Root/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... */
33struct files_stat_struct files_stat = {
34    .max_files = NR_FILE
35};
36
37DECLARE_LGLOCK(files_lglock);
38DEFINE_LGLOCK(files_lglock);
39
40/* SLAB cache for file structures */
41static struct kmem_cache *filp_cachep __read_mostly;
42
43static struct percpu_counter nr_files __cacheline_aligned_in_smp;
44
45static 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
53static 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 */
63static 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 */
71unsigned long get_max_files(void)
72{
73    return files_stat.max_files;
74}
75EXPORT_SYMBOL_GPL(get_max_files);
76
77/*
78 * Handle nr_files sysctl
79 */
80#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
81int 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
88int 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 */
105struct 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
140over:
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
148fail_sec:
149    file_free(f);
150fail:
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 */
169struct 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}
197EXPORT_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 */
207void 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}
222EXPORT_SYMBOL_GPL(drop_file_write_access);
223
224/* the real guts of fput() - releasing the last reference to file
225 */
226static 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
268void fput(struct file *file)
269{
270    if (atomic_long_dec_and_test(&file->f_count))
271        __fput(file);
272}
273
274EXPORT_SYMBOL(fput);
275
276struct 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
294EXPORT_SYMBOL(fget);
295
296struct 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
313EXPORT_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 */
331struct 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
358struct 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
382void 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
391static 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 */
401static 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 */
423void 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 */
437void 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
477int 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. */
495too_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 */
507void mark_files_ro(struct super_block *sb)
508{
509    struct file *f;
510
511retry:
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
537void __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

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