xref: /openbmc/linux/fs/file_table.c (revision 3213486f) 
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/cred.h>
17 #include <linux/eventpoll.h>
18 #include <linux/rcupdate.h>
19 #include <linux/mount.h>
20 #include <linux/capability.h>
21 #include <linux/cdev.h>
22 #include <linux/fsnotify.h>
23 #include <linux/sysctl.h>
24 #include <linux/percpu_counter.h>
25 #include <linux/percpu.h>
26 #include <linux/task_work.h>
27 #include <linux/ima.h>
28 #include <linux/swap.h>
29 
30 #include <linux/atomic.h>
31 
32 #include "internal.h"
33 
34 /* sysctl tunables... */
35 struct files_stat_struct files_stat = {
36 	.max_files = NR_FILE
37 };
38 
39 /* SLAB cache for file structures */
40 static struct kmem_cache *filp_cachep __read_mostly;
41 
42 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
43 
44 static 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 
52 static inline void file_free(struct file *f)
53 {
54 	security_file_free(f);
55 	if (!(f->f_mode & FMODE_NOACCOUNT))
56 		percpu_counter_dec(&nr_files);
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(struct 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(struct ctl_table *table, int write,
89                      void __user *buffer, size_t *lenp, loff_t *ppos)
90 {
91 	return -ENOSYS;
92 }
93 #endif
94 
95 static struct file *__alloc_file(int flags, const struct cred *cred)
96 {
97 	struct file *f;
98 	int error;
99 
100 	f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
101 	if (unlikely(!f))
102 		return ERR_PTR(-ENOMEM);
103 
104 	f->f_cred = get_cred(cred);
105 	error = security_file_alloc(f);
106 	if (unlikely(error)) {
107 		file_free_rcu(&f->f_u.fu_rcuhead);
108 		return ERR_PTR(error);
109 	}
110 
111 	atomic_long_set(&f->f_count, 1);
112 	rwlock_init(&f->f_owner.lock);
113 	spin_lock_init(&f->f_lock);
114 	mutex_init(&f->f_pos_lock);
115 	eventpoll_init_file(f);
116 	f->f_flags = flags;
117 	f->f_mode = OPEN_FMODE(flags);
118 	/* f->f_version: 0 */
119 
120 	return f;
121 }
122 
123 /* Find an unused file structure and return a pointer to it.
124  * Returns an error pointer if some error happend e.g. we over file
125  * structures limit, run out of memory or operation is not permitted.
126  *
127  * Be very careful using this.  You are responsible for
128  * getting write access to any mount that you might assign
129  * to this filp, if it is opened for write.  If this is not
130  * done, you will imbalance int the mount's writer count
131  * and a warning at __fput() time.
132  */
133 struct file *alloc_empty_file(int flags, const struct cred *cred)
134 {
135 	static long old_max;
136 	struct file *f;
137 
138 	/*
139 	 * Privileged users can go above max_files
140 	 */
141 	if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
142 		/*
143 		 * percpu_counters are inaccurate.  Do an expensive check before
144 		 * we go and fail.
145 		 */
146 		if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
147 			goto over;
148 	}
149 
150 	f = __alloc_file(flags, cred);
151 	if (!IS_ERR(f))
152 		percpu_counter_inc(&nr_files);
153 
154 	return f;
155 
156 over:
157 	/* Ran out of filps - report that */
158 	if (get_nr_files() > old_max) {
159 		pr_info("VFS: file-max limit %lu reached\n", get_max_files());
160 		old_max = get_nr_files();
161 	}
162 	return ERR_PTR(-ENFILE);
163 }
164 
165 /*
166  * Variant of alloc_empty_file() that doesn't check and modify nr_files.
167  *
168  * Should not be used unless there's a very good reason to do so.
169  */
170 struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
171 {
172 	struct file *f = __alloc_file(flags, cred);
173 
174 	if (!IS_ERR(f))
175 		f->f_mode |= FMODE_NOACCOUNT;
176 
177 	return f;
178 }
179 
180 /**
181  * alloc_file - allocate and initialize a 'struct file'
182  *
183  * @path: the (dentry, vfsmount) pair for the new file
184  * @flags: O_... flags with which the new file will be opened
185  * @fop: the 'struct file_operations' for the new file
186  */
187 static struct file *alloc_file(const struct path *path, int flags,
188 		const struct file_operations *fop)
189 {
190 	struct file *file;
191 
192 	file = alloc_empty_file(flags, current_cred());
193 	if (IS_ERR(file))
194 		return file;
195 
196 	file->f_path = *path;
197 	file->f_inode = path->dentry->d_inode;
198 	file->f_mapping = path->dentry->d_inode->i_mapping;
199 	file->f_wb_err = filemap_sample_wb_err(file->f_mapping);
200 	if ((file->f_mode & FMODE_READ) &&
201 	     likely(fop->read || fop->read_iter))
202 		file->f_mode |= FMODE_CAN_READ;
203 	if ((file->f_mode & FMODE_WRITE) &&
204 	     likely(fop->write || fop->write_iter))
205 		file->f_mode |= FMODE_CAN_WRITE;
206 	file->f_mode |= FMODE_OPENED;
207 	file->f_op = fop;
208 	if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
209 		i_readcount_inc(path->dentry->d_inode);
210 	return file;
211 }
212 
213 struct file *alloc_file_pseudo(struct inode *inode, struct vfsmount *mnt,
214 				const char *name, int flags,
215 				const struct file_operations *fops)
216 {
217 	static const struct dentry_operations anon_ops = {
218 		.d_dname = simple_dname
219 	};
220 	struct qstr this = QSTR_INIT(name, strlen(name));
221 	struct path path;
222 	struct file *file;
223 
224 	path.dentry = d_alloc_pseudo(mnt->mnt_sb, &this);
225 	if (!path.dentry)
226 		return ERR_PTR(-ENOMEM);
227 	if (!mnt->mnt_sb->s_d_op)
228 		d_set_d_op(path.dentry, &anon_ops);
229 	path.mnt = mntget(mnt);
230 	d_instantiate(path.dentry, inode);
231 	file = alloc_file(&path, flags, fops);
232 	if (IS_ERR(file)) {
233 		ihold(inode);
234 		path_put(&path);
235 	}
236 	return file;
237 }
238 EXPORT_SYMBOL(alloc_file_pseudo);
239 
240 struct file *alloc_file_clone(struct file *base, int flags,
241 				const struct file_operations *fops)
242 {
243 	struct file *f = alloc_file(&base->f_path, flags, fops);
244 	if (!IS_ERR(f)) {
245 		path_get(&f->f_path);
246 		f->f_mapping = base->f_mapping;
247 	}
248 	return f;
249 }
250 
251 /* the real guts of fput() - releasing the last reference to file
252  */
253 static void __fput(struct file *file)
254 {
255 	struct dentry *dentry = file->f_path.dentry;
256 	struct vfsmount *mnt = file->f_path.mnt;
257 	struct inode *inode = file->f_inode;
258 
259 	if (unlikely(!(file->f_mode & FMODE_OPENED)))
260 		goto out;
261 
262 	might_sleep();
263 
264 	fsnotify_close(file);
265 	/*
266 	 * The function eventpoll_release() should be the first called
267 	 * in the file cleanup chain.
268 	 */
269 	eventpoll_release(file);
270 	locks_remove_file(file);
271 
272 	ima_file_free(file);
273 	if (unlikely(file->f_flags & FASYNC)) {
274 		if (file->f_op->fasync)
275 			file->f_op->fasync(-1, file, 0);
276 	}
277 	if (file->f_op->release)
278 		file->f_op->release(inode, file);
279 	if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
280 		     !(file->f_mode & FMODE_PATH))) {
281 		cdev_put(inode->i_cdev);
282 	}
283 	fops_put(file->f_op);
284 	put_pid(file->f_owner.pid);
285 	if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
286 		i_readcount_dec(inode);
287 	if (file->f_mode & FMODE_WRITER) {
288 		put_write_access(inode);
289 		__mnt_drop_write(mnt);
290 	}
291 	dput(dentry);
292 	mntput(mnt);
293 out:
294 	file_free(file);
295 }
296 
297 static LLIST_HEAD(delayed_fput_list);
298 static void delayed_fput(struct work_struct *unused)
299 {
300 	struct llist_node *node = llist_del_all(&delayed_fput_list);
301 	struct file *f, *t;
302 
303 	llist_for_each_entry_safe(f, t, node, f_u.fu_llist)
304 		__fput(f);
305 }
306 
307 static void ____fput(struct callback_head *work)
308 {
309 	__fput(container_of(work, struct file, f_u.fu_rcuhead));
310 }
311 
312 /*
313  * If kernel thread really needs to have the final fput() it has done
314  * to complete, call this.  The only user right now is the boot - we
315  * *do* need to make sure our writes to binaries on initramfs has
316  * not left us with opened struct file waiting for __fput() - execve()
317  * won't work without that.  Please, don't add more callers without
318  * very good reasons; in particular, never call that with locks
319  * held and never call that from a thread that might need to do
320  * some work on any kind of umount.
321  */
322 void flush_delayed_fput(void)
323 {
324 	delayed_fput(NULL);
325 }
326 
327 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
328 
329 void fput_many(struct file *file, unsigned int refs)
330 {
331 	if (atomic_long_sub_and_test(refs, &file->f_count)) {
332 		struct task_struct *task = current;
333 
334 		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
335 			init_task_work(&file->f_u.fu_rcuhead, ____fput);
336 			if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
337 				return;
338 			/*
339 			 * After this task has run exit_task_work(),
340 			 * task_work_add() will fail.  Fall through to delayed
341 			 * fput to avoid leaking *file.
342 			 */
343 		}
344 
345 		if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
346 			schedule_delayed_work(&delayed_fput_work, 1);
347 	}
348 }
349 
350 void fput(struct file *file)
351 {
352 	fput_many(file, 1);
353 }
354 
355 /*
356  * synchronous analog of fput(); for kernel threads that might be needed
357  * in some umount() (and thus can't use flush_delayed_fput() without
358  * risking deadlocks), need to wait for completion of __fput() and know
359  * for this specific struct file it won't involve anything that would
360  * need them.  Use only if you really need it - at the very least,
361  * don't blindly convert fput() by kernel thread to that.
362  */
363 void __fput_sync(struct file *file)
364 {
365 	if (atomic_long_dec_and_test(&file->f_count)) {
366 		struct task_struct *task = current;
367 		BUG_ON(!(task->flags & PF_KTHREAD));
368 		__fput(file);
369 	}
370 }
371 
372 EXPORT_SYMBOL(fput);
373 
374 void __init files_init(void)
375 {
376 	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
377 			SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT, NULL);
378 	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
379 }
380 
381 /*
382  * One file with associated inode and dcache is very roughly 1K. Per default
383  * do not use more than 10% of our memory for files.
384  */
385 void __init files_maxfiles_init(void)
386 {
387 	unsigned long n;
388 	unsigned long nr_pages = totalram_pages();
389 	unsigned long memreserve = (nr_pages - nr_free_pages()) * 3/2;
390 
391 	memreserve = min(memreserve, nr_pages - 1);
392 	n = ((nr_pages - memreserve) * (PAGE_SIZE / 1024)) / 10;
393 
394 	files_stat.max_files = max_t(unsigned long, n, NR_FILE);
395 }
396