1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  linux/fs/file.c
  4 *
  5 *  Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
  6 *
  7 *  Manage the dynamic fd arrays in the process files_struct.
  8 */
  9
 10#include <linux/syscalls.h>
 11#include <linux/export.h>
 12#include <linux/fs.h>
 13#include <linux/mm.h>
 14#include <linux/sched/signal.h>
 
 
 15#include <linux/slab.h>
 
 16#include <linux/file.h>
 17#include <linux/fdtable.h>
 18#include <linux/bitops.h>
 
 19#include <linux/spinlock.h>
 20#include <linux/rcupdate.h>
 
 21
 22unsigned int sysctl_nr_open __read_mostly = 1024*1024;
 23unsigned int sysctl_nr_open_min = BITS_PER_LONG;
 24/* our min() is unusable in constant expressions ;-/ */
 25#define __const_min(x, y) ((x) < (y) ? (x) : (y))
 26unsigned int sysctl_nr_open_max =
 27	__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 28
 29static void __free_fdtable(struct fdtable *fdt)
 30{
 31	kvfree(fdt->fd);
 32	kvfree(fdt->open_fds);
 33	kfree(fdt);
 34}
 35
 36static void free_fdtable_rcu(struct rcu_head *rcu)
 37{
 38	__free_fdtable(container_of(rcu, struct fdtable, rcu));
 39}
 
 40
 41#define BITBIT_NR(nr)	BITS_TO_LONGS(BITS_TO_LONGS(nr))
 42#define BITBIT_SIZE(nr)	(BITBIT_NR(nr) * sizeof(long))
 
 
 
 
 43
 44/*
 45 * Copy 'count' fd bits from the old table to the new table and clear the extra
 46 * space if any.  This does not copy the file pointers.  Called with the files
 47 * spinlock held for write.
 48 */
 49static void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt,
 50			    unsigned int count)
 51{
 52	unsigned int cpy, set;
 
 53
 54	cpy = count / BITS_PER_BYTE;
 55	set = (nfdt->max_fds - count) / BITS_PER_BYTE;
 56	memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
 57	memset((char *)nfdt->open_fds + cpy, 0, set);
 58	memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
 59	memset((char *)nfdt->close_on_exec + cpy, 0, set);
 60
 61	cpy = BITBIT_SIZE(count);
 62	set = BITBIT_SIZE(nfdt->max_fds) - cpy;
 63	memcpy(nfdt->full_fds_bits, ofdt->full_fds_bits, cpy);
 64	memset((char *)nfdt->full_fds_bits + cpy, 0, set);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 65}
 66
 67/*
 68 * Copy all file descriptors from the old table to the new, expanded table and
 69 * clear the extra space.  Called with the files spinlock held for write.
 70 */
 71static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
 72{
 73	unsigned int cpy, set;
 74
 75	BUG_ON(nfdt->max_fds < ofdt->max_fds);
 76
 77	cpy = ofdt->max_fds * sizeof(struct file *);
 78	set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
 79	memcpy(nfdt->fd, ofdt->fd, cpy);
 80	memset((char *)nfdt->fd + cpy, 0, set);
 81
 82	copy_fd_bitmaps(nfdt, ofdt, ofdt->max_fds);
 
 
 
 
 
 83}
 84
 85static struct fdtable * alloc_fdtable(unsigned int nr)
 86{
 87	struct fdtable *fdt;
 88	void *data;
 89
 90	/*
 91	 * Figure out how many fds we actually want to support in this fdtable.
 92	 * Allocation steps are keyed to the size of the fdarray, since it
 93	 * grows far faster than any of the other dynamic data. We try to fit
 94	 * the fdarray into comfortable page-tuned chunks: starting at 1024B
 95	 * and growing in powers of two from there on.
 96	 */
 97	nr /= (1024 / sizeof(struct file *));
 98	nr = roundup_pow_of_two(nr + 1);
 99	nr *= (1024 / sizeof(struct file *));
100	/*
101	 * Note that this can drive nr *below* what we had passed if sysctl_nr_open
102	 * had been set lower between the check in expand_files() and here.  Deal
103	 * with that in caller, it's cheaper that way.
104	 *
105	 * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
106	 * bitmaps handling below becomes unpleasant, to put it mildly...
107	 */
108	if (unlikely(nr > sysctl_nr_open))
109		nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
110
111	fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL_ACCOUNT);
112	if (!fdt)
113		goto out;
114	fdt->max_fds = nr;
115	data = kvmalloc_array(nr, sizeof(struct file *), GFP_KERNEL_ACCOUNT);
116	if (!data)
117		goto out_fdt;
118	fdt->fd = data;
119
120	data = kvmalloc(max_t(size_t,
121				 2 * nr / BITS_PER_BYTE + BITBIT_SIZE(nr), L1_CACHE_BYTES),
122				 GFP_KERNEL_ACCOUNT);
123	if (!data)
124		goto out_arr;
125	fdt->open_fds = data;
126	data += nr / BITS_PER_BYTE;
127	fdt->close_on_exec = data;
128	data += nr / BITS_PER_BYTE;
129	fdt->full_fds_bits = data;
 
130
131	return fdt;
132
133out_arr:
134	kvfree(fdt->fd);
135out_fdt:
136	kfree(fdt);
137out:
138	return NULL;
139}
140
141/*
142 * Expand the file descriptor table.
143 * This function will allocate a new fdtable and both fd array and fdset, of
144 * the given size.
145 * Return <0 error code on error; 1 on successful completion.
146 * The files->file_lock should be held on entry, and will be held on exit.
147 */
148static int expand_fdtable(struct files_struct *files, unsigned int nr)
149	__releases(files->file_lock)
150	__acquires(files->file_lock)
151{
152	struct fdtable *new_fdt, *cur_fdt;
153
154	spin_unlock(&files->file_lock);
155	new_fdt = alloc_fdtable(nr);
156
157	/* make sure all __fd_install() have seen resize_in_progress
158	 * or have finished their rcu_read_lock_sched() section.
159	 */
160	if (atomic_read(&files->count) > 1)
161		synchronize_sched();
162
163	spin_lock(&files->file_lock);
164	if (!new_fdt)
165		return -ENOMEM;
166	/*
167	 * extremely unlikely race - sysctl_nr_open decreased between the check in
168	 * caller and alloc_fdtable().  Cheaper to catch it here...
169	 */
170	if (unlikely(new_fdt->max_fds <= nr)) {
171		__free_fdtable(new_fdt);
172		return -EMFILE;
173	}
 
 
 
 
174	cur_fdt = files_fdtable(files);
175	BUG_ON(nr < cur_fdt->max_fds);
176	copy_fdtable(new_fdt, cur_fdt);
177	rcu_assign_pointer(files->fdt, new_fdt);
178	if (cur_fdt != &files->fdtab)
179		call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
180	/* coupled with smp_rmb() in __fd_install() */
181	smp_wmb();
 
 
 
182	return 1;
183}
184
185/*
186 * Expand files.
187 * This function will expand the file structures, if the requested size exceeds
188 * the current capacity and there is room for expansion.
189 * Return <0 error code on error; 0 when nothing done; 1 when files were
190 * expanded and execution may have blocked.
191 * The files->file_lock should be held on entry, and will be held on exit.
192 */
193static int expand_files(struct files_struct *files, unsigned int nr)
194	__releases(files->file_lock)
195	__acquires(files->file_lock)
196{
197	struct fdtable *fdt;
198	int expanded = 0;
199
200repeat:
201	fdt = files_fdtable(files);
202
 
 
 
 
 
 
 
203	/* Do we need to expand? */
204	if (nr < fdt->max_fds)
205		return expanded;
206
207	/* Can we expand? */
208	if (nr >= sysctl_nr_open)
209		return -EMFILE;
210
211	if (unlikely(files->resize_in_progress)) {
212		spin_unlock(&files->file_lock);
213		expanded = 1;
214		wait_event(files->resize_wait, !files->resize_in_progress);
215		spin_lock(&files->file_lock);
216		goto repeat;
217	}
218
219	/* All good, so we try */
220	files->resize_in_progress = true;
221	expanded = expand_fdtable(files, nr);
222	files->resize_in_progress = false;
223
224	wake_up_all(&files->resize_wait);
225	return expanded;
226}
227
228static inline void __set_close_on_exec(unsigned int fd, struct fdtable *fdt)
229{
230	__set_bit(fd, fdt->close_on_exec);
231}
232
233static inline void __clear_close_on_exec(unsigned int fd, struct fdtable *fdt)
234{
235	if (test_bit(fd, fdt->close_on_exec))
236		__clear_bit(fd, fdt->close_on_exec);
237}
238
239static inline void __set_open_fd(unsigned int fd, struct fdtable *fdt)
240{
241	__set_bit(fd, fdt->open_fds);
242	fd /= BITS_PER_LONG;
243	if (!~fdt->open_fds[fd])
244		__set_bit(fd, fdt->full_fds_bits);
245}
246
247static inline void __clear_open_fd(unsigned int fd, struct fdtable *fdt)
248{
249	__clear_bit(fd, fdt->open_fds);
250	__clear_bit(fd / BITS_PER_LONG, fdt->full_fds_bits);
251}
252
253static unsigned int count_open_files(struct fdtable *fdt)
254{
255	unsigned int size = fdt->max_fds;
256	unsigned int i;
257
258	/* Find the last open fd */
259	for (i = size / BITS_PER_LONG; i > 0; ) {
260		if (fdt->open_fds[--i])
261			break;
262	}
263	i = (i + 1) * BITS_PER_LONG;
264	return i;
265}
266
267/*
268 * Allocate a new files structure and copy contents from the
269 * passed in files structure.
270 * errorp will be valid only when the returned files_struct is NULL.
271 */
272struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
273{
274	struct files_struct *newf;
275	struct file **old_fds, **new_fds;
276	unsigned int open_files, i;
277	struct fdtable *old_fdt, *new_fdt;
278
279	*errorp = -ENOMEM;
280	newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
281	if (!newf)
282		goto out;
283
284	atomic_set(&newf->count, 1);
285
286	spin_lock_init(&newf->file_lock);
287	newf->resize_in_progress = false;
288	init_waitqueue_head(&newf->resize_wait);
289	newf->next_fd = 0;
290	new_fdt = &newf->fdtab;
291	new_fdt->max_fds = NR_OPEN_DEFAULT;
292	new_fdt->close_on_exec = newf->close_on_exec_init;
293	new_fdt->open_fds = newf->open_fds_init;
294	new_fdt->full_fds_bits = newf->full_fds_bits_init;
295	new_fdt->fd = &newf->fd_array[0];
 
296
297	spin_lock(&oldf->file_lock);
298	old_fdt = files_fdtable(oldf);
299	open_files = count_open_files(old_fdt);
300
301	/*
302	 * Check whether we need to allocate a larger fd array and fd set.
303	 */
304	while (unlikely(open_files > new_fdt->max_fds)) {
305		spin_unlock(&oldf->file_lock);
306
307		if (new_fdt != &newf->fdtab)
308			__free_fdtable(new_fdt);
309
310		new_fdt = alloc_fdtable(open_files - 1);
311		if (!new_fdt) {
312			*errorp = -ENOMEM;
313			goto out_release;
314		}
315
316		/* beyond sysctl_nr_open; nothing to do */
317		if (unlikely(new_fdt->max_fds < open_files)) {
318			__free_fdtable(new_fdt);
319			*errorp = -EMFILE;
320			goto out_release;
321		}
322
323		/*
324		 * Reacquire the oldf lock and a pointer to its fd table
325		 * who knows it may have a new bigger fd table. We need
326		 * the latest pointer.
327		 */
328		spin_lock(&oldf->file_lock);
329		old_fdt = files_fdtable(oldf);
330		open_files = count_open_files(old_fdt);
331	}
332
333	copy_fd_bitmaps(new_fdt, old_fdt, open_files);
334
335	old_fds = old_fdt->fd;
336	new_fds = new_fdt->fd;
337
 
 
 
 
 
338	for (i = open_files; i != 0; i--) {
339		struct file *f = *old_fds++;
340		if (f) {
341			get_file(f);
342		} else {
343			/*
344			 * The fd may be claimed in the fd bitmap but not yet
345			 * instantiated in the files array if a sibling thread
346			 * is partway through open().  So make sure that this
347			 * fd is available to the new process.
348			 */
349			__clear_open_fd(open_files - i, new_fdt);
350		}
351		rcu_assign_pointer(*new_fds++, f);
352	}
353	spin_unlock(&oldf->file_lock);
354
355	/* clear the remainder */
356	memset(new_fds, 0, (new_fdt->max_fds - open_files) * sizeof(struct file *));
 
 
 
 
 
 
 
 
 
 
 
357
358	rcu_assign_pointer(newf->fdt, new_fdt);
359
360	return newf;
361
362out_release:
363	kmem_cache_free(files_cachep, newf);
364out:
365	return NULL;
366}
367
368static 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	unsigned 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();
390				}
391			}
392			i++;
393			set >>= 1;
394		}
395	}
396
397	return fdt;
398}
399
400struct 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
413void 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
425void 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
437void 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
449struct 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		.full_fds_bits	= init_files.full_fds_bits_init,
458	},
459	.file_lock	= __SPIN_LOCK_UNLOCKED(init_files.file_lock),
460};
461
462static unsigned int find_next_fd(struct fdtable *fdt, unsigned int start)
463{
464	unsigned int maxfd = fdt->max_fds;
465	unsigned int maxbit = maxfd / BITS_PER_LONG;
466	unsigned int bitbit = start / BITS_PER_LONG;
467
468	bitbit = find_next_zero_bit(fdt->full_fds_bits, maxbit, bitbit) * BITS_PER_LONG;
469	if (bitbit > maxfd)
470		return maxfd;
471	if (bitbit > start)
472		start = bitbit;
473	return find_next_zero_bit(fdt->open_fds, maxfd, start);
474}
475
476/*
477 * allocate a file descriptor, mark it busy.
478 */
479int __alloc_fd(struct files_struct *files,
480	       unsigned start, unsigned end, unsigned flags)
481{
 
482	unsigned int fd;
483	int error;
484	struct fdtable *fdt;
485
486	spin_lock(&files->file_lock);
487repeat:
488	fdt = files_fdtable(files);
489	fd = start;
490	if (fd < files->next_fd)
491		fd = files->next_fd;
492
493	if (fd < fdt->max_fds)
494		fd = find_next_fd(fdt, fd);
495
496	/*
497	 * N.B. For clone tasks sharing a files structure, this test
498	 * will limit the total number of files that can be opened.
499	 */
500	error = -EMFILE;
501	if (fd >= end)
502		goto out;
503
504	error = expand_files(files, fd);
505	if (error < 0)
506		goto out;
507
508	/*
509	 * If we needed to expand the fs array we
510	 * might have blocked - try again.
511	 */
512	if (error)
513		goto repeat;
514
515	if (start <= files->next_fd)
516		files->next_fd = fd + 1;
517
518	__set_open_fd(fd, fdt);
519	if (flags & O_CLOEXEC)
520		__set_close_on_exec(fd, fdt);
521	else
522		__clear_close_on_exec(fd, fdt);
523	error = fd;
524#if 1
525	/* Sanity check */
526	if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
527		printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
528		rcu_assign_pointer(fdt->fd[fd], NULL);
529	}
530#endif
531
532out:
533	spin_unlock(&files->file_lock);
534	return error;
535}
536
537static int alloc_fd(unsigned start, unsigned flags)
538{
539	return __alloc_fd(current->files, start, rlimit(RLIMIT_NOFILE), flags);
540}
541
542int get_unused_fd_flags(unsigned flags)
543{
544	return __alloc_fd(current->files, 0, rlimit(RLIMIT_NOFILE), flags);
545}
546EXPORT_SYMBOL(get_unused_fd_flags);
547
548static void __put_unused_fd(struct files_struct *files, unsigned int fd)
549{
550	struct fdtable *fdt = files_fdtable(files);
551	__clear_open_fd(fd, fdt);
552	if (fd < files->next_fd)
553		files->next_fd = fd;
554}
555
556void put_unused_fd(unsigned int fd)
557{
558	struct files_struct *files = current->files;
559	spin_lock(&files->file_lock);
560	__put_unused_fd(files, fd);
561	spin_unlock(&files->file_lock);
562}
563
564EXPORT_SYMBOL(put_unused_fd);
565
566/*
567 * Install a file pointer in the fd array.
568 *
569 * The VFS is full of places where we drop the files lock between
570 * setting the open_fds bitmap and installing the file in the file
571 * array.  At any such point, we are vulnerable to a dup2() race
572 * installing a file in the array before us.  We need to detect this and
573 * fput() the struct file we are about to overwrite in this case.
574 *
575 * It should never happen - if we allow dup2() do it, _really_ bad things
576 * will follow.
577 *
578 * NOTE: __fd_install() variant is really, really low-level; don't
579 * use it unless you are forced to by truly lousy API shoved down
580 * your throat.  'files' *MUST* be either current->files or obtained
581 * by get_files_struct(current) done by whoever had given it to you,
582 * or really bad things will happen.  Normally you want to use
583 * fd_install() instead.
584 */
585
586void __fd_install(struct files_struct *files, unsigned int fd,
587		struct file *file)
588{
589	struct fdtable *fdt;
590
591	rcu_read_lock_sched();
592
593	if (unlikely(files->resize_in_progress)) {
594		rcu_read_unlock_sched();
595		spin_lock(&files->file_lock);
596		fdt = files_fdtable(files);
597		BUG_ON(fdt->fd[fd] != NULL);
598		rcu_assign_pointer(fdt->fd[fd], file);
599		spin_unlock(&files->file_lock);
600		return;
601	}
602	/* coupled with smp_wmb() in expand_fdtable() */
603	smp_rmb();
604	fdt = rcu_dereference_sched(files->fdt);
605	BUG_ON(fdt->fd[fd] != NULL);
606	rcu_assign_pointer(fdt->fd[fd], file);
607	rcu_read_unlock_sched();
608}
609
610void fd_install(unsigned int fd, struct file *file)
611{
612	__fd_install(current->files, fd, file);
613}
614
615EXPORT_SYMBOL(fd_install);
616
617/*
618 * The same warnings as for __alloc_fd()/__fd_install() apply here...
619 */
620int __close_fd(struct files_struct *files, unsigned fd)
621{
622	struct file *file;
623	struct fdtable *fdt;
624
625	spin_lock(&files->file_lock);
626	fdt = files_fdtable(files);
627	if (fd >= fdt->max_fds)
628		goto out_unlock;
629	file = fdt->fd[fd];
630	if (!file)
631		goto out_unlock;
632	rcu_assign_pointer(fdt->fd[fd], NULL);
633	__put_unused_fd(files, fd);
634	spin_unlock(&files->file_lock);
635	return filp_close(file, files);
636
637out_unlock:
638	spin_unlock(&files->file_lock);
639	return -EBADF;
640}
641EXPORT_SYMBOL(__close_fd); /* for ksys_close() */
642
643void do_close_on_exec(struct files_struct *files)
644{
645	unsigned i;
646	struct fdtable *fdt;
647
648	/* exec unshares first */
649	spin_lock(&files->file_lock);
650	for (i = 0; ; i++) {
651		unsigned long set;
652		unsigned fd = i * BITS_PER_LONG;
653		fdt = files_fdtable(files);
654		if (fd >= fdt->max_fds)
655			break;
656		set = fdt->close_on_exec[i];
657		if (!set)
658			continue;
659		fdt->close_on_exec[i] = 0;
660		for ( ; set ; fd++, set >>= 1) {
661			struct file *file;
662			if (!(set & 1))
663				continue;
664			file = fdt->fd[fd];
665			if (!file)
666				continue;
667			rcu_assign_pointer(fdt->fd[fd], NULL);
668			__put_unused_fd(files, fd);
669			spin_unlock(&files->file_lock);
670			filp_close(file, files);
671			cond_resched();
672			spin_lock(&files->file_lock);
673		}
674
675	}
676	spin_unlock(&files->file_lock);
677}
678
679static struct file *__fget(unsigned int fd, fmode_t mask)
680{
681	struct files_struct *files = current->files;
682	struct file *file;
683
684	rcu_read_lock();
685loop:
686	file = fcheck_files(files, fd);
687	if (file) {
688		/* File object ref couldn't be taken.
689		 * dup2() atomicity guarantee is the reason
690		 * we loop to catch the new file (or NULL pointer)
691		 */
692		if (file->f_mode & mask)
693			file = NULL;
694		else if (!get_file_rcu(file))
695			goto loop;
696	}
697	rcu_read_unlock();
698
699	return file;
700}
701
702struct file *fget(unsigned int fd)
703{
704	return __fget(fd, FMODE_PATH);
705}
706EXPORT_SYMBOL(fget);
707
708struct file *fget_raw(unsigned int fd)
709{
710	return __fget(fd, 0);
711}
712EXPORT_SYMBOL(fget_raw);
713
714/*
715 * Lightweight file lookup - no refcnt increment if fd table isn't shared.
716 *
717 * You can use this instead of fget if you satisfy all of the following
718 * conditions:
719 * 1) You must call fput_light before exiting the syscall and returning control
720 *    to userspace (i.e. you cannot remember the returned struct file * after
721 *    returning to userspace).
722 * 2) You must not call filp_close on the returned struct file * in between
723 *    calls to fget_light and fput_light.
724 * 3) You must not clone the current task in between the calls to fget_light
725 *    and fput_light.
726 *
727 * The fput_needed flag returned by fget_light should be passed to the
728 * corresponding fput_light.
729 */
730static unsigned long __fget_light(unsigned int fd, fmode_t mask)
731{
732	struct files_struct *files = current->files;
733	struct file *file;
734
735	if (atomic_read(&files->count) == 1) {
736		file = __fcheck_files(files, fd);
737		if (!file || unlikely(file->f_mode & mask))
738			return 0;
739		return (unsigned long)file;
740	} else {
741		file = __fget(fd, mask);
742		if (!file)
743			return 0;
744		return FDPUT_FPUT | (unsigned long)file;
745	}
746}
747unsigned long __fdget(unsigned int fd)
748{
749	return __fget_light(fd, FMODE_PATH);
750}
751EXPORT_SYMBOL(__fdget);
752
753unsigned long __fdget_raw(unsigned int fd)
754{
755	return __fget_light(fd, 0);
756}
757
758unsigned long __fdget_pos(unsigned int fd)
759{
760	unsigned long v = __fdget(fd);
761	struct file *file = (struct file *)(v & ~3);
762
763	if (file && (file->f_mode & FMODE_ATOMIC_POS)) {
764		if (file_count(file) > 1) {
765			v |= FDPUT_POS_UNLOCK;
766			mutex_lock(&file->f_pos_lock);
767		}
768	}
769	return v;
770}
771
772void __f_unlock_pos(struct file *f)
773{
774	mutex_unlock(&f->f_pos_lock);
775}
776
777/*
778 * We only lock f_pos if we have threads or if the file might be
779 * shared with another process. In both cases we'll have an elevated
780 * file count (done either by fdget() or by fork()).
781 */
782
783void set_close_on_exec(unsigned int fd, int flag)
784{
785	struct files_struct *files = current->files;
786	struct fdtable *fdt;
787	spin_lock(&files->file_lock);
788	fdt = files_fdtable(files);
789	if (flag)
790		__set_close_on_exec(fd, fdt);
791	else
792		__clear_close_on_exec(fd, fdt);
793	spin_unlock(&files->file_lock);
794}
795
796bool get_close_on_exec(unsigned int fd)
797{
798	struct files_struct *files = current->files;
799	struct fdtable *fdt;
800	bool res;
801	rcu_read_lock();
802	fdt = files_fdtable(files);
803	res = close_on_exec(fd, fdt);
804	rcu_read_unlock();
805	return res;
806}
807
808static int do_dup2(struct files_struct *files,
809	struct file *file, unsigned fd, unsigned flags)
810__releases(&files->file_lock)
811{
812	struct file *tofree;
813	struct fdtable *fdt;
814
815	/*
816	 * We need to detect attempts to do dup2() over allocated but still
817	 * not finished descriptor.  NB: OpenBSD avoids that at the price of
818	 * extra work in their equivalent of fget() - they insert struct
819	 * file immediately after grabbing descriptor, mark it larval if
820	 * more work (e.g. actual opening) is needed and make sure that
821	 * fget() treats larval files as absent.  Potentially interesting,
822	 * but while extra work in fget() is trivial, locking implications
823	 * and amount of surgery on open()-related paths in VFS are not.
824	 * FreeBSD fails with -EBADF in the same situation, NetBSD "solution"
825	 * deadlocks in rather amusing ways, AFAICS.  All of that is out of
826	 * scope of POSIX or SUS, since neither considers shared descriptor
827	 * tables and this condition does not arise without those.
828	 */
829	fdt = files_fdtable(files);
830	tofree = fdt->fd[fd];
831	if (!tofree && fd_is_open(fd, fdt))
832		goto Ebusy;
833	get_file(file);
834	rcu_assign_pointer(fdt->fd[fd], file);
835	__set_open_fd(fd, fdt);
836	if (flags & O_CLOEXEC)
837		__set_close_on_exec(fd, fdt);
838	else
839		__clear_close_on_exec(fd, fdt);
840	spin_unlock(&files->file_lock);
841
842	if (tofree)
843		filp_close(tofree, files);
844
845	return fd;
846
847Ebusy:
848	spin_unlock(&files->file_lock);
849	return -EBUSY;
850}
851
852int replace_fd(unsigned fd, struct file *file, unsigned flags)
853{
854	int err;
855	struct files_struct *files = current->files;
856
857	if (!file)
858		return __close_fd(files, fd);
859
860	if (fd >= rlimit(RLIMIT_NOFILE))
861		return -EBADF;
862
863	spin_lock(&files->file_lock);
864	err = expand_files(files, fd);
865	if (unlikely(err < 0))
866		goto out_unlock;
867	return do_dup2(files, file, fd, flags);
868
869out_unlock:
870	spin_unlock(&files->file_lock);
871	return err;
872}
873
874static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
875{
876	int err = -EBADF;
877	struct file *file;
878	struct files_struct *files = current->files;
879
880	if ((flags & ~O_CLOEXEC) != 0)
881		return -EINVAL;
882
883	if (unlikely(oldfd == newfd))
884		return -EINVAL;
885
886	if (newfd >= rlimit(RLIMIT_NOFILE))
887		return -EBADF;
888
889	spin_lock(&files->file_lock);
890	err = expand_files(files, newfd);
891	file = fcheck(oldfd);
892	if (unlikely(!file))
893		goto Ebadf;
894	if (unlikely(err < 0)) {
895		if (err == -EMFILE)
896			goto Ebadf;
897		goto out_unlock;
898	}
899	return do_dup2(files, file, newfd, flags);
900
901Ebadf:
902	err = -EBADF;
903out_unlock:
904	spin_unlock(&files->file_lock);
905	return err;
906}
907
908SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
909{
910	return ksys_dup3(oldfd, newfd, flags);
911}
912
913SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
914{
915	if (unlikely(newfd == oldfd)) { /* corner case */
916		struct files_struct *files = current->files;
917		int retval = oldfd;
918
919		rcu_read_lock();
920		if (!fcheck_files(files, oldfd))
921			retval = -EBADF;
922		rcu_read_unlock();
923		return retval;
924	}
925	return ksys_dup3(oldfd, newfd, 0);
926}
927
928int ksys_dup(unsigned int fildes)
929{
930	int ret = -EBADF;
931	struct file *file = fget_raw(fildes);
932
933	if (file) {
934		ret = get_unused_fd_flags(0);
935		if (ret >= 0)
936			fd_install(ret, file);
937		else
938			fput(file);
939	}
940	return ret;
941}
942
943SYSCALL_DEFINE1(dup, unsigned int, fildes)
944{
945	return ksys_dup(fildes);
946}
947
948int f_dupfd(unsigned int from, struct file *file, unsigned flags)
949{
950	int err;
951	if (from >= rlimit(RLIMIT_NOFILE))
952		return -EINVAL;
953	err = alloc_fd(from, flags);
954	if (err >= 0) {
955		get_file(file);
956		fd_install(err, file);
957	}
958	return err;
959}
960
961int iterate_fd(struct files_struct *files, unsigned n,
962		int (*f)(const void *, struct file *, unsigned),
963		const void *p)
964{
965	struct fdtable *fdt;
966	int res = 0;
967	if (!files)
968		return 0;
969	spin_lock(&files->file_lock);
970	for (fdt = files_fdtable(files); n < fdt->max_fds; n++) {
971		struct file *file;
972		file = rcu_dereference_check_fdtable(files, fdt->fd[n]);
973		if (!file)
974			continue;
975		res = f(p, file, n);
976		if (res)
977			break;
978	}
979	spin_unlock(&files->file_lock);
980	return res;
981}
982EXPORT_SYMBOL(iterate_fd);