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 (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 } 505