fs/file_table.c

   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/ima.h>
  27
  28 #include <asm/atomic.h>
  29
  30 #include "internal.h"
  31
  32 /* sysctl tunables... */
  33 struct files_stat_struct files_stat = {
  34         .max_files = NR_FILE
  35 };
  36
  37 DECLARE_LGLOCK(files_lglock);
  38 DEFINE_LGLOCK(files_lglock);
  39
  40 /* SLAB cache for file structures */
  41 static struct kmem_cache *filp_cachep __read_mostly;
  42
  43 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  44
  45 static inline void file_free_rcu(struct rcu_head *head)
  46 {
  47         struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
  48
  49         put_cred(f->f_cred);
  50         kmem_cache_free(filp_cachep, f);
  51 }
  52
  53 static inline void file_free(struct file *f)
  54 {
  55         percpu_counter_dec(&nr_files);
  56         file_check_state(f);
  57         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  58 }
  59
  60 /*
  61  * Return the total number of open files in the system
  62  */
  63 static int get_nr_files(void)
  64 {
  65         return percpu_counter_read_positive(&nr_files);
  66 }
  67
  68 /*
  69  * Return the maximum number of open files in the system
  70  */
  71 int get_max_files(void)
  72 {
  73         return files_stat.max_files;
  74 }
  75 EXPORT_SYMBOL_GPL(get_max_files);
  76
  77 /*
  78  * Handle nr_files sysctl
  79  */
  80 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  81 int proc_nr_files(ctl_table *table, int write,
  82                      void __user *buffer, size_t *lenp, loff_t *ppos)
  83 {
  84         files_stat.nr_files = get_nr_files();
  85         return proc_dointvec(table, write, buffer, lenp, ppos);
  86 }
  87 #else
  88 int proc_nr_files(ctl_table *table, int write,
  89                      void __user *buffer, size_t *lenp, loff_t *ppos)
  90 {
  91         return -ENOSYS;
  92 }
  93 #endif
  94
  95 /* Find an unused file structure and return a pointer to it.
  96  * Returns NULL, if there are no more free file structures or
  97  * we run out of memory.
  98  *
  99  * Be very careful using this.  You are responsible for
 100  * getting write access to any mount that you might assign
 101  * to this filp, if it is opened for write.  If this is not
 102  * done, you will imbalance int the mount's writer count
 103  * and a warning at __fput() time.
 104  */
 105 struct file *get_empty_filp(void)
 106 {
 107         const struct cred *cred = current_cred();
 108         static int old_max;
 109         struct file * f;
 110
 111         /*
 112          * Privileged users can go above max_files
 113          */
 114         if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
 115                 /*
 116                  * percpu_counters are inaccurate.  Do an expensive check before
 117                  * we go and fail.
 118                  */
 119                 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
 120                         goto over;
 121         }
 122
 123         f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
 124         if (f == NULL)
 125                 goto fail;
 126
 127         percpu_counter_inc(&nr_files);
 128         if (security_file_alloc(f))
 129                 goto fail_sec;
 130
 131         INIT_LIST_HEAD(&f->f_u.fu_list);
 132         atomic_long_set(&f->f_count, 1);
 133         rwlock_init(&f->f_owner.lock);
 134         f->f_cred = get_cred(cred);
 135         spin_lock_init(&f->f_lock);
 136         eventpoll_init_file(f);
 137         /* f->f_version: 0 */
 138         return f;
 139
 140 over:
 141         /* Ran out of filps - report that */
 142         if (get_nr_files() > old_max) {
 143                 printk(KERN_INFO "VFS: file-max limit %d reached\n",
 144                                         get_max_files());
 145                 old_max = get_nr_files();
 146         }
 147         goto fail;
 148
 149 fail_sec:
 150         file_free(f);
 151 fail:
 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  */
 170 struct 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         ima_counts_get(file);
 195         return file;
 196 }
 197 EXPORT_SYMBOL(alloc_file);
 198
 199 /**
 200  * drop_file_write_access - give up ability to write to a file
 201  * @file: the file to which we will stop writing
 202  *
 203  * This is a central place which will give up the ability
 204  * to write to @file, along with access to write through
 205  * its vfsmount.
 206  */
 207 void drop_file_write_access(struct file *file)
 208 {
 209         struct vfsmount *mnt = file->f_path.mnt;
 210         struct dentry *dentry = file->f_path.dentry;
 211         struct inode *inode = dentry->d_inode;
 212
 213         put_write_access(inode);
 214
 215         if (special_file(inode->i_mode))
 216                 return;
 217         if (file_check_writeable(file) != 0)
 218                 return;
 219         mnt_drop_write(mnt);
 220         file_release_write(file);
 221 }
 222 EXPORT_SYMBOL_GPL(drop_file_write_access);
 223
 224 /* the real guts of fput() - releasing the last reference to file
 225  */
 226 static 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                 cdev_put(inode->i_cdev);
 252         fops_put(file->f_op);
 253         put_pid(file->f_owner.pid);
 254         file_sb_list_del(file);
 255         if (file->f_mode & FMODE_WRITE)
 256                 drop_file_write_access(file);
 257         file->f_path.dentry = NULL;
 258         file->f_path.mnt = NULL;
 259         file_free(file);
 260         dput(dentry);
 261         mntput(mnt);
 262 }
 263
 264 void fput(struct file *file)
 265 {
 266         if (atomic_long_dec_and_test(&file->f_count))
 267                 __fput(file);
 268 }
 269
 270 EXPORT_SYMBOL(fput);
 271
 272 struct file *fget(unsigned int fd)
 273 {
 274         struct file *file;
 275         struct files_struct *files = current->files;
 276
 277         rcu_read_lock();
 278         file = fcheck_files(files, fd);
 279         if (file) {
 280                 if (!atomic_long_inc_not_zero(&file->f_count)) {
 281                         /* File object ref couldn't be taken */
 282                         rcu_read_unlock();
 283                         return NULL;
 284                 }
 285         }
 286         rcu_read_unlock();
 287
 288         return file;
 289 }
 290
 291 EXPORT_SYMBOL(fget);
 292
 293 /*
 294  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 295  *
 296  * You can use this instead of fget if you satisfy all of the following
 297  * conditions:
 298  * 1) You must call fput_light before exiting the syscall and returning control
 299  *    to userspace (i.e. you cannot remember the returned struct file * after
 300  *    returning to userspace).
 301  * 2) You must not call filp_close on the returned struct file * in between
 302  *    calls to fget_light and fput_light.
 303  * 3) You must not clone the current task in between the calls to fget_light
 304  *    and fput_light.
 305  *
 306  * The fput_needed flag returned by fget_light should be passed to the
 307  * corresponding fput_light.
 308  */
 309 struct file *fget_light(unsigned int fd, int *fput_needed)
 310 {
 311         struct file *file;
 312         struct files_struct *files = current->files;
 313
 314         *fput_needed = 0;
 315         if (likely((atomic_read(&files->count) == 1))) {
 316                 file = fcheck_files(files, fd);
 317         } else {
 318                 rcu_read_lock();
 319                 file = fcheck_files(files, fd);
 320                 if (file) {
 321                         if (atomic_long_inc_not_zero(&file->f_count))
 322                                 *fput_needed = 1;
 323                         else
 324                                 /* Didn't get the reference, someone's freed */
 325                                 file = NULL;
 326                 }
 327                 rcu_read_unlock();
 328         }
 329
 330         return file;
 331 }
 332
 333 void put_filp(struct file *file)
 334 {
 335         if (atomic_long_dec_and_test(&file->f_count)) {
 336                 security_file_free(file);
 337                 file_sb_list_del(file);
 338                 file_free(file);
 339         }
 340 }
 341
 342 static inline int file_list_cpu(struct file *file)
 343 {
 344 #ifdef CONFIG_SMP
 345         return file->f_sb_list_cpu;
 346 #else
 347         return smp_processor_id();
 348 #endif
 349 }
 350
 351 /* helper for file_sb_list_add to reduce ifdefs */
 352 static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
 353 {
 354         struct list_head *list;
 355 #ifdef CONFIG_SMP
 356         int cpu;
 357         cpu = smp_processor_id();
 358         file->f_sb_list_cpu = cpu;
 359         list = per_cpu_ptr(sb->s_files, cpu);
 360 #else
 361         list = &sb->s_files;
 362 #endif
 363         list_add(&file->f_u.fu_list, list);
 364 }
 365
 366 /**
 367  * file_sb_list_add - add a file to the sb's file list
 368  * @file: file to add
 369  * @sb: sb to add it to
 370  *
 371  * Use this function to associate a file with the superblock of the inode it
 372  * refers to.
 373  */
 374 void file_sb_list_add(struct file *file, struct super_block *sb)
 375 {
 376         lg_local_lock(files_lglock);
 377         __file_sb_list_add(file, sb);
 378         lg_local_unlock(files_lglock);
 379 }
 380
 381 /**
 382  * file_sb_list_del - remove a file from the sb's file list
 383  * @file: file to remove
 384  * @sb: sb to remove it from
 385  *
 386  * Use this function to remove a file from its superblock.
 387  */
 388 void file_sb_list_del(struct file *file)
 389 {
 390         if (!list_empty(&file->f_u.fu_list)) {
 391                 lg_local_lock_cpu(files_lglock, file_list_cpu(file));
 392                 list_del_init(&file->f_u.fu_list);
 393                 lg_local_unlock_cpu(files_lglock, file_list_cpu(file));
 394         }
 395 }
 396
 397 #ifdef CONFIG_SMP
 398
 399 /*
 400  * These macros iterate all files on all CPUs for a given superblock.
 401  * files_lglock must be held globally.
 402  */
 403 #define do_file_list_for_each_entry(__sb, __file)               \
 404 {                                                               \
 405         int i;                                                  \
 406         for_each_possible_cpu(i) {                              \
 407                 struct list_head *list;                         \
 408                 list = per_cpu_ptr((__sb)->s_files, i);         \
 409                 list_for_each_entry((__file), list, f_u.fu_list)
 410
 411 #define while_file_list_for_each_entry                          \
 412         }                                                       \
 413 }
 414
 415 #else
 416
 417 #define do_file_list_for_each_entry(__sb, __file)               \
 418 {                                                               \
 419         struct list_head *list;                                 \
 420         list = &(sb)->s_files;                                  \
 421         list_for_each_entry((__file), list, f_u.fu_list)
 422
 423 #define while_file_list_for_each_entry                          \
 424 }
 425
 426 #endif
 427
 428 int fs_may_remount_ro(struct super_block *sb)
 429 {
 430         struct file *file;
 431         /* Check that no files are currently opened for writing. */
 432         lg_global_lock(files_lglock);
 433         do_file_list_for_each_entry(sb, file) {
 434                 struct inode *inode = file->f_path.dentry->d_inode;
 435
 436                 /* File with pending delete? */
 437                 if (inode->i_nlink == 0)
 438                         goto too_bad;
 439
 440                 /* Writeable file? */
 441                 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
 442                         goto too_bad;
 443         } while_file_list_for_each_entry;
 444         lg_global_unlock(files_lglock);
 445         return 1; /* Tis' cool bro. */
 446 too_bad:
 447         lg_global_unlock(files_lglock);
 448         return 0;
 449 }
 450
 451 /**
 452  *      mark_files_ro - mark all files read-only
 453  *      @sb: superblock in question
 454  *
 455  *      All files are marked read-only.  We don't care about pending
 456  *      delete files so this should be used in 'force' mode only.
 457  */
 458 void mark_files_ro(struct super_block *sb)
 459 {
 460         struct file *f;
 461
 462 retry:
 463         lg_global_lock(files_lglock);
 464         do_file_list_for_each_entry(sb, f) {
 465                 struct vfsmount *mnt;
 466                 if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
 467                        continue;
 468                 if (!file_count(f))
 469                         continue;
 470                 if (!(f->f_mode & FMODE_WRITE))
 471                         continue;
 472                 spin_lock(&f->f_lock);
 473                 f->f_mode &= ~FMODE_WRITE;
 474                 spin_unlock(&f->f_lock);
 475                 if (file_check_writeable(f) != 0)
 476                         continue;
 477                 file_release_write(f);
 478                 mnt = mntget(f->f_path.mnt);
 479                 /* This can sleep, so we can't hold the spinlock. */
 480                 lg_global_unlock(files_lglock);
 481                 mnt_drop_write(mnt);
 482                 mntput(mnt);
 483                 goto retry;
 484         } while_file_list_for_each_entry;
 485         lg_global_unlock(files_lglock);
 486 }
 487
 488 void __init files_init(unsigned long mempages)
 489 {
 490         int n;
 491
 492         filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 493                         SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 494
 495         /*
 496          * One file with associated inode and dcache is very roughly 1K.
 497          * Per default don't use more than 10% of our memory for files.
 498          */
 499
 500         n = (mempages * (PAGE_SIZE / 1024)) / 10;
 501         files_stat.max_files = n;
 502         if (files_stat.max_files < NR_FILE)
 503                 files_stat.max_files = NR_FILE;
 504         files_defer_init();
 505         lg_lock_init(files_lglock);
 506         percpu_counter_init(&nr_files, 0);
 507 }