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