priv = pts_inode->i_private; 661 662 dput(dentry); 663 664 return priv; 665} 666 667/** 668 * devpts_pty_kill -- remove inode form /dev/pts/ 669 * @inode: inode of the slave to be removed 670 * 671 * This is an inverse operation of devpts_pty_new. 672 */ 673void devpts_pty_kill(struct inode *inode) 674{ 675 struct super_block *sb = pts_sb_from_inode(inode); 676 struct dentry *root = sb->s_root; 677 struct dentry *dentry; 678 679 BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR)); 680 681 mutex_lock(&d_inode(root)->i_mutex); 682 683 dentry = d_find_alias(inode); 684 685 drop_nlink(inode); 686 d_delete(dentry); 687 dput(dentry); /* d_alloc_name() in devpts_pty_new() */ 688 dput(dentry); /* d_find_alias above */ 689 690 mutex_unlock(&d_inode(root)->i_mutex); 691} 692 693static int __init init_devpts_fs(void) 694{ 695 int err = register_filesystem(&devpts_fs_type); 696 struct ctl_table_header *table; 697 698 if (!err) { 699 table = register_sysctl_table(pty_root_table); 700 devpts_mnt = kern_mount(&devpts_fs_type); 701 if (IS_ERR(devpts_mnt)) { 702 err = PTR_ERR(devpts_mnt); 703 unregister_filesystem(&devpts_fs_type); 704 unregister_sysctl_table(table); 705 } 706 } 707 return err; 708} 709module_init(init_devpts_fs) 710