xref: /linux/fs/file_table.c (revision 0be3ff0c) 
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *  linux/fs/file_table.c
4  *
5  *  Copyright (C) 1991, 1992  Linus Torvalds
6  *  Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
7  */
8 
9 #include <linux/string.h>
10 #include <linux/slab.h>
11 #include <linux/file.h>
12 #include <linux/fdtable.h>
13 #include <linux/init.h>
14 #include <linux/module.h>
15 #include <linux/fs.h>
16 #include <linux/security.h>
17 #include <linux/cred.h>
18 #include <linux/eventpoll.h>
19 #include <linux/rcupdate.h>
20 #include <linux/mount.h>
21 #include <linux/capability.h>
22 #include <linux/cdev.h>
23 #include <linux/fsnotify.h>
24 #include <linux/sysctl.h>
25 #include <linux/percpu_counter.h>
26 #include <linux/percpu.h>
27 #include <linux/task_work.h>
28 #include <linux/ima.h>
29 #include <linux/swap.h>
30 #include <linux/kmemleak.h>
31 
32 #include <linux/atomic.h>
33 
34 #include "internal.h"
35 
36 /* sysctl tunables... */
37 static struct files_stat_struct files_stat = {
38 	.max_files = NR_FILE
39 };
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 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 	security_file_free(f);
57 	if (!(f->f_mode & FMODE_NOACCOUNT))
58 		percpu_counter_dec(&nr_files);
59 	call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
60 }
61 
62 /*
63  * Return the total number of open files in the system
64  */
65 static long get_nr_files(void)
66 {
67 	return percpu_counter_read_positive(&nr_files);
68 }
69 
70 /*
71  * Return the maximum number of open files in the system
72  */
73 unsigned long get_max_files(void)
74 {
75 	return files_stat.max_files;
76 }
77 EXPORT_SYMBOL_GPL(get_max_files);
78 
79 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
80 
81 /*
82  * Handle nr_files sysctl
83  */
84 static int proc_nr_files(struct ctl_table *table, int write, void *buffer,
85 			 size_t *lenp, loff_t *ppos)
86 {
87 	files_stat.nr_files = get_nr_files();
88 	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
89 }
90 
91 static struct ctl_table fs_stat_sysctls[] = {
92 	{
93 		.procname	= "file-nr",
94 		.data		= &files_stat,
95 		.maxlen		= sizeof(files_stat),
96 		.mode		= 0444,
97 		.proc_handler	= proc_nr_files,
98 	},
99 	{
100 		.procname	= "file-max",
101 		.data		= &files_stat.max_files,
102 		.maxlen		= sizeof(files_stat.max_files),
103 		.mode		= 0644,
104 		.proc_handler	= proc_doulongvec_minmax,
105 		.extra1		= SYSCTL_LONG_ZERO,
106 		.extra2		= SYSCTL_LONG_MAX,
107 	},
108 	{
109 		.procname	= "nr_open",
110 		.data		= &sysctl_nr_open,
111 		.maxlen		= sizeof(unsigned int),
112 		.mode		= 0644,
113 		.proc_handler	= proc_dointvec_minmax,
114 		.extra1		= &sysctl_nr_open_min,
115 		.extra2		= &sysctl_nr_open_max,
116 	},
117 	{ }
118 };
119 
120 static int __init init_fs_stat_sysctls(void)
121 {
122 	register_sysctl_init("fs", fs_stat_sysctls);
123 	if (IS_ENABLED(CONFIG_BINFMT_MISC)) {
124 		struct ctl_table_header *hdr;
125 		hdr = register_sysctl_mount_point("fs/binfmt_misc");
126 		kmemleak_not_leak(hdr);
127 	}
128 	return 0;
129 }
130 fs_initcall(init_fs_stat_sysctls);
131 #endif
132 
133 static struct file *__alloc_file(int flags, const struct cred *cred)
134 {
135 	struct file *f;
136 	int error;
137 
138 	f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
139 	if (unlikely(!f))
140 		return ERR_PTR(-ENOMEM);
141 
142 	f->f_cred = get_cred(cred);
143 	error = security_file_alloc(f);
144 	if (unlikely(error)) {
145 		file_free_rcu(&f->f_u.fu_rcuhead);
146 		return ERR_PTR(error);
147 	}
148 
149 	atomic_long_set(&f->f_count, 1);
150 	rwlock_init(&f->f_owner.lock);
151 	spin_lock_init(&f->f_lock);
152 	mutex_init(&f->f_pos_lock);
153 	f->f_flags = flags;
154 	f->f_mode = OPEN_FMODE(flags);
155 	/* f->f_version: 0 */
156 
157 	return f;
158 }
159 
160 /* Find an unused file structure and return a pointer to it.
161  * Returns an error pointer if some error happend e.g. we over file
162  * structures limit, run out of memory or operation is not permitted.
163  *
164  * Be very careful using this.  You are responsible for
165  * getting write access to any mount that you might assign
166  * to this filp, if it is opened for write.  If this is not
167  * done, you will imbalance int the mount's writer count
168  * and a warning at __fput() time.
169  */
170 struct file *alloc_empty_file(int flags, const struct cred *cred)
171 {
172 	static long old_max;
173 	struct file *f;
174 
175 	/*
176 	 * Privileged users can go above max_files
177 	 */
178 	if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
179 		/*
180 		 * percpu_counters are inaccurate.  Do an expensive check before
181 		 * we go and fail.
182 		 */
183 		if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
184 			goto over;
185 	}
186 
187 	f = __alloc_file(flags, cred);
188 	if (!IS_ERR(f))
189 		percpu_counter_inc(&nr_files);
190 
191 	return f;
192 
193 over:
194 	/* Ran out of filps - report that */
195 	if (get_nr_files() > old_max) {
196 		pr_info("VFS: file-max limit %lu reached\n", get_max_files());
197 		old_max = get_nr_files();
198 	}
199 	return ERR_PTR(-ENFILE);
200 }
201 
202 /*
203  * Variant of alloc_empty_file() that doesn't check and modify nr_files.
204  *
205  * Should not be used unless there's a very good reason to do so.
206  */
207 struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
208 {
209 	struct file *f = __alloc_file(flags, cred);
210 
211 	if (!IS_ERR(f))
212 		f->f_mode |= FMODE_NOACCOUNT;
213 
214 	return f;
215 }
216 
217 /**
218  * alloc_file - allocate and initialize a 'struct file'
219  *
220  * @path: the (dentry, vfsmount) pair for the new file
221  * @flags: O_... flags with which the new file will be opened
222  * @fop: the 'struct file_operations' for the new file
223  */
224 static struct file *alloc_file(const struct path *path, int flags,
225 		const struct file_operations *fop)
226 {
227 	struct file *file;
228 
229 	file = alloc_empty_file(flags, current_cred());
230 	if (IS_ERR(file))
231 		return file;
232 
233 	file->f_path = *path;
234 	file->f_inode = path->dentry->d_inode;
235 	file->f_mapping = path->dentry->d_inode->i_mapping;
236 	file->f_wb_err = filemap_sample_wb_err(file->f_mapping);
237 	file->f_sb_err = file_sample_sb_err(file);
238 	if ((file->f_mode & FMODE_READ) &&
239 	     likely(fop->read || fop->read_iter))
240 		file->f_mode |= FMODE_CAN_READ;
241 	if ((file->f_mode & FMODE_WRITE) &&
242 	     likely(fop->write || fop->write_iter))
243 		file->f_mode |= FMODE_CAN_WRITE;
244 	file->f_mode |= FMODE_OPENED;
245 	file->f_op = fop;
246 	if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
247 		i_readcount_inc(path->dentry->d_inode);
248 	return file;
249 }
250 
251 struct file *alloc_file_pseudo(struct inode *inode, struct vfsmount *mnt,
252 				const char *name, int flags,
253 				const struct file_operations *fops)
254 {
255 	static const struct dentry_operations anon_ops = {
256 		.d_dname = simple_dname
257 	};
258 	struct qstr this = QSTR_INIT(name, strlen(name));
259 	struct path path;
260 	struct file *file;
261 
262 	path.dentry = d_alloc_pseudo(mnt->mnt_sb, &this);
263 	if (!path.dentry)
264 		return ERR_PTR(-ENOMEM);
265 	if (!mnt->mnt_sb->s_d_op)
266 		d_set_d_op(path.dentry, &anon_ops);
267 	path.mnt = mntget(mnt);
268 	d_instantiate(path.dentry, inode);
269 	file = alloc_file(&path, flags, fops);
270 	if (IS_ERR(file)) {
271 		ihold(inode);
272 		path_put(&path);
273 	}
274 	return file;
275 }
276 EXPORT_SYMBOL(alloc_file_pseudo);
277 
278 struct file *alloc_file_clone(struct file *base, int flags,
279 				const struct file_operations *fops)
280 {
281 	struct file *f = alloc_file(&base->f_path, flags, fops);
282 	if (!IS_ERR(f)) {
283 		path_get(&f->f_path);
284 		f->f_mapping = base->f_mapping;
285 	}
286 	return f;
287 }
288 
289 /* the real guts of fput() - releasing the last reference to file
290  */
291 static void __fput(struct file *file)
292 {
293 	struct dentry *dentry = file->f_path.dentry;
294 	struct vfsmount *mnt = file->f_path.mnt;
295 	struct inode *inode = file->f_inode;
296 	fmode_t mode = file->f_mode;
297 
298 	if (unlikely(!(file->f_mode & FMODE_OPENED)))
299 		goto out;
300 
301 	might_sleep();
302 
303 	fsnotify_close(file);
304 	/*
305 	 * The function eventpoll_release() should be the first called
306 	 * in the file cleanup chain.
307 	 */
308 	eventpoll_release(file);
309 	locks_remove_file(file);
310 
311 	ima_file_free(file);
312 	if (unlikely(file->f_flags & FASYNC)) {
313 		if (file->f_op->fasync)
314 			file->f_op->fasync(-1, file, 0);
315 	}
316 	if (file->f_op->release)
317 		file->f_op->release(inode, file);
318 	if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
319 		     !(mode & FMODE_PATH))) {
320 		cdev_put(inode->i_cdev);
321 	}
322 	fops_put(file->f_op);
323 	put_pid(file->f_owner.pid);
324 	if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
325 		i_readcount_dec(inode);
326 	if (mode & FMODE_WRITER) {
327 		put_write_access(inode);
328 		__mnt_drop_write(mnt);
329 	}
330 	dput(dentry);
331 	if (unlikely(mode & FMODE_NEED_UNMOUNT))
332 		dissolve_on_fput(mnt);
333 	mntput(mnt);
334 out:
335 	file_free(file);
336 }
337 
338 static LLIST_HEAD(delayed_fput_list);
339 static void delayed_fput(struct work_struct *unused)
340 {
341 	struct llist_node *node = llist_del_all(&delayed_fput_list);
342 	struct file *f, *t;
343 
344 	llist_for_each_entry_safe(f, t, node, f_u.fu_llist)
345 		__fput(f);
346 }
347 
348 static void ____fput(struct callback_head *work)
349 {
350 	__fput(container_of(work, struct file, f_u.fu_rcuhead));
351 }
352 
353 /*
354  * If kernel thread really needs to have the final fput() it has done
355  * to complete, call this.  The only user right now is the boot - we
356  * *do* need to make sure our writes to binaries on initramfs has
357  * not left us with opened struct file waiting for __fput() - execve()
358  * won't work without that.  Please, don't add more callers without
359  * very good reasons; in particular, never call that with locks
360  * held and never call that from a thread that might need to do
361  * some work on any kind of umount.
362  */
363 void flush_delayed_fput(void)
364 {
365 	delayed_fput(NULL);
366 }
367 EXPORT_SYMBOL_GPL(flush_delayed_fput);
368 
369 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
370 
371 void fput_many(struct file *file, unsigned int refs)
372 {
373 	if (atomic_long_sub_and_test(refs, &file->f_count)) {
374 		struct task_struct *task = current;
375 
376 		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
377 			init_task_work(&file->f_u.fu_rcuhead, ____fput);
378 			if (!task_work_add(task, &file->f_u.fu_rcuhead, TWA_RESUME))
379 				return;
380 			/*
381 			 * After this task has run exit_task_work(),
382 			 * task_work_add() will fail.  Fall through to delayed
383 			 * fput to avoid leaking *file.
384 			 */
385 		}
386 
387 		if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
388 			schedule_delayed_work(&delayed_fput_work, 1);
389 	}
390 }
391 
392 void fput(struct file *file)
393 {
394 	fput_many(file, 1);
395 }
396 
397 /*
398  * synchronous analog of fput(); for kernel threads that might be needed
399  * in some umount() (and thus can't use flush_delayed_fput() without
400  * risking deadlocks), need to wait for completion of __fput() and know
401  * for this specific struct file it won't involve anything that would
402  * need them.  Use only if you really need it - at the very least,
403  * don't blindly convert fput() by kernel thread to that.
404  */
405 void __fput_sync(struct file *file)
406 {
407 	if (atomic_long_dec_and_test(&file->f_count)) {
408 		struct task_struct *task = current;
409 		BUG_ON(!(task->flags & PF_KTHREAD));
410 		__fput(file);
411 	}
412 }
413 
414 EXPORT_SYMBOL(fput);
415 EXPORT_SYMBOL(__fput_sync);
416 
417 void __init files_init(void)
418 {
419 	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
420 			SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT, NULL);
421 	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
422 }
423 
424 /*
425  * One file with associated inode and dcache is very roughly 1K. Per default
426  * do not use more than 10% of our memory for files.
427  */
428 void __init files_maxfiles_init(void)
429 {
430 	unsigned long n;
431 	unsigned long nr_pages = totalram_pages();
432 	unsigned long memreserve = (nr_pages - nr_free_pages()) * 3/2;
433 
434 	memreserve = min(memreserve, nr_pages - 1);
435 	n = ((nr_pages - memreserve) * (PAGE_SIZE / 1024)) / 10;
436 
437 	files_stat.max_files = max_t(unsigned long, n, NR_FILE);
438 }
439