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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  14
  15 #include <linux/module.h>
  16 #include <linux/init.h>
  17 #include <linux/fs.h>
  18 #include <linux/sched.h>
  19 #include <linux/namei.h>
  20 #include <linux/slab.h>
  21 #include <linux/mount.h>
  22 #include <linux/tty.h>
  23 #include <linux/mutex.h>
  24 #include <linux/magic.h>
  25 #include <linux/idr.h>
  26 #include <linux/devpts_fs.h>
  27 #include <linux/parser.h>
  28 #include <linux/fsnotify.h>
  29 #include <linux/seq_file.h>
  30
  31 #define DEVPTS_DEFAULT_MODE 0600
  32 /*
  33  * ptmx is a new node in /dev/pts and will be unused in legacy (single-
  34  * instance) mode. To prevent surprises in user space, set permissions of
  35  * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
  36  * permissions.
  37  */
  38 #define DEVPTS_DEFAULT_PTMX_MODE 0000
  39 #define PTMX_MINOR      2
  40
  41 /*
  42  * sysctl support for setting limits on the number of Unix98 ptys allocated.
  43  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
  44  */
  45 static int pty_limit = NR_UNIX98_PTY_DEFAULT;
  46 static int pty_reserve = NR_UNIX98_PTY_RESERVE;
  47 static int pty_limit_min;
  48 static int pty_limit_max = INT_MAX;
  49 static int pty_count;
  50
  51 static struct ctl_table pty_table[] = {
  52         {
  53                 .procname       = "max",
  54                 .maxlen         = sizeof(int),
  55                 .mode           = 0644,
  56                 .data           = &pty_limit,
  57                 .proc_handler   = proc_dointvec_minmax,
  58                 .extra1         = &pty_limit_min,
  59                 .extra2         = &pty_limit_max,
  60         }, {
  61                 .procname       = "reserve",
  62                 .maxlen         = sizeof(int),
  63                 .mode           = 0644,
  64                 .data           = &pty_reserve,
  65                 .proc_handler   = proc_dointvec_minmax,
  66                 .extra1         = &pty_limit_min,
  67                 .extra2         = &pty_limit_max,
  68         }, {
  69                 .procname       = "nr",
  70                 .maxlen         = sizeof(int),
  71                 .mode           = 0444,
  72                 .data           = &pty_count,
  73                 .proc_handler   = proc_dointvec,
  74         },
  75         {}
  76 };
  77
  78 static struct ctl_table pty_kern_table[] = {
  79         {
  80                 .procname       = "pty",
  81                 .mode           = 0555,
  82                 .child          = pty_table,
  83         },
  84         {}
  85 };
  86
  87 static struct ctl_table pty_root_table[] = {
  88         {
  89                 .procname       = "kernel",
  90                 .mode           = 0555,
  91                 .child          = pty_kern_table,
  92         },
  93         {}
  94 };
  95
  96 static DEFINE_MUTEX(allocated_ptys_lock);
  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 reserve;
 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         {Opt_ptmxmode, "ptmxmode=%o"},
 119         {Opt_newinstance, "newinstance"},
 120         {Opt_max, "max=%d"},
 121         {Opt_err, NULL}
 122 };
 123
 124 struct pts_fs_info {
 125         struct ida allocated_ptys;
 126         struct pts_mount_opts mount_opts;
 127         struct super_block *sb;
 128         struct dentry *ptmx_dentry;
 129 };
 130
 131 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
 132 {
 133         return sb->s_fs_info;
 134 }
 135
 136 struct pts_fs_info *devpts_acquire(struct file *filp)
 137 {
 138         struct pts_fs_info *result;
 139         struct path path;
 140         struct super_block *sb;
 141         int err;
 142
 143         path = filp->f_path;
 144         path_get(&path);
 145
 146         /* Has the devpts filesystem already been found? */
 147         sb = path.mnt->mnt_sb;
 148         if (sb->s_magic != DEVPTS_SUPER_MAGIC) {
 149                 /* Is a devpts filesystem at "pts" in the same directory? */
 150                 err = path_pts(&path);
 151                 if (err) {
 152                         result = ERR_PTR(err);
 153                         goto out;
 154                 }
 155
 156                 /* Is the path the root of a devpts filesystem? */
 157                 result = ERR_PTR(-ENODEV);
 158                 sb = path.mnt->mnt_sb;
 159                 if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
 160                     (path.mnt->mnt_root != sb->s_root))
 161                         goto out;
 162         }
 163
 164         /*
 165          * pty code needs to hold extra references in case of last /dev/tty close
 166          */
 167         atomic_inc(&sb->s_active);
 168         result = DEVPTS_SB(sb);
 169
 170 out:
 171         path_put(&path);
 172         return result;
 173 }
 174
 175 void devpts_release(struct pts_fs_info *fsi)
 176 {
 177         deactivate_super(fsi->sb);
 178 }
 179
 180 #define PARSE_MOUNT     0
 181 #define PARSE_REMOUNT   1
 182
 183 /*
 184  * parse_mount_options():
 185  *      Set @opts to mount options specified in @data. If an option is not
 186  *      specified in @data, set it to its default value.
 187  *
 188  * Note: @data may be NULL (in which case all options are set to default).
 189  */
 190 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
 191 {
 192         char *p;
 193         kuid_t uid;
 194         kgid_t gid;
 195
 196         opts->setuid  = 0;
 197         opts->setgid  = 0;
 198         opts->uid     = GLOBAL_ROOT_UID;
 199         opts->gid     = GLOBAL_ROOT_GID;
 200         opts->mode    = DEVPTS_DEFAULT_MODE;
 201         opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 202         opts->max     = NR_UNIX98_PTY_MAX;
 203
 204         /* Only allow instances mounted from the initial mount
 205          * namespace to tap the reserve pool of ptys.
 206          */
 207         if (op == PARSE_MOUNT)
 208                 opts->reserve =
 209                         (current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
 210
 211         while ((p = strsep(&data, ",")) != NULL) {
 212                 substring_t args[MAX_OPT_ARGS];
 213                 int token;
 214                 int option;
 215
 216                 if (!*p)
 217                         continue;
 218
 219                 token = match_token(p, tokens, args);
 220                 switch (token) {
 221                 case Opt_uid:
 222                         if (match_int(&args[0], &option))
 223                                 return -EINVAL;
 224                         uid = make_kuid(current_user_ns(), option);
 225                         if (!uid_valid(uid))
 226                                 return -EINVAL;
 227                         opts->uid = uid;
 228                         opts->setuid = 1;
 229                         break;
 230                 case Opt_gid:
 231                         if (match_int(&args[0], &option))
 232                                 return -EINVAL;
 233                         gid = make_kgid(current_user_ns(), option);
 234                         if (!gid_valid(gid))
 235                                 return -EINVAL;
 236                         opts->gid = gid;
 237                         opts->setgid = 1;
 238                         break;
 239                 case Opt_mode:
 240                         if (match_octal(&args[0], &option))
 241                                 return -EINVAL;
 242                         opts->mode = option & S_IALLUGO;
 243                         break;
 244                 case Opt_ptmxmode:
 245                         if (match_octal(&args[0], &option))
 246                                 return -EINVAL;
 247                         opts->ptmxmode = option & S_IALLUGO;
 248                         break;
 249                 case Opt_newinstance:
 250                         break;
 251                 case Opt_max:
 252                         if (match_int(&args[0], &option) ||
 253                             option < 0 || option > NR_UNIX98_PTY_MAX)
 254                                 return -EINVAL;
 255                         opts->max = option;
 256                         break;
 257                 default:
 258                         pr_err("called with bogus options\n");
 259                         return -EINVAL;
 260                 }
 261         }
 262
 263         return 0;
 264 }
 265
 266 static int mknod_ptmx(struct super_block *sb)
 267 {
 268         int mode;
 269         int rc = -ENOMEM;
 270         struct dentry *dentry;
 271         struct inode *inode;
 272         struct dentry *root = sb->s_root;
 273         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 274         struct pts_mount_opts *opts = &fsi->mount_opts;
 275         kuid_t ptmx_uid = current_fsuid();
 276         kgid_t ptmx_gid = current_fsgid();
 277
 278         inode_lock(d_inode(root));
 279
 280         /* If we have already created ptmx node, return */
 281         if (fsi->ptmx_dentry) {
 282                 rc = 0;
 283                 goto out;
 284         }
 285
 286         dentry = d_alloc_name(root, "ptmx");
 287         if (!dentry) {
 288                 pr_err("Unable to alloc dentry for ptmx node\n");
 289                 goto out;
 290         }
 291
 292         /*
 293          * Create a new 'ptmx' node in this mount of devpts.
 294          */
 295         inode = new_inode(sb);
 296         if (!inode) {
 297                 pr_err("Unable to alloc inode for ptmx node\n");
 298                 dput(dentry);
 299                 goto out;
 300         }
 301
 302         inode->i_ino = 2;
 303         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
 304
 305         mode = S_IFCHR|opts->ptmxmode;
 306         init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
 307         inode->i_uid = ptmx_uid;
 308         inode->i_gid = ptmx_gid;
 309
 310         d_add(dentry, inode);
 311
 312         fsi->ptmx_dentry = dentry;
 313         rc = 0;
 314 out:
 315         inode_unlock(d_inode(root));
 316         return rc;
 317 }
 318
 319 static void update_ptmx_mode(struct pts_fs_info *fsi)
 320 {
 321         struct inode *inode;
 322         if (fsi->ptmx_dentry) {
 323                 inode = d_inode(fsi->ptmx_dentry);
 324                 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
 325         }
 326 }
 327
 328 static int devpts_remount(struct super_block *sb, int *flags, char *data)
 329 {
 330         int err;
 331         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 332         struct pts_mount_opts *opts = &fsi->mount_opts;
 333
 334         err = parse_mount_options(data, PARSE_REMOUNT, opts);
 335
 336         /*
 337          * parse_mount_options() restores options to default values
 338          * before parsing and may have changed ptmxmode. So, update the
 339          * mode in the inode too. Bogus options don't fail the remount,
 340          * so do this even on error return.
 341          */
 342         update_ptmx_mode(fsi);
 343
 344         return err;
 345 }
 346
 347 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
 348 {
 349         struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
 350         struct pts_mount_opts *opts = &fsi->mount_opts;
 351
 352         if (opts->setuid)
 353                 seq_printf(seq, ",uid=%u",
 354                            from_kuid_munged(&init_user_ns, opts->uid));
 355         if (opts->setgid)
 356                 seq_printf(seq, ",gid=%u",
 357                            from_kgid_munged(&init_user_ns, opts->gid));
 358         seq_printf(seq, ",mode=%03o", opts->mode);
 359         seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
 360         if (opts->max < NR_UNIX98_PTY_MAX)
 361                 seq_printf(seq, ",max=%d", opts->max);
 362
 363         return 0;
 364 }
 365
 366 static const struct super_operations devpts_sops = {
 367         .statfs         = simple_statfs,
 368         .remount_fs     = devpts_remount,
 369         .show_options   = devpts_show_options,
 370 };
 371
 372 static void *new_pts_fs_info(struct super_block *sb)
 373 {
 374         struct pts_fs_info *fsi;
 375
 376         fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
 377         if (!fsi)
 378                 return NULL;
 379
 380         ida_init(&fsi->allocated_ptys);
 381         fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
 382         fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 383         fsi->sb = sb;
 384
 385         return fsi;
 386 }
 387
 388 static int
 389 devpts_fill_super(struct super_block *s, void *data, int silent)
 390 {
 391         struct inode *inode;
 392         int error;
 393
 394         s->s_iflags &= ~SB_I_NODEV;
 395         s->s_blocksize = 1024;
 396         s->s_blocksize_bits = 10;
 397         s->s_magic = DEVPTS_SUPER_MAGIC;
 398         s->s_op = &devpts_sops;
 399         s->s_time_gran = 1;
 400
 401         error = -ENOMEM;
 402         s->s_fs_info = new_pts_fs_info(s);
 403         if (!s->s_fs_info)
 404                 goto fail;
 405
 406         error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
 407         if (error)
 408                 goto fail;
 409
 410         error = -ENOMEM;
 411         inode = new_inode(s);
 412         if (!inode)
 413                 goto fail;
 414         inode->i_ino = 1;
 415         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
 416         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
 417         inode->i_op = &simple_dir_inode_operations;
 418         inode->i_fop = &simple_dir_operations;
 419         set_nlink(inode, 2);
 420
 421         s->s_root = d_make_root(inode);
 422         if (!s->s_root) {
 423                 pr_err("get root dentry failed\n");
 424                 goto fail;
 425         }
 426
 427         error = mknod_ptmx(s);
 428         if (error)
 429                 goto fail_dput;
 430
 431         return 0;
 432 fail_dput:
 433         dput(s->s_root);
 434         s->s_root = NULL;
 435 fail:
 436         return error;
 437 }
 438
 439 /*
 440  * devpts_mount()
 441  *
 442  *     Mount a new (private) instance of devpts.  PTYs created in this
 443  *     instance are independent of the PTYs in other devpts instances.
 444  */
 445 static struct dentry *devpts_mount(struct file_system_type *fs_type,
 446         int flags, const char *dev_name, void *data)
 447 {
 448         return mount_nodev(fs_type, flags, data, devpts_fill_super);
 449 }
 450
 451 static void devpts_kill_sb(struct super_block *sb)
 452 {
 453         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 454
 455         if (fsi)
 456                 ida_destroy(&fsi->allocated_ptys);
 457         kfree(fsi);
 458         kill_litter_super(sb);
 459 }
 460
 461 static struct file_system_type devpts_fs_type = {
 462         .name           = "devpts",
 463         .mount          = devpts_mount,
 464         .kill_sb        = devpts_kill_sb,
 465         .fs_flags       = FS_USERNS_MOUNT,
 466 };
 467
 468 /*
 469  * The normal naming convention is simply /dev/pts/<number>; this conforms
 470  * to the System V naming convention
 471  */
 472
 473 int devpts_new_index(struct pts_fs_info *fsi)
 474 {
 475         int index;
 476         int ida_ret;
 477
 478 retry:
 479         if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
 480                 return -ENOMEM;
 481
 482         mutex_lock(&allocated_ptys_lock);
 483         if (pty_count >= (pty_limit -
 484                           (fsi->mount_opts.reserve ? 0 : pty_reserve))) {
 485                 mutex_unlock(&allocated_ptys_lock);
 486                 return -ENOSPC;
 487         }
 488
 489         ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
 490         if (ida_ret < 0) {
 491                 mutex_unlock(&allocated_ptys_lock);
 492                 if (ida_ret == -EAGAIN)
 493                         goto retry;
 494                 return -EIO;
 495         }
 496
 497         if (index >= fsi->mount_opts.max) {
 498                 ida_remove(&fsi->allocated_ptys, index);
 499                 mutex_unlock(&allocated_ptys_lock);
 500                 return -ENOSPC;
 501         }
 502         pty_count++;
 503         mutex_unlock(&allocated_ptys_lock);
 504         return index;
 505 }
 506
 507 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
 508 {
 509         mutex_lock(&allocated_ptys_lock);
 510         ida_remove(&fsi->allocated_ptys, idx);
 511         pty_count--;
 512         mutex_unlock(&allocated_ptys_lock);
 513 }
 514
 515 /**
 516  * devpts_pty_new -- create a new inode in /dev/pts/
 517  * @ptmx_inode: inode of the master
 518  * @device: major+minor of the node to be created
 519  * @index: used as a name of the node
 520  * @priv: what's given back by devpts_get_priv
 521  *
 522  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
 523  */
 524 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
 525 {
 526         struct dentry *dentry;
 527         struct super_block *sb = fsi->sb;
 528         struct inode *inode;
 529         struct dentry *root;
 530         struct pts_mount_opts *opts;
 531         char s[12];
 532
 533         root = sb->s_root;
 534         opts = &fsi->mount_opts;
 535
 536         inode = new_inode(sb);
 537         if (!inode)
 538                 return ERR_PTR(-ENOMEM);
 539
 540         inode->i_ino = index + 3;
 541         inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
 542         inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
 543         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
 544         init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
 545
 546         sprintf(s, "%d", index);
 547
 548         dentry = d_alloc_name(root, s);
 549         if (dentry) {
 550                 dentry->d_fsdata = priv;
 551                 d_add(dentry, inode);
 552                 fsnotify_create(d_inode(root), dentry);
 553         } else {
 554                 iput(inode);
 555                 dentry = ERR_PTR(-ENOMEM);
 556         }
 557
 558         return dentry;
 559 }
 560
 561 /**
 562  * devpts_get_priv -- get private data for a slave
 563  * @pts_inode: inode of the slave
 564  *
 565  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
 566  */
 567 void *devpts_get_priv(struct dentry *dentry)
 568 {
 569         if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
 570                 return NULL;
 571         return dentry->d_fsdata;
 572 }
 573
 574 /**
 575  * devpts_pty_kill -- remove inode form /dev/pts/
 576  * @inode: inode of the slave to be removed
 577  *
 578  * This is an inverse operation of devpts_pty_new.
 579  */
 580 void devpts_pty_kill(struct dentry *dentry)
 581 {
 582         WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
 583
 584         dentry->d_fsdata = NULL;
 585         drop_nlink(dentry->d_inode);
 586         d_delete(dentry);
 587         dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
 588 }
 589
 590 static int __init init_devpts_fs(void)
 591 {
 592         int err = register_filesystem(&devpts_fs_type);
 593         if (!err) {
 594                 register_sysctl_table(pty_root_table);
 595         }
 596         return err;
 597 }
 598 module_init(init_devpts_fs)