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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/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 | 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 | 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 | } |