linux/fs/tracefs/inode.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 *  inode.c - part of tracefs, a pseudo file system for activating tracing
   4 *
   5 * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
   6 *
   7 *  Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
   8 *
   9 * tracefs is the file system that is used by the tracing infrastructure.
  10 */
  11
  12#include <linux/module.h>
  13#include <linux/fs.h>
  14#include <linux/mount.h>
  15#include <linux/kobject.h>
  16#include <linux/namei.h>
  17#include <linux/tracefs.h>
  18#include <linux/fsnotify.h>
  19#include <linux/security.h>
  20#include <linux/seq_file.h>
  21#include <linux/parser.h>
  22#include <linux/magic.h>
  23#include <linux/slab.h>
  24
  25#define TRACEFS_DEFAULT_MODE    0700
  26
  27static struct vfsmount *tracefs_mount;
  28static int tracefs_mount_count;
  29static bool tracefs_registered;
  30
  31static ssize_t default_read_file(struct file *file, char __user *buf,
  32                                 size_t count, loff_t *ppos)
  33{
  34        return 0;
  35}
  36
  37static ssize_t default_write_file(struct file *file, const char __user *buf,
  38                                   size_t count, loff_t *ppos)
  39{
  40        return count;
  41}
  42
  43static const struct file_operations tracefs_file_operations = {
  44        .read =         default_read_file,
  45        .write =        default_write_file,
  46        .open =         simple_open,
  47        .llseek =       noop_llseek,
  48};
  49
  50static struct tracefs_dir_ops {
  51        int (*mkdir)(const char *name);
  52        int (*rmdir)(const char *name);
  53} tracefs_ops __ro_after_init;
  54
  55static char *get_dname(struct dentry *dentry)
  56{
  57        const char *dname;
  58        char *name;
  59        int len = dentry->d_name.len;
  60
  61        dname = dentry->d_name.name;
  62        name = kmalloc(len + 1, GFP_KERNEL);
  63        if (!name)
  64                return NULL;
  65        memcpy(name, dname, len);
  66        name[len] = 0;
  67        return name;
  68}
  69
  70static int tracefs_syscall_mkdir(struct user_namespace *mnt_userns,
  71                                 struct inode *inode, struct dentry *dentry,
  72                                 umode_t mode)
  73{
  74        char *name;
  75        int ret;
  76
  77        name = get_dname(dentry);
  78        if (!name)
  79                return -ENOMEM;
  80
  81        /*
  82         * The mkdir call can call the generic functions that create
  83         * the files within the tracefs system. It is up to the individual
  84         * mkdir routine to handle races.
  85         */
  86        inode_unlock(inode);
  87        ret = tracefs_ops.mkdir(name);
  88        inode_lock(inode);
  89
  90        kfree(name);
  91
  92        return ret;
  93}
  94
  95static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
  96{
  97        char *name;
  98        int ret;
  99
 100        name = get_dname(dentry);
 101        if (!name)
 102                return -ENOMEM;
 103
 104        /*
 105         * The rmdir call can call the generic functions that create
 106         * the files within the tracefs system. It is up to the individual
 107         * rmdir routine to handle races.
 108         * This time we need to unlock not only the parent (inode) but
 109         * also the directory that is being deleted.
 110         */
 111        inode_unlock(inode);
 112        inode_unlock(d_inode(dentry));
 113
 114        ret = tracefs_ops.rmdir(name);
 115
 116        inode_lock_nested(inode, I_MUTEX_PARENT);
 117        inode_lock(d_inode(dentry));
 118
 119        kfree(name);
 120
 121        return ret;
 122}
 123
 124static const struct inode_operations tracefs_dir_inode_operations = {
 125        .lookup         = simple_lookup,
 126        .mkdir          = tracefs_syscall_mkdir,
 127        .rmdir          = tracefs_syscall_rmdir,
 128};
 129
 130static struct inode *tracefs_get_inode(struct super_block *sb)
 131{
 132        struct inode *inode = new_inode(sb);
 133        if (inode) {
 134                inode->i_ino = get_next_ino();
 135                inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
 136        }
 137        return inode;
 138}
 139
 140struct tracefs_mount_opts {
 141        kuid_t uid;
 142        kgid_t gid;
 143        umode_t mode;
 144};
 145
 146enum {
 147        Opt_uid,
 148        Opt_gid,
 149        Opt_mode,
 150        Opt_err
 151};
 152
 153static const match_table_t tokens = {
 154        {Opt_uid, "uid=%u"},
 155        {Opt_gid, "gid=%u"},
 156        {Opt_mode, "mode=%o"},
 157        {Opt_err, NULL}
 158};
 159
 160struct tracefs_fs_info {
 161        struct tracefs_mount_opts mount_opts;
 162};
 163
 164static void change_gid(struct dentry *dentry, kgid_t gid)
 165{
 166        if (!dentry->d_inode)
 167                return;
 168        dentry->d_inode->i_gid = gid;
 169}
 170
 171/*
 172 * Taken from d_walk, but without he need for handling renames.
 173 * Nothing can be renamed while walking the list, as tracefs
 174 * does not support renames. This is only called when mounting
 175 * or remounting the file system, to set all the files to
 176 * the given gid.
 177 */
 178static void set_gid(struct dentry *parent, kgid_t gid)
 179{
 180        struct dentry *this_parent;
 181        struct list_head *next;
 182
 183        this_parent = parent;
 184        spin_lock(&this_parent->d_lock);
 185
 186        change_gid(this_parent, gid);
 187repeat:
 188        next = this_parent->d_subdirs.next;
 189resume:
 190        while (next != &this_parent->d_subdirs) {
 191                struct list_head *tmp = next;
 192                struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
 193                next = tmp->next;
 194
 195                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
 196
 197                change_gid(dentry, gid);
 198
 199                if (!list_empty(&dentry->d_subdirs)) {
 200                        spin_unlock(&this_parent->d_lock);
 201                        spin_release(&dentry->d_lock.dep_map, _RET_IP_);
 202                        this_parent = dentry;
 203                        spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
 204                        goto repeat;
 205                }
 206                spin_unlock(&dentry->d_lock);
 207        }
 208        /*
 209         * All done at this level ... ascend and resume the search.
 210         */
 211        rcu_read_lock();
 212ascend:
 213        if (this_parent != parent) {
 214                struct dentry *child = this_parent;
 215                this_parent = child->d_parent;
 216
 217                spin_unlock(&child->d_lock);
 218                spin_lock(&this_parent->d_lock);
 219
 220                /* go into the first sibling still alive */
 221                do {
 222                        next = child->d_child.next;
 223                        if (next == &this_parent->d_subdirs)
 224                                goto ascend;
 225                        child = list_entry(next, struct dentry, d_child);
 226                } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
 227                rcu_read_unlock();
 228                goto resume;
 229        }
 230        rcu_read_unlock();
 231        spin_unlock(&this_parent->d_lock);
 232        return;
 233}
 234
 235static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
 236{
 237        substring_t args[MAX_OPT_ARGS];
 238        int option;
 239        int token;
 240        kuid_t uid;
 241        kgid_t gid;
 242        char *p;
 243
 244        opts->mode = TRACEFS_DEFAULT_MODE;
 245
 246        while ((p = strsep(&data, ",")) != NULL) {
 247                if (!*p)
 248                        continue;
 249
 250                token = match_token(p, tokens, args);
 251                switch (token) {
 252                case Opt_uid:
 253                        if (match_int(&args[0], &option))
 254                                return -EINVAL;
 255                        uid = make_kuid(current_user_ns(), option);
 256                        if (!uid_valid(uid))
 257                                return -EINVAL;
 258                        opts->uid = uid;
 259                        break;
 260                case Opt_gid:
 261                        if (match_int(&args[0], &option))
 262                                return -EINVAL;
 263                        gid = make_kgid(current_user_ns(), option);
 264                        if (!gid_valid(gid))
 265                                return -EINVAL;
 266                        opts->gid = gid;
 267                        break;
 268                case Opt_mode:
 269                        if (match_octal(&args[0], &option))
 270                                return -EINVAL;
 271                        opts->mode = option & S_IALLUGO;
 272                        break;
 273                /*
 274                 * We might like to report bad mount options here;
 275                 * but traditionally tracefs has ignored all mount options
 276                 */
 277                }
 278        }
 279
 280        return 0;
 281}
 282
 283static int tracefs_apply_options(struct super_block *sb)
 284{
 285        struct tracefs_fs_info *fsi = sb->s_fs_info;
 286        struct inode *inode = d_inode(sb->s_root);
 287        struct tracefs_mount_opts *opts = &fsi->mount_opts;
 288
 289        inode->i_mode &= ~S_IALLUGO;
 290        inode->i_mode |= opts->mode;
 291
 292        inode->i_uid = opts->uid;
 293
 294        /* Set all the group ids to the mount option */
 295        set_gid(sb->s_root, opts->gid);
 296
 297        return 0;
 298}
 299
 300static int tracefs_remount(struct super_block *sb, int *flags, char *data)
 301{
 302        int err;
 303        struct tracefs_fs_info *fsi = sb->s_fs_info;
 304
 305        sync_filesystem(sb);
 306        err = tracefs_parse_options(data, &fsi->mount_opts);
 307        if (err)
 308                goto fail;
 309
 310        tracefs_apply_options(sb);
 311
 312fail:
 313        return err;
 314}
 315
 316static int tracefs_show_options(struct seq_file *m, struct dentry *root)
 317{
 318        struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
 319        struct tracefs_mount_opts *opts = &fsi->mount_opts;
 320
 321        if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
 322                seq_printf(m, ",uid=%u",
 323                           from_kuid_munged(&init_user_ns, opts->uid));
 324        if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
 325                seq_printf(m, ",gid=%u",
 326                           from_kgid_munged(&init_user_ns, opts->gid));
 327        if (opts->mode != TRACEFS_DEFAULT_MODE)
 328                seq_printf(m, ",mode=%o", opts->mode);
 329
 330        return 0;
 331}
 332
 333static const struct super_operations tracefs_super_operations = {
 334        .statfs         = simple_statfs,
 335        .remount_fs     = tracefs_remount,
 336        .show_options   = tracefs_show_options,
 337};
 338
 339static int trace_fill_super(struct super_block *sb, void *data, int silent)
 340{
 341        static const struct tree_descr trace_files[] = {{""}};
 342        struct tracefs_fs_info *fsi;
 343        int err;
 344
 345        fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
 346        sb->s_fs_info = fsi;
 347        if (!fsi) {
 348                err = -ENOMEM;
 349                goto fail;
 350        }
 351
 352        err = tracefs_parse_options(data, &fsi->mount_opts);
 353        if (err)
 354                goto fail;
 355
 356        err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
 357        if (err)
 358                goto fail;
 359
 360        sb->s_op = &tracefs_super_operations;
 361
 362        tracefs_apply_options(sb);
 363
 364        return 0;
 365
 366fail:
 367        kfree(fsi);
 368        sb->s_fs_info = NULL;
 369        return err;
 370}
 371
 372static struct dentry *trace_mount(struct file_system_type *fs_type,
 373                        int flags, const char *dev_name,
 374                        void *data)
 375{
 376        return mount_single(fs_type, flags, data, trace_fill_super);
 377}
 378
 379static struct file_system_type trace_fs_type = {
 380        .owner =        THIS_MODULE,
 381        .name =         "tracefs",
 382        .mount =        trace_mount,
 383        .kill_sb =      kill_litter_super,
 384};
 385MODULE_ALIAS_FS("tracefs");
 386
 387static struct dentry *start_creating(const char *name, struct dentry *parent)
 388{
 389        struct dentry *dentry;
 390        int error;
 391
 392        pr_debug("tracefs: creating file '%s'\n",name);
 393
 394        error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
 395                              &tracefs_mount_count);
 396        if (error)
 397                return ERR_PTR(error);
 398
 399        /* If the parent is not specified, we create it in the root.
 400         * We need the root dentry to do this, which is in the super
 401         * block. A pointer to that is in the struct vfsmount that we
 402         * have around.
 403         */
 404        if (!parent)
 405                parent = tracefs_mount->mnt_root;
 406
 407        inode_lock(d_inode(parent));
 408        if (unlikely(IS_DEADDIR(d_inode(parent))))
 409                dentry = ERR_PTR(-ENOENT);
 410        else
 411                dentry = lookup_one_len(name, parent, strlen(name));
 412        if (!IS_ERR(dentry) && d_inode(dentry)) {
 413                dput(dentry);
 414                dentry = ERR_PTR(-EEXIST);
 415        }
 416
 417        if (IS_ERR(dentry)) {
 418                inode_unlock(d_inode(parent));
 419                simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 420        }
 421
 422        return dentry;
 423}
 424
 425static struct dentry *failed_creating(struct dentry *dentry)
 426{
 427        inode_unlock(d_inode(dentry->d_parent));
 428        dput(dentry);
 429        simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 430        return NULL;
 431}
 432
 433static struct dentry *end_creating(struct dentry *dentry)
 434{
 435        inode_unlock(d_inode(dentry->d_parent));
 436        return dentry;
 437}
 438
 439/**
 440 * tracefs_create_file - create a file in the tracefs filesystem
 441 * @name: a pointer to a string containing the name of the file to create.
 442 * @mode: the permission that the file should have.
 443 * @parent: a pointer to the parent dentry for this file.  This should be a
 444 *          directory dentry if set.  If this parameter is NULL, then the
 445 *          file will be created in the root of the tracefs filesystem.
 446 * @data: a pointer to something that the caller will want to get to later
 447 *        on.  The inode.i_private pointer will point to this value on
 448 *        the open() call.
 449 * @fops: a pointer to a struct file_operations that should be used for
 450 *        this file.
 451 *
 452 * This is the basic "create a file" function for tracefs.  It allows for a
 453 * wide range of flexibility in creating a file, or a directory (if you want
 454 * to create a directory, the tracefs_create_dir() function is
 455 * recommended to be used instead.)
 456 *
 457 * This function will return a pointer to a dentry if it succeeds.  This
 458 * pointer must be passed to the tracefs_remove() function when the file is
 459 * to be removed (no automatic cleanup happens if your module is unloaded,
 460 * you are responsible here.)  If an error occurs, %NULL will be returned.
 461 *
 462 * If tracefs is not enabled in the kernel, the value -%ENODEV will be
 463 * returned.
 464 */
 465struct dentry *tracefs_create_file(const char *name, umode_t mode,
 466                                   struct dentry *parent, void *data,
 467                                   const struct file_operations *fops)
 468{
 469        struct dentry *dentry;
 470        struct inode *inode;
 471
 472        if (security_locked_down(LOCKDOWN_TRACEFS))
 473                return NULL;
 474
 475        if (!(mode & S_IFMT))
 476                mode |= S_IFREG;
 477        BUG_ON(!S_ISREG(mode));
 478        dentry = start_creating(name, parent);
 479
 480        if (IS_ERR(dentry))
 481                return NULL;
 482
 483        inode = tracefs_get_inode(dentry->d_sb);
 484        if (unlikely(!inode))
 485                return failed_creating(dentry);
 486
 487        inode->i_mode = mode;
 488        inode->i_fop = fops ? fops : &tracefs_file_operations;
 489        inode->i_private = data;
 490        inode->i_uid = d_inode(dentry->d_parent)->i_uid;
 491        inode->i_gid = d_inode(dentry->d_parent)->i_gid;
 492        d_instantiate(dentry, inode);
 493        fsnotify_create(d_inode(dentry->d_parent), dentry);
 494        return end_creating(dentry);
 495}
 496
 497static struct dentry *__create_dir(const char *name, struct dentry *parent,
 498                                   const struct inode_operations *ops)
 499{
 500        struct dentry *dentry = start_creating(name, parent);
 501        struct inode *inode;
 502
 503        if (IS_ERR(dentry))
 504                return NULL;
 505
 506        inode = tracefs_get_inode(dentry->d_sb);
 507        if (unlikely(!inode))
 508                return failed_creating(dentry);
 509
 510        /* Do not set bits for OTH */
 511        inode->i_mode = S_IFDIR | S_IRWXU | S_IRUSR| S_IRGRP | S_IXUSR | S_IXGRP;
 512        inode->i_op = ops;
 513        inode->i_fop = &simple_dir_operations;
 514        inode->i_uid = d_inode(dentry->d_parent)->i_uid;
 515        inode->i_gid = d_inode(dentry->d_parent)->i_gid;
 516
 517        /* directory inodes start off with i_nlink == 2 (for "." entry) */
 518        inc_nlink(inode);
 519        d_instantiate(dentry, inode);
 520        inc_nlink(d_inode(dentry->d_parent));
 521        fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
 522        return end_creating(dentry);
 523}
 524
 525/**
 526 * tracefs_create_dir - create a directory in the tracefs filesystem
 527 * @name: a pointer to a string containing the name of the directory to
 528 *        create.
 529 * @parent: a pointer to the parent dentry for this file.  This should be a
 530 *          directory dentry if set.  If this parameter is NULL, then the
 531 *          directory will be created in the root of the tracefs filesystem.
 532 *
 533 * This function creates a directory in tracefs with the given name.
 534 *
 535 * This function will return a pointer to a dentry if it succeeds.  This
 536 * pointer must be passed to the tracefs_remove() function when the file is
 537 * to be removed. If an error occurs, %NULL will be returned.
 538 *
 539 * If tracing is not enabled in the kernel, the value -%ENODEV will be
 540 * returned.
 541 */
 542struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
 543{
 544        return __create_dir(name, parent, &simple_dir_inode_operations);
 545}
 546
 547/**
 548 * tracefs_create_instance_dir - create the tracing instances directory
 549 * @name: The name of the instances directory to create
 550 * @parent: The parent directory that the instances directory will exist
 551 * @mkdir: The function to call when a mkdir is performed.
 552 * @rmdir: The function to call when a rmdir is performed.
 553 *
 554 * Only one instances directory is allowed.
 555 *
 556 * The instances directory is special as it allows for mkdir and rmdir
 557 * to be done by userspace. When a mkdir or rmdir is performed, the inode
 558 * locks are released and the methods passed in (@mkdir and @rmdir) are
 559 * called without locks and with the name of the directory being created
 560 * within the instances directory.
 561 *
 562 * Returns the dentry of the instances directory.
 563 */
 564__init struct dentry *tracefs_create_instance_dir(const char *name,
 565                                          struct dentry *parent,
 566                                          int (*mkdir)(const char *name),
 567                                          int (*rmdir)(const char *name))
 568{
 569        struct dentry *dentry;
 570
 571        /* Only allow one instance of the instances directory. */
 572        if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
 573                return NULL;
 574
 575        dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
 576        if (!dentry)
 577                return NULL;
 578
 579        tracefs_ops.mkdir = mkdir;
 580        tracefs_ops.rmdir = rmdir;
 581
 582        return dentry;
 583}
 584
 585static void remove_one(struct dentry *victim)
 586{
 587        simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 588}
 589
 590/**
 591 * tracefs_remove - recursively removes a directory
 592 * @dentry: a pointer to a the dentry of the directory to be removed.
 593 *
 594 * This function recursively removes a directory tree in tracefs that
 595 * was previously created with a call to another tracefs function
 596 * (like tracefs_create_file() or variants thereof.)
 597 */
 598void tracefs_remove(struct dentry *dentry)
 599{
 600        if (IS_ERR_OR_NULL(dentry))
 601                return;
 602
 603        simple_pin_fs(&trace_fs_type, &tracefs_mount, &tracefs_mount_count);
 604        simple_recursive_removal(dentry, remove_one);
 605        simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 606}
 607
 608/**
 609 * tracefs_initialized - Tells whether tracefs has been registered
 610 */
 611bool tracefs_initialized(void)
 612{
 613        return tracefs_registered;
 614}
 615
 616static int __init tracefs_init(void)
 617{
 618        int retval;
 619
 620        retval = sysfs_create_mount_point(kernel_kobj, "tracing");
 621        if (retval)
 622                return -EINVAL;
 623
 624        retval = register_filesystem(&trace_fs_type);
 625        if (!retval)
 626                tracefs_registered = true;
 627
 628        return retval;
 629}
 630core_initcall(tracefs_init);
 631