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TOMOYO Linux Cross Reference
Linux/fs/proc/generic.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /*
  3  * proc/fs/generic.c --- generic routines for the proc-fs
  4  *
  5  * This file contains generic proc-fs routines for handling
  6  * directories and files.
  7  * 
  8  * Copyright (C) 1991, 1992 Linus Torvalds.
  9  * Copyright (C) 1997 Theodore Ts'o
 10  */
 11 
 12 #include <linux/cache.h>
 13 #include <linux/errno.h>
 14 #include <linux/time.h>
 15 #include <linux/proc_fs.h>
 16 #include <linux/stat.h>
 17 #include <linux/mm.h>
 18 #include <linux/module.h>
 19 #include <linux/namei.h>
 20 #include <linux/slab.h>
 21 #include <linux/printk.h>
 22 #include <linux/mount.h>
 23 #include <linux/init.h>
 24 #include <linux/idr.h>
 25 #include <linux/bitops.h>
 26 #include <linux/spinlock.h>
 27 #include <linux/completion.h>
 28 #include <linux/uaccess.h>
 29 #include <linux/seq_file.h>
 30 
 31 #include "internal.h"
 32 
 33 static DEFINE_RWLOCK(proc_subdir_lock);
 34 
 35 struct kmem_cache *proc_dir_entry_cache __ro_after_init;
 36 
 37 void pde_free(struct proc_dir_entry *pde)
 38 {
 39         if (S_ISLNK(pde->mode))
 40                 kfree(pde->data);
 41         if (pde->name != pde->inline_name)
 42                 kfree(pde->name);
 43         kmem_cache_free(proc_dir_entry_cache, pde);
 44 }
 45 
 46 static int proc_match(const char *name, struct proc_dir_entry *de, unsigned int len)
 47 {
 48         if (len < de->namelen)
 49                 return -1;
 50         if (len > de->namelen)
 51                 return 1;
 52 
 53         return memcmp(name, de->name, len);
 54 }
 55 
 56 static struct proc_dir_entry *pde_subdir_first(struct proc_dir_entry *dir)
 57 {
 58         return rb_entry_safe(rb_first(&dir->subdir), struct proc_dir_entry,
 59                              subdir_node);
 60 }
 61 
 62 static struct proc_dir_entry *pde_subdir_next(struct proc_dir_entry *dir)
 63 {
 64         return rb_entry_safe(rb_next(&dir->subdir_node), struct proc_dir_entry,
 65                              subdir_node);
 66 }
 67 
 68 static struct proc_dir_entry *pde_subdir_find(struct proc_dir_entry *dir,
 69                                               const char *name,
 70                                               unsigned int len)
 71 {
 72         struct rb_node *node = dir->subdir.rb_node;
 73 
 74         while (node) {
 75                 struct proc_dir_entry *de = rb_entry(node,
 76                                                      struct proc_dir_entry,
 77                                                      subdir_node);
 78                 int result = proc_match(name, de, len);
 79 
 80                 if (result < 0)
 81                         node = node->rb_left;
 82                 else if (result > 0)
 83                         node = node->rb_right;
 84                 else
 85                         return de;
 86         }
 87         return NULL;
 88 }
 89 
 90 static bool pde_subdir_insert(struct proc_dir_entry *dir,
 91                               struct proc_dir_entry *de)
 92 {
 93         struct rb_root *root = &dir->subdir;
 94         struct rb_node **new = &root->rb_node, *parent = NULL;
 95 
 96         /* Figure out where to put new node */
 97         while (*new) {
 98                 struct proc_dir_entry *this = rb_entry(*new,
 99                                                        struct proc_dir_entry,
100                                                        subdir_node);
101                 int result = proc_match(de->name, this, de->namelen);
102 
103                 parent = *new;
104                 if (result < 0)
105                         new = &(*new)->rb_left;
106                 else if (result > 0)
107                         new = &(*new)->rb_right;
108                 else
109                         return false;
110         }
111 
112         /* Add new node and rebalance tree. */
113         rb_link_node(&de->subdir_node, parent, new);
114         rb_insert_color(&de->subdir_node, root);
115         return true;
116 }
117 
118 static int proc_notify_change(struct dentry *dentry, struct iattr *iattr)
119 {
120         struct inode *inode = d_inode(dentry);
121         struct proc_dir_entry *de = PDE(inode);
122         int error;
123 
124         error = setattr_prepare(dentry, iattr);
125         if (error)
126                 return error;
127 
128         setattr_copy(inode, iattr);
129         mark_inode_dirty(inode);
130 
131         proc_set_user(de, inode->i_uid, inode->i_gid);
132         de->mode = inode->i_mode;
133         return 0;
134 }
135 
136 static int proc_getattr(const struct path *path, struct kstat *stat,
137                         u32 request_mask, unsigned int query_flags)
138 {
139         struct inode *inode = d_inode(path->dentry);
140         struct proc_dir_entry *de = PDE(inode);
141         if (de) {
142                 nlink_t nlink = READ_ONCE(de->nlink);
143                 if (nlink > 0) {
144                         set_nlink(inode, nlink);
145                 }
146         }
147 
148         generic_fillattr(inode, stat);
149         return 0;
150 }
151 
152 static const struct inode_operations proc_file_inode_operations = {
153         .setattr        = proc_notify_change,
154 };
155 
156 /*
157  * This function parses a name such as "tty/driver/serial", and
158  * returns the struct proc_dir_entry for "/proc/tty/driver", and
159  * returns "serial" in residual.
160  */
161 static int __xlate_proc_name(const char *name, struct proc_dir_entry **ret,
162                              const char **residual)
163 {
164         const char              *cp = name, *next;
165         struct proc_dir_entry   *de;
166 
167         de = *ret;
168         if (!de)
169                 de = &proc_root;
170 
171         while (1) {
172                 next = strchr(cp, '/');
173                 if (!next)
174                         break;
175 
176                 de = pde_subdir_find(de, cp, next - cp);
177                 if (!de) {
178                         WARN(1, "name '%s'\n", name);
179                         return -ENOENT;
180                 }
181                 cp = next + 1;
182         }
183         *residual = cp;
184         *ret = de;
185         return 0;
186 }
187 
188 static int xlate_proc_name(const char *name, struct proc_dir_entry **ret,
189                            const char **residual)
190 {
191         int rv;
192 
193         read_lock(&proc_subdir_lock);
194         rv = __xlate_proc_name(name, ret, residual);
195         read_unlock(&proc_subdir_lock);
196         return rv;
197 }
198 
199 static DEFINE_IDA(proc_inum_ida);
200 
201 #define PROC_DYNAMIC_FIRST 0xF0000000U
202 
203 /*
204  * Return an inode number between PROC_DYNAMIC_FIRST and
205  * 0xffffffff, or zero on failure.
206  */
207 int proc_alloc_inum(unsigned int *inum)
208 {
209         int i;
210 
211         i = ida_simple_get(&proc_inum_ida, 0, UINT_MAX - PROC_DYNAMIC_FIRST + 1,
212                            GFP_KERNEL);
213         if (i < 0)
214                 return i;
215 
216         *inum = PROC_DYNAMIC_FIRST + (unsigned int)i;
217         return 0;
218 }
219 
220 void proc_free_inum(unsigned int inum)
221 {
222         ida_simple_remove(&proc_inum_ida, inum - PROC_DYNAMIC_FIRST);
223 }
224 
225 static int proc_misc_d_revalidate(struct dentry *dentry, unsigned int flags)
226 {
227         if (flags & LOOKUP_RCU)
228                 return -ECHILD;
229 
230         if (atomic_read(&PDE(d_inode(dentry))->in_use) < 0)
231                 return 0; /* revalidate */
232         return 1;
233 }
234 
235 static int proc_misc_d_delete(const struct dentry *dentry)
236 {
237         return atomic_read(&PDE(d_inode(dentry))->in_use) < 0;
238 }
239 
240 static const struct dentry_operations proc_misc_dentry_ops = {
241         .d_revalidate   = proc_misc_d_revalidate,
242         .d_delete       = proc_misc_d_delete,
243 };
244 
245 /*
246  * Don't create negative dentries here, return -ENOENT by hand
247  * instead.
248  */
249 struct dentry *proc_lookup_de(struct inode *dir, struct dentry *dentry,
250                               struct proc_dir_entry *de)
251 {
252         struct inode *inode;
253 
254         read_lock(&proc_subdir_lock);
255         de = pde_subdir_find(de, dentry->d_name.name, dentry->d_name.len);
256         if (de) {
257                 pde_get(de);
258                 read_unlock(&proc_subdir_lock);
259                 inode = proc_get_inode(dir->i_sb, de);
260                 if (!inode)
261                         return ERR_PTR(-ENOMEM);
262                 d_set_d_op(dentry, de->proc_dops);
263                 return d_splice_alias(inode, dentry);
264         }
265         read_unlock(&proc_subdir_lock);
266         return ERR_PTR(-ENOENT);
267 }
268 
269 struct dentry *proc_lookup(struct inode *dir, struct dentry *dentry,
270                 unsigned int flags)
271 {
272         return proc_lookup_de(dir, dentry, PDE(dir));
273 }
274 
275 /*
276  * This returns non-zero if at EOF, so that the /proc
277  * root directory can use this and check if it should
278  * continue with the <pid> entries..
279  *
280  * Note that the VFS-layer doesn't care about the return
281  * value of the readdir() call, as long as it's non-negative
282  * for success..
283  */
284 int proc_readdir_de(struct file *file, struct dir_context *ctx,
285                     struct proc_dir_entry *de)
286 {
287         int i;
288 
289         if (!dir_emit_dots(file, ctx))
290                 return 0;
291 
292         i = ctx->pos - 2;
293         read_lock(&proc_subdir_lock);
294         de = pde_subdir_first(de);
295         for (;;) {
296                 if (!de) {
297                         read_unlock(&proc_subdir_lock);
298                         return 0;
299                 }
300                 if (!i)
301                         break;
302                 de = pde_subdir_next(de);
303                 i--;
304         }
305 
306         do {
307                 struct proc_dir_entry *next;
308                 pde_get(de);
309                 read_unlock(&proc_subdir_lock);
310                 if (!dir_emit(ctx, de->name, de->namelen,
311                             de->low_ino, de->mode >> 12)) {
312                         pde_put(de);
313                         return 0;
314                 }
315                 ctx->pos++;
316                 read_lock(&proc_subdir_lock);
317                 next = pde_subdir_next(de);
318                 pde_put(de);
319                 de = next;
320         } while (de);
321         read_unlock(&proc_subdir_lock);
322         return 1;
323 }
324 
325 int proc_readdir(struct file *file, struct dir_context *ctx)
326 {
327         struct inode *inode = file_inode(file);
328 
329         return proc_readdir_de(file, ctx, PDE(inode));
330 }
331 
332 /*
333  * These are the generic /proc directory operations. They
334  * use the in-memory "struct proc_dir_entry" tree to parse
335  * the /proc directory.
336  */
337 static const struct file_operations proc_dir_operations = {
338         .llseek                 = generic_file_llseek,
339         .read                   = generic_read_dir,
340         .iterate_shared         = proc_readdir,
341 };
342 
343 /*
344  * proc directories can do almost nothing..
345  */
346 static const struct inode_operations proc_dir_inode_operations = {
347         .lookup         = proc_lookup,
348         .getattr        = proc_getattr,
349         .setattr        = proc_notify_change,
350 };
351 
352 /* returns the registered entry, or frees dp and returns NULL on failure */
353 struct proc_dir_entry *proc_register(struct proc_dir_entry *dir,
354                 struct proc_dir_entry *dp)
355 {
356         if (proc_alloc_inum(&dp->low_ino))
357                 goto out_free_entry;
358 
359         write_lock(&proc_subdir_lock);
360         dp->parent = dir;
361         if (pde_subdir_insert(dir, dp) == false) {
362                 WARN(1, "proc_dir_entry '%s/%s' already registered\n",
363                      dir->name, dp->name);
364                 write_unlock(&proc_subdir_lock);
365                 goto out_free_inum;
366         }
367         dir->nlink++;
368         write_unlock(&proc_subdir_lock);
369 
370         return dp;
371 out_free_inum:
372         proc_free_inum(dp->low_ino);
373 out_free_entry:
374         pde_free(dp);
375         return NULL;
376 }
377 
378 static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
379                                           const char *name,
380                                           umode_t mode,
381                                           nlink_t nlink)
382 {
383         struct proc_dir_entry *ent = NULL;
384         const char *fn;
385         struct qstr qstr;
386 
387         if (xlate_proc_name(name, parent, &fn) != 0)
388                 goto out;
389         qstr.name = fn;
390         qstr.len = strlen(fn);
391         if (qstr.len == 0 || qstr.len >= 256) {
392                 WARN(1, "name len %u\n", qstr.len);
393                 return NULL;
394         }
395         if (qstr.len == 1 && fn[0] == '.') {
396                 WARN(1, "name '.'\n");
397                 return NULL;
398         }
399         if (qstr.len == 2 && fn[0] == '.' && fn[1] == '.') {
400                 WARN(1, "name '..'\n");
401                 return NULL;
402         }
403         if (*parent == &proc_root && name_to_int(&qstr) != ~0U) {
404                 WARN(1, "create '/proc/%s' by hand\n", qstr.name);
405                 return NULL;
406         }
407         if (is_empty_pde(*parent)) {
408                 WARN(1, "attempt to add to permanently empty directory");
409                 return NULL;
410         }
411 
412         ent = kmem_cache_zalloc(proc_dir_entry_cache, GFP_KERNEL);
413         if (!ent)
414                 goto out;
415 
416         if (qstr.len + 1 <= SIZEOF_PDE_INLINE_NAME) {
417                 ent->name = ent->inline_name;
418         } else {
419                 ent->name = kmalloc(qstr.len + 1, GFP_KERNEL);
420                 if (!ent->name) {
421                         pde_free(ent);
422                         return NULL;
423                 }
424         }
425 
426         memcpy(ent->name, fn, qstr.len + 1);
427         ent->namelen = qstr.len;
428         ent->mode = mode;
429         ent->nlink = nlink;
430         ent->subdir = RB_ROOT;
431         refcount_set(&ent->refcnt, 1);
432         spin_lock_init(&ent->pde_unload_lock);
433         INIT_LIST_HEAD(&ent->pde_openers);
434         proc_set_user(ent, (*parent)->uid, (*parent)->gid);
435 
436         ent->proc_dops = &proc_misc_dentry_ops;
437 
438 out:
439         return ent;
440 }
441 
442 struct proc_dir_entry *proc_symlink(const char *name,
443                 struct proc_dir_entry *parent, const char *dest)
444 {
445         struct proc_dir_entry *ent;
446 
447         ent = __proc_create(&parent, name,
448                           (S_IFLNK | S_IRUGO | S_IWUGO | S_IXUGO),1);
449 
450         if (ent) {
451                 ent->data = kmalloc((ent->size=strlen(dest))+1, GFP_KERNEL);
452                 if (ent->data) {
453                         strcpy((char*)ent->data,dest);
454                         ent->proc_iops = &proc_link_inode_operations;
455                         ent = proc_register(parent, ent);
456                 } else {
457                         pde_free(ent);
458                         ent = NULL;
459                 }
460         }
461         return ent;
462 }
463 EXPORT_SYMBOL(proc_symlink);
464 
465 struct proc_dir_entry *proc_mkdir_data(const char *name, umode_t mode,
466                 struct proc_dir_entry *parent, void *data)
467 {
468         struct proc_dir_entry *ent;
469 
470         if (mode == 0)
471                 mode = S_IRUGO | S_IXUGO;
472 
473         ent = __proc_create(&parent, name, S_IFDIR | mode, 2);
474         if (ent) {
475                 ent->data = data;
476                 ent->proc_fops = &proc_dir_operations;
477                 ent->proc_iops = &proc_dir_inode_operations;
478                 ent = proc_register(parent, ent);
479         }
480         return ent;
481 }
482 EXPORT_SYMBOL_GPL(proc_mkdir_data);
483 
484 struct proc_dir_entry *proc_mkdir_mode(const char *name, umode_t mode,
485                                        struct proc_dir_entry *parent)
486 {
487         return proc_mkdir_data(name, mode, parent, NULL);
488 }
489 EXPORT_SYMBOL(proc_mkdir_mode);
490 
491 struct proc_dir_entry *proc_mkdir(const char *name,
492                 struct proc_dir_entry *parent)
493 {
494         return proc_mkdir_data(name, 0, parent, NULL);
495 }
496 EXPORT_SYMBOL(proc_mkdir);
497 
498 struct proc_dir_entry *proc_create_mount_point(const char *name)
499 {
500         umode_t mode = S_IFDIR | S_IRUGO | S_IXUGO;
501         struct proc_dir_entry *ent, *parent = NULL;
502 
503         ent = __proc_create(&parent, name, mode, 2);
504         if (ent) {
505                 ent->data = NULL;
506                 ent->proc_fops = NULL;
507                 ent->proc_iops = NULL;
508                 ent = proc_register(parent, ent);
509         }
510         return ent;
511 }
512 EXPORT_SYMBOL(proc_create_mount_point);
513 
514 struct proc_dir_entry *proc_create_reg(const char *name, umode_t mode,
515                 struct proc_dir_entry **parent, void *data)
516 {
517         struct proc_dir_entry *p;
518 
519         if ((mode & S_IFMT) == 0)
520                 mode |= S_IFREG;
521         if ((mode & S_IALLUGO) == 0)
522                 mode |= S_IRUGO;
523         if (WARN_ON_ONCE(!S_ISREG(mode)))
524                 return NULL;
525 
526         p = __proc_create(parent, name, mode, 1);
527         if (p) {
528                 p->proc_iops = &proc_file_inode_operations;
529                 p->data = data;
530         }
531         return p;
532 }
533 
534 struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
535                 struct proc_dir_entry *parent,
536                 const struct file_operations *proc_fops, void *data)
537 {
538         struct proc_dir_entry *p;
539 
540         BUG_ON(proc_fops == NULL);
541 
542         p = proc_create_reg(name, mode, &parent, data);
543         if (!p)
544                 return NULL;
545         p->proc_fops = proc_fops;
546         return proc_register(parent, p);
547 }
548 EXPORT_SYMBOL(proc_create_data);
549  
550 struct proc_dir_entry *proc_create(const char *name, umode_t mode,
551                                    struct proc_dir_entry *parent,
552                                    const struct file_operations *proc_fops)
553 {
554         return proc_create_data(name, mode, parent, proc_fops, NULL);
555 }
556 EXPORT_SYMBOL(proc_create);
557 
558 static int proc_seq_open(struct inode *inode, struct file *file)
559 {
560         struct proc_dir_entry *de = PDE(inode);
561 
562         if (de->state_size)
563                 return seq_open_private(file, de->seq_ops, de->state_size);
564         return seq_open(file, de->seq_ops);
565 }
566 
567 static int proc_seq_release(struct inode *inode, struct file *file)
568 {
569         struct proc_dir_entry *de = PDE(inode);
570 
571         if (de->state_size)
572                 return seq_release_private(inode, file);
573         return seq_release(inode, file);
574 }
575 
576 static const struct file_operations proc_seq_fops = {
577         .open           = proc_seq_open,
578         .read           = seq_read,
579         .llseek         = seq_lseek,
580         .release        = proc_seq_release,
581 };
582 
583 struct proc_dir_entry *proc_create_seq_private(const char *name, umode_t mode,
584                 struct proc_dir_entry *parent, const struct seq_operations *ops,
585                 unsigned int state_size, void *data)
586 {
587         struct proc_dir_entry *p;
588 
589         p = proc_create_reg(name, mode, &parent, data);
590         if (!p)
591                 return NULL;
592         p->proc_fops = &proc_seq_fops;
593         p->seq_ops = ops;
594         p->state_size = state_size;
595         return proc_register(parent, p);
596 }
597 EXPORT_SYMBOL(proc_create_seq_private);
598 
599 static int proc_single_open(struct inode *inode, struct file *file)
600 {
601         struct proc_dir_entry *de = PDE(inode);
602 
603         return single_open(file, de->single_show, de->data);
604 }
605 
606 static const struct file_operations proc_single_fops = {
607         .open           = proc_single_open,
608         .read           = seq_read,
609         .llseek         = seq_lseek,
610         .release        = single_release,
611 };
612 
613 struct proc_dir_entry *proc_create_single_data(const char *name, umode_t mode,
614                 struct proc_dir_entry *parent,
615                 int (*show)(struct seq_file *, void *), void *data)
616 {
617         struct proc_dir_entry *p;
618 
619         p = proc_create_reg(name, mode, &parent, data);
620         if (!p)
621                 return NULL;
622         p->proc_fops = &proc_single_fops;
623         p->single_show = show;
624         return proc_register(parent, p);
625 }
626 EXPORT_SYMBOL(proc_create_single_data);
627 
628 void proc_set_size(struct proc_dir_entry *de, loff_t size)
629 {
630         de->size = size;
631 }
632 EXPORT_SYMBOL(proc_set_size);
633 
634 void proc_set_user(struct proc_dir_entry *de, kuid_t uid, kgid_t gid)
635 {
636         de->uid = uid;
637         de->gid = gid;
638 }
639 EXPORT_SYMBOL(proc_set_user);
640 
641 void pde_put(struct proc_dir_entry *pde)
642 {
643         if (refcount_dec_and_test(&pde->refcnt)) {
644                 proc_free_inum(pde->low_ino);
645                 pde_free(pde);
646         }
647 }
648 
649 /*
650  * Remove a /proc entry and free it if it's not currently in use.
651  */
652 void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
653 {
654         struct proc_dir_entry *de = NULL;
655         const char *fn = name;
656         unsigned int len;
657 
658         write_lock(&proc_subdir_lock);
659         if (__xlate_proc_name(name, &parent, &fn) != 0) {
660                 write_unlock(&proc_subdir_lock);
661                 return;
662         }
663         len = strlen(fn);
664 
665         de = pde_subdir_find(parent, fn, len);
666         if (de) {
667                 rb_erase(&de->subdir_node, &parent->subdir);
668                 if (S_ISDIR(de->mode)) {
669                         parent->nlink--;
670                 }
671         }
672         write_unlock(&proc_subdir_lock);
673         if (!de) {
674                 WARN(1, "name '%s'\n", name);
675                 return;
676         }
677 
678         proc_entry_rundown(de);
679 
680         WARN(pde_subdir_first(de),
681              "%s: removing non-empty directory '%s/%s', leaking at least '%s'\n",
682              __func__, de->parent->name, de->name, pde_subdir_first(de)->name);
683         pde_put(de);
684 }
685 EXPORT_SYMBOL(remove_proc_entry);
686 
687 int remove_proc_subtree(const char *name, struct proc_dir_entry *parent)
688 {
689         struct proc_dir_entry *root = NULL, *de, *next;
690         const char *fn = name;
691         unsigned int len;
692 
693         write_lock(&proc_subdir_lock);
694         if (__xlate_proc_name(name, &parent, &fn) != 0) {
695                 write_unlock(&proc_subdir_lock);
696                 return -ENOENT;
697         }
698         len = strlen(fn);
699 
700         root = pde_subdir_find(parent, fn, len);
701         if (!root) {
702                 write_unlock(&proc_subdir_lock);
703                 return -ENOENT;
704         }
705         rb_erase(&root->subdir_node, &parent->subdir);
706 
707         de = root;
708         while (1) {
709                 next = pde_subdir_first(de);
710                 if (next) {
711                         rb_erase(&next->subdir_node, &de->subdir);
712                         de = next;
713                         continue;
714                 }
715                 next = de->parent;
716                 if (S_ISDIR(de->mode))
717                         next->nlink--;
718                 write_unlock(&proc_subdir_lock);
719 
720                 proc_entry_rundown(de);
721                 if (de == root)
722                         break;
723                 pde_put(de);
724 
725                 write_lock(&proc_subdir_lock);
726                 de = next;
727         }
728         pde_put(root);
729         return 0;
730 }
731 EXPORT_SYMBOL(remove_proc_subtree);
732 
733 void *proc_get_parent_data(const struct inode *inode)
734 {
735         struct proc_dir_entry *de = PDE(inode);
736         return de->parent->data;
737 }
738 EXPORT_SYMBOL_GPL(proc_get_parent_data);
739 
740 void proc_remove(struct proc_dir_entry *de)
741 {
742         if (de)
743                 remove_proc_subtree(de->name, de->parent);
744 }
745 EXPORT_SYMBOL(proc_remove);
746 
747 void *PDE_DATA(const struct inode *inode)
748 {
749         return __PDE_DATA(inode);
750 }
751 EXPORT_SYMBOL(PDE_DATA);
752 
753 /*
754  * Pull a user buffer into memory and pass it to the file's write handler if
755  * one is supplied.  The ->write() method is permitted to modify the
756  * kernel-side buffer.
757  */
758 ssize_t proc_simple_write(struct file *f, const char __user *ubuf, size_t size,
759                           loff_t *_pos)
760 {
761         struct proc_dir_entry *pde = PDE(file_inode(f));
762         char *buf;
763         int ret;
764 
765         if (!pde->write)
766                 return -EACCES;
767         if (size == 0 || size > PAGE_SIZE - 1)
768                 return -EINVAL;
769         buf = memdup_user_nul(ubuf, size);
770         if (IS_ERR(buf))
771                 return PTR_ERR(buf);
772         ret = pde->write(f, buf, size);
773         kfree(buf);
774         return ret == 0 ? size : ret;
775 }
776 

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