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/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... */
35struct files_stat_struct files_stat = {
36    .max_files = NR_FILE
37};
38
39DEFINE_STATIC_LGLOCK(files_lglock);
40
41/* SLAB cache for file structures */
42static struct kmem_cache *filp_cachep __read_mostly;
43
44static struct percpu_counter nr_files __cacheline_aligned_in_smp;
45
46static 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
54static 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 */
64static 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 */
72unsigned long get_max_files(void)
73{
74    return files_stat.max_files;
75}
76EXPORT_SYMBOL_GPL(get_max_files);
77
78/*
79 * Handle nr_files sysctl
80 */
81#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
82int 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
89int 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 an error pointer if some error happend e.g. we over file
98 * structures limit, run out of memory or operation is not permitted.
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 */
106struct file *get_empty_filp(void)
107{
108    const struct cred *cred = current_cred();
109    static long old_max;
110    struct file *f;
111    int error;
112
113    /*
114     * Privileged users can go above max_files
115     */
116    if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
117        /*
118         * percpu_counters are inaccurate. Do an expensive check before
119         * we go and fail.
120         */
121        if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
122            goto over;
123    }
124
125    f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
126    if (unlikely(!f))
127        return ERR_PTR(-ENOMEM);
128
129    percpu_counter_inc(&nr_files);
130    f->f_cred = get_cred(cred);
131    error = security_file_alloc(f);
132    if (unlikely(error)) {
133        file_free(f);
134        return ERR_PTR(error);
135    }
136
137    INIT_LIST_HEAD(&f->f_u.fu_list);
138    atomic_long_set(&f->f_count, 1);
139    rwlock_init(&f->f_owner.lock);
140    spin_lock_init(&f->f_lock);
141    eventpoll_init_file(f);
142    /* f->f_version: 0 */
143    return f;
144
145over:
146    /* Ran out of filps - report that */
147    if (get_nr_files() > old_max) {
148        pr_info("VFS: file-max limit %lu reached\n", get_max_files());
149        old_max = get_nr_files();
150    }
151    return ERR_PTR(-ENFILE);
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 (IS_ERR(file))
176        return file;
177
178    file->f_path = *path;
179    file->f_inode = path->dentry->d_inode;
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}
198EXPORT_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 */
208static 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 */
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 = file->f_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    ima_file_free(file);
247    if (file->f_op && file->f_op->release)
248        file->f_op->release(inode, file);
249    security_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->f_inode = NULL;
263    file_free(file);
264    dput(dentry);
265    mntput(mnt);
266}
267
268static LLIST_HEAD(delayed_fput_list);
269static void delayed_fput(struct work_struct *unused)
270{
271    struct llist_node *node = llist_del_all(&delayed_fput_list);
272    struct llist_node *next;
273
274    for (; node; node = next) {
275        next = llist_next(node);
276        __fput(llist_entry(node, struct file, f_u.fu_llist));
277    }
278}
279
280static void ____fput(struct callback_head *work)
281{
282    __fput(container_of(work, struct file, f_u.fu_rcuhead));
283}
284
285/*
286 * If kernel thread really needs to have the final fput() it has done
287 * to complete, call this. The only user right now is the boot - we
288 * *do* need to make sure our writes to binaries on initramfs has
289 * not left us with opened struct file waiting for __fput() - execve()
290 * won't work without that. Please, don't add more callers without
291 * very good reasons; in particular, never call that with locks
292 * held and never call that from a thread that might need to do
293 * some work on any kind of umount.
294 */
295void flush_delayed_fput(void)
296{
297    delayed_fput(NULL);
298}
299
300static DECLARE_WORK(delayed_fput_work, delayed_fput);
301
302void fput(struct file *file)
303{
304    if (atomic_long_dec_and_test(&file->f_count)) {
305        struct task_struct *task = current;
306
307        file_sb_list_del(file);
308        if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
309            init_task_work(&file->f_u.fu_rcuhead, ____fput);
310            if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
311                return;
312            /*
313             * After this task has run exit_task_work(),
314             * task_work_add() will fail. free_ipc_ns()->
315             * shm_destroy() can do this. Fall through to delayed
316             * fput to avoid leaking *file.
317             */
318        }
319
320        if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
321            schedule_work(&delayed_fput_work);
322    }
323}
324
325/*
326 * synchronous analog of fput(); for kernel threads that might be needed
327 * in some umount() (and thus can't use flush_delayed_fput() without
328 * risking deadlocks), need to wait for completion of __fput() and know
329 * for this specific struct file it won't involve anything that would
330 * need them. Use only if you really need it - at the very least,
331 * don't blindly convert fput() by kernel thread to that.
332 */
333void __fput_sync(struct file *file)
334{
335    if (atomic_long_dec_and_test(&file->f_count)) {
336        struct task_struct *task = current;
337        file_sb_list_del(file);
338        BUG_ON(!(task->flags & PF_KTHREAD));
339        __fput(file);
340    }
341}
342
343EXPORT_SYMBOL(fput);
344
345void put_filp(struct file *file)
346{
347    if (atomic_long_dec_and_test(&file->f_count)) {
348        security_file_free(file);
349        file_sb_list_del(file);
350        file_free(file);
351    }
352}
353
354static inline int file_list_cpu(struct file *file)
355{
356#ifdef CONFIG_SMP
357    return file->f_sb_list_cpu;
358#else
359    return smp_processor_id();
360#endif
361}
362
363/* helper for file_sb_list_add to reduce ifdefs */
364static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
365{
366    struct list_head *list;
367#ifdef CONFIG_SMP
368    int cpu;
369    cpu = smp_processor_id();
370    file->f_sb_list_cpu = cpu;
371    list = per_cpu_ptr(sb->s_files, cpu);
372#else
373    list = &sb->s_files;
374#endif
375    list_add(&file->f_u.fu_list, list);
376}
377
378/**
379 * file_sb_list_add - add a file to the sb's file list
380 * @file: file to add
381 * @sb: sb to add it to
382 *
383 * Use this function to associate a file with the superblock of the inode it
384 * refers to.
385 */
386void file_sb_list_add(struct file *file, struct super_block *sb)
387{
388    lg_local_lock(&files_lglock);
389    __file_sb_list_add(file, sb);
390    lg_local_unlock(&files_lglock);
391}
392
393/**
394 * file_sb_list_del - remove a file from the sb's file list
395 * @file: file to remove
396 * @sb: sb to remove it from
397 *
398 * Use this function to remove a file from its superblock.
399 */
400void file_sb_list_del(struct file *file)
401{
402    if (!list_empty(&file->f_u.fu_list)) {
403        lg_local_lock_cpu(&files_lglock, file_list_cpu(file));
404        list_del_init(&file->f_u.fu_list);
405        lg_local_unlock_cpu(&files_lglock, file_list_cpu(file));
406    }
407}
408
409#ifdef CONFIG_SMP
410
411/*
412 * These macros iterate all files on all CPUs for a given superblock.
413 * files_lglock must be held globally.
414 */
415#define do_file_list_for_each_entry(__sb, __file) \
416{ \
417    int i; \
418    for_each_possible_cpu(i) { \
419        struct list_head *list; \
420        list = per_cpu_ptr((__sb)->s_files, i); \
421        list_for_each_entry((__file), list, f_u.fu_list)
422
423#define while_file_list_for_each_entry \
424    } \
425}
426
427#else
428
429#define do_file_list_for_each_entry(__sb, __file) \
430{ \
431    struct list_head *list; \
432    list = &(sb)->s_files; \
433    list_for_each_entry((__file), list, f_u.fu_list)
434
435#define while_file_list_for_each_entry \
436}
437
438#endif
439
440/**
441 * mark_files_ro - mark all files read-only
442 * @sb: superblock in question
443 *
444 * All files are marked read-only. We don't care about pending
445 * delete files so this should be used in 'force' mode only.
446 */
447void mark_files_ro(struct super_block *sb)
448{
449    struct file *f;
450
451    lg_global_lock(&files_lglock);
452    do_file_list_for_each_entry(sb, f) {
453        if (!S_ISREG(file_inode(f)->i_mode))
454               continue;
455        if (!file_count(f))
456            continue;
457        if (!(f->f_mode & FMODE_WRITE))
458            continue;
459        spin_lock(&f->f_lock);
460        f->f_mode &= ~FMODE_WRITE;
461        spin_unlock(&f->f_lock);
462        if (file_check_writeable(f) != 0)
463            continue;
464        __mnt_drop_write(f->f_path.mnt);
465        file_release_write(f);
466    } while_file_list_for_each_entry;
467    lg_global_unlock(&files_lglock);
468}
469
470void __init files_init(unsigned long mempages)
471{
472    unsigned long n;
473
474    filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
475            SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
476
477    /*
478     * One file with associated inode and dcache is very roughly 1K.
479     * Per default don't use more than 10% of our memory for files.
480     */
481
482    n = (mempages * (PAGE_SIZE / 1024)) / 10;
483    files_stat.max_files = max_t(unsigned long, n, NR_FILE);
484    files_defer_init();
485    lg_lock_init(&files_lglock, "files_lglock");
486    percpu_counter_init(&nr_files, 0);
487}
488

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