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 <linux/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 if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) 194 i_readcount_inc(path->dentry->d_inode); 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 !(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 file_sb_list_del(file); 257 if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) 258 i_readcount_dec(inode); 259 if (file->f_mode & FMODE_WRITE) 260 drop_file_write_access(file); 261 file->f_path.dentry = NULL; 262 file->f_path.mnt = NULL; 263 file_free(file); 264 dput(dentry); 265 mntput(mnt); 266 } 267 268 void fput(struct file *file) 269 { 270 if (atomic_long_dec_and_test(&file->f_count)) 271 __fput(file); 272 } 273 274 EXPORT_SYMBOL(fput); 275 276 struct file *fget(unsigned int fd) 277 { 278 struct file *file; 279 struct files_struct *files = current->files; 280 281 rcu_read_lock(); 282 file = fcheck_files(files, fd); 283 if (file) { 284 /* File object ref couldn't be taken */ 285 if (file->f_mode & FMODE_PATH || 286 !atomic_long_inc_not_zero(&file->f_count)) 287 file = NULL; 288 } 289 rcu_read_unlock(); 290 291 return file; 292 } 293 294 EXPORT_SYMBOL(fget); 295 296 struct file *fget_raw(unsigned int fd) 297 { 298 struct file *file; 299 struct files_struct *files = current->files; 300 301 rcu_read_lock(); 302 file = fcheck_files(files, fd); 303 if (file) { 304 /* File object ref couldn't be taken */ 305 if (!atomic_long_inc_not_zero(&file->f_count)) 306 file = NULL; 307 } 308 rcu_read_unlock(); 309 310 return file; 311 } 312 313 EXPORT_SYMBOL(fget_raw); 314 315 /* 316 * Lightweight file lookup - no refcnt increment if fd table isn't shared. 317 * 318 * You can use this instead of fget if you satisfy all of the following 319 * conditions: 320 * 1) You must call fput_light before exiting the syscall and returning control 321 * to userspace (i.e. you cannot remember the returned struct file * after 322 * returning to userspace). 323 * 2) You must not call filp_close on the returned struct file * in between 324 * calls to fget_light and fput_light. 325 * 3) You must not clone the current task in between the calls to fget_light 326 * and fput_light. 327 * 328 * The fput_needed flag returned by fget_light should be passed to the 329 * corresponding fput_light. 330 */ 331 struct file *fget_light(unsigned int fd, int *fput_needed) 332 { 333 struct file *file; 334 struct files_struct *files = current->files; 335 336 *fput_needed = 0; 337 if (atomic_read(&files->count) == 1) { 338 file = fcheck_files(files, fd); 339 if (file && (file->f_mode & FMODE_PATH)) 340 file = NULL; 341 } else { 342 rcu_read_lock(); 343 file = fcheck_files(files, fd); 344 if (file) { 345 if (!(file->f_mode & FMODE_PATH) && 346 atomic_long_inc_not_zero(&file->f_count)) 347 *fput_needed = 1; 348 else 349 /* Didn't get the reference, someone's freed */ 350 file = NULL; 351 } 352 rcu_read_unlock(); 353 } 354 355 return file; 356 } 357 358 struct file *fget_raw_light(unsigned int fd, int *fput_needed) 359 { 360 struct file *file; 361 struct files_struct *files = current->files; 362 363 *fput_needed = 0; 364 if (atomic_read(&files->count) == 1) { 365 file = fcheck_files(files, fd); 366 } else { 367 rcu_read_lock(); 368 file = fcheck_files(files, fd); 369 if (file) { 370 if (atomic_long_inc_not_zero(&file->f_count)) 371 *fput_needed = 1; 372 else 373 /* Didn't get the reference, someone's freed */ 374 file = NULL; 375 } 376 rcu_read_unlock(); 377 } 378 379 return file; 380 } 381 382 void put_filp(struct file *file) 383 { 384 if (atomic_long_dec_and_test(&file->f_count)) { 385 security_file_free(file); 386 file_sb_list_del(file); 387 file_free(file); 388 } 389 } 390 391 static inline int file_list_cpu(struct file *file) 392 { 393 #ifdef CONFIG_SMP 394 return file->f_sb_list_cpu; 395 #else 396 return smp_processor_id(); 397 #endif 398 } 399 400 /* helper for file_sb_list_add to reduce ifdefs */ 401 static inline void __file_sb_list_add(struct file *file, struct super_block *sb) 402 { 403 struct list_head *list; 404 #ifdef CONFIG_SMP 405 int cpu; 406 cpu = smp_processor_id(); 407 file->f_sb_list_cpu = cpu; 408 list = per_cpu_ptr(sb->s_files, cpu); 409 #else 410 list = &sb->s_files; 411 #endif 412 list_add(&file->f_u.fu_list, list); 413 } 414 415 /** 416 * file_sb_list_add - add a file to the sb's file list 417 * @file: file to add 418 * @sb: sb to add it to 419 * 420 * Use this function to associate a file with the superblock of the inode it 421 * refers to. 422 */ 423 void file_sb_list_add(struct file *file, struct super_block *sb) 424 { 425 lg_local_lock(files_lglock); 426 __file_sb_list_add(file, sb); 427 lg_local_unlock(files_lglock); 428 } 429 430 /** 431 * file_sb_list_del - remove a file from the sb's file list 432 * @file: file to remove 433 * @sb: sb to remove it from 434 * 435 * Use this function to remove a file from its superblock. 436 */ 437 void file_sb_list_del(struct file *file) 438 { 439 if (!list_empty(&file->f_u.fu_list)) { 440 lg_local_lock_cpu(files_lglock, file_list_cpu(file)); 441 list_del_init(&file->f_u.fu_list); 442 lg_local_unlock_cpu(files_lglock, file_list_cpu(file)); 443 } 444 } 445 446 #ifdef CONFIG_SMP 447 448 /* 449 * These macros iterate all files on all CPUs for a given superblock. 450 * files_lglock must be held globally. 451 */ 452 #define do_file_list_for_each_entry(__sb, __file) \ 453 { \ 454 int i; \ 455 for_each_possible_cpu(i) { \ 456 struct list_head *list; \ 457 list = per_cpu_ptr((__sb)->s_files, i); \ 458 list_for_each_entry((__file), list, f_u.fu_list) 459 460 #define while_file_list_for_each_entry \ 461 } \ 462 } 463 464 #else 465 466 #define do_file_list_for_each_entry(__sb, __file) \ 467 { \ 468 struct list_head *list; \ 469 list = &(sb)->s_files; \ 470 list_for_each_entry((__file), list, f_u.fu_list) 471 472 #define while_file_list_for_each_entry \ 473 } 474 475 #endif 476 477 int fs_may_remount_ro(struct super_block *sb) 478 { 479 struct file *file; 480 /* Check that no files are currently opened for writing. */ 481 lg_global_lock(files_lglock); 482 do_file_list_for_each_entry(sb, file) { 483 struct inode *inode = file->f_path.dentry->d_inode; 484 485 /* File with pending delete? */ 486 if (inode->i_nlink == 0) 487 goto too_bad; 488 489 /* Writeable file? */ 490 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE)) 491 goto too_bad; 492 } while_file_list_for_each_entry; 493 lg_global_unlock(files_lglock); 494 return 1; /* Tis' cool bro. */ 495 too_bad: 496 lg_global_unlock(files_lglock); 497 return 0; 498 } 499 500 /** 501 * mark_files_ro - mark all files read-only 502 * @sb: superblock in question 503 * 504 * All files are marked read-only. We don't care about pending 505 * delete files so this should be used in 'force' mode only. 506 */ 507 void mark_files_ro(struct super_block *sb) 508 { 509 struct file *f; 510 511 retry: 512 lg_global_lock(files_lglock); 513 do_file_list_for_each_entry(sb, f) { 514 struct vfsmount *mnt; 515 if (!S_ISREG(f->f_path.dentry->d_inode->i_mode)) 516 continue; 517 if (!file_count(f)) 518 continue; 519 if (!(f->f_mode & FMODE_WRITE)) 520 continue; 521 spin_lock(&f->f_lock); 522 f->f_mode &= ~FMODE_WRITE; 523 spin_unlock(&f->f_lock); 524 if (file_check_writeable(f) != 0) 525 continue; 526 file_release_write(f); 527 mnt = mntget(f->f_path.mnt); 528 /* This can sleep, so we can't hold the spinlock. */ 529 lg_global_unlock(files_lglock); 530 mnt_drop_write(mnt); 531 mntput(mnt); 532 goto retry; 533 } while_file_list_for_each_entry; 534 lg_global_unlock(files_lglock); 535 } 536 537 void __init files_init(unsigned long mempages) 538 { 539 unsigned long n; 540 541 filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0, 542 SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); 543 544 /* 545 * One file with associated inode and dcache is very roughly 1K. 546 * Per default don't use more than 10% of our memory for files. 547 */ 548 549 n = (mempages * (PAGE_SIZE / 1024)) / 10; 550 files_stat.max_files = max_t(unsigned long, n, NR_FILE); 551 files_defer_init(); 552 lg_lock_init(files_lglock); 553 percpu_counter_init(&nr_files, 0); 554 } 555