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 uid_t uid; 102 gid_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; 161 162 opts->setuid = 0; 163 opts->setgid = 0; 164 opts->uid = 0; 165 opts->gid = 0; 166 opts->mode = DEVPTS_DEFAULT_MODE; 167 opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE; 168 opts->max = NR_UNIX98_PTY_MAX; 169 170 /* newinstance makes sense only on initial mount */ 171 if (op == PARSE_MOUNT) 172 opts->newinstance = 0; 173 174 while ((p = strsep(&data, ",")) != NULL) { 175 substring_t args[MAX_OPT_ARGS]; 176 int token; 177 int option; 178 179 if (!*p) 180 continue; 181 182 token = match_token(p, tokens, args); 183 switch (token) { 184 case Opt_uid: 185 if (match_int(&args[0], &option)) 186 return -EINVAL; 187 opts->uid = option; 188 opts->setuid = 1; 189 break; 190 case Opt_gid: 191 if (match_int(&args[0], &option)) 192 return -EINVAL; 193 opts->gid = option; 194 opts->setgid = 1; 195 break; 196 case Opt_mode: 197 if (match_octal(&args[0], &option)) 198 return -EINVAL; 199 opts->mode = option & S_IALLUGO; 200 break; 201 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 202 case Opt_ptmxmode: 203 if (match_octal(&args[0], &option)) 204 return -EINVAL; 205 opts->ptmxmode = option & S_IALLUGO; 206 break; 207 case Opt_newinstance: 208 /* newinstance makes sense only on initial mount */ 209 if (op == PARSE_MOUNT) 210 opts->newinstance = 1; 211 break; 212 case Opt_max: 213 if (match_int(&args[0], &option) || 214 option < 0 || option > NR_UNIX98_PTY_MAX) 215 return -EINVAL; 216 opts->max = option; 217 break; 218 #endif 219 default: 220 printk(KERN_ERR "devpts: called with bogus options\n"); 221 return -EINVAL; 222 } 223 } 224 225 return 0; 226 } 227 228 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 229 static int mknod_ptmx(struct super_block *sb) 230 { 231 int mode; 232 int rc = -ENOMEM; 233 struct dentry *dentry; 234 struct inode *inode; 235 struct dentry *root = sb->s_root; 236 struct pts_fs_info *fsi = DEVPTS_SB(sb); 237 struct pts_mount_opts *opts = &fsi->mount_opts; 238 239 mutex_lock(&root->d_inode->i_mutex); 240 241 /* If we have already created ptmx node, return */ 242 if (fsi->ptmx_dentry) { 243 rc = 0; 244 goto out; 245 } 246 247 dentry = d_alloc_name(root, "ptmx"); 248 if (!dentry) { 249 printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n"); 250 goto out; 251 } 252 253 /* 254 * Create a new 'ptmx' node in this mount of devpts. 255 */ 256 inode = new_inode(sb); 257 if (!inode) { 258 printk(KERN_ERR "Unable to alloc inode for ptmx node\n"); 259 dput(dentry); 260 goto out; 261 } 262 263 inode->i_ino = 2; 264 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; 265 266 mode = S_IFCHR|opts->ptmxmode; 267 init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2)); 268 269 d_add(dentry, inode); 270 271 fsi->ptmx_dentry = dentry; 272 rc = 0; 273 out: 274 mutex_unlock(&root->d_inode->i_mutex); 275 return rc; 276 } 277 278 static void update_ptmx_mode(struct pts_fs_info *fsi) 279 { 280 struct inode *inode; 281 if (fsi->ptmx_dentry) { 282 inode = fsi->ptmx_dentry->d_inode; 283 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode; 284 } 285 } 286 #else 287 static inline void update_ptmx_mode(struct pts_fs_info *fsi) 288 { 289 return; 290 } 291 #endif 292 293 static int devpts_remount(struct super_block *sb, int *flags, char *data) 294 { 295 int err; 296 struct pts_fs_info *fsi = DEVPTS_SB(sb); 297 struct pts_mount_opts *opts = &fsi->mount_opts; 298 299 err = parse_mount_options(data, PARSE_REMOUNT, opts); 300 301 /* 302 * parse_mount_options() restores options to default values 303 * before parsing and may have changed ptmxmode. So, update the 304 * mode in the inode too. Bogus options don't fail the remount, 305 * so do this even on error return. 306 */ 307 update_ptmx_mode(fsi); 308 309 return err; 310 } 311 312 static int devpts_show_options(struct seq_file *seq, struct dentry *root) 313 { 314 struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb); 315 struct pts_mount_opts *opts = &fsi->mount_opts; 316 317 if (opts->setuid) 318 seq_printf(seq, ",uid=%u", opts->uid); 319 if (opts->setgid) 320 seq_printf(seq, ",gid=%u", opts->gid); 321 seq_printf(seq, ",mode=%03o", opts->mode); 322 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 323 seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode); 324 if (opts->max < NR_UNIX98_PTY_MAX) 325 seq_printf(seq, ",max=%d", opts->max); 326 #endif 327 328 return 0; 329 } 330 331 static const struct super_operations devpts_sops = { 332 .statfs = simple_statfs, 333 .remount_fs = devpts_remount, 334 .show_options = devpts_show_options, 335 }; 336 337 static void *new_pts_fs_info(void) 338 { 339 struct pts_fs_info *fsi; 340 341 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL); 342 if (!fsi) 343 return NULL; 344 345 ida_init(&fsi->allocated_ptys); 346 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE; 347 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE; 348 349 return fsi; 350 } 351 352 static int 353 devpts_fill_super(struct super_block *s, void *data, int silent) 354 { 355 struct inode *inode; 356 357 s->s_blocksize = 1024; 358 s->s_blocksize_bits = 10; 359 s->s_magic = DEVPTS_SUPER_MAGIC; 360 s->s_op = &devpts_sops; 361 s->s_time_gran = 1; 362 363 s->s_fs_info = new_pts_fs_info(); 364 if (!s->s_fs_info) 365 goto fail; 366 367 inode = new_inode(s); 368 if (!inode) 369 goto fail; 370 inode->i_ino = 1; 371 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; 372 inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR; 373 inode->i_op = &simple_dir_inode_operations; 374 inode->i_fop = &simple_dir_operations; 375 set_nlink(inode, 2); 376 377 s->s_root = d_make_root(inode); 378 if (s->s_root) 379 return 0; 380 381 printk(KERN_ERR "devpts: get root dentry failed\n"); 382 383 fail: 384 return -ENOMEM; 385 } 386 387 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES 388 static int compare_init_pts_sb(struct super_block *s, void *p) 389 { 390 if (devpts_mnt) 391 return devpts_mnt->mnt_sb == s; 392 return 0; 393 } 394 395 /* 396 * devpts_mount() 397 * 398 * If the '-o newinstance' mount option was specified, mount a new 399 * (private) instance of devpts. PTYs created in this instance are 400 * independent of the PTYs in other devpts instances. 401 * 402 * If the '-o newinstance' option was not specified, mount/remount the 403 * initial kernel mount of devpts. This type of mount gives the 404 * legacy, single-instance semantics. 405 * 406 * The 'newinstance' option is needed to support multiple namespace 407 * semantics in devpts while preserving backward compatibility of the 408 * current 'single-namespace' semantics. i.e all mounts of devpts 409 * without the 'newinstance' mount option should bind to the initial 410 * kernel mount, like mount_single(). 411 * 412 * Mounts with 'newinstance' option create a new, private namespace. 413 * 414 * NOTE: 415 * 416 * For single-mount semantics, devpts cannot use mount_single(), 417 * because mount_single()/sget() find and use the super-block from 418 * the most recent mount of devpts. But that recent mount may be a 419 * 'newinstance' mount and mount_single() would pick the newinstance 420 * super-block instead of the initial super-block. 421 */ 422 static struct dentry *devpts_mount(struct file_system_type *fs_type, 423 int flags, const char *dev_name, void *data) 424 { 425 int error; 426 struct pts_mount_opts opts; 427 struct super_block *s; 428 429 error = parse_mount_options(data, PARSE_MOUNT, &opts); 430 if (error) 431 return ERR_PTR(error); 432 433 if (opts.newinstance) 434 s = sget(fs_type, NULL, set_anon_super, NULL); 435 else 436 s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL); 437 438 if (IS_ERR(s)) 439 return ERR_CAST(s); 440 441 if (!s->s_root) { 442 s->s_flags = flags; 443 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0); 444 if (error) 445 goto out_undo_sget; 446 s->s_flags |= MS_ACTIVE; 447 } 448 449 memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts)); 450 451 error = mknod_ptmx(s); 452 if (error) 453 goto out_undo_sget; 454 455 return dget(s->s_root); 456 457 out_undo_sget: 458 deactivate_locked_super(s); 459 return ERR_PTR(error); 460 } 461 462 #else 463 /* 464 * This supports only the legacy single-instance semantics (no 465 * multiple-instance semantics) 466 */ 467 static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags, 468 const char *dev_name, void *data) 469 { 470 return mount_single(fs_type, flags, data, devpts_fill_super); 471 } 472 #endif 473 474 static void devpts_kill_sb(struct super_block *sb) 475 { 476 struct pts_fs_info *fsi = DEVPTS_SB(sb); 477 478 kfree(fsi); 479 kill_litter_super(sb); 480 } 481 482 static struct file_system_type devpts_fs_type = { 483 .name = "devpts", 484 .mount = devpts_mount, 485 .kill_sb = devpts_kill_sb, 486 }; 487 488 /* 489 * The normal naming convention is simply /dev/pts/<number>; this conforms 490 * to the System V naming convention 491 */ 492 493 int devpts_new_index(struct inode *ptmx_inode) 494 { 495 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 496 struct pts_fs_info *fsi = DEVPTS_SB(sb); 497 int index; 498 int ida_ret; 499 500 retry: 501 if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL)) 502 return -ENOMEM; 503 504 mutex_lock(&allocated_ptys_lock); 505 if (pty_count >= pty_limit - 506 (fsi->mount_opts.newinstance ? pty_reserve : 0)) { 507 mutex_unlock(&allocated_ptys_lock); 508 return -ENOSPC; 509 } 510 511 ida_ret = ida_get_new(&fsi->allocated_ptys, &index); 512 if (ida_ret < 0) { 513 mutex_unlock(&allocated_ptys_lock); 514 if (ida_ret == -EAGAIN) 515 goto retry; 516 return -EIO; 517 } 518 519 if (index >= fsi->mount_opts.max) { 520 ida_remove(&fsi->allocated_ptys, index); 521 mutex_unlock(&allocated_ptys_lock); 522 return -ENOSPC; 523 } 524 pty_count++; 525 mutex_unlock(&allocated_ptys_lock); 526 return index; 527 } 528 529 void devpts_kill_index(struct inode *ptmx_inode, int idx) 530 { 531 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 532 struct pts_fs_info *fsi = DEVPTS_SB(sb); 533 534 mutex_lock(&allocated_ptys_lock); 535 ida_remove(&fsi->allocated_ptys, idx); 536 pty_count--; 537 mutex_unlock(&allocated_ptys_lock); 538 } 539 540 int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty) 541 { 542 /* tty layer puts index from devpts_new_index() in here */ 543 int number = tty->index; 544 struct tty_driver *driver = tty->driver; 545 dev_t device = MKDEV(driver->major, driver->minor_start+number); 546 struct dentry *dentry; 547 struct super_block *sb = pts_sb_from_inode(ptmx_inode); 548 struct inode *inode = new_inode(sb); 549 struct dentry *root = sb->s_root; 550 struct pts_fs_info *fsi = DEVPTS_SB(sb); 551 struct pts_mount_opts *opts = &fsi->mount_opts; 552 int ret = 0; 553 char s[12]; 554 555 /* We're supposed to be given the slave end of a pty */ 556 BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY); 557 BUG_ON(driver->subtype != PTY_TYPE_SLAVE); 558 559 if (!inode) 560 return -ENOMEM; 561 562 inode->i_ino = number + 3; 563 inode->i_uid = opts->setuid ? opts->uid : current_fsuid(); 564 inode->i_gid = opts->setgid ? opts->gid : current_fsgid(); 565 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; 566 init_special_inode(inode, S_IFCHR|opts->mode, device); 567 inode->i_private = tty; 568 tty->driver_data = inode; 569 570 sprintf(s, "%d", number); 571 572 mutex_lock(&root->d_inode->i_mutex); 573 574 dentry = d_alloc_name(root, s); 575 if (dentry) { 576 d_add(dentry, inode); 577 fsnotify_create(root->d_inode, dentry); 578 } else { 579 iput(inode); 580 ret = -ENOMEM; 581 } 582 583 mutex_unlock(&root->d_inode->i_mutex); 584 585 return ret; 586 } 587 588 struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number) 589 { 590 struct dentry *dentry; 591 struct tty_struct *tty; 592 593 BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR)); 594 595 /* Ensure dentry has not been deleted by devpts_pty_kill() */ 596 dentry = d_find_alias(pts_inode); 597 if (!dentry) 598 return NULL; 599 600 tty = NULL; 601 if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC) 602 tty = (struct tty_struct *)pts_inode->i_private; 603 604 dput(dentry); 605 606 return tty; 607 } 608 609 void devpts_pty_kill(struct tty_struct *tty) 610 { 611 struct inode *inode = tty->driver_data; 612 struct super_block *sb = pts_sb_from_inode(inode); 613 struct dentry *root = sb->s_root; 614 struct dentry *dentry; 615 616 BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR)); 617 618 mutex_lock(&root->d_inode->i_mutex); 619 620 dentry = d_find_alias(inode); 621 622 drop_nlink(inode); 623 d_delete(dentry); 624 dput(dentry); /* d_alloc_name() in devpts_pty_new() */ 625 dput(dentry); /* d_find_alias above */ 626 627 mutex_unlock(&root->d_inode->i_mutex); 628 } 629 630 static int __init init_devpts_fs(void) 631 { 632 int err = register_filesystem(&devpts_fs_type); 633 struct ctl_table_header *table; 634 635 if (!err) { 636 table = register_sysctl_table(pty_root_table); 637 devpts_mnt = kern_mount(&devpts_fs_type); 638 if (IS_ERR(devpts_mnt)) { 639 err = PTR_ERR(devpts_mnt); 640 unregister_filesystem(&devpts_fs_type); 641 unregister_sysctl_table(table); 642 } 643 } 644 return err; 645 } 646 module_init(init_devpts_fs) 647