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 long 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 unsigned long 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_doulongvec_minmax(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 long 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         f->f_cred = get_cred(cred);
 129         if (security_file_alloc(f))
 130                 goto fail_sec;
 131
 132         INIT_LIST_HEAD(&f->f_u.fu_list);
 133         atomic_long_set(&f->f_count, 1);
 134         rwlock_init(&f->f_owner.lock);
 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                 pr_info("VFS: file-max limit %lu reached\n", get_max_files());
 144                 old_max = get_nr_files();
 145         }
 146         goto fail;
 147
 148 fail_sec:
 149         file_free(f);
 150 fail:
 151         return NULL;
 152 }
 153
 154 /**
 155  * alloc_file - allocate and initialize a 'struct file'
 156  * @mnt: the vfsmount on which the file will reside
 157  * @dentry: the dentry representing the new file
 158  * @mode: the mode with which the new file will be opened
 159  * @fop: the 'struct file_operations' for the new file
 160  *
 161  * Use this instead of get_empty_filp() to get a new
 162  * 'struct file'.  Do so because of the same initialization
 163  * pitfalls reasons listed for init_file().  This is a
 164  * preferred interface to using init_file().
 165  *
 166  * If all the callers of init_file() are eliminated, its
 167  * code should be moved into this function.
 168  */
 169 struct file *alloc_file(struct path *path, fmode_t mode,
 170                 const struct file_operations *fop)
 171 {
 172         struct file *file;
 173
 174         file = get_empty_filp();
 175         if (!file)
 176                 return NULL;
 177
 178         file->f_path = *path;
 179         file->f_mapping = path->dentry->d_inode->i_mapping;
 180         file->f_mode = mode;
 181         file->f_op = fop;
 182
 183         /*
 184          * These mounts don't really matter in practice
 185          * for r/o bind mounts.  They aren't userspace-
 186          * visible.  We do this for consistency, and so
 187          * that we can do debugging checks at __fput()
 188          */
 189         if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
 190                 file_take_write(file);
 191                 WARN_ON(mnt_clone_write(path->mnt));
 192         }
 193         ima_counts_get(file);
 194         return file;
 195 }
 196 EXPORT_SYMBOL(alloc_file);
 197
 198 /**
 199  * drop_file_write_access - give up ability to write to a file
 200  * @file: the file to which we will stop writing
 201  *
 202  * This is a central place which will give up the ability
 203  * to write to @file, along with access to write through
 204  * its vfsmount.
 205  */
 206 void drop_file_write_access(struct file *file)
 207 {
 208         struct vfsmount *mnt = file->f_path.mnt;
 209         struct dentry *dentry = file->f_path.dentry;
 210         struct inode *inode = dentry->d_inode;
 211
 212         put_write_access(inode);
 213
 214         if (special_file(inode->i_mode))
 215                 return;
 216         if (file_check_writeable(file) != 0)
 217                 return;
 218         mnt_drop_write(mnt);
 219         file_release_write(file);
 220 }
 221 EXPORT_SYMBOL_GPL(drop_file_write_access);
 222
 223 /* the real guts of fput() - releasing the last reference to file
 224  */
 225 static void __fput(struct file *file)
 226 {
 227         struct dentry *dentry = file->f_path.dentry;
 228         struct vfsmount *mnt = file->f_path.mnt;
 229         struct inode *inode = dentry->d_inode;
 230
 231         might_sleep();
 232
 233         fsnotify_close(file);
 234         /*
 235          * The function eventpoll_release() should be the first called
 236          * in the file cleanup chain.
 237          */
 238         eventpoll_release(file);
 239         locks_remove_flock(file);
 240
 241         if (unlikely(file->f_flags & FASYNC)) {
 242                 if (file->f_op && file->f_op->fasync)
 243                         file->f_op->fasync(-1, file, 0);
 244         }
 245         if (file->f_op && file->f_op->release)
 246                 file->f_op->release(inode, file);
 247         security_file_free(file);
 248         ima_file_free(file);
 249         if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
 250                 cdev_put(inode->i_cdev);
 251         fops_put(file->f_op);
 252         put_pid(file->f_owner.pid);
 253         file_sb_list_del(file);
 254         if (file->f_mode & FMODE_WRITE)
 255                 drop_file_write_access(file);
 256         file->f_path.dentry = NULL;
 257         file->f_path.mnt = NULL;
 258         file_free(file);
 259         dput(dentry);
 260         mntput(mnt);
 261 }
 262
 263 void fput(struct file *file)
 264 {
 265         if (atomic_long_dec_and_test(&file->f_count))
 266                 __fput(file);
 267 }
 268
 269 EXPORT_SYMBOL(fput);
 270
 271 struct file *fget(unsigned int fd)
 272 {
 273         struct file *file;
 274         struct files_struct *files = current->files;
 275
 276         rcu_read_lock();
 277         file = fcheck_files(files, fd);
 278         if (file) {
 279                 if (!atomic_long_inc_not_zero(&file->f_count)) {
 280                         /* File object ref couldn't be taken */
 281                         rcu_read_unlock();
 282                         return NULL;
 283                 }
 284         }
 285         rcu_read_unlock();
 286
 287         return file;
 288 }
 289
 290 EXPORT_SYMBOL(fget);
 291
 292 /*
 293  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 294  *
 295  * You can use this instead of fget if you satisfy all of the following
 296  * conditions:
 297  * 1) You must call fput_light before exiting the syscall and returning control
 298  *    to userspace (i.e. you cannot remember the returned struct file * after
 299  *    returning to userspace).
 300  * 2) You must not call filp_close on the returned struct file * in between
 301  *    calls to fget_light and fput_light.
 302  * 3) You must not clone the current task in between the calls to fget_light
 303  *    and fput_light.
 304  *
 305  * The fput_needed flag returned by fget_light should be passed to the
 306  * corresponding fput_light.
 307  */
 308 struct file *fget_light(unsigned int fd, int *fput_needed)
 309 {
 310         struct file *file;
 311         struct files_struct *files = current->files;
 312
 313         *fput_needed = 0;
 314         if (likely((atomic_read(&files->count) == 1))) {
 315                 file = fcheck_files(files, fd);
 316         } else {
 317                 rcu_read_lock();
 318                 file = fcheck_files(files, fd);
 319                 if (file) {
 320                         if (atomic_long_inc_not_zero(&file->f_count))
 321                                 *fput_needed = 1;
 322                         else
 323                                 /* Didn't get the reference, someone's freed */
 324                                 file = NULL;
 325                 }
 326                 rcu_read_unlock();
 327         }
 328
 329         return file;
 330 }
 331
 332 void put_filp(struct file *file)
 333 {
 334         if (atomic_long_dec_and_test(&file->f_count)) {
 335                 security_file_free(file);
 336                 file_sb_list_del(file);
 337                 file_free(file);
 338         }
 339 }
 340
 341 static inline int file_list_cpu(struct file *file)
 342 {
 343 #ifdef CONFIG_SMP
 344         return file->f_sb_list_cpu;
 345 #else
 346         return smp_processor_id();
 347 #endif
 348 }
 349
 350 /* helper for file_sb_list_add to reduce ifdefs */
 351 static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
 352 {
 353         struct list_head *list;
 354 #ifdef CONFIG_SMP
 355         int cpu;
 356         cpu = smp_processor_id();
 357         file->f_sb_list_cpu = cpu;
 358         list = per_cpu_ptr(sb->s_files, cpu);
 359 #else
 360         list = &sb->s_files;
 361 #endif
 362         list_add(&file->f_u.fu_list, list);
 363 }
 364
 365 /**
 366  * file_sb_list_add - add a file to the sb's file list
 367  * @file: file to add
 368  * @sb: sb to add it to
 369  *
 370  * Use this function to associate a file with the superblock of the inode it
 371  * refers to.
 372  */
 373 void file_sb_list_add(struct file *file, struct super_block *sb)
 374 {
 375         lg_local_lock(files_lglock);
 376         __file_sb_list_add(file, sb);
 377         lg_local_unlock(files_lglock);
 378 }
 379
 380 /**
 381  * file_sb_list_del - remove a file from the sb's file list
 382  * @file: file to remove
 383  * @sb: sb to remove it from
 384  *
 385  * Use this function to remove a file from its superblock.
 386  */
 387 void file_sb_list_del(struct file *file)
 388 {
 389         if (!list_empty(&file->f_u.fu_list)) {
 390                 lg_local_lock_cpu(files_lglock, file_list_cpu(file));
 391                 list_del_init(&file->f_u.fu_list);
 392                 lg_local_unlock_cpu(files_lglock, file_list_cpu(file));
 393         }
 394 }
 395
 396 #ifdef CONFIG_SMP
 397
 398 /*
 399  * These macros iterate all files on all CPUs for a given superblock.
 400  * files_lglock must be held globally.
 401  */
 402 #define do_file_list_for_each_entry(__sb, __file)               \
 403 {                                                               \
 404         int i;                                                  \
 405         for_each_possible_cpu(i) {                              \
 406                 struct list_head *list;                         \
 407                 list = per_cpu_ptr((__sb)->s_files, i);         \
 408                 list_for_each_entry((__file), list, f_u.fu_list)
 409
 410 #define while_file_list_for_each_entry                          \
 411         }                                                       \
 412 }
 413
 414 #else
 415
 416 #define do_file_list_for_each_entry(__sb, __file)               \
 417 {                                                               \
 418         struct list_head *list;                                 \
 419         list = &(sb)->s_files;                                  \
 420         list_for_each_entry((__file), list, f_u.fu_list)
 421
 422 #define while_file_list_for_each_entry                          \
 423 }
 424
 425 #endif
 426
 427 int fs_may_remount_ro(struct super_block *sb)
 428 {
 429         struct file *file;
 430         /* Check that no files are currently opened for writing. */
 431         lg_global_lock(files_lglock);
 432         do_file_list_for_each_entry(sb, file) {
 433                 struct inode *inode = file->f_path.dentry->d_inode;
 434
 435                 /* File with pending delete? */
 436                 if (inode->i_nlink == 0)
 437                         goto too_bad;
 438
 439                 /* Writeable file? */
 440                 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
 441                         goto too_bad;
 442         } while_file_list_for_each_entry;
 443         lg_global_unlock(files_lglock);
 444         return 1; /* Tis' cool bro. */
 445 too_bad:
 446         lg_global_unlock(files_lglock);
 447         return 0;
 448 }
 449
 450 /**
 451  *      mark_files_ro - mark all files read-only
 452  *      @sb: superblock in question
 453  *
 454  *      All files are marked read-only.  We don't care about pending
 455  *      delete files so this should be used in 'force' mode only.
 456  */
 457 void mark_files_ro(struct super_block *sb)
 458 {
 459         struct file *f;
 460
 461 retry:
 462         lg_global_lock(files_lglock);
 463         do_file_list_for_each_entry(sb, f) {
 464                 struct vfsmount *mnt;
 465                 if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
 466                        continue;
 467                 if (!file_count(f))
 468                         continue;
 469                 if (!(f->f_mode & FMODE_WRITE))
 470                         continue;
 471                 spin_lock(&f->f_lock);
 472                 f->f_mode &= ~FMODE_WRITE;
 473                 spin_unlock(&f->f_lock);
 474                 if (file_check_writeable(f) != 0)
 475                         continue;
 476                 file_release_write(f);
 477                 mnt = mntget(f->f_path.mnt);
 478                 /* This can sleep, so we can't hold the spinlock. */
 479                 lg_global_unlock(files_lglock);
 480                 mnt_drop_write(mnt);
 481                 mntput(mnt);
 482                 goto retry;
 483         } while_file_list_for_each_entry;
 484         lg_global_unlock(files_lglock);
 485 }
 486
 487 void __init files_init(unsigned long mempages)
 488 {
 489         unsigned long n;
 490
 491         filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 492                         SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 493
 494         /*
 495          * One file with associated inode and dcache is very roughly 1K.
 496          * Per default don't use more than 10% of our memory for files.
 497          */
 498
 499         n = (mempages * (PAGE_SIZE / 1024)) / 10;
 500         files_stat.max_files = max_t(unsigned long, n, NR_FILE);
 501         files_defer_init();
 502         lg_lock_init(files_lglock);
 503         percpu_counter_init(&nr_files, 0);
 504 }