linux/fs/file_table.c
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   1/*
   2 *  linux/fs/file_table.c
   3 *
   4 *  Copyright (C) 1991, 1992  Linus Torvalds
   5 *  Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
   6 */
   7
   8#include <linux/string.h>
   9#include <linux/slab.h>
  10#include <linux/file.h>
  11#include <linux/fdtable.h>
  12#include <linux/init.h>
  13#include <linux/module.h>
  14#include <linux/fs.h>
  15#include <linux/security.h>
  16#include <linux/eventpoll.h>
  17#include <linux/rcupdate.h>
  18#include <linux/mount.h>
  19#include <linux/capability.h>
  20#include <linux/cdev.h>
  21#include <linux/fsnotify.h>
  22#include <linux/sysctl.h>
  23#include <linux/lglock.h>
  24#include <linux/percpu_counter.h>
  25#include <linux/percpu.h>
  26#include <linux/hardirq.h>
  27#include <linux/task_work.h>
  28#include <linux/ima.h>
  29
  30#include <linux/atomic.h>
  31
  32#include "internal.h"
  33
  34/* sysctl tunables... */
  35struct files_stat_struct files_stat = {
  36        .max_files = NR_FILE
  37};
  38
  39DEFINE_LGLOCK(files_lglock);
  40
  41/* SLAB cache for file structures */
  42static struct kmem_cache *filp_cachep __read_mostly;
  43
  44static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  45
  46static void file_free_rcu(struct rcu_head *head)
  47{
  48        struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
  49
  50        put_cred(f->f_cred);
  51        kmem_cache_free(filp_cachep, f);
  52}
  53
  54static inline void file_free(struct file *f)
  55{
  56        percpu_counter_dec(&nr_files);
  57        file_check_state(f);
  58        call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  59}
  60
  61/*
  62 * Return the total number of open files in the system
  63 */
  64static long get_nr_files(void)
  65{
  66        return percpu_counter_read_positive(&nr_files);
  67}
  68
  69/*
  70 * Return the maximum number of open files in the system
  71 */
  72unsigned long get_max_files(void)
  73{
  74        return files_stat.max_files;
  75}
  76EXPORT_SYMBOL_GPL(get_max_files);
  77
  78/*
  79 * Handle nr_files sysctl
  80 */
  81#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  82int proc_nr_files(ctl_table *table, int write,
  83                     void __user *buffer, size_t *lenp, loff_t *ppos)
  84{
  85        files_stat.nr_files = get_nr_files();
  86        return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  87}
  88#else
  89int proc_nr_files(ctl_table *table, int write,
  90                     void __user *buffer, size_t *lenp, loff_t *ppos)
  91{
  92        return -ENOSYS;
  93}
  94#endif
  95
  96/* Find an unused file structure and return a pointer to it.
  97 * Returns NULL, if there are no more free file structures or
  98 * we run out of memory.
  99 *
 100 * Be very careful using this.  You are responsible for
 101 * getting write access to any mount that you might assign
 102 * to this filp, if it is opened for write.  If this is not
 103 * done, you will imbalance int the mount's writer count
 104 * and a warning at __fput() time.
 105 */
 106struct file *get_empty_filp(void)
 107{
 108        const struct cred *cred = current_cred();
 109        static long old_max;
 110        struct file * f;
 111
 112        /*
 113         * Privileged users can go above max_files
 114         */
 115        if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
 116                /*
 117                 * percpu_counters are inaccurate.  Do an expensive check before
 118                 * we go and fail.
 119                 */
 120                if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
 121                        goto over;
 122        }
 123
 124        f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
 125        if (f == NULL)
 126                goto fail;
 127
 128        percpu_counter_inc(&nr_files);
 129        f->f_cred = get_cred(cred);
 130        if (security_file_alloc(f))
 131                goto fail_sec;
 132
 133        INIT_LIST_HEAD(&f->f_u.fu_list);
 134        atomic_long_set(&f->f_count, 1);
 135        rwlock_init(&f->f_owner.lock);
 136        spin_lock_init(&f->f_lock);
 137        eventpoll_init_file(f);
 138        /* f->f_version: 0 */
 139        return f;
 140
 141over:
 142        /* Ran out of filps - report that */
 143        if (get_nr_files() > old_max) {
 144                pr_info("VFS: file-max limit %lu reached\n", get_max_files());
 145                old_max = get_nr_files();
 146        }
 147        goto fail;
 148
 149fail_sec:
 150        file_free(f);
 151fail:
 152        return NULL;
 153}
 154
 155/**
 156 * alloc_file - allocate and initialize a 'struct file'
 157 * @mnt: the vfsmount on which the file will reside
 158 * @dentry: the dentry representing the new file
 159 * @mode: the mode with which the new file will be opened
 160 * @fop: the 'struct file_operations' for the new file
 161 *
 162 * Use this instead of get_empty_filp() to get a new
 163 * 'struct file'.  Do so because of the same initialization
 164 * pitfalls reasons listed for init_file().  This is a
 165 * preferred interface to using init_file().
 166 *
 167 * If all the callers of init_file() are eliminated, its
 168 * code should be moved into this function.
 169 */
 170struct file *alloc_file(struct path *path, fmode_t mode,
 171                const struct file_operations *fop)
 172{
 173        struct file *file;
 174
 175        file = get_empty_filp();
 176        if (!file)
 177                return NULL;
 178
 179        file->f_path = *path;
 180        file->f_mapping = path->dentry->d_inode->i_mapping;
 181        file->f_mode = mode;
 182        file->f_op = fop;
 183
 184        /*
 185         * These mounts don't really matter in practice
 186         * for r/o bind mounts.  They aren't userspace-
 187         * visible.  We do this for consistency, and so
 188         * that we can do debugging checks at __fput()
 189         */
 190        if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
 191                file_take_write(file);
 192                WARN_ON(mnt_clone_write(path->mnt));
 193        }
 194        if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 195                i_readcount_inc(path->dentry->d_inode);
 196        return file;
 197}
 198EXPORT_SYMBOL(alloc_file);
 199
 200/**
 201 * drop_file_write_access - give up ability to write to a file
 202 * @file: the file to which we will stop writing
 203 *
 204 * This is a central place which will give up the ability
 205 * to write to @file, along with access to write through
 206 * its vfsmount.
 207 */
 208static void drop_file_write_access(struct file *file)
 209{
 210        struct vfsmount *mnt = file->f_path.mnt;
 211        struct dentry *dentry = file->f_path.dentry;
 212        struct inode *inode = dentry->d_inode;
 213
 214        put_write_access(inode);
 215
 216        if (special_file(inode->i_mode))
 217                return;
 218        if (file_check_writeable(file) != 0)
 219                return;
 220        __mnt_drop_write(mnt);
 221        file_release_write(file);
 222}
 223
 224/* the real guts of fput() - releasing the last reference to file
 225 */
 226static void __fput(struct file *file)
 227{
 228        struct dentry *dentry = file->f_path.dentry;
 229        struct vfsmount *mnt = file->f_path.mnt;
 230        struct inode *inode = dentry->d_inode;
 231
 232        might_sleep();
 233
 234        fsnotify_close(file);
 235        /*
 236         * The function eventpoll_release() should be the first called
 237         * in the file cleanup chain.
 238         */
 239        eventpoll_release(file);
 240        locks_remove_flock(file);
 241
 242        if (unlikely(file->f_flags & FASYNC)) {
 243                if (file->f_op && file->f_op->fasync)
 244                        file->f_op->fasync(-1, file, 0);
 245        }
 246        if (file->f_op && file->f_op->release)
 247                file->f_op->release(inode, file);
 248        security_file_free(file);
 249        ima_file_free(file);
 250        if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
 251                     !(file->f_mode & FMODE_PATH))) {
 252                cdev_put(inode->i_cdev);
 253        }
 254        fops_put(file->f_op);
 255        put_pid(file->f_owner.pid);
 256        if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 257                i_readcount_dec(inode);
 258        if (file->f_mode & FMODE_WRITE)
 259                drop_file_write_access(file);
 260        file->f_path.dentry = NULL;
 261        file->f_path.mnt = NULL;
 262        file_free(file);
 263        dput(dentry);
 264        mntput(mnt);
 265}
 266
 267static DEFINE_SPINLOCK(delayed_fput_lock);
 268static LIST_HEAD(delayed_fput_list);
 269static void delayed_fput(struct work_struct *unused)
 270{
 271        LIST_HEAD(head);
 272        spin_lock_irq(&delayed_fput_lock);
 273        list_splice_init(&delayed_fput_list, &head);
 274        spin_unlock_irq(&delayed_fput_lock);
 275        while (!list_empty(&head)) {
 276                struct file *f = list_first_entry(&head, struct file, f_u.fu_list);
 277                list_del_init(&f->f_u.fu_list);
 278                __fput(f);
 279        }
 280}
 281
 282static void ____fput(struct callback_head *work)
 283{
 284        __fput(container_of(work, struct file, f_u.fu_rcuhead));
 285}
 286
 287/*
 288 * If kernel thread really needs to have the final fput() it has done
 289 * to complete, call this.  The only user right now is the boot - we
 290 * *do* need to make sure our writes to binaries on initramfs has
 291 * not left us with opened struct file waiting for __fput() - execve()
 292 * won't work without that.  Please, don't add more callers without
 293 * very good reasons; in particular, never call that with locks
 294 * held and never call that from a thread that might need to do
 295 * some work on any kind of umount.
 296 */
 297void flush_delayed_fput(void)
 298{
 299        delayed_fput(NULL);
 300}
 301
 302static DECLARE_WORK(delayed_fput_work, delayed_fput);
 303
 304void fput(struct file *file)
 305{
 306        if (atomic_long_dec_and_test(&file->f_count)) {
 307                struct task_struct *task = current;
 308                file_sb_list_del(file);
 309                if (unlikely(in_interrupt() || task->flags & PF_KTHREAD)) {
 310                        unsigned long flags;
 311                        spin_lock_irqsave(&delayed_fput_lock, flags);
 312                        list_add(&file->f_u.fu_list, &delayed_fput_list);
 313                        schedule_work(&delayed_fput_work);
 314                        spin_unlock_irqrestore(&delayed_fput_lock, flags);
 315                        return;
 316                }
 317                init_task_work(&file->f_u.fu_rcuhead, ____fput);
 318                task_work_add(task, &file->f_u.fu_rcuhead, true);
 319        }
 320}
 321
 322/*
 323 * synchronous analog of fput(); for kernel threads that might be needed
 324 * in some umount() (and thus can't use flush_delayed_fput() without
 325 * risking deadlocks), need to wait for completion of __fput() and know
 326 * for this specific struct file it won't involve anything that would
 327 * need them.  Use only if you really need it - at the very least,
 328 * don't blindly convert fput() by kernel thread to that.
 329 */
 330void __fput_sync(struct file *file)
 331{
 332        if (atomic_long_dec_and_test(&file->f_count)) {
 333                struct task_struct *task = current;
 334                file_sb_list_del(file);
 335                BUG_ON(!(task->flags & PF_KTHREAD));
 336                __fput(file);
 337        }
 338}
 339
 340EXPORT_SYMBOL(fput);
 341
 342struct file *fget(unsigned int fd)
 343{
 344        struct file *file;
 345        struct files_struct *files = current->files;
 346
 347        rcu_read_lock();
 348        file = fcheck_files(files, fd);
 349        if (file) {
 350                /* File object ref couldn't be taken */
 351                if (file->f_mode & FMODE_PATH ||
 352                    !atomic_long_inc_not_zero(&file->f_count))
 353                        file = NULL;
 354        }
 355        rcu_read_unlock();
 356
 357        return file;
 358}
 359
 360EXPORT_SYMBOL(fget);
 361
 362struct file *fget_raw(unsigned int fd)
 363{
 364        struct file *file;
 365        struct files_struct *files = current->files;
 366
 367        rcu_read_lock();
 368        file = fcheck_files(files, fd);
 369        if (file) {
 370                /* File object ref couldn't be taken */
 371                if (!atomic_long_inc_not_zero(&file->f_count))
 372                        file = NULL;
 373        }
 374        rcu_read_unlock();
 375
 376        return file;
 377}
 378
 379EXPORT_SYMBOL(fget_raw);
 380
 381/*
 382 * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 383 *
 384 * You can use this instead of fget if you satisfy all of the following
 385 * conditions:
 386 * 1) You must call fput_light before exiting the syscall and returning control
 387 *    to userspace (i.e. you cannot remember the returned struct file * after
 388 *    returning to userspace).
 389 * 2) You must not call filp_close on the returned struct file * in between
 390 *    calls to fget_light and fput_light.
 391 * 3) You must not clone the current task in between the calls to fget_light
 392 *    and fput_light.
 393 *
 394 * The fput_needed flag returned by fget_light should be passed to the
 395 * corresponding fput_light.
 396 */
 397struct file *fget_light(unsigned int fd, int *fput_needed)
 398{
 399        struct file *file;
 400        struct files_struct *files = current->files;
 401
 402        *fput_needed = 0;
 403        if (atomic_read(&files->count) == 1) {
 404                file = fcheck_files(files, fd);
 405                if (file && (file->f_mode & FMODE_PATH))
 406                        file = NULL;
 407        } else {
 408                rcu_read_lock();
 409                file = fcheck_files(files, fd);
 410                if (file) {
 411                        if (!(file->f_mode & FMODE_PATH) &&
 412                            atomic_long_inc_not_zero(&file->f_count))
 413                                *fput_needed = 1;
 414                        else
 415                                /* Didn't get the reference, someone's freed */
 416                                file = NULL;
 417                }
 418                rcu_read_unlock();
 419        }
 420
 421        return file;
 422}
 423
 424struct file *fget_raw_light(unsigned int fd, int *fput_needed)
 425{
 426        struct file *file;
 427        struct files_struct *files = current->files;
 428
 429        *fput_needed = 0;
 430        if (atomic_read(&files->count) == 1) {
 431                file = fcheck_files(files, fd);
 432        } else {
 433                rcu_read_lock();
 434                file = fcheck_files(files, fd);
 435                if (file) {
 436                        if (atomic_long_inc_not_zero(&file->f_count))
 437                                *fput_needed = 1;
 438                        else
 439                                /* Didn't get the reference, someone's freed */
 440                                file = NULL;
 441                }
 442                rcu_read_unlock();
 443        }
 444
 445        return file;
 446}
 447
 448void put_filp(struct file *file)
 449{
 450        if (atomic_long_dec_and_test(&file->f_count)) {
 451                security_file_free(file);
 452                file_sb_list_del(file);
 453                file_free(file);
 454        }
 455}
 456
 457static inline int file_list_cpu(struct file *file)
 458{
 459#ifdef CONFIG_SMP
 460        return file->f_sb_list_cpu;
 461#else
 462        return smp_processor_id();
 463#endif
 464}
 465
 466/* helper for file_sb_list_add to reduce ifdefs */
 467static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
 468{
 469        struct list_head *list;
 470#ifdef CONFIG_SMP
 471        int cpu;
 472        cpu = smp_processor_id();
 473        file->f_sb_list_cpu = cpu;
 474        list = per_cpu_ptr(sb->s_files, cpu);
 475#else
 476        list = &sb->s_files;
 477#endif
 478        list_add(&file->f_u.fu_list, list);
 479}
 480
 481/**
 482 * file_sb_list_add - add a file to the sb's file list
 483 * @file: file to add
 484 * @sb: sb to add it to
 485 *
 486 * Use this function to associate a file with the superblock of the inode it
 487 * refers to.
 488 */
 489void file_sb_list_add(struct file *file, struct super_block *sb)
 490{
 491        lg_local_lock(&files_lglock);
 492        __file_sb_list_add(file, sb);
 493        lg_local_unlock(&files_lglock);
 494}
 495
 496/**
 497 * file_sb_list_del - remove a file from the sb's file list
 498 * @file: file to remove
 499 * @sb: sb to remove it from
 500 *
 501 * Use this function to remove a file from its superblock.
 502 */
 503void file_sb_list_del(struct file *file)
 504{
 505        if (!list_empty(&file->f_u.fu_list)) {
 506                lg_local_lock_cpu(&files_lglock, file_list_cpu(file));
 507                list_del_init(&file->f_u.fu_list);
 508                lg_local_unlock_cpu(&files_lglock, file_list_cpu(file));
 509        }
 510}
 511
 512#ifdef CONFIG_SMP
 513
 514/*
 515 * These macros iterate all files on all CPUs for a given superblock.
 516 * files_lglock must be held globally.
 517 */
 518#define do_file_list_for_each_entry(__sb, __file)               \
 519{                                                               \
 520        int i;                                                  \
 521        for_each_possible_cpu(i) {                              \
 522                struct list_head *list;                         \
 523                list = per_cpu_ptr((__sb)->s_files, i);         \
 524                list_for_each_entry((__file), list, f_u.fu_list)
 525
 526#define while_file_list_for_each_entry                          \
 527        }                                                       \
 528}
 529
 530#else
 531
 532#define do_file_list_for_each_entry(__sb, __file)               \
 533{                                                               \
 534        struct list_head *list;                                 \
 535        list = &(sb)->s_files;                                  \
 536        list_for_each_entry((__file), list, f_u.fu_list)
 537
 538#define while_file_list_for_each_entry                          \
 539}
 540
 541#endif
 542
 543/**
 544 *      mark_files_ro - mark all files read-only
 545 *      @sb: superblock in question
 546 *
 547 *      All files are marked read-only.  We don't care about pending
 548 *      delete files so this should be used in 'force' mode only.
 549 */
 550void mark_files_ro(struct super_block *sb)
 551{
 552        struct file *f;
 553
 554        lg_global_lock(&files_lglock);
 555        do_file_list_for_each_entry(sb, f) {
 556                if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
 557                       continue;
 558                if (!file_count(f))
 559                        continue;
 560                if (!(f->f_mode & FMODE_WRITE))
 561                        continue;
 562                spin_lock(&f->f_lock);
 563                f->f_mode &= ~FMODE_WRITE;
 564                spin_unlock(&f->f_lock);
 565                if (file_check_writeable(f) != 0)
 566                        continue;
 567                file_release_write(f);
 568                mnt_drop_write_file(f);
 569        } while_file_list_for_each_entry;
 570        lg_global_unlock(&files_lglock);
 571}
 572
 573void __init files_init(unsigned long mempages)
 574{ 
 575        unsigned long n;
 576
 577        filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 578                        SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 579
 580        /*
 581         * One file with associated inode and dcache is very roughly 1K.
 582         * Per default don't use more than 10% of our memory for files. 
 583         */ 
 584
 585        n = (mempages * (PAGE_SIZE / 1024)) / 10;
 586        files_stat.max_files = max_t(unsigned long, n, NR_FILE);
 587        files_defer_init();
 588        lg_lock_init(&files_lglock, "files_lglock");
 589        percpu_counter_init(&nr_files, 0);
 590} 
 591
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