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TOMOYO Linux Cross Reference
Linux/fs/file.c

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  1 /*
  2  *  linux/fs/file.c
  3  *
  4  *  Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
  5  *
  6  *  Manage the dynamic fd arrays in the process files_struct.
  7  */
  8 
  9 #include <linux/syscalls.h>
 10 #include <linux/export.h>
 11 #include <linux/fs.h>
 12 #include <linux/mm.h>
 13 #include <linux/mmzone.h>
 14 #include <linux/time.h>
 15 #include <linux/sched.h>
 16 #include <linux/slab.h>
 17 #include <linux/vmalloc.h>
 18 #include <linux/file.h>
 19 #include <linux/fdtable.h>
 20 #include <linux/bitops.h>
 21 #include <linux/interrupt.h>
 22 #include <linux/spinlock.h>
 23 #include <linux/rcupdate.h>
 24 #include <linux/workqueue.h>
 25 
 26 int sysctl_nr_open __read_mostly = 1024*1024;
 27 int sysctl_nr_open_min = BITS_PER_LONG;
 28 /* our max() is unusable in constant expressions ;-/ */
 29 #define __const_max(x, y) ((x) < (y) ? (x) : (y))
 30 int sysctl_nr_open_max = __const_max(INT_MAX, ~(size_t)0/sizeof(void *)) &
 31                          -BITS_PER_LONG;
 32 
 33 static void *alloc_fdmem(size_t size)
 34 {
 35         /*
 36          * Very large allocations can stress page reclaim, so fall back to
 37          * vmalloc() if the allocation size will be considered "large" by the VM.
 38          */
 39         if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
 40                 void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY);
 41                 if (data != NULL)
 42                         return data;
 43         }
 44         return vmalloc(size);
 45 }
 46 
 47 static void __free_fdtable(struct fdtable *fdt)
 48 {
 49         kvfree(fdt->fd);
 50         kvfree(fdt->open_fds);
 51         kfree(fdt);
 52 }
 53 
 54 static void free_fdtable_rcu(struct rcu_head *rcu)
 55 {
 56         __free_fdtable(container_of(rcu, struct fdtable, rcu));
 57 }
 58 
 59 /*
 60  * Expand the fdset in the files_struct.  Called with the files spinlock
 61  * held for write.
 62  */
 63 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
 64 {
 65         unsigned int cpy, set;
 66 
 67         BUG_ON(nfdt->max_fds < ofdt->max_fds);
 68 
 69         cpy = ofdt->max_fds * sizeof(struct file *);
 70         set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
 71         memcpy(nfdt->fd, ofdt->fd, cpy);
 72         memset((char *)(nfdt->fd) + cpy, 0, set);
 73 
 74         cpy = ofdt->max_fds / BITS_PER_BYTE;
 75         set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
 76         memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
 77         memset((char *)(nfdt->open_fds) + cpy, 0, set);
 78         memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
 79         memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
 80 }
 81 
 82 static struct fdtable * alloc_fdtable(unsigned int nr)
 83 {
 84         struct fdtable *fdt;
 85         void *data;
 86 
 87         /*
 88          * Figure out how many fds we actually want to support in this fdtable.
 89          * Allocation steps are keyed to the size of the fdarray, since it
 90          * grows far faster than any of the other dynamic data. We try to fit
 91          * the fdarray into comfortable page-tuned chunks: starting at 1024B
 92          * and growing in powers of two from there on.
 93          */
 94         nr /= (1024 / sizeof(struct file *));
 95         nr = roundup_pow_of_two(nr + 1);
 96         nr *= (1024 / sizeof(struct file *));
 97         /*
 98          * Note that this can drive nr *below* what we had passed if sysctl_nr_open
 99          * had been set lower between the check in expand_files() and here.  Deal
100          * with that in caller, it's cheaper that way.
101          *
102          * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
103          * bitmaps handling below becomes unpleasant, to put it mildly...
104          */
105         if (unlikely(nr > sysctl_nr_open))
106                 nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
107 
108         fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
109         if (!fdt)
110                 goto out;
111         fdt->max_fds = nr;
112         data = alloc_fdmem(nr * sizeof(struct file *));
113         if (!data)
114                 goto out_fdt;
115         fdt->fd = data;
116 
117         data = alloc_fdmem(max_t(size_t,
118                                  2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
119         if (!data)
120                 goto out_arr;
121         fdt->open_fds = data;
122         data += nr / BITS_PER_BYTE;
123         fdt->close_on_exec = data;
124 
125         return fdt;
126 
127 out_arr:
128         kvfree(fdt->fd);
129 out_fdt:
130         kfree(fdt);
131 out:
132         return NULL;
133 }
134 
135 /*
136  * Expand the file descriptor table.
137  * This function will allocate a new fdtable and both fd array and fdset, of
138  * the given size.
139  * Return <0 error code on error; 1 on successful completion.
140  * The files->file_lock should be held on entry, and will be held on exit.
141  */
142 static int expand_fdtable(struct files_struct *files, int nr)
143         __releases(files->file_lock)
144         __acquires(files->file_lock)
145 {
146         struct fdtable *new_fdt, *cur_fdt;
147 
148         spin_unlock(&files->file_lock);
149         new_fdt = alloc_fdtable(nr);
150 
151         /* make sure all __fd_install() have seen resize_in_progress
152          * or have finished their rcu_read_lock_sched() section.
153          */
154         if (atomic_read(&files->count) > 1)
155                 synchronize_sched();
156 
157         spin_lock(&files->file_lock);
158         if (!new_fdt)
159                 return -ENOMEM;
160         /*
161          * extremely unlikely race - sysctl_nr_open decreased between the check in
162          * caller and alloc_fdtable().  Cheaper to catch it here...
163          */
164         if (unlikely(new_fdt->max_fds <= nr)) {
165                 __free_fdtable(new_fdt);
166                 return -EMFILE;
167         }
168         cur_fdt = files_fdtable(files);
169         BUG_ON(nr < cur_fdt->max_fds);
170         copy_fdtable(new_fdt, cur_fdt);
171         rcu_assign_pointer(files->fdt, new_fdt);
172         if (cur_fdt != &files->fdtab)
173                 call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
174         /* coupled with smp_rmb() in __fd_install() */
175         smp_wmb();
176         return 1;
177 }
178 
179 /*
180  * Expand files.
181  * This function will expand the file structures, if the requested size exceeds
182  * the current capacity and there is room for expansion.
183  * Return <0 error code on error; 0 when nothing done; 1 when files were
184  * expanded and execution may have blocked.
185  * The files->file_lock should be held on entry, and will be held on exit.
186  */
187 static int expand_files(struct files_struct *files, int nr)
188         __releases(files->file_lock)
189         __acquires(files->file_lock)
190 {
191         struct fdtable *fdt;
192         int expanded = 0;
193 
194 repeat:
195         fdt = files_fdtable(files);
196 
197         /* Do we need to expand? */
198         if (nr < fdt->max_fds)
199                 return expanded;
200 
201         /* Can we expand? */
202         if (nr >= sysctl_nr_open)
203                 return -EMFILE;
204 
205         if (unlikely(files->resize_in_progress)) {
206                 spin_unlock(&files->file_lock);
207                 expanded = 1;
208                 wait_event(files->resize_wait, !files->resize_in_progress);
209                 spin_lock(&files->file_lock);
210                 goto repeat;
211         }
212 
213         /* All good, so we try */
214         files->resize_in_progress = true;
215         expanded = expand_fdtable(files, nr);
216         files->resize_in_progress = false;
217 
218         wake_up_all(&files->resize_wait);
219         return expanded;
220 }
221 
222 static inline void __set_close_on_exec(int fd, struct fdtable *fdt)
223 {
224         __set_bit(fd, fdt->close_on_exec);
225 }
226 
227 static inline void __clear_close_on_exec(int fd, struct fdtable *fdt)
228 {
229         __clear_bit(fd, fdt->close_on_exec);
230 }
231 
232 static inline void __set_open_fd(int fd, struct fdtable *fdt)
233 {
234         __set_bit(fd, fdt->open_fds);
235 }
236 
237 static inline void __clear_open_fd(int fd, struct fdtable *fdt)
238 {
239         __clear_bit(fd, fdt->open_fds);
240 }
241 
242 static int count_open_files(struct fdtable *fdt)
243 {
244         int size = fdt->max_fds;
245         int i;
246 
247         /* Find the last open fd */
248         for (i = size / BITS_PER_LONG; i > 0; ) {
249                 if (fdt->open_fds[--i])
250                         break;
251         }
252         i = (i + 1) * BITS_PER_LONG;
253         return i;
254 }
255 
256 /*
257  * Allocate a new files structure and copy contents from the
258  * passed in files structure.
259  * errorp will be valid only when the returned files_struct is NULL.
260  */
261 struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
262 {
263         struct files_struct *newf;
264         struct file **old_fds, **new_fds;
265         int open_files, size, i;
266         struct fdtable *old_fdt, *new_fdt;
267 
268         *errorp = -ENOMEM;
269         newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
270         if (!newf)
271                 goto out;
272 
273         atomic_set(&newf->count, 1);
274 
275         spin_lock_init(&newf->file_lock);
276         newf->resize_in_progress = false;
277         init_waitqueue_head(&newf->resize_wait);
278         newf->next_fd = 0;
279         new_fdt = &newf->fdtab;
280         new_fdt->max_fds = NR_OPEN_DEFAULT;
281         new_fdt->close_on_exec = newf->close_on_exec_init;
282         new_fdt->open_fds = newf->open_fds_init;
283         new_fdt->fd = &newf->fd_array[0];
284 
285         spin_lock(&oldf->file_lock);
286         old_fdt = files_fdtable(oldf);
287         open_files = count_open_files(old_fdt);
288 
289         /*
290          * Check whether we need to allocate a larger fd array and fd set.
291          */
292         while (unlikely(open_files > new_fdt->max_fds)) {
293                 spin_unlock(&oldf->file_lock);
294 
295                 if (new_fdt != &newf->fdtab)
296                         __free_fdtable(new_fdt);
297 
298                 new_fdt = alloc_fdtable(open_files - 1);
299                 if (!new_fdt) {
300                         *errorp = -ENOMEM;
301                         goto out_release;
302                 }
303 
304                 /* beyond sysctl_nr_open; nothing to do */
305                 if (unlikely(new_fdt->max_fds < open_files)) {
306                         __free_fdtable(new_fdt);
307                         *errorp = -EMFILE;
308                         goto out_release;
309                 }
310 
311                 /*
312                  * Reacquire the oldf lock and a pointer to its fd table
313                  * who knows it may have a new bigger fd table. We need
314                  * the latest pointer.
315                  */
316                 spin_lock(&oldf->file_lock);
317                 old_fdt = files_fdtable(oldf);
318                 open_files = count_open_files(old_fdt);
319         }
320 
321         old_fds = old_fdt->fd;
322         new_fds = new_fdt->fd;
323 
324         memcpy(new_fdt->open_fds, old_fdt->open_fds, open_files / 8);
325         memcpy(new_fdt->close_on_exec, old_fdt->close_on_exec, open_files / 8);
326 
327         for (i = open_files; i != 0; i--) {
328                 struct file *f = *old_fds++;
329                 if (f) {
330                         get_file(f);
331                 } else {
332                         /*
333                          * The fd may be claimed in the fd bitmap but not yet
334                          * instantiated in the files array if a sibling thread
335                          * is partway through open().  So make sure that this
336                          * fd is available to the new process.
337                          */
338                         __clear_open_fd(open_files - i, new_fdt);
339                 }
340                 rcu_assign_pointer(*new_fds++, f);
341         }
342         spin_unlock(&oldf->file_lock);
343 
344         /* compute the remainder to be cleared */
345         size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
346 
347         /* This is long word aligned thus could use a optimized version */
348         memset(new_fds, 0, size);
349 
350         if (new_fdt->max_fds > open_files) {
351                 int left = (new_fdt->max_fds - open_files) / 8;
352                 int start = open_files / BITS_PER_LONG;
353 
354                 memset(&new_fdt->open_fds[start], 0, left);
355                 memset(&new_fdt->close_on_exec[start], 0, left);
356         }
357 
358         rcu_assign_pointer(newf->fdt, new_fdt);
359 
360         return newf;
361 
362 out_release:
363         kmem_cache_free(files_cachep, newf);
364 out:
365         return NULL;
366 }
367 
368 static struct fdtable *close_files(struct files_struct * files)
369 {
370         /*
371          * It is safe to dereference the fd table without RCU or
372          * ->file_lock because this is the last reference to the
373          * files structure.
374          */
375         struct fdtable *fdt = rcu_dereference_raw(files->fdt);
376         int i, j = 0;
377 
378         for (;;) {
379                 unsigned long set;
380                 i = j * BITS_PER_LONG;
381                 if (i >= fdt->max_fds)
382                         break;
383                 set = fdt->open_fds[j++];
384                 while (set) {
385                         if (set & 1) {
386                                 struct file * file = xchg(&fdt->fd[i], NULL);
387                                 if (file) {
388                                         filp_close(file, files);
389                                         cond_resched_rcu_qs();
390                                 }
391                         }
392                         i++;
393                         set >>= 1;
394                 }
395         }
396 
397         return fdt;
398 }
399 
400 struct files_struct *get_files_struct(struct task_struct *task)
401 {
402         struct files_struct *files;
403 
404         task_lock(task);
405         files = task->files;
406         if (files)
407                 atomic_inc(&files->count);
408         task_unlock(task);
409 
410         return files;
411 }
412 
413 void put_files_struct(struct files_struct *files)
414 {
415         if (atomic_dec_and_test(&files->count)) {
416                 struct fdtable *fdt = close_files(files);
417 
418                 /* free the arrays if they are not embedded */
419                 if (fdt != &files->fdtab)
420                         __free_fdtable(fdt);
421                 kmem_cache_free(files_cachep, files);
422         }
423 }
424 
425 void reset_files_struct(struct files_struct *files)
426 {
427         struct task_struct *tsk = current;
428         struct files_struct *old;
429 
430         old = tsk->files;
431         task_lock(tsk);
432         tsk->files = files;
433         task_unlock(tsk);
434         put_files_struct(old);
435 }
436 
437 void exit_files(struct task_struct *tsk)
438 {
439         struct files_struct * files = tsk->files;
440 
441         if (files) {
442                 task_lock(tsk);
443                 tsk->files = NULL;
444                 task_unlock(tsk);
445                 put_files_struct(files);
446         }
447 }
448 
449 struct files_struct init_files = {
450         .count          = ATOMIC_INIT(1),
451         .fdt            = &init_files.fdtab,
452         .fdtab          = {
453                 .max_fds        = NR_OPEN_DEFAULT,
454                 .fd             = &init_files.fd_array[0],
455                 .close_on_exec  = init_files.close_on_exec_init,
456                 .open_fds       = init_files.open_fds_init,
457         },
458         .file_lock      = __SPIN_LOCK_UNLOCKED(init_files.file_lock),
459 };
460 
461 /*
462  * allocate a file descriptor, mark it busy.
463  */
464 int __alloc_fd(struct files_struct *files,
465                unsigned start, unsigned end, unsigned flags)
466 {
467         unsigned int fd;
468         int error;
469         struct fdtable *fdt;
470 
471         spin_lock(&files->file_lock);
472 repeat:
473         fdt = files_fdtable(files);
474         fd = start;
475         if (fd < files->next_fd)
476                 fd = files->next_fd;
477 
478         if (fd < fdt->max_fds)
479                 fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd);
480 
481         /*
482          * N.B. For clone tasks sharing a files structure, this test
483          * will limit the total number of files that can be opened.
484          */
485         error = -EMFILE;
486         if (fd >= end)
487                 goto out;
488 
489         error = expand_files(files, fd);
490         if (error < 0)
491                 goto out;
492 
493         /*
494          * If we needed to expand the fs array we
495          * might have blocked - try again.
496          */
497         if (error)
498                 goto repeat;
499 
500         if (start <= files->next_fd)
501                 files->next_fd = fd + 1;
502 
503         __set_open_fd(fd, fdt);
504         if (flags & O_CLOEXEC)
505                 __set_close_on_exec(fd, fdt);
506         else
507                 __clear_close_on_exec(fd, fdt);
508         error = fd;
509 #if 1
510         /* Sanity check */
511         if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
512                 printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
513                 rcu_assign_pointer(fdt->fd[fd], NULL);
514         }
515 #endif
516 
517 out:
518         spin_unlock(&files->file_lock);
519         return error;
520 }
521 
522 static int alloc_fd(unsigned start, unsigned flags)
523 {
524         return __alloc_fd(current->files, start, rlimit(RLIMIT_NOFILE), flags);
525 }
526 
527 int get_unused_fd_flags(unsigned flags)
528 {
529         return __alloc_fd(current->files, 0, rlimit(RLIMIT_NOFILE), flags);
530 }
531 EXPORT_SYMBOL(get_unused_fd_flags);
532 
533 static void __put_unused_fd(struct files_struct *files, unsigned int fd)
534 {
535         struct fdtable *fdt = files_fdtable(files);
536         __clear_open_fd(fd, fdt);
537         if (fd < files->next_fd)
538                 files->next_fd = fd;
539 }
540 
541 void put_unused_fd(unsigned int fd)
542 {
543         struct files_struct *files = current->files;
544         spin_lock(&files->file_lock);
545         __put_unused_fd(files, fd);
546         spin_unlock(&files->file_lock);
547 }
548 
549 EXPORT_SYMBOL(put_unused_fd);
550 
551 /*
552  * Install a file pointer in the fd array.
553  *
554  * The VFS is full of places where we drop the files lock between
555  * setting the open_fds bitmap and installing the file in the file
556  * array.  At any such point, we are vulnerable to a dup2() race
557  * installing a file in the array before us.  We need to detect this and
558  * fput() the struct file we are about to overwrite in this case.
559  *
560  * It should never happen - if we allow dup2() do it, _really_ bad things
561  * will follow.
562  *
563  * NOTE: __fd_install() variant is really, really low-level; don't
564  * use it unless you are forced to by truly lousy API shoved down
565  * your throat.  'files' *MUST* be either current->files or obtained
566  * by get_files_struct(current) done by whoever had given it to you,
567  * or really bad things will happen.  Normally you want to use
568  * fd_install() instead.
569  */
570 
571 void __fd_install(struct files_struct *files, unsigned int fd,
572                 struct file *file)
573 {
574         struct fdtable *fdt;
575 
576         might_sleep();
577         rcu_read_lock_sched();
578 
579         while (unlikely(files->resize_in_progress)) {
580                 rcu_read_unlock_sched();
581                 wait_event(files->resize_wait, !files->resize_in_progress);
582                 rcu_read_lock_sched();
583         }
584         /* coupled with smp_wmb() in expand_fdtable() */
585         smp_rmb();
586         fdt = rcu_dereference_sched(files->fdt);
587         BUG_ON(fdt->fd[fd] != NULL);
588         rcu_assign_pointer(fdt->fd[fd], file);
589         rcu_read_unlock_sched();
590 }
591 
592 void fd_install(unsigned int fd, struct file *file)
593 {
594         __fd_install(current->files, fd, file);
595 }
596 
597 EXPORT_SYMBOL(fd_install);
598 
599 /*
600  * The same warnings as for __alloc_fd()/__fd_install() apply here...
601  */
602 int __close_fd(struct files_struct *files, unsigned fd)
603 {
604         struct file *file;
605         struct fdtable *fdt;
606 
607         spin_lock(&files->file_lock);
608         fdt = files_fdtable(files);
609         if (fd >= fdt->max_fds)
610                 goto out_unlock;
611         file = fdt->fd[fd];
612         if (!file)
613                 goto out_unlock;
614         rcu_assign_pointer(fdt->fd[fd], NULL);
615         __clear_close_on_exec(fd, fdt);
616         __put_unused_fd(files, fd);
617         spin_unlock(&files->file_lock);
618         return filp_close(file, files);
619 
620 out_unlock:
621         spin_unlock(&files->file_lock);
622         return -EBADF;
623 }
624 
625 void do_close_on_exec(struct files_struct *files)
626 {
627         unsigned i;
628         struct fdtable *fdt;
629 
630         /* exec unshares first */
631         spin_lock(&files->file_lock);
632         for (i = 0; ; i++) {
633                 unsigned long set;
634                 unsigned fd = i * BITS_PER_LONG;
635                 fdt = files_fdtable(files);
636                 if (fd >= fdt->max_fds)
637                         break;
638                 set = fdt->close_on_exec[i];
639                 if (!set)
640                         continue;
641                 fdt->close_on_exec[i] = 0;
642                 for ( ; set ; fd++, set >>= 1) {
643                         struct file *file;
644                         if (!(set & 1))
645                                 continue;
646                         file = fdt->fd[fd];
647                         if (!file)
648                                 continue;
649                         rcu_assign_pointer(fdt->fd[fd], NULL);
650                         __put_unused_fd(files, fd);
651                         spin_unlock(&files->file_lock);
652                         filp_close(file, files);
653                         cond_resched();
654                         spin_lock(&files->file_lock);
655                 }
656 
657         }
658         spin_unlock(&files->file_lock);
659 }
660 
661 static struct file *__fget(unsigned int fd, fmode_t mask)
662 {
663         struct files_struct *files = current->files;
664         struct file *file;
665 
666         rcu_read_lock();
667 loop:
668         file = fcheck_files(files, fd);
669         if (file) {
670                 /* File object ref couldn't be taken.
671                  * dup2() atomicity guarantee is the reason
672                  * we loop to catch the new file (or NULL pointer)
673                  */
674                 if (file->f_mode & mask)
675                         file = NULL;
676                 else if (!get_file_rcu(file))
677                         goto loop;
678         }
679         rcu_read_unlock();
680 
681         return file;
682 }
683 
684 struct file *fget(unsigned int fd)
685 {
686         return __fget(fd, FMODE_PATH);
687 }
688 EXPORT_SYMBOL(fget);
689 
690 struct file *fget_raw(unsigned int fd)
691 {
692         return __fget(fd, 0);
693 }
694 EXPORT_SYMBOL(fget_raw);
695 
696 /*
697  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
698  *
699  * You can use this instead of fget if you satisfy all of the following
700  * conditions:
701  * 1) You must call fput_light before exiting the syscall and returning control
702  *    to userspace (i.e. you cannot remember the returned struct file * after
703  *    returning to userspace).
704  * 2) You must not call filp_close on the returned struct file * in between
705  *    calls to fget_light and fput_light.
706  * 3) You must not clone the current task in between the calls to fget_light
707  *    and fput_light.
708  *
709  * The fput_needed flag returned by fget_light should be passed to the
710  * corresponding fput_light.
711  */
712 static unsigned long __fget_light(unsigned int fd, fmode_t mask)
713 {
714         struct files_struct *files = current->files;
715         struct file *file;
716 
717         if (atomic_read(&files->count) == 1) {
718                 file = __fcheck_files(files, fd);
719                 if (!file || unlikely(file->f_mode & mask))
720                         return 0;
721                 return (unsigned long)file;
722         } else {
723                 file = __fget(fd, mask);
724                 if (!file)
725                         return 0;
726                 return FDPUT_FPUT | (unsigned long)file;
727         }
728 }
729 unsigned long __fdget(unsigned int fd)
730 {
731         return __fget_light(fd, FMODE_PATH);
732 }
733 EXPORT_SYMBOL(__fdget);
734 
735 unsigned long __fdget_raw(unsigned int fd)
736 {
737         return __fget_light(fd, 0);
738 }
739 
740 unsigned long __fdget_pos(unsigned int fd)
741 {
742         unsigned long v = __fdget(fd);
743         struct file *file = (struct file *)(v & ~3);
744 
745         if (file && (file->f_mode & FMODE_ATOMIC_POS)) {
746                 if (file_count(file) > 1) {
747                         v |= FDPUT_POS_UNLOCK;
748                         mutex_lock(&file->f_pos_lock);
749                 }
750         }
751         return v;
752 }
753 
754 /*
755  * We only lock f_pos if we have threads or if the file might be
756  * shared with another process. In both cases we'll have an elevated
757  * file count (done either by fdget() or by fork()).
758  */
759 
760 void set_close_on_exec(unsigned int fd, int flag)
761 {
762         struct files_struct *files = current->files;
763         struct fdtable *fdt;
764         spin_lock(&files->file_lock);
765         fdt = files_fdtable(files);
766         if (flag)
767                 __set_close_on_exec(fd, fdt);
768         else
769                 __clear_close_on_exec(fd, fdt);
770         spin_unlock(&files->file_lock);
771 }
772 
773 bool get_close_on_exec(unsigned int fd)
774 {
775         struct files_struct *files = current->files;
776         struct fdtable *fdt;
777         bool res;
778         rcu_read_lock();
779         fdt = files_fdtable(files);
780         res = close_on_exec(fd, fdt);
781         rcu_read_unlock();
782         return res;
783 }
784 
785 static int do_dup2(struct files_struct *files,
786         struct file *file, unsigned fd, unsigned flags)
787 __releases(&files->file_lock)
788 {
789         struct file *tofree;
790         struct fdtable *fdt;
791 
792         /*
793          * We need to detect attempts to do dup2() over allocated but still
794          * not finished descriptor.  NB: OpenBSD avoids that at the price of
795          * extra work in their equivalent of fget() - they insert struct
796          * file immediately after grabbing descriptor, mark it larval if
797          * more work (e.g. actual opening) is needed and make sure that
798          * fget() treats larval files as absent.  Potentially interesting,
799          * but while extra work in fget() is trivial, locking implications
800          * and amount of surgery on open()-related paths in VFS are not.
801          * FreeBSD fails with -EBADF in the same situation, NetBSD "solution"
802          * deadlocks in rather amusing ways, AFAICS.  All of that is out of
803          * scope of POSIX or SUS, since neither considers shared descriptor
804          * tables and this condition does not arise without those.
805          */
806         fdt = files_fdtable(files);
807         tofree = fdt->fd[fd];
808         if (!tofree && fd_is_open(fd, fdt))
809                 goto Ebusy;
810         get_file(file);
811         rcu_assign_pointer(fdt->fd[fd], file);
812         __set_open_fd(fd, fdt);
813         if (flags & O_CLOEXEC)
814                 __set_close_on_exec(fd, fdt);
815         else
816                 __clear_close_on_exec(fd, fdt);
817         spin_unlock(&files->file_lock);
818 
819         if (tofree)
820                 filp_close(tofree, files);
821 
822         return fd;
823 
824 Ebusy:
825         spin_unlock(&files->file_lock);
826         return -EBUSY;
827 }
828 
829 int replace_fd(unsigned fd, struct file *file, unsigned flags)
830 {
831         int err;
832         struct files_struct *files = current->files;
833 
834         if (!file)
835                 return __close_fd(files, fd);
836 
837         if (fd >= rlimit(RLIMIT_NOFILE))
838                 return -EBADF;
839 
840         spin_lock(&files->file_lock);
841         err = expand_files(files, fd);
842         if (unlikely(err < 0))
843                 goto out_unlock;
844         return do_dup2(files, file, fd, flags);
845 
846 out_unlock:
847         spin_unlock(&files->file_lock);
848         return err;
849 }
850 
851 SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
852 {
853         int err = -EBADF;
854         struct file *file;
855         struct files_struct *files = current->files;
856 
857         if ((flags & ~O_CLOEXEC) != 0)
858                 return -EINVAL;
859 
860         if (unlikely(oldfd == newfd))
861                 return -EINVAL;
862 
863         if (newfd >= rlimit(RLIMIT_NOFILE))
864                 return -EBADF;
865 
866         spin_lock(&files->file_lock);
867         err = expand_files(files, newfd);
868         file = fcheck(oldfd);
869         if (unlikely(!file))
870                 goto Ebadf;
871         if (unlikely(err < 0)) {
872                 if (err == -EMFILE)
873                         goto Ebadf;
874                 goto out_unlock;
875         }
876         return do_dup2(files, file, newfd, flags);
877 
878 Ebadf:
879         err = -EBADF;
880 out_unlock:
881         spin_unlock(&files->file_lock);
882         return err;
883 }
884 
885 SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
886 {
887         if (unlikely(newfd == oldfd)) { /* corner case */
888                 struct files_struct *files = current->files;
889                 int retval = oldfd;
890 
891                 rcu_read_lock();
892                 if (!fcheck_files(files, oldfd))
893                         retval = -EBADF;
894                 rcu_read_unlock();
895                 return retval;
896         }
897         return sys_dup3(oldfd, newfd, 0);
898 }
899 
900 SYSCALL_DEFINE1(dup, unsigned int, fildes)
901 {
902         int ret = -EBADF;
903         struct file *file = fget_raw(fildes);
904 
905         if (file) {
906                 ret = get_unused_fd_flags(0);
907                 if (ret >= 0)
908                         fd_install(ret, file);
909                 else
910                         fput(file);
911         }
912         return ret;
913 }
914 
915 int f_dupfd(unsigned int from, struct file *file, unsigned flags)
916 {
917         int err;
918         if (from >= rlimit(RLIMIT_NOFILE))
919                 return -EINVAL;
920         err = alloc_fd(from, flags);
921         if (err >= 0) {
922                 get_file(file);
923                 fd_install(err, file);
924         }
925         return err;
926 }
927 
928 int iterate_fd(struct files_struct *files, unsigned n,
929                 int (*f)(const void *, struct file *, unsigned),
930                 const void *p)
931 {
932         struct fdtable *fdt;
933         int res = 0;
934         if (!files)
935                 return 0;
936         spin_lock(&files->file_lock);
937         for (fdt = files_fdtable(files); n < fdt->max_fds; n++) {
938                 struct file *file;
939                 file = rcu_dereference_check_fdtable(files, fdt->fd[n]);
940                 if (!file)
941                         continue;
942                 res = f(p, file, n);
943                 if (res)
944                         break;
945         }
946         spin_unlock(&files->file_lock);
947         return res;
948 }
949 EXPORT_SYMBOL(iterate_fd);
950 

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