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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... */ | |
35 | struct files_stat_struct files_stat = { | |
36 | .max_files = NR_FILE | |
37 | }; | |
38 | ||
39 | DEFINE_LGLOCK(files_lglock); | |
40 | ||
41 | /* SLAB cache for file structures */ | |
42 | static struct kmem_cache *filp_cachep __read_mostly; | |
43 | ||
44 | static struct percpu_counter nr_files __cacheline_aligned_in_smp; | |
45 | ||
46 | static inline 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 | ||
54 | static 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 | */ | |
64 | static 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 | */ | |
72 | unsigned long get_max_files(void) | |
73 | { | |
74 | return files_stat.max_files; | |
75 | } | |
76 | EXPORT_SYMBOL_GPL(get_max_files); | |
77 | ||
78 | /* | |
79 | * Handle nr_files sysctl | |
80 | */ | |
81 | #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS) | |
82 | int 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 | |
89 | int 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 | */ | |
106 | struct 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 | ||
141 | over: | |
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 | ||
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 | if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) | |
195 | i_readcount_inc(path->dentry->d_inode); | |
196 | return file; | |
197 | } | |
198 | EXPORT_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 | */ | |
208 | static 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 | */ | |
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 | 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 | ||
267 | static DEFINE_SPINLOCK(delayed_fput_lock); | |
268 | static LIST_HEAD(delayed_fput_list); | |
269 | static 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 | ||
282 | static 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 | */ | |
297 | void flush_delayed_fput(void) | |
298 | { | |
299 | delayed_fput(NULL); | |
300 | } | |
301 | ||
302 | static DECLARE_WORK(delayed_fput_work, delayed_fput); | |
303 | ||
304 | void 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 | */ | |
330 | void __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 | ||
340 | EXPORT_SYMBOL(fput); | |
341 | ||
342 | struct 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 | ||
360 | EXPORT_SYMBOL(fget); | |
361 | ||
362 | struct 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 | ||
379 | EXPORT_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 | */ | |
397 | struct 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 | ||
424 | struct 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 | ||
448 | void 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 | ||
457 | static 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 */ | |
467 | static 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 | */ | |
489 | void 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 | */ | |
503 | void 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 | */ | |
550 | void 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 | ||
573 | void __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 | } |