xref: /linux/fs/fcntl.c (revision c80544dc0b87bb65038355e7aafdc30be16b26ab) 
1 /*
2  *  linux/fs/fcntl.c
3  *
4  *  Copyright (C) 1991, 1992  Linus Torvalds
5  */
6 
7 #include <linux/syscalls.h>
8 #include <linux/init.h>
9 #include <linux/mm.h>
10 #include <linux/fs.h>
11 #include <linux/file.h>
12 #include <linux/capability.h>
13 #include <linux/dnotify.h>
14 #include <linux/smp_lock.h>
15 #include <linux/slab.h>
16 #include <linux/module.h>
17 #include <linux/security.h>
18 #include <linux/ptrace.h>
19 #include <linux/signal.h>
20 #include <linux/rcupdate.h>
21 
22 #include <asm/poll.h>
23 #include <asm/siginfo.h>
24 #include <asm/uaccess.h>
25 
26 void fastcall set_close_on_exec(unsigned int fd, int flag)
27 {
28 	struct files_struct *files = current->files;
29 	struct fdtable *fdt;
30 	spin_lock(&files->file_lock);
31 	fdt = files_fdtable(files);
32 	if (flag)
33 		FD_SET(fd, fdt->close_on_exec);
34 	else
35 		FD_CLR(fd, fdt->close_on_exec);
36 	spin_unlock(&files->file_lock);
37 }
38 
39 static int get_close_on_exec(unsigned int fd)
40 {
41 	struct files_struct *files = current->files;
42 	struct fdtable *fdt;
43 	int res;
44 	rcu_read_lock();
45 	fdt = files_fdtable(files);
46 	res = FD_ISSET(fd, fdt->close_on_exec);
47 	rcu_read_unlock();
48 	return res;
49 }
50 
51 /*
52  * locate_fd finds a free file descriptor in the open_fds fdset,
53  * expanding the fd arrays if necessary.  Must be called with the
54  * file_lock held for write.
55  */
56 
57 static int locate_fd(struct files_struct *files,
58 			    struct file *file, unsigned int orig_start)
59 {
60 	unsigned int newfd;
61 	unsigned int start;
62 	int error;
63 	struct fdtable *fdt;
64 
65 	error = -EINVAL;
66 	if (orig_start >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
67 		goto out;
68 
69 repeat:
70 	fdt = files_fdtable(files);
71 	/*
72 	 * Someone might have closed fd's in the range
73 	 * orig_start..fdt->next_fd
74 	 */
75 	start = orig_start;
76 	if (start < files->next_fd)
77 		start = files->next_fd;
78 
79 	newfd = start;
80 	if (start < fdt->max_fds)
81 		newfd = find_next_zero_bit(fdt->open_fds->fds_bits,
82 					   fdt->max_fds, start);
83 
84 	error = -EMFILE;
85 	if (newfd >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
86 		goto out;
87 
88 	error = expand_files(files, newfd);
89 	if (error < 0)
90 		goto out;
91 
92 	/*
93 	 * If we needed to expand the fs array we
94 	 * might have blocked - try again.
95 	 */
96 	if (error)
97 		goto repeat;
98 
99 	/*
100 	 * We reacquired files_lock, so we are safe as long as
101 	 * we reacquire the fdtable pointer and use it while holding
102 	 * the lock, no one can free it during that time.
103 	 */
104 	if (start <= files->next_fd)
105 		files->next_fd = newfd + 1;
106 
107 	error = newfd;
108 
109 out:
110 	return error;
111 }
112 
113 static int dupfd(struct file *file, unsigned int start, int cloexec)
114 {
115 	struct files_struct * files = current->files;
116 	struct fdtable *fdt;
117 	int fd;
118 
119 	spin_lock(&files->file_lock);
120 	fd = locate_fd(files, file, start);
121 	if (fd >= 0) {
122 		/* locate_fd() may have expanded fdtable, load the ptr */
123 		fdt = files_fdtable(files);
124 		FD_SET(fd, fdt->open_fds);
125 		if (cloexec)
126 			FD_SET(fd, fdt->close_on_exec);
127 		else
128 			FD_CLR(fd, fdt->close_on_exec);
129 		spin_unlock(&files->file_lock);
130 		fd_install(fd, file);
131 	} else {
132 		spin_unlock(&files->file_lock);
133 		fput(file);
134 	}
135 
136 	return fd;
137 }
138 
139 asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
140 {
141 	int err = -EBADF;
142 	struct file * file, *tofree;
143 	struct files_struct * files = current->files;
144 	struct fdtable *fdt;
145 
146 	spin_lock(&files->file_lock);
147 	if (!(file = fcheck(oldfd)))
148 		goto out_unlock;
149 	err = newfd;
150 	if (newfd == oldfd)
151 		goto out_unlock;
152 	err = -EBADF;
153 	if (newfd >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
154 		goto out_unlock;
155 	get_file(file);			/* We are now finished with oldfd */
156 
157 	err = expand_files(files, newfd);
158 	if (err < 0)
159 		goto out_fput;
160 
161 	/* To avoid races with open() and dup(), we will mark the fd as
162 	 * in-use in the open-file bitmap throughout the entire dup2()
163 	 * process.  This is quite safe: do_close() uses the fd array
164 	 * entry, not the bitmap, to decide what work needs to be
165 	 * done.  --sct */
166 	/* Doesn't work. open() might be there first. --AV */
167 
168 	/* Yes. It's a race. In user space. Nothing sane to do */
169 	err = -EBUSY;
170 	fdt = files_fdtable(files);
171 	tofree = fdt->fd[newfd];
172 	if (!tofree && FD_ISSET(newfd, fdt->open_fds))
173 		goto out_fput;
174 
175 	rcu_assign_pointer(fdt->fd[newfd], file);
176 	FD_SET(newfd, fdt->open_fds);
177 	FD_CLR(newfd, fdt->close_on_exec);
178 	spin_unlock(&files->file_lock);
179 
180 	if (tofree)
181 		filp_close(tofree, files);
182 	err = newfd;
183 out:
184 	return err;
185 out_unlock:
186 	spin_unlock(&files->file_lock);
187 	goto out;
188 
189 out_fput:
190 	spin_unlock(&files->file_lock);
191 	fput(file);
192 	goto out;
193 }
194 
195 asmlinkage long sys_dup(unsigned int fildes)
196 {
197 	int ret = -EBADF;
198 	struct file * file = fget(fildes);
199 
200 	if (file)
201 		ret = dupfd(file, 0, 0);
202 	return ret;
203 }
204 
205 #define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | FASYNC | O_DIRECT | O_NOATIME)
206 
207 static int setfl(int fd, struct file * filp, unsigned long arg)
208 {
209 	struct inode * inode = filp->f_path.dentry->d_inode;
210 	int error = 0;
211 
212 	/*
213 	 * O_APPEND cannot be cleared if the file is marked as append-only
214 	 * and the file is open for write.
215 	 */
216 	if (((arg ^ filp->f_flags) & O_APPEND) && IS_APPEND(inode))
217 		return -EPERM;
218 
219 	/* O_NOATIME can only be set by the owner or superuser */
220 	if ((arg & O_NOATIME) && !(filp->f_flags & O_NOATIME))
221 		if (!is_owner_or_cap(inode))
222 			return -EPERM;
223 
224 	/* required for strict SunOS emulation */
225 	if (O_NONBLOCK != O_NDELAY)
226 	       if (arg & O_NDELAY)
227 		   arg |= O_NONBLOCK;
228 
229 	if (arg & O_DIRECT) {
230 		if (!filp->f_mapping || !filp->f_mapping->a_ops ||
231 			!filp->f_mapping->a_ops->direct_IO)
232 				return -EINVAL;
233 	}
234 
235 	if (filp->f_op && filp->f_op->check_flags)
236 		error = filp->f_op->check_flags(arg);
237 	if (error)
238 		return error;
239 
240 	lock_kernel();
241 	if ((arg ^ filp->f_flags) & FASYNC) {
242 		if (filp->f_op && filp->f_op->fasync) {
243 			error = filp->f_op->fasync(fd, filp, (arg & FASYNC) != 0);
244 			if (error < 0)
245 				goto out;
246 		}
247 	}
248 
249 	filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK);
250  out:
251 	unlock_kernel();
252 	return error;
253 }
254 
255 static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
256                      uid_t uid, uid_t euid, int force)
257 {
258 	write_lock_irq(&filp->f_owner.lock);
259 	if (force || !filp->f_owner.pid) {
260 		put_pid(filp->f_owner.pid);
261 		filp->f_owner.pid = get_pid(pid);
262 		filp->f_owner.pid_type = type;
263 		filp->f_owner.uid = uid;
264 		filp->f_owner.euid = euid;
265 	}
266 	write_unlock_irq(&filp->f_owner.lock);
267 }
268 
269 int __f_setown(struct file *filp, struct pid *pid, enum pid_type type,
270 		int force)
271 {
272 	int err;
273 
274 	err = security_file_set_fowner(filp);
275 	if (err)
276 		return err;
277 
278 	f_modown(filp, pid, type, current->uid, current->euid, force);
279 	return 0;
280 }
281 EXPORT_SYMBOL(__f_setown);
282 
283 int f_setown(struct file *filp, unsigned long arg, int force)
284 {
285 	enum pid_type type;
286 	struct pid *pid;
287 	int who = arg;
288 	int result;
289 	type = PIDTYPE_PID;
290 	if (who < 0) {
291 		type = PIDTYPE_PGID;
292 		who = -who;
293 	}
294 	rcu_read_lock();
295 	pid = find_pid(who);
296 	result = __f_setown(filp, pid, type, force);
297 	rcu_read_unlock();
298 	return result;
299 }
300 EXPORT_SYMBOL(f_setown);
301 
302 void f_delown(struct file *filp)
303 {
304 	f_modown(filp, NULL, PIDTYPE_PID, 0, 0, 1);
305 }
306 
307 pid_t f_getown(struct file *filp)
308 {
309 	pid_t pid;
310 	read_lock(&filp->f_owner.lock);
311 	pid = pid_nr(filp->f_owner.pid);
312 	if (filp->f_owner.pid_type == PIDTYPE_PGID)
313 		pid = -pid;
314 	read_unlock(&filp->f_owner.lock);
315 	return pid;
316 }
317 
318 static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
319 		struct file *filp)
320 {
321 	long err = -EINVAL;
322 
323 	switch (cmd) {
324 	case F_DUPFD:
325 	case F_DUPFD_CLOEXEC:
326 		get_file(filp);
327 		err = dupfd(filp, arg, cmd == F_DUPFD_CLOEXEC);
328 		break;
329 	case F_GETFD:
330 		err = get_close_on_exec(fd) ? FD_CLOEXEC : 0;
331 		break;
332 	case F_SETFD:
333 		err = 0;
334 		set_close_on_exec(fd, arg & FD_CLOEXEC);
335 		break;
336 	case F_GETFL:
337 		err = filp->f_flags;
338 		break;
339 	case F_SETFL:
340 		err = setfl(fd, filp, arg);
341 		break;
342 	case F_GETLK:
343 		err = fcntl_getlk(filp, (struct flock __user *) arg);
344 		break;
345 	case F_SETLK:
346 	case F_SETLKW:
347 		err = fcntl_setlk(fd, filp, cmd, (struct flock __user *) arg);
348 		break;
349 	case F_GETOWN:
350 		/*
351 		 * XXX If f_owner is a process group, the
352 		 * negative return value will get converted
353 		 * into an error.  Oops.  If we keep the
354 		 * current syscall conventions, the only way
355 		 * to fix this will be in libc.
356 		 */
357 		err = f_getown(filp);
358 		force_successful_syscall_return();
359 		break;
360 	case F_SETOWN:
361 		err = f_setown(filp, arg, 1);
362 		break;
363 	case F_GETSIG:
364 		err = filp->f_owner.signum;
365 		break;
366 	case F_SETSIG:
367 		/* arg == 0 restores default behaviour. */
368 		if (!valid_signal(arg)) {
369 			break;
370 		}
371 		err = 0;
372 		filp->f_owner.signum = arg;
373 		break;
374 	case F_GETLEASE:
375 		err = fcntl_getlease(filp);
376 		break;
377 	case F_SETLEASE:
378 		err = fcntl_setlease(fd, filp, arg);
379 		break;
380 	case F_NOTIFY:
381 		err = fcntl_dirnotify(fd, filp, arg);
382 		break;
383 	default:
384 		break;
385 	}
386 	return err;
387 }
388 
389 asmlinkage long sys_fcntl(unsigned int fd, unsigned int cmd, unsigned long arg)
390 {
391 	struct file *filp;
392 	long err = -EBADF;
393 
394 	filp = fget(fd);
395 	if (!filp)
396 		goto out;
397 
398 	err = security_file_fcntl(filp, cmd, arg);
399 	if (err) {
400 		fput(filp);
401 		return err;
402 	}
403 
404 	err = do_fcntl(fd, cmd, arg, filp);
405 
406  	fput(filp);
407 out:
408 	return err;
409 }
410 
411 #if BITS_PER_LONG == 32
412 asmlinkage long sys_fcntl64(unsigned int fd, unsigned int cmd, unsigned long arg)
413 {
414 	struct file * filp;
415 	long err;
416 
417 	err = -EBADF;
418 	filp = fget(fd);
419 	if (!filp)
420 		goto out;
421 
422 	err = security_file_fcntl(filp, cmd, arg);
423 	if (err) {
424 		fput(filp);
425 		return err;
426 	}
427 	err = -EBADF;
428 
429 	switch (cmd) {
430 		case F_GETLK64:
431 			err = fcntl_getlk64(filp, (struct flock64 __user *) arg);
432 			break;
433 		case F_SETLK64:
434 		case F_SETLKW64:
435 			err = fcntl_setlk64(fd, filp, cmd,
436 					(struct flock64 __user *) arg);
437 			break;
438 		default:
439 			err = do_fcntl(fd, cmd, arg, filp);
440 			break;
441 	}
442 	fput(filp);
443 out:
444 	return err;
445 }
446 #endif
447 
448 /* Table to convert sigio signal codes into poll band bitmaps */
449 
450 static const long band_table[NSIGPOLL] = {
451 	POLLIN | POLLRDNORM,			/* POLL_IN */
452 	POLLOUT | POLLWRNORM | POLLWRBAND,	/* POLL_OUT */
453 	POLLIN | POLLRDNORM | POLLMSG,		/* POLL_MSG */
454 	POLLERR,				/* POLL_ERR */
455 	POLLPRI | POLLRDBAND,			/* POLL_PRI */
456 	POLLHUP | POLLERR			/* POLL_HUP */
457 };
458 
459 static inline int sigio_perm(struct task_struct *p,
460                              struct fown_struct *fown, int sig)
461 {
462 	return (((fown->euid == 0) ||
463 		 (fown->euid == p->suid) || (fown->euid == p->uid) ||
464 		 (fown->uid == p->suid) || (fown->uid == p->uid)) &&
465 		!security_file_send_sigiotask(p, fown, sig));
466 }
467 
468 static void send_sigio_to_task(struct task_struct *p,
469 			       struct fown_struct *fown,
470 			       int fd,
471 			       int reason)
472 {
473 	if (!sigio_perm(p, fown, fown->signum))
474 		return;
475 
476 	switch (fown->signum) {
477 		siginfo_t si;
478 		default:
479 			/* Queue a rt signal with the appropriate fd as its
480 			   value.  We use SI_SIGIO as the source, not
481 			   SI_KERNEL, since kernel signals always get
482 			   delivered even if we can't queue.  Failure to
483 			   queue in this case _should_ be reported; we fall
484 			   back to SIGIO in that case. --sct */
485 			si.si_signo = fown->signum;
486 			si.si_errno = 0;
487 		        si.si_code  = reason;
488 			/* Make sure we are called with one of the POLL_*
489 			   reasons, otherwise we could leak kernel stack into
490 			   userspace.  */
491 			BUG_ON((reason & __SI_MASK) != __SI_POLL);
492 			if (reason - POLL_IN >= NSIGPOLL)
493 				si.si_band  = ~0L;
494 			else
495 				si.si_band = band_table[reason - POLL_IN];
496 			si.si_fd    = fd;
497 			if (!group_send_sig_info(fown->signum, &si, p))
498 				break;
499 		/* fall-through: fall back on the old plain SIGIO signal */
500 		case 0:
501 			group_send_sig_info(SIGIO, SEND_SIG_PRIV, p);
502 	}
503 }
504 
505 void send_sigio(struct fown_struct *fown, int fd, int band)
506 {
507 	struct task_struct *p;
508 	enum pid_type type;
509 	struct pid *pid;
510 
511 	read_lock(&fown->lock);
512 	type = fown->pid_type;
513 	pid = fown->pid;
514 	if (!pid)
515 		goto out_unlock_fown;
516 
517 	read_lock(&tasklist_lock);
518 	do_each_pid_task(pid, type, p) {
519 		send_sigio_to_task(p, fown, fd, band);
520 	} while_each_pid_task(pid, type, p);
521 	read_unlock(&tasklist_lock);
522  out_unlock_fown:
523 	read_unlock(&fown->lock);
524 }
525 
526 static void send_sigurg_to_task(struct task_struct *p,
527                                 struct fown_struct *fown)
528 {
529 	if (sigio_perm(p, fown, SIGURG))
530 		group_send_sig_info(SIGURG, SEND_SIG_PRIV, p);
531 }
532 
533 int send_sigurg(struct fown_struct *fown)
534 {
535 	struct task_struct *p;
536 	enum pid_type type;
537 	struct pid *pid;
538 	int ret = 0;
539 
540 	read_lock(&fown->lock);
541 	type = fown->pid_type;
542 	pid = fown->pid;
543 	if (!pid)
544 		goto out_unlock_fown;
545 
546 	ret = 1;
547 
548 	read_lock(&tasklist_lock);
549 	do_each_pid_task(pid, type, p) {
550 		send_sigurg_to_task(p, fown);
551 	} while_each_pid_task(pid, type, p);
552 	read_unlock(&tasklist_lock);
553  out_unlock_fown:
554 	read_unlock(&fown->lock);
555 	return ret;
556 }
557 
558 static DEFINE_RWLOCK(fasync_lock);
559 static struct kmem_cache *fasync_cache __read_mostly;
560 
561 /*
562  * fasync_helper() is used by some character device drivers (mainly mice)
563  * to set up the fasync queue. It returns negative on error, 0 if it did
564  * no changes and positive if it added/deleted the entry.
565  */
566 int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)
567 {
568 	struct fasync_struct *fa, **fp;
569 	struct fasync_struct *new = NULL;
570 	int result = 0;
571 
572 	if (on) {
573 		new = kmem_cache_alloc(fasync_cache, GFP_KERNEL);
574 		if (!new)
575 			return -ENOMEM;
576 	}
577 	write_lock_irq(&fasync_lock);
578 	for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {
579 		if (fa->fa_file == filp) {
580 			if(on) {
581 				fa->fa_fd = fd;
582 				kmem_cache_free(fasync_cache, new);
583 			} else {
584 				*fp = fa->fa_next;
585 				kmem_cache_free(fasync_cache, fa);
586 				result = 1;
587 			}
588 			goto out;
589 		}
590 	}
591 
592 	if (on) {
593 		new->magic = FASYNC_MAGIC;
594 		new->fa_file = filp;
595 		new->fa_fd = fd;
596 		new->fa_next = *fapp;
597 		*fapp = new;
598 		result = 1;
599 	}
600 out:
601 	write_unlock_irq(&fasync_lock);
602 	return result;
603 }
604 
605 EXPORT_SYMBOL(fasync_helper);
606 
607 void __kill_fasync(struct fasync_struct *fa, int sig, int band)
608 {
609 	while (fa) {
610 		struct fown_struct * fown;
611 		if (fa->magic != FASYNC_MAGIC) {
612 			printk(KERN_ERR "kill_fasync: bad magic number in "
613 			       "fasync_struct!\n");
614 			return;
615 		}
616 		fown = &fa->fa_file->f_owner;
617 		/* Don't send SIGURG to processes which have not set a
618 		   queued signum: SIGURG has its own default signalling
619 		   mechanism. */
620 		if (!(sig == SIGURG && fown->signum == 0))
621 			send_sigio(fown, fa->fa_fd, band);
622 		fa = fa->fa_next;
623 	}
624 }
625 
626 EXPORT_SYMBOL(__kill_fasync);
627 
628 void kill_fasync(struct fasync_struct **fp, int sig, int band)
629 {
630 	/* First a quick test without locking: usually
631 	 * the list is empty.
632 	 */
633 	if (*fp) {
634 		read_lock(&fasync_lock);
635 		/* reread *fp after obtaining the lock */
636 		__kill_fasync(*fp, sig, band);
637 		read_unlock(&fasync_lock);
638 	}
639 }
640 EXPORT_SYMBOL(kill_fasync);
641 
642 static int __init fasync_init(void)
643 {
644 	fasync_cache = kmem_cache_create("fasync_cache",
645 		sizeof(struct fasync_struct), 0, SLAB_PANIC, NULL);
646 	return 0;
647 }
648 
649 module_init(fasync_init)
650