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