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
39/* SLAB cache for file structures */
40static struct kmem_cache *filp_cachep __read_mostly;
41
42static struct percpu_counter nr_files __cacheline_aligned_in_smp;
43
44static void file_free_rcu(struct rcu_head *head)
45{
46	struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
47
48	put_cred(f->f_cred);
49	kmem_cache_free(filp_cachep, f);
50}
51
52static inline void file_free(struct file *f)
53{
54	percpu_counter_dec(&nr_files);
55	call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
56}
57
58/*
59 * Return the total number of open files in the system
60 */
61static long get_nr_files(void)
62{
63	return percpu_counter_read_positive(&nr_files);
64}
65
66/*
67 * Return the maximum number of open files in the system
68 */
69unsigned long get_max_files(void)
70{
71	return files_stat.max_files;
72}
73EXPORT_SYMBOL_GPL(get_max_files);
74
75/*
76 * Handle nr_files sysctl
77 */
78#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
79int proc_nr_files(struct ctl_table *table, int write,
80                     void __user *buffer, size_t *lenp, loff_t *ppos)
81{
82	files_stat.nr_files = get_nr_files();
83	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
84}
85#else
86int proc_nr_files(struct ctl_table *table, int write,
87                     void __user *buffer, size_t *lenp, loff_t *ppos)
88{
89	return -ENOSYS;
90}
91#endif
92
93/* Find an unused file structure and return a pointer to it.
94 * Returns an error pointer if some error happend e.g. we over file
95 * structures limit, run out of memory or operation is not permitted.
96 *
97 * Be very careful using this.  You are responsible for
98 * getting write access to any mount that you might assign
99 * to this filp, if it is opened for write.  If this is not
100 * done, you will imbalance int the mount's writer count
101 * and a warning at __fput() time.
102 */
103struct file *get_empty_filp(void)
104{
105	const struct cred *cred = current_cred();
106	static long old_max;
107	struct file *f;
108	int error;
109
110	/*
111	 * Privileged users can go above max_files
112	 */
113	if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
114		/*
115		 * percpu_counters are inaccurate.  Do an expensive check before
116		 * we go and fail.
117		 */
118		if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
119			goto over;
120	}
121
122	f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
123	if (unlikely(!f))
124		return ERR_PTR(-ENOMEM);
125
126	percpu_counter_inc(&nr_files);
127	f->f_cred = get_cred(cred);
128	error = security_file_alloc(f);
129	if (unlikely(error)) {
130		file_free(f);
131		return ERR_PTR(error);
132	}
133
134	atomic_long_set(&f->f_count, 1);
135	rwlock_init(&f->f_owner.lock);
136	spin_lock_init(&f->f_lock);
137	mutex_init(&f->f_pos_lock);
138	eventpoll_init_file(f);
139	/* f->f_version: 0 */
140	return f;
141
142over:
143	/* Ran out of filps - report that */
144	if (get_nr_files() > old_max) {
145		pr_info("VFS: file-max limit %lu reached\n", get_max_files());
146		old_max = get_nr_files();
147	}
148	return ERR_PTR(-ENFILE);
149}
150
151/**
152 * alloc_file - allocate and initialize a 'struct file'
153 *
154 * @path: the (dentry, vfsmount) pair for the new file
155 * @mode: the mode with which the new file will be opened
156 * @fop: the 'struct file_operations' for the new file
157 */
158struct file *alloc_file(struct path *path, fmode_t mode,
159		const struct file_operations *fop)
160{
161	struct file *file;
162
163	file = get_empty_filp();
164	if (IS_ERR(file))
165		return file;
166
167	file->f_path = *path;
168	file->f_inode = path->dentry->d_inode;
169	file->f_mapping = path->dentry->d_inode->i_mapping;
170	if ((mode & FMODE_READ) &&
171	     likely(fop->read || fop->read_iter))
172		mode |= FMODE_CAN_READ;
173	if ((mode & FMODE_WRITE) &&
174	     likely(fop->write || fop->write_iter))
175		mode |= FMODE_CAN_WRITE;
176	file->f_mode = mode;
177	file->f_op = fop;
178	if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
179		i_readcount_inc(path->dentry->d_inode);
180	return file;
181}
182EXPORT_SYMBOL(alloc_file);
183
184/* the real guts of fput() - releasing the last reference to file
185 */
186static void __fput(struct file *file)
187{
188	struct dentry *dentry = file->f_path.dentry;
189	struct vfsmount *mnt = file->f_path.mnt;
190	struct inode *inode = file->f_inode;
191
192	might_sleep();
193
194	fsnotify_close(file);
195	/*
196	 * The function eventpoll_release() should be the first called
197	 * in the file cleanup chain.
198	 */
199	eventpoll_release(file);
200	locks_remove_file(file);
201
202	if (unlikely(file->f_flags & FASYNC)) {
203		if (file->f_op->fasync)
204			file->f_op->fasync(-1, file, 0);
205	}
206	ima_file_free(file);
207	if (file->f_op->release)
208		file->f_op->release(inode, file);
209	security_file_free(file);
210	if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
211		     !(file->f_mode & FMODE_PATH))) {
212		cdev_put(inode->i_cdev);
213	}
214	fops_put(file->f_op);
215	put_pid(file->f_owner.pid);
216	if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
217		i_readcount_dec(inode);
218	if (file->f_mode & FMODE_WRITER) {
219		put_write_access(inode);
220		__mnt_drop_write(mnt);
221	}
222	file->f_path.dentry = NULL;
223	file->f_path.mnt = NULL;
224	file->f_inode = NULL;
225	file_free(file);
226	dput(dentry);
227	mntput(mnt);
228}
229
230static LLIST_HEAD(delayed_fput_list);
231static void delayed_fput(struct work_struct *unused)
232{
233	struct llist_node *node = llist_del_all(&delayed_fput_list);
234	struct llist_node *next;
235
236	for (; node; node = next) {
237		next = llist_next(node);
238		__fput(llist_entry(node, struct file, f_u.fu_llist));
239	}
240}
241
242static void ____fput(struct callback_head *work)
243{
244	__fput(container_of(work, struct file, f_u.fu_rcuhead));
245}
246
247/*
248 * If kernel thread really needs to have the final fput() it has done
249 * to complete, call this.  The only user right now is the boot - we
250 * *do* need to make sure our writes to binaries on initramfs has
251 * not left us with opened struct file waiting for __fput() - execve()
252 * won't work without that.  Please, don't add more callers without
253 * very good reasons; in particular, never call that with locks
254 * held and never call that from a thread that might need to do
255 * some work on any kind of umount.
256 */
257void flush_delayed_fput(void)
258{
259	delayed_fput(NULL);
260}
261
262static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
263
264void fput(struct file *file)
265{
266	if (atomic_long_dec_and_test(&file->f_count)) {
267		struct task_struct *task = current;
268
269		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
270			init_task_work(&file->f_u.fu_rcuhead, ____fput);
271			if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
272				return;
273			/*
274			 * After this task has run exit_task_work(),
275			 * task_work_add() will fail.  Fall through to delayed
276			 * fput to avoid leaking *file.
277			 */
278		}
279
280		if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
281			schedule_delayed_work(&delayed_fput_work, 1);
282	}
283}
284
285/*
286 * synchronous analog of fput(); for kernel threads that might be needed
287 * in some umount() (and thus can't use flush_delayed_fput() without
288 * risking deadlocks), need to wait for completion of __fput() and know
289 * for this specific struct file it won't involve anything that would
290 * need them.  Use only if you really need it - at the very least,
291 * don't blindly convert fput() by kernel thread to that.
292 */
293void __fput_sync(struct file *file)
294{
295	if (atomic_long_dec_and_test(&file->f_count)) {
296		struct task_struct *task = current;
297		BUG_ON(!(task->flags & PF_KTHREAD));
298		__fput(file);
299	}
300}
301
302EXPORT_SYMBOL(fput);
303
304void put_filp(struct file *file)
305{
306	if (atomic_long_dec_and_test(&file->f_count)) {
307		security_file_free(file);
308		file_free(file);
309	}
310}
311
312void __init files_init(unsigned long mempages)
313{
314	unsigned long n;
315
316	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
317			SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
318
319	/*
320	 * One file with associated inode and dcache is very roughly 1K.
321	 * Per default don't use more than 10% of our memory for files.
322	 */
323
324	n = (mempages * (PAGE_SIZE / 1024)) / 10;
325	files_stat.max_files = max_t(unsigned long, n, NR_FILE);
326	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
327}
328