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... */
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
file_free_rcu(struct rcu_head * head)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
file_free(struct file * f)52 static 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 */
get_nr_files(void)61 static 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 */
get_max_files(void)69 unsigned long get_max_files(void)
70 {
71 return files_stat.max_files;
72 }
73 EXPORT_SYMBOL_GPL(get_max_files);
74
75 /*
76 * Handle nr_files sysctl
77 */
78 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
proc_nr_files(struct ctl_table * table,int write,void __user * buffer,size_t * lenp,loff_t * ppos)79 int 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
proc_nr_files(struct ctl_table * table,int write,void __user * buffer,size_t * lenp,loff_t * ppos)86 int 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 */
get_empty_filp(void)103 struct 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
142 over:
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 */
alloc_file(struct path * path,fmode_t mode,const struct file_operations * fop)158 struct 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->aio_read || fop->read_iter))
172 mode |= FMODE_CAN_READ;
173 if ((mode & FMODE_WRITE) &&
174 likely(fop->write || fop->aio_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 }
182 EXPORT_SYMBOL(alloc_file);
183
184 /* the real guts of fput() - releasing the last reference to file
185 */
__fput(struct file * file)186 static 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
230 static LLIST_HEAD(delayed_fput_list);
delayed_fput(struct work_struct * unused)231 static 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
____fput(struct callback_head * work)242 static 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 */
flush_delayed_fput(void)257 void flush_delayed_fput(void)
258 {
259 delayed_fput(NULL);
260 }
261
262 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
263
fput(struct file * file)264 void 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 */
__fput_sync(struct file * file)293 void __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
302 EXPORT_SYMBOL(fput);
303
put_filp(struct file * file)304 void 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
files_init(unsigned long mempages)312 void __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