xref: /linux/fs/fcntl.c (revision b8bb76713ec50df2f11efee386e16f93d51e1076) 
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/fdtable.h>
13 #include <linux/capability.h>
14 #include <linux/dnotify.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 #include <linux/pid_namespace.h>
22 #include <linux/smp_lock.h>
23 
24 #include <asm/poll.h>
25 #include <asm/siginfo.h>
26 #include <asm/uaccess.h>
27 
28 void set_close_on_exec(unsigned int fd, int flag)
29 {
30 	struct files_struct *files = current->files;
31 	struct fdtable *fdt;
32 	spin_lock(&files->file_lock);
33 	fdt = files_fdtable(files);
34 	if (flag)
35 		FD_SET(fd, fdt->close_on_exec);
36 	else
37 		FD_CLR(fd, fdt->close_on_exec);
38 	spin_unlock(&files->file_lock);
39 }
40 
41 static int get_close_on_exec(unsigned int fd)
42 {
43 	struct files_struct *files = current->files;
44 	struct fdtable *fdt;
45 	int res;
46 	rcu_read_lock();
47 	fdt = files_fdtable(files);
48 	res = FD_ISSET(fd, fdt->close_on_exec);
49 	rcu_read_unlock();
50 	return res;
51 }
52 
53 SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
54 {
55 	int err = -EBADF;
56 	struct file * file, *tofree;
57 	struct files_struct * files = current->files;
58 	struct fdtable *fdt;
59 
60 	if ((flags & ~O_CLOEXEC) != 0)
61 		return -EINVAL;
62 
63 	if (unlikely(oldfd == newfd))
64 		return -EINVAL;
65 
66 	spin_lock(&files->file_lock);
67 	err = expand_files(files, newfd);
68 	file = fcheck(oldfd);
69 	if (unlikely(!file))
70 		goto Ebadf;
71 	if (unlikely(err < 0)) {
72 		if (err == -EMFILE)
73 			goto Ebadf;
74 		goto out_unlock;
75 	}
76 	/*
77 	 * We need to detect attempts to do dup2() over allocated but still
78 	 * not finished descriptor.  NB: OpenBSD avoids that at the price of
79 	 * extra work in their equivalent of fget() - they insert struct
80 	 * file immediately after grabbing descriptor, mark it larval if
81 	 * more work (e.g. actual opening) is needed and make sure that
82 	 * fget() treats larval files as absent.  Potentially interesting,
83 	 * but while extra work in fget() is trivial, locking implications
84 	 * and amount of surgery on open()-related paths in VFS are not.
85 	 * FreeBSD fails with -EBADF in the same situation, NetBSD "solution"
86 	 * deadlocks in rather amusing ways, AFAICS.  All of that is out of
87 	 * scope of POSIX or SUS, since neither considers shared descriptor
88 	 * tables and this condition does not arise without those.
89 	 */
90 	err = -EBUSY;
91 	fdt = files_fdtable(files);
92 	tofree = fdt->fd[newfd];
93 	if (!tofree && FD_ISSET(newfd, fdt->open_fds))
94 		goto out_unlock;
95 	get_file(file);
96 	rcu_assign_pointer(fdt->fd[newfd], file);
97 	FD_SET(newfd, fdt->open_fds);
98 	if (flags & O_CLOEXEC)
99 		FD_SET(newfd, fdt->close_on_exec);
100 	else
101 		FD_CLR(newfd, fdt->close_on_exec);
102 	spin_unlock(&files->file_lock);
103 
104 	if (tofree)
105 		filp_close(tofree, files);
106 
107 	return newfd;
108 
109 Ebadf:
110 	err = -EBADF;
111 out_unlock:
112 	spin_unlock(&files->file_lock);
113 	return err;
114 }
115 
116 SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
117 {
118 	if (unlikely(newfd == oldfd)) { /* corner case */
119 		struct files_struct *files = current->files;
120 		rcu_read_lock();
121 		if (!fcheck_files(files, oldfd))
122 			oldfd = -EBADF;
123 		rcu_read_unlock();
124 		return oldfd;
125 	}
126 	return sys_dup3(oldfd, newfd, 0);
127 }
128 
129 SYSCALL_DEFINE1(dup, unsigned int, fildes)
130 {
131 	int ret = -EBADF;
132 	struct file *file = fget(fildes);
133 
134 	if (file) {
135 		ret = get_unused_fd();
136 		if (ret >= 0)
137 			fd_install(ret, file);
138 		else
139 			fput(file);
140 	}
141 	return ret;
142 }
143 
144 #define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_NOATIME)
145 
146 static int setfl(int fd, struct file * filp, unsigned long arg)
147 {
148 	struct inode * inode = filp->f_path.dentry->d_inode;
149 	int error = 0;
150 
151 	/*
152 	 * O_APPEND cannot be cleared if the file is marked as append-only
153 	 * and the file is open for write.
154 	 */
155 	if (((arg ^ filp->f_flags) & O_APPEND) && IS_APPEND(inode))
156 		return -EPERM;
157 
158 	/* O_NOATIME can only be set by the owner or superuser */
159 	if ((arg & O_NOATIME) && !(filp->f_flags & O_NOATIME))
160 		if (!is_owner_or_cap(inode))
161 			return -EPERM;
162 
163 	/* required for strict SunOS emulation */
164 	if (O_NONBLOCK != O_NDELAY)
165 	       if (arg & O_NDELAY)
166 		   arg |= O_NONBLOCK;
167 
168 	if (arg & O_DIRECT) {
169 		if (!filp->f_mapping || !filp->f_mapping->a_ops ||
170 			!filp->f_mapping->a_ops->direct_IO)
171 				return -EINVAL;
172 	}
173 
174 	if (filp->f_op && filp->f_op->check_flags)
175 		error = filp->f_op->check_flags(arg);
176 	if (error)
177 		return error;
178 
179 	/*
180 	 * ->fasync() is responsible for setting the FASYNC bit.
181 	 */
182 	if (((arg ^ filp->f_flags) & FASYNC) && filp->f_op &&
183 			filp->f_op->fasync) {
184 		error = filp->f_op->fasync(fd, filp, (arg & FASYNC) != 0);
185 		if (error < 0)
186 			goto out;
187 		if (error > 0)
188 			error = 0;
189 	}
190 	spin_lock(&filp->f_lock);
191 	filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK);
192 	spin_unlock(&filp->f_lock);
193 
194  out:
195 	return error;
196 }
197 
198 static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
199                      uid_t uid, uid_t euid, int force)
200 {
201 	write_lock_irq(&filp->f_owner.lock);
202 	if (force || !filp->f_owner.pid) {
203 		put_pid(filp->f_owner.pid);
204 		filp->f_owner.pid = get_pid(pid);
205 		filp->f_owner.pid_type = type;
206 		filp->f_owner.uid = uid;
207 		filp->f_owner.euid = euid;
208 	}
209 	write_unlock_irq(&filp->f_owner.lock);
210 }
211 
212 int __f_setown(struct file *filp, struct pid *pid, enum pid_type type,
213 		int force)
214 {
215 	const struct cred *cred = current_cred();
216 	int err;
217 
218 	err = security_file_set_fowner(filp);
219 	if (err)
220 		return err;
221 
222 	f_modown(filp, pid, type, cred->uid, cred->euid, force);
223 	return 0;
224 }
225 EXPORT_SYMBOL(__f_setown);
226 
227 int f_setown(struct file *filp, unsigned long arg, int force)
228 {
229 	enum pid_type type;
230 	struct pid *pid;
231 	int who = arg;
232 	int result;
233 	type = PIDTYPE_PID;
234 	if (who < 0) {
235 		type = PIDTYPE_PGID;
236 		who = -who;
237 	}
238 	rcu_read_lock();
239 	pid = find_vpid(who);
240 	result = __f_setown(filp, pid, type, force);
241 	rcu_read_unlock();
242 	return result;
243 }
244 EXPORT_SYMBOL(f_setown);
245 
246 void f_delown(struct file *filp)
247 {
248 	f_modown(filp, NULL, PIDTYPE_PID, 0, 0, 1);
249 }
250 
251 pid_t f_getown(struct file *filp)
252 {
253 	pid_t pid;
254 	read_lock(&filp->f_owner.lock);
255 	pid = pid_vnr(filp->f_owner.pid);
256 	if (filp->f_owner.pid_type == PIDTYPE_PGID)
257 		pid = -pid;
258 	read_unlock(&filp->f_owner.lock);
259 	return pid;
260 }
261 
262 static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
263 		struct file *filp)
264 {
265 	long err = -EINVAL;
266 
267 	switch (cmd) {
268 	case F_DUPFD:
269 	case F_DUPFD_CLOEXEC:
270 		if (arg >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
271 			break;
272 		err = alloc_fd(arg, cmd == F_DUPFD_CLOEXEC ? O_CLOEXEC : 0);
273 		if (err >= 0) {
274 			get_file(filp);
275 			fd_install(err, filp);
276 		}
277 		break;
278 	case F_GETFD:
279 		err = get_close_on_exec(fd) ? FD_CLOEXEC : 0;
280 		break;
281 	case F_SETFD:
282 		err = 0;
283 		set_close_on_exec(fd, arg & FD_CLOEXEC);
284 		break;
285 	case F_GETFL:
286 		err = filp->f_flags;
287 		break;
288 	case F_SETFL:
289 		err = setfl(fd, filp, arg);
290 		break;
291 	case F_GETLK:
292 		err = fcntl_getlk(filp, (struct flock __user *) arg);
293 		break;
294 	case F_SETLK:
295 	case F_SETLKW:
296 		err = fcntl_setlk(fd, filp, cmd, (struct flock __user *) arg);
297 		break;
298 	case F_GETOWN:
299 		/*
300 		 * XXX If f_owner is a process group, the
301 		 * negative return value will get converted
302 		 * into an error.  Oops.  If we keep the
303 		 * current syscall conventions, the only way
304 		 * to fix this will be in libc.
305 		 */
306 		err = f_getown(filp);
307 		force_successful_syscall_return();
308 		break;
309 	case F_SETOWN:
310 		err = f_setown(filp, arg, 1);
311 		break;
312 	case F_GETSIG:
313 		err = filp->f_owner.signum;
314 		break;
315 	case F_SETSIG:
316 		/* arg == 0 restores default behaviour. */
317 		if (!valid_signal(arg)) {
318 			break;
319 		}
320 		err = 0;
321 		filp->f_owner.signum = arg;
322 		break;
323 	case F_GETLEASE:
324 		err = fcntl_getlease(filp);
325 		break;
326 	case F_SETLEASE:
327 		err = fcntl_setlease(fd, filp, arg);
328 		break;
329 	case F_NOTIFY:
330 		err = fcntl_dirnotify(fd, filp, arg);
331 		break;
332 	default:
333 		break;
334 	}
335 	return err;
336 }
337 
338 SYSCALL_DEFINE3(fcntl, unsigned int, fd, unsigned int, cmd, unsigned long, arg)
339 {
340 	struct file *filp;
341 	long err = -EBADF;
342 
343 	filp = fget(fd);
344 	if (!filp)
345 		goto out;
346 
347 	err = security_file_fcntl(filp, cmd, arg);
348 	if (err) {
349 		fput(filp);
350 		return err;
351 	}
352 
353 	err = do_fcntl(fd, cmd, arg, filp);
354 
355  	fput(filp);
356 out:
357 	return err;
358 }
359 
360 #if BITS_PER_LONG == 32
361 SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
362 		unsigned long, arg)
363 {
364 	struct file * filp;
365 	long err;
366 
367 	err = -EBADF;
368 	filp = fget(fd);
369 	if (!filp)
370 		goto out;
371 
372 	err = security_file_fcntl(filp, cmd, arg);
373 	if (err) {
374 		fput(filp);
375 		return err;
376 	}
377 	err = -EBADF;
378 
379 	switch (cmd) {
380 		case F_GETLK64:
381 			err = fcntl_getlk64(filp, (struct flock64 __user *) arg);
382 			break;
383 		case F_SETLK64:
384 		case F_SETLKW64:
385 			err = fcntl_setlk64(fd, filp, cmd,
386 					(struct flock64 __user *) arg);
387 			break;
388 		default:
389 			err = do_fcntl(fd, cmd, arg, filp);
390 			break;
391 	}
392 	fput(filp);
393 out:
394 	return err;
395 }
396 #endif
397 
398 /* Table to convert sigio signal codes into poll band bitmaps */
399 
400 static const long band_table[NSIGPOLL] = {
401 	POLLIN | POLLRDNORM,			/* POLL_IN */
402 	POLLOUT | POLLWRNORM | POLLWRBAND,	/* POLL_OUT */
403 	POLLIN | POLLRDNORM | POLLMSG,		/* POLL_MSG */
404 	POLLERR,				/* POLL_ERR */
405 	POLLPRI | POLLRDBAND,			/* POLL_PRI */
406 	POLLHUP | POLLERR			/* POLL_HUP */
407 };
408 
409 static inline int sigio_perm(struct task_struct *p,
410                              struct fown_struct *fown, int sig)
411 {
412 	const struct cred *cred;
413 	int ret;
414 
415 	rcu_read_lock();
416 	cred = __task_cred(p);
417 	ret = ((fown->euid == 0 ||
418 		fown->euid == cred->suid || fown->euid == cred->uid ||
419 		fown->uid  == cred->suid || fown->uid  == cred->uid) &&
420 	       !security_file_send_sigiotask(p, fown, sig));
421 	rcu_read_unlock();
422 	return ret;
423 }
424 
425 static void send_sigio_to_task(struct task_struct *p,
426 			       struct fown_struct *fown,
427 			       int fd,
428 			       int reason)
429 {
430 	if (!sigio_perm(p, fown, fown->signum))
431 		return;
432 
433 	switch (fown->signum) {
434 		siginfo_t si;
435 		default:
436 			/* Queue a rt signal with the appropriate fd as its
437 			   value.  We use SI_SIGIO as the source, not
438 			   SI_KERNEL, since kernel signals always get
439 			   delivered even if we can't queue.  Failure to
440 			   queue in this case _should_ be reported; we fall
441 			   back to SIGIO in that case. --sct */
442 			si.si_signo = fown->signum;
443 			si.si_errno = 0;
444 		        si.si_code  = reason;
445 			/* Make sure we are called with one of the POLL_*
446 			   reasons, otherwise we could leak kernel stack into
447 			   userspace.  */
448 			BUG_ON((reason & __SI_MASK) != __SI_POLL);
449 			if (reason - POLL_IN >= NSIGPOLL)
450 				si.si_band  = ~0L;
451 			else
452 				si.si_band = band_table[reason - POLL_IN];
453 			si.si_fd    = fd;
454 			if (!group_send_sig_info(fown->signum, &si, p))
455 				break;
456 		/* fall-through: fall back on the old plain SIGIO signal */
457 		case 0:
458 			group_send_sig_info(SIGIO, SEND_SIG_PRIV, p);
459 	}
460 }
461 
462 void send_sigio(struct fown_struct *fown, int fd, int band)
463 {
464 	struct task_struct *p;
465 	enum pid_type type;
466 	struct pid *pid;
467 
468 	read_lock(&fown->lock);
469 	type = fown->pid_type;
470 	pid = fown->pid;
471 	if (!pid)
472 		goto out_unlock_fown;
473 
474 	read_lock(&tasklist_lock);
475 	do_each_pid_task(pid, type, p) {
476 		send_sigio_to_task(p, fown, fd, band);
477 	} while_each_pid_task(pid, type, p);
478 	read_unlock(&tasklist_lock);
479  out_unlock_fown:
480 	read_unlock(&fown->lock);
481 }
482 
483 static void send_sigurg_to_task(struct task_struct *p,
484                                 struct fown_struct *fown)
485 {
486 	if (sigio_perm(p, fown, SIGURG))
487 		group_send_sig_info(SIGURG, SEND_SIG_PRIV, p);
488 }
489 
490 int send_sigurg(struct fown_struct *fown)
491 {
492 	struct task_struct *p;
493 	enum pid_type type;
494 	struct pid *pid;
495 	int ret = 0;
496 
497 	read_lock(&fown->lock);
498 	type = fown->pid_type;
499 	pid = fown->pid;
500 	if (!pid)
501 		goto out_unlock_fown;
502 
503 	ret = 1;
504 
505 	read_lock(&tasklist_lock);
506 	do_each_pid_task(pid, type, p) {
507 		send_sigurg_to_task(p, fown);
508 	} while_each_pid_task(pid, type, p);
509 	read_unlock(&tasklist_lock);
510  out_unlock_fown:
511 	read_unlock(&fown->lock);
512 	return ret;
513 }
514 
515 static DEFINE_RWLOCK(fasync_lock);
516 static struct kmem_cache *fasync_cache __read_mostly;
517 
518 /*
519  * fasync_helper() is used by almost all character device drivers
520  * to set up the fasync queue. It returns negative on error, 0 if it did
521  * no changes and positive if it added/deleted the entry.
522  */
523 int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)
524 {
525 	struct fasync_struct *fa, **fp;
526 	struct fasync_struct *new = NULL;
527 	int result = 0;
528 
529 	if (on) {
530 		new = kmem_cache_alloc(fasync_cache, GFP_KERNEL);
531 		if (!new)
532 			return -ENOMEM;
533 	}
534 
535 	/*
536 	 * We need to take f_lock first since it's not an IRQ-safe
537 	 * lock.
538 	 */
539 	spin_lock(&filp->f_lock);
540 	write_lock_irq(&fasync_lock);
541 	for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {
542 		if (fa->fa_file == filp) {
543 			if(on) {
544 				fa->fa_fd = fd;
545 				kmem_cache_free(fasync_cache, new);
546 			} else {
547 				*fp = fa->fa_next;
548 				kmem_cache_free(fasync_cache, fa);
549 				result = 1;
550 			}
551 			goto out;
552 		}
553 	}
554 
555 	if (on) {
556 		new->magic = FASYNC_MAGIC;
557 		new->fa_file = filp;
558 		new->fa_fd = fd;
559 		new->fa_next = *fapp;
560 		*fapp = new;
561 		result = 1;
562 	}
563 out:
564 	if (on)
565 		filp->f_flags |= FASYNC;
566 	else
567 		filp->f_flags &= ~FASYNC;
568 	write_unlock_irq(&fasync_lock);
569 	spin_unlock(&filp->f_lock);
570 	return result;
571 }
572 
573 EXPORT_SYMBOL(fasync_helper);
574 
575 void __kill_fasync(struct fasync_struct *fa, int sig, int band)
576 {
577 	while (fa) {
578 		struct fown_struct * fown;
579 		if (fa->magic != FASYNC_MAGIC) {
580 			printk(KERN_ERR "kill_fasync: bad magic number in "
581 			       "fasync_struct!\n");
582 			return;
583 		}
584 		fown = &fa->fa_file->f_owner;
585 		/* Don't send SIGURG to processes which have not set a
586 		   queued signum: SIGURG has its own default signalling
587 		   mechanism. */
588 		if (!(sig == SIGURG && fown->signum == 0))
589 			send_sigio(fown, fa->fa_fd, band);
590 		fa = fa->fa_next;
591 	}
592 }
593 
594 EXPORT_SYMBOL(__kill_fasync);
595 
596 void kill_fasync(struct fasync_struct **fp, int sig, int band)
597 {
598 	/* First a quick test without locking: usually
599 	 * the list is empty.
600 	 */
601 	if (*fp) {
602 		read_lock(&fasync_lock);
603 		/* reread *fp after obtaining the lock */
604 		__kill_fasync(*fp, sig, band);
605 		read_unlock(&fasync_lock);
606 	}
607 }
608 EXPORT_SYMBOL(kill_fasync);
609 
610 static int __init fasync_init(void)
611 {
612 	fasync_cache = kmem_cache_create("fasync_cache",
613 		sizeof(struct fasync_struct), 0, SLAB_PANIC, NULL);
614 	return 0;
615 }
616 
617 module_init(fasync_init)
618