fs/devpts/inode.c

   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/mount.h>
  19 #include <linux/tty.h>
  20 #include <linux/mutex.h>
  21 #include <linux/idr.h>
  22 #include <linux/devpts_fs.h>
  23 #include <linux/parser.h>
  24 #include <linux/fsnotify.h>
  25 #include <linux/seq_file.h>
  26
  27 #define DEVPTS_SUPER_MAGIC 0x1cd1
  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 extern int pty_limit;                   /* Config limit on Unix98 ptys */
  40 static DEFINE_MUTEX(allocated_ptys_lock);
  41
  42 static struct vfsmount *devpts_mnt;
  43
  44 struct pts_mount_opts {
  45         int setuid;
  46         int setgid;
  47         uid_t   uid;
  48         gid_t   gid;
  49         umode_t mode;
  50         umode_t ptmxmode;
  51         int newinstance;
  52 };
  53
  54 enum {
  55         Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,
  56         Opt_err
  57 };
  58
  59 static const match_table_t tokens = {
  60         {Opt_uid, "uid=%u"},
  61         {Opt_gid, "gid=%u"},
  62         {Opt_mode, "mode=%o"},
  63 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
  64         {Opt_ptmxmode, "ptmxmode=%o"},
  65         {Opt_newinstance, "newinstance"},
  66 #endif
  67         {Opt_err, NULL}
  68 };
  69
  70 struct pts_fs_info {
  71         struct ida allocated_ptys;
  72         struct pts_mount_opts mount_opts;
  73         struct dentry *ptmx_dentry;
  74 };
  75
  76 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
  77 {
  78         return sb->s_fs_info;
  79 }
  80
  81 static inline struct super_block *pts_sb_from_inode(struct inode *inode)
  82 {
  83 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
  84         if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
  85                 return inode->i_sb;
  86 #endif
  87         return devpts_mnt->mnt_sb;
  88 }
  89
  90 #define PARSE_MOUNT     0
  91 #define PARSE_REMOUNT   1
  92
  93 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
  94 {
  95         char *p;
  96
  97         opts->setuid  = 0;
  98         opts->setgid  = 0;
  99         opts->uid     = 0;
 100         opts->gid     = 0;
 101         opts->mode    = DEVPTS_DEFAULT_MODE;
 102         opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 103
 104         /* newinstance makes sense only on initial mount */
 105         if (op == PARSE_MOUNT)
 106                 opts->newinstance = 0;
 107
 108         while ((p = strsep(&data, ",")) != NULL) {
 109                 substring_t args[MAX_OPT_ARGS];
 110                 int token;
 111                 int option;
 112
 113                 if (!*p)
 114                         continue;
 115
 116                 token = match_token(p, tokens, args);
 117                 switch (token) {
 118                 case Opt_uid:
 119                         if (match_int(&args[0], &option))
 120                                 return -EINVAL;
 121                         opts->uid = option;
 122                         opts->setuid = 1;
 123                         break;
 124                 case Opt_gid:
 125                         if (match_int(&args[0], &option))
 126                                 return -EINVAL;
 127                         opts->gid = option;
 128                         opts->setgid = 1;
 129                         break;
 130                 case Opt_mode:
 131                         if (match_octal(&args[0], &option))
 132                                 return -EINVAL;
 133                         opts->mode = option & S_IALLUGO;
 134                         break;
 135 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 136                 case Opt_ptmxmode:
 137                         if (match_octal(&args[0], &option))
 138                                 return -EINVAL;
 139                         opts->ptmxmode = option & S_IALLUGO;
 140                         break;
 141                 case Opt_newinstance:
 142                         /* newinstance makes sense only on initial mount */
 143                         if (op == PARSE_MOUNT)
 144                                 opts->newinstance = 1;
 145                         break;
 146 #endif
 147                 default:
 148                         printk(KERN_ERR "devpts: called with bogus options\n");
 149                         return -EINVAL;
 150                 }
 151         }
 152
 153         return 0;
 154 }
 155
 156 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 157 static int mknod_ptmx(struct super_block *sb)
 158 {
 159         int mode;
 160         int rc = -ENOMEM;
 161         struct dentry *dentry;
 162         struct inode *inode;
 163         struct dentry *root = sb->s_root;
 164         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 165         struct pts_mount_opts *opts = &fsi->mount_opts;
 166
 167         mutex_lock(&root->d_inode->i_mutex);
 168
 169         /* If we have already created ptmx node, return */
 170         if (fsi->ptmx_dentry) {
 171                 rc = 0;
 172                 goto out;
 173         }
 174
 175         dentry = d_alloc_name(root, "ptmx");
 176         if (!dentry) {
 177                 printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n");
 178                 goto out;
 179         }
 180
 181         /*
 182          * Create a new 'ptmx' node in this mount of devpts.
 183          */
 184         inode = new_inode(sb);
 185         if (!inode) {
 186                 printk(KERN_ERR "Unable to alloc inode for ptmx node\n");
 187                 dput(dentry);
 188                 goto out;
 189         }
 190
 191         inode->i_ino = 2;
 192         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 193
 194         mode = S_IFCHR|opts->ptmxmode;
 195         init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
 196
 197         d_add(dentry, inode);
 198
 199         fsi->ptmx_dentry = dentry;
 200         rc = 0;
 201 out:
 202         mutex_unlock(&root->d_inode->i_mutex);
 203         return rc;
 204 }
 205
 206 static void update_ptmx_mode(struct pts_fs_info *fsi)
 207 {
 208         struct inode *inode;
 209         if (fsi->ptmx_dentry) {
 210                 inode = fsi->ptmx_dentry->d_inode;
 211                 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
 212         }
 213 }
 214 #else
 215 static inline void update_ptmx_mode(struct pts_fs_info *fsi)
 216 {
 217        return;
 218 }
 219 #endif
 220
 221 static int devpts_remount(struct super_block *sb, int *flags, char *data)
 222 {
 223         int err;
 224         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 225         struct pts_mount_opts *opts = &fsi->mount_opts;
 226
 227         err = parse_mount_options(data, PARSE_REMOUNT, opts);
 228
 229         /*
 230          * parse_mount_options() restores options to default values
 231          * before parsing and may have changed ptmxmode. So, update the
 232          * mode in the inode too. Bogus options don't fail the remount,
 233          * so do this even on error return.
 234          */
 235         update_ptmx_mode(fsi);
 236
 237         return err;
 238 }
 239
 240 static int devpts_show_options(struct seq_file *seq, struct vfsmount *vfs)
 241 {
 242         struct pts_fs_info *fsi = DEVPTS_SB(vfs->mnt_sb);
 243         struct pts_mount_opts *opts = &fsi->mount_opts;
 244
 245         if (opts->setuid)
 246                 seq_printf(seq, ",uid=%u", opts->uid);
 247         if (opts->setgid)
 248                 seq_printf(seq, ",gid=%u", opts->gid);
 249         seq_printf(seq, ",mode=%03o", opts->mode);
 250 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 251         seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
 252 #endif
 253
 254         return 0;
 255 }
 256
 257 static const struct super_operations devpts_sops = {
 258         .statfs         = simple_statfs,
 259         .remount_fs     = devpts_remount,
 260         .show_options   = devpts_show_options,
 261 };
 262
 263 static void *new_pts_fs_info(void)
 264 {
 265         struct pts_fs_info *fsi;
 266
 267         fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
 268         if (!fsi)
 269                 return NULL;
 270
 271         ida_init(&fsi->allocated_ptys);
 272         fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
 273         fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 274
 275         return fsi;
 276 }
 277
 278 static int
 279 devpts_fill_super(struct super_block *s, void *data, int silent)
 280 {
 281         struct inode *inode;
 282
 283         s->s_blocksize = 1024;
 284         s->s_blocksize_bits = 10;
 285         s->s_magic = DEVPTS_SUPER_MAGIC;
 286         s->s_op = &devpts_sops;
 287         s->s_time_gran = 1;
 288
 289         s->s_fs_info = new_pts_fs_info();
 290         if (!s->s_fs_info)
 291                 goto fail;
 292
 293         inode = new_inode(s);
 294         if (!inode)
 295                 goto free_fsi;
 296         inode->i_ino = 1;
 297         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 298         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
 299         inode->i_op = &simple_dir_inode_operations;
 300         inode->i_fop = &simple_dir_operations;
 301         inode->i_nlink = 2;
 302
 303         s->s_root = d_alloc_root(inode);
 304         if (s->s_root)
 305                 return 0;
 306
 307         printk(KERN_ERR "devpts: get root dentry failed\n");
 308         iput(inode);
 309
 310 free_fsi:
 311         kfree(s->s_fs_info);
 312 fail:
 313         return -ENOMEM;
 314 }
 315
 316 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 317 static int compare_init_pts_sb(struct super_block *s, void *p)
 318 {
 319         if (devpts_mnt)
 320                 return devpts_mnt->mnt_sb == s;
 321         return 0;
 322 }
 323
 324 /*
 325  * Mount a new (private) instance of devpts.  PTYs created in this
 326  * instance are independent of the PTYs in other devpts instances.
 327  */
 328 static int new_pts_mount(struct file_system_type *fs_type, int flags,
 329                 void *data, struct pts_mount_opts *opts, struct vfsmount *mnt)
 330 {
 331         int err;
 332         struct pts_fs_info *fsi;
 333
 334         err = get_sb_nodev(fs_type, flags, data, devpts_fill_super, mnt);
 335         if (err)
 336                 return err;
 337
 338         fsi = DEVPTS_SB(mnt->mnt_sb);
 339         memcpy(&fsi->mount_opts, opts, sizeof(opts));
 340
 341         return 0;
 342 }
 343
 344 /*
 345  * init_pts_mount()
 346  *
 347  *     Mount or remount the initial kernel mount of devpts. This type of
 348  *     mount maintains the legacy, single-instance semantics, while the
 349  *     kernel still allows multiple-instances.
 350  *
 351  *     This interface is needed to support multiple namespace semantics in
 352  *     devpts while preserving backward compatibility of the current 'single-
 353  *     namespace' semantics. i.e all mounts of devpts without the 'newinstance'
 354  *     mount option should bind to the initial kernel mount, like
 355  *     get_sb_single().
 356  *
 357  *     Mounts with 'newinstance' option create a new private namespace.
 358  *
 359  *     But for single-mount semantics, devpts cannot use get_sb_single(),
 360  *     because get_sb_single()/sget() find and use the super-block from
 361  *     the most recent mount of devpts. But that recent mount may be a
 362  *     'newinstance' mount and get_sb_single() would pick the newinstance
 363  *     super-block instead of the initial super-block.
 364  *
 365  *     This interface is identical to get_sb_single() except that it
 366  *     consistently selects the 'single-namespace' superblock even in the
 367  *     presence of the private namespace (i.e 'newinstance') super-blocks.
 368  */
 369 static int init_pts_mount(struct file_system_type *fs_type, int flags,
 370                 void *data, struct pts_mount_opts *opts, struct vfsmount *mnt)
 371 {
 372         struct super_block *s;
 373         struct pts_fs_info *fsi;
 374         int error;
 375
 376         s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);
 377         if (IS_ERR(s))
 378                 return PTR_ERR(s);
 379
 380         if (!s->s_root) {
 381                 s->s_flags = flags;
 382                 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
 383                 if (error) {
 384                         up_write(&s->s_umount);
 385                         deactivate_super(s);
 386                         return error;
 387                 }
 388                 s->s_flags |= MS_ACTIVE;
 389         }
 390
 391         simple_set_mnt(mnt, s);
 392
 393         fsi = DEVPTS_SB(mnt->mnt_sb);
 394         memcpy(&fsi->mount_opts, opts, sizeof(opts));
 395
 396         return 0;
 397 }
 398
 399 static int devpts_get_sb(struct file_system_type *fs_type,
 400         int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 401 {
 402         int error;
 403         struct pts_mount_opts opts;
 404
 405         memset(&opts, 0, sizeof(opts));
 406         if (data) {
 407                 error = parse_mount_options(data, PARSE_MOUNT, &opts);
 408                 if (error)
 409                         return error;
 410         }
 411
 412         if (opts.newinstance)
 413                 error = new_pts_mount(fs_type, flags, data, &opts, mnt);
 414         else
 415                 error = init_pts_mount(fs_type, flags, data, &opts, mnt);
 416
 417         if (error)
 418                 return error;
 419
 420         error = mknod_ptmx(mnt->mnt_sb);
 421         if (error)
 422                 goto out_dput;
 423
 424         return 0;
 425
 426 out_dput:
 427         dput(mnt->mnt_sb->s_root);
 428         up_write(&mnt->mnt_sb->s_umount);
 429         deactivate_super(mnt->mnt_sb);
 430         return error;
 431 }
 432
 433 #else
 434 /*
 435  * This supports only the legacy single-instance semantics (no
 436  * multiple-instance semantics)
 437  */
 438 static int devpts_get_sb(struct file_system_type *fs_type, int flags,
 439                 const char *dev_name, void *data, struct vfsmount *mnt)
 440 {
 441         return get_sb_single(fs_type, flags, data, devpts_fill_super, mnt);
 442 }
 443 #endif
 444
 445 static void devpts_kill_sb(struct super_block *sb)
 446 {
 447         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 448
 449         kfree(fsi);
 450         kill_litter_super(sb);
 451 }
 452
 453 static struct file_system_type devpts_fs_type = {
 454         .owner          = THIS_MODULE,
 455         .name           = "devpts",
 456         .get_sb         = devpts_get_sb,
 457         .kill_sb        = devpts_kill_sb,
 458 };
 459
 460 /*
 461  * The normal naming convention is simply /dev/pts/<number>; this conforms
 462  * to the System V naming convention
 463  */
 464
 465 int devpts_new_index(struct inode *ptmx_inode)
 466 {
 467         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 468         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 469         int index;
 470         int ida_ret;
 471
 472 retry:
 473         if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
 474                 return -ENOMEM;
 475
 476         mutex_lock(&allocated_ptys_lock);
 477         ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
 478         if (ida_ret < 0) {
 479                 mutex_unlock(&allocated_ptys_lock);
 480                 if (ida_ret == -EAGAIN)
 481                         goto retry;
 482                 return -EIO;
 483         }
 484
 485         if (index >= pty_limit) {
 486                 ida_remove(&fsi->allocated_ptys, index);
 487                 mutex_unlock(&allocated_ptys_lock);
 488                 return -EIO;
 489         }
 490         mutex_unlock(&allocated_ptys_lock);
 491         return index;
 492 }
 493
 494 void devpts_kill_index(struct inode *ptmx_inode, int idx)
 495 {
 496         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 497         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 498
 499         mutex_lock(&allocated_ptys_lock);
 500         ida_remove(&fsi->allocated_ptys, idx);
 501         mutex_unlock(&allocated_ptys_lock);
 502 }
 503
 504 int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
 505 {
 506         /* tty layer puts index from devpts_new_index() in here */
 507         int number = tty->index;
 508         struct tty_driver *driver = tty->driver;
 509         dev_t device = MKDEV(driver->major, driver->minor_start+number);
 510         struct dentry *dentry;
 511         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 512         struct inode *inode = new_inode(sb);
 513         struct dentry *root = sb->s_root;
 514         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 515         struct pts_mount_opts *opts = &fsi->mount_opts;
 516         char s[12];
 517
 518         /* We're supposed to be given the slave end of a pty */
 519         BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
 520         BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
 521
 522         if (!inode)
 523                 return -ENOMEM;
 524
 525         inode->i_ino = number + 3;
 526         inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
 527         inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
 528         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 529         init_special_inode(inode, S_IFCHR|opts->mode, device);
 530         inode->i_private = tty;
 531         tty->driver_data = inode;
 532
 533         sprintf(s, "%d", number);
 534
 535         mutex_lock(&root->d_inode->i_mutex);
 536
 537         dentry = d_alloc_name(root, s);
 538         if (!IS_ERR(dentry)) {
 539                 d_add(dentry, inode);
 540                 fsnotify_create(root->d_inode, dentry);
 541         }
 542
 543         mutex_unlock(&root->d_inode->i_mutex);
 544
 545         return 0;
 546 }
 547
 548 struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number)
 549 {
 550         BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
 551
 552         if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
 553                 return (struct tty_struct *)pts_inode->i_private;
 554         return NULL;
 555 }
 556
 557 void devpts_pty_kill(struct tty_struct *tty)
 558 {
 559         struct inode *inode = tty->driver_data;
 560         struct super_block *sb = pts_sb_from_inode(inode);
 561         struct dentry *root = sb->s_root;
 562         struct dentry *dentry;
 563
 564         BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
 565
 566         mutex_lock(&root->d_inode->i_mutex);
 567
 568         dentry = d_find_alias(inode);
 569         if (IS_ERR(dentry))
 570                 goto out;
 571
 572         if (dentry) {
 573                 inode->i_nlink--;
 574                 d_delete(dentry);
 575                 dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
 576         }
 577
 578         dput(dentry);           /* d_find_alias above */
 579 out:
 580         mutex_unlock(&root->d_inode->i_mutex);
 581 }
 582
 583 static int __init init_devpts_fs(void)
 584 {
 585         int err = register_filesystem(&devpts_fs_type);
 586         if (!err) {
 587                 devpts_mnt = kern_mount(&devpts_fs_type);
 588                 if (IS_ERR(devpts_mnt))
 589                         err = PTR_ERR(devpts_mnt);
 590         }
 591         return err;
 592 }
 593
 594 static void __exit exit_devpts_fs(void)
 595 {
 596         unregister_filesystem(&devpts_fs_type);
 597         mntput(devpts_mnt);
 598 }
 599
 600 module_init(init_devpts_fs)
 601 module_exit(exit_devpts_fs)
 602 MODULE_LICENSE("GPL");