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