linux/fs/devpts/inode.c
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   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 */
  43static int pty_limit = NR_UNIX98_PTY_DEFAULT;
  44static int pty_reserve = NR_UNIX98_PTY_RESERVE;
  45static int pty_limit_min;
  46static int pty_limit_max = INT_MAX;
  47static int pty_count;
  48
  49static 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
  76static struct ctl_table pty_kern_table[] = {
  77        {
  78                .procname       = "pty",
  79                .mode           = 0555,
  80                .child          = pty_table,
  81        },
  82        {}
  83};
  84
  85static struct ctl_table pty_root_table[] = {
  86        {
  87                .procname       = "kernel",
  88                .mode           = 0555,
  89                .child          = pty_kern_table,
  90        },
  91        {}
  92};
  93
  94static DEFINE_MUTEX(allocated_ptys_lock);
  95
  96static struct vfsmount *devpts_mnt;
  97
  98struct 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 newinstance;
 106        int max;
 107};
 108
 109enum {
 110        Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,  Opt_max,
 111        Opt_err
 112};
 113
 114static 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
 126struct pts_fs_info {
 127        struct ida allocated_ptys;
 128        struct pts_mount_opts mount_opts;
 129        struct dentry *ptmx_dentry;
 130};
 131
 132static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
 133{
 134        return sb->s_fs_info;
 135}
 136
 137static 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 */
 158static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
 159{
 160        char *p;
 161        kuid_t uid;
 162        kgid_t gid;
 163
 164        opts->setuid  = 0;
 165        opts->setgid  = 0;
 166        opts->uid     = GLOBAL_ROOT_UID;
 167        opts->gid     = GLOBAL_ROOT_GID;
 168        opts->mode    = DEVPTS_DEFAULT_MODE;
 169        opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 170        opts->max     = NR_UNIX98_PTY_MAX;
 171
 172        /* newinstance makes sense only on initial mount */
 173        if (op == PARSE_MOUNT)
 174                opts->newinstance = 0;
 175
 176        while ((p = strsep(&data, ",")) != NULL) {
 177                substring_t args[MAX_OPT_ARGS];
 178                int token;
 179                int option;
 180
 181                if (!*p)
 182                        continue;
 183
 184                token = match_token(p, tokens, args);
 185                switch (token) {
 186                case Opt_uid:
 187                        if (match_int(&args[0], &option))
 188                                return -EINVAL;
 189                        uid = make_kuid(current_user_ns(), option);
 190                        if (!uid_valid(uid))
 191                                return -EINVAL;
 192                        opts->uid = uid;
 193                        opts->setuid = 1;
 194                        break;
 195                case Opt_gid:
 196                        if (match_int(&args[0], &option))
 197                                return -EINVAL;
 198                        gid = make_kgid(current_user_ns(), option);
 199                        if (!gid_valid(gid))
 200                                return -EINVAL;
 201                        opts->gid = gid;
 202                        opts->setgid = 1;
 203                        break;
 204                case Opt_mode:
 205                        if (match_octal(&args[0], &option))
 206                                return -EINVAL;
 207                        opts->mode = option & S_IALLUGO;
 208                        break;
 209#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 210                case Opt_ptmxmode:
 211                        if (match_octal(&args[0], &option))
 212                                return -EINVAL;
 213                        opts->ptmxmode = option & S_IALLUGO;
 214                        break;
 215                case Opt_newinstance:
 216                        /* newinstance makes sense only on initial mount */
 217                        if (op == PARSE_MOUNT)
 218                                opts->newinstance = 1;
 219                        break;
 220                case Opt_max:
 221                        if (match_int(&args[0], &option) ||
 222                            option < 0 || option > NR_UNIX98_PTY_MAX)
 223                                return -EINVAL;
 224                        opts->max = option;
 225                        break;
 226#endif
 227                default:
 228                        printk(KERN_ERR "devpts: called with bogus options\n");
 229                        return -EINVAL;
 230                }
 231        }
 232
 233        return 0;
 234}
 235
 236#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 237static int mknod_ptmx(struct super_block *sb)
 238{
 239        int mode;
 240        int rc = -ENOMEM;
 241        struct dentry *dentry;
 242        struct inode *inode;
 243        struct dentry *root = sb->s_root;
 244        struct pts_fs_info *fsi = DEVPTS_SB(sb);
 245        struct pts_mount_opts *opts = &fsi->mount_opts;
 246
 247        mutex_lock(&root->d_inode->i_mutex);
 248
 249        /* If we have already created ptmx node, return */
 250        if (fsi->ptmx_dentry) {
 251                rc = 0;
 252                goto out;
 253        }
 254
 255        dentry = d_alloc_name(root, "ptmx");
 256        if (!dentry) {
 257                printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n");
 258                goto out;
 259        }
 260
 261        /*
 262         * Create a new 'ptmx' node in this mount of devpts.
 263         */
 264        inode = new_inode(sb);
 265        if (!inode) {
 266                printk(KERN_ERR "Unable to alloc inode for ptmx node\n");
 267                dput(dentry);
 268                goto out;
 269        }
 270
 271        inode->i_ino = 2;
 272        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 273
 274        mode = S_IFCHR|opts->ptmxmode;
 275        init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
 276
 277        d_add(dentry, inode);
 278
 279        fsi->ptmx_dentry = dentry;
 280        rc = 0;
 281out:
 282        mutex_unlock(&root->d_inode->i_mutex);
 283        return rc;
 284}
 285
 286static void update_ptmx_mode(struct pts_fs_info *fsi)
 287{
 288        struct inode *inode;
 289        if (fsi->ptmx_dentry) {
 290                inode = fsi->ptmx_dentry->d_inode;
 291                inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
 292        }
 293}
 294#else
 295static inline void update_ptmx_mode(struct pts_fs_info *fsi)
 296{
 297       return;
 298}
 299#endif
 300
 301static int devpts_remount(struct super_block *sb, int *flags, char *data)
 302{
 303        int err;
 304        struct pts_fs_info *fsi = DEVPTS_SB(sb);
 305        struct pts_mount_opts *opts = &fsi->mount_opts;
 306
 307        err = parse_mount_options(data, PARSE_REMOUNT, opts);
 308
 309        /*
 310         * parse_mount_options() restores options to default values
 311         * before parsing and may have changed ptmxmode. So, update the
 312         * mode in the inode too. Bogus options don't fail the remount,
 313         * so do this even on error return.
 314         */
 315        update_ptmx_mode(fsi);
 316
 317        return err;
 318}
 319
 320static int devpts_show_options(struct seq_file *seq, struct dentry *root)
 321{
 322        struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
 323        struct pts_mount_opts *opts = &fsi->mount_opts;
 324
 325        if (opts->setuid)
 326                seq_printf(seq, ",uid=%u", from_kuid_munged(&init_user_ns, opts->uid));
 327        if (opts->setgid)
 328                seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, opts->gid));
 329        seq_printf(seq, ",mode=%03o", opts->mode);
 330#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 331        seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
 332        if (opts->max < NR_UNIX98_PTY_MAX)
 333                seq_printf(seq, ",max=%d", opts->max);
 334#endif
 335
 336        return 0;
 337}
 338
 339static const struct super_operations devpts_sops = {
 340        .statfs         = simple_statfs,
 341        .remount_fs     = devpts_remount,
 342        .show_options   = devpts_show_options,
 343};
 344
 345static void *new_pts_fs_info(void)
 346{
 347        struct pts_fs_info *fsi;
 348
 349        fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
 350        if (!fsi)
 351                return NULL;
 352
 353        ida_init(&fsi->allocated_ptys);
 354        fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
 355        fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 356
 357        return fsi;
 358}
 359
 360static int
 361devpts_fill_super(struct super_block *s, void *data, int silent)
 362{
 363        struct inode *inode;
 364
 365        s->s_blocksize = 1024;
 366        s->s_blocksize_bits = 10;
 367        s->s_magic = DEVPTS_SUPER_MAGIC;
 368        s->s_op = &devpts_sops;
 369        s->s_time_gran = 1;
 370
 371        s->s_fs_info = new_pts_fs_info();
 372        if (!s->s_fs_info)
 373                goto fail;
 374
 375        inode = new_inode(s);
 376        if (!inode)
 377                goto fail;
 378        inode->i_ino = 1;
 379        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 380        inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
 381        inode->i_op = &simple_dir_inode_operations;
 382        inode->i_fop = &simple_dir_operations;
 383        set_nlink(inode, 2);
 384
 385        s->s_root = d_make_root(inode);
 386        if (s->s_root)
 387                return 0;
 388
 389        printk(KERN_ERR "devpts: get root dentry failed\n");
 390
 391fail:
 392        return -ENOMEM;
 393}
 394
 395#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 396static int compare_init_pts_sb(struct super_block *s, void *p)
 397{
 398        if (devpts_mnt)
 399                return devpts_mnt->mnt_sb == s;
 400        return 0;
 401}
 402
 403/*
 404 * devpts_mount()
 405 *
 406 *     If the '-o newinstance' mount option was specified, mount a new
 407 *     (private) instance of devpts.  PTYs created in this instance are
 408 *     independent of the PTYs in other devpts instances.
 409 *
 410 *     If the '-o newinstance' option was not specified, mount/remount the
 411 *     initial kernel mount of devpts.  This type of mount gives the
 412 *     legacy, single-instance semantics.
 413 *
 414 *     The 'newinstance' option is needed to support multiple namespace
 415 *     semantics in devpts while preserving backward compatibility of the
 416 *     current 'single-namespace' semantics. i.e all mounts of devpts
 417 *     without the 'newinstance' mount option should bind to the initial
 418 *     kernel mount, like mount_single().
 419 *
 420 *     Mounts with 'newinstance' option create a new, private namespace.
 421 *
 422 *     NOTE:
 423 *
 424 *     For single-mount semantics, devpts cannot use mount_single(),
 425 *     because mount_single()/sget() find and use the super-block from
 426 *     the most recent mount of devpts. But that recent mount may be a
 427 *     'newinstance' mount and mount_single() would pick the newinstance
 428 *     super-block instead of the initial super-block.
 429 */
 430static struct dentry *devpts_mount(struct file_system_type *fs_type,
 431        int flags, const char *dev_name, void *data)
 432{
 433        int error;
 434        struct pts_mount_opts opts;
 435        struct super_block *s;
 436
 437        error = parse_mount_options(data, PARSE_MOUNT, &opts);
 438        if (error)
 439                return ERR_PTR(error);
 440
 441        if (opts.newinstance)
 442                s = sget(fs_type, NULL, set_anon_super, flags, NULL);
 443        else
 444                s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
 445                         NULL);
 446
 447        if (IS_ERR(s))
 448                return ERR_CAST(s);
 449
 450        if (!s->s_root) {
 451                error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
 452                if (error)
 453                        goto out_undo_sget;
 454                s->s_flags |= MS_ACTIVE;
 455        }
 456
 457        memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
 458
 459        error = mknod_ptmx(s);
 460        if (error)
 461                goto out_undo_sget;
 462
 463        return dget(s->s_root);
 464
 465out_undo_sget:
 466        deactivate_locked_super(s);
 467        return ERR_PTR(error);
 468}
 469
 470#else
 471/*
 472 * This supports only the legacy single-instance semantics (no
 473 * multiple-instance semantics)
 474 */
 475static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
 476                const char *dev_name, void *data)
 477{
 478        return mount_single(fs_type, flags, data, devpts_fill_super);
 479}
 480#endif
 481
 482static void devpts_kill_sb(struct super_block *sb)
 483{
 484        struct pts_fs_info *fsi = DEVPTS_SB(sb);
 485
 486        kfree(fsi);
 487        kill_litter_super(sb);
 488}
 489
 490static struct file_system_type devpts_fs_type = {
 491        .name           = "devpts",
 492        .mount          = devpts_mount,
 493        .kill_sb        = devpts_kill_sb,
 494};
 495
 496/*
 497 * The normal naming convention is simply /dev/pts/<number>; this conforms
 498 * to the System V naming convention
 499 */
 500
 501int devpts_new_index(struct inode *ptmx_inode)
 502{
 503        struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 504        struct pts_fs_info *fsi = DEVPTS_SB(sb);
 505        int index;
 506        int ida_ret;
 507
 508retry:
 509        if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
 510                return -ENOMEM;
 511
 512        mutex_lock(&allocated_ptys_lock);
 513        if (pty_count >= pty_limit -
 514                        (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
 515                mutex_unlock(&allocated_ptys_lock);
 516                return -ENOSPC;
 517        }
 518
 519        ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
 520        if (ida_ret < 0) {
 521                mutex_unlock(&allocated_ptys_lock);
 522                if (ida_ret == -EAGAIN)
 523                        goto retry;
 524                return -EIO;
 525        }
 526
 527        if (index >= fsi->mount_opts.max) {
 528                ida_remove(&fsi->allocated_ptys, index);
 529                mutex_unlock(&allocated_ptys_lock);
 530                return -ENOSPC;
 531        }
 532        pty_count++;
 533        mutex_unlock(&allocated_ptys_lock);
 534        return index;
 535}
 536
 537void devpts_kill_index(struct inode *ptmx_inode, int idx)
 538{
 539        struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 540        struct pts_fs_info *fsi = DEVPTS_SB(sb);
 541
 542        mutex_lock(&allocated_ptys_lock);
 543        ida_remove(&fsi->allocated_ptys, idx);
 544        pty_count--;
 545        mutex_unlock(&allocated_ptys_lock);
 546}
 547
 548int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
 549{
 550        /* tty layer puts index from devpts_new_index() in here */
 551        int number = tty->index;
 552        struct tty_driver *driver = tty->driver;
 553        dev_t device = MKDEV(driver->major, driver->minor_start+number);
 554        struct dentry *dentry;
 555        struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 556        struct inode *inode = new_inode(sb);
 557        struct dentry *root = sb->s_root;
 558        struct pts_fs_info *fsi = DEVPTS_SB(sb);
 559        struct pts_mount_opts *opts = &fsi->mount_opts;
 560        int ret = 0;
 561        char s[12];
 562
 563        /* We're supposed to be given the slave end of a pty */
 564        BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
 565        BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
 566
 567        if (!inode)
 568                return -ENOMEM;
 569
 570        inode->i_ino = number + 3;
 571        inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
 572        inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
 573        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 574        init_special_inode(inode, S_IFCHR|opts->mode, device);
 575        inode->i_private = tty;
 576        tty->driver_data = inode;
 577
 578        sprintf(s, "%d", number);
 579
 580        mutex_lock(&root->d_inode->i_mutex);
 581
 582        dentry = d_alloc_name(root, s);
 583        if (dentry) {
 584                d_add(dentry, inode);
 585                fsnotify_create(root->d_inode, dentry);
 586        } else {
 587                iput(inode);
 588                ret = -ENOMEM;
 589        }
 590
 591        mutex_unlock(&root->d_inode->i_mutex);
 592
 593        return ret;
 594}
 595
 596struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number)
 597{
 598        struct dentry *dentry;
 599        struct tty_struct *tty;
 600
 601        BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
 602
 603        /* Ensure dentry has not been deleted by devpts_pty_kill() */
 604        dentry = d_find_alias(pts_inode);
 605        if (!dentry)
 606                return NULL;
 607
 608        tty = NULL;
 609        if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
 610                tty = (struct tty_struct *)pts_inode->i_private;
 611
 612        dput(dentry);
 613
 614        return tty;
 615}
 616
 617void devpts_pty_kill(struct tty_struct *tty)
 618{
 619        struct inode *inode = tty->driver_data;
 620        struct super_block *sb = pts_sb_from_inode(inode);
 621        struct dentry *root = sb->s_root;
 622        struct dentry *dentry;
 623
 624        BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
 625
 626        mutex_lock(&root->d_inode->i_mutex);
 627
 628        dentry = d_find_alias(inode);
 629
 630        drop_nlink(inode);
 631        d_delete(dentry);
 632        dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
 633        dput(dentry);           /* d_find_alias above */
 634
 635        mutex_unlock(&root->d_inode->i_mutex);
 636}
 637
 638static int __init init_devpts_fs(void)
 639{
 640        int err = register_filesystem(&devpts_fs_type);
 641        struct ctl_table_header *table;
 642
 643        if (!err) {
 644                table = register_sysctl_table(pty_root_table);
 645                devpts_mnt = kern_mount(&devpts_fs_type);
 646                if (IS_ERR(devpts_mnt)) {
 647                        err = PTR_ERR(devpts_mnt);
 648                        unregister_filesystem(&devpts_fs_type);
 649                        unregister_sysctl_table(table);
 650                }
 651        }
 652        return err;
 653}
 654module_init(init_devpts_fs)
 655
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