signalfd.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  fs/signalfd.c
  4 *
  5 *  Copyright (C) 2003  Linus Torvalds
  6 *
  7 *  Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
  8 *      Changed ->read() to return a siginfo strcture instead of signal number.
  9 *      Fixed locking in ->poll().
 10 *      Added sighand-detach notification.
 11 *      Added fd re-use in sys_signalfd() syscall.
 12 *      Now using anonymous inode source.
 13 *      Thanks to Oleg Nesterov for useful code review and suggestions.
 14 *      More comments and suggestions from Arnd Bergmann.
 15 *  Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
 16 *      Retrieve multiple signals with one read() call
 17 *  Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
 18 *      Attach to the sighand only during read() and poll().
 19 */
 20
 21#include <linux/file.h>
 22#include <linux/poll.h>
 23#include <linux/init.h>
 24#include <linux/fs.h>
 25#include <linux/sched.h>
 26#include <linux/slab.h>
 27#include <linux/kernel.h>
 28#include <linux/signal.h>
 29#include <linux/list.h>
 30#include <linux/anon_inodes.h>
 31#include <linux/signalfd.h>
 32#include <linux/syscalls.h>
 33#include <linux/proc_fs.h>
 34#include <linux/compat.h>
 35
 36void signalfd_cleanup(struct sighand_struct *sighand)
 37{
 38	wake_up_pollfree(&sighand->signalfd_wqh);
 39}
 40
 41struct signalfd_ctx {
 42	sigset_t sigmask;
 43};
 44
 45static int signalfd_release(struct inode *inode, struct file *file)
 46{
 47	kfree(file->private_data);
 48	return 0;
 49}
 50
 51static __poll_t signalfd_poll(struct file *file, poll_table *wait)
 52{
 53	struct signalfd_ctx *ctx = file->private_data;
 54	__poll_t events = 0;
 55
 56	poll_wait(file, &current->sighand->signalfd_wqh, wait);
 57
 58	spin_lock_irq(&current->sighand->siglock);
 59	if (next_signal(&current->pending, &ctx->sigmask) ||
 60	    next_signal(&current->signal->shared_pending,
 61			&ctx->sigmask))
 62		events |= EPOLLIN;
 63	spin_unlock_irq(&current->sighand->siglock);
 64
 65	return events;
 66}
 67
 68/*
 69 * Copied from copy_siginfo_to_user() in kernel/signal.c
 70 */
 71static int signalfd_copyinfo(struct iov_iter *to, kernel_siginfo_t const *kinfo)
 72{
 73	struct signalfd_siginfo new;
 74
 75	BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
 76
 77	/*
 78	 * Unused members should be zero ...
 79	 */
 80	memset(&new, 0, sizeof(new));
 81
 82	/*
 83	 * If you change siginfo_t structure, please be sure
 84	 * this code is fixed accordingly.
 85	 */
 86	new.ssi_signo = kinfo->si_signo;
 87	new.ssi_errno = kinfo->si_errno;
 88	new.ssi_code  = kinfo->si_code;
 89	switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
 90	case SIL_KILL:
 91		new.ssi_pid = kinfo->si_pid;
 92		new.ssi_uid = kinfo->si_uid;
 93		break;
 94	case SIL_TIMER:
 95		new.ssi_tid = kinfo->si_tid;
 96		new.ssi_overrun = kinfo->si_overrun;
 97		new.ssi_ptr = (long) kinfo->si_ptr;
 98		new.ssi_int = kinfo->si_int;
 99		break;
100	case SIL_POLL:
101		new.ssi_band = kinfo->si_band;
102		new.ssi_fd   = kinfo->si_fd;
103		break;
104	case SIL_FAULT_BNDERR:
105	case SIL_FAULT_PKUERR:
106	case SIL_FAULT_PERF_EVENT:
107		/*
108		 * Fall through to the SIL_FAULT case.  SIL_FAULT_BNDERR,
109		 * SIL_FAULT_PKUERR, and SIL_FAULT_PERF_EVENT are only
110		 * generated by faults that deliver them synchronously to
111		 * userspace.  In case someone injects one of these signals
112		 * and signalfd catches it treat it as SIL_FAULT.
113		 */
114	case SIL_FAULT:
115		new.ssi_addr = (long) kinfo->si_addr;
116		break;
117	case SIL_FAULT_TRAPNO:
118		new.ssi_addr = (long) kinfo->si_addr;
119		new.ssi_trapno = kinfo->si_trapno;
120		break;
121	case SIL_FAULT_MCEERR:
122		new.ssi_addr = (long) kinfo->si_addr;
123		new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
124		break;
125	case SIL_CHLD:
126		new.ssi_pid    = kinfo->si_pid;
127		new.ssi_uid    = kinfo->si_uid;
128		new.ssi_status = kinfo->si_status;
129		new.ssi_utime  = kinfo->si_utime;
130		new.ssi_stime  = kinfo->si_stime;
131		break;
132	case SIL_RT:
133		/*
134		 * This case catches also the signals queued by sigqueue().
135		 */
136		new.ssi_pid = kinfo->si_pid;
137		new.ssi_uid = kinfo->si_uid;
138		new.ssi_ptr = (long) kinfo->si_ptr;
139		new.ssi_int = kinfo->si_int;
140		break;
141	case SIL_SYS:
142		new.ssi_call_addr = (long) kinfo->si_call_addr;
143		new.ssi_syscall   = kinfo->si_syscall;
144		new.ssi_arch      = kinfo->si_arch;
145		break;
146	}
147
148	if (!copy_to_iter_full(&new, sizeof(struct signalfd_siginfo), to))
149		return -EFAULT;
150
151	return sizeof(struct signalfd_siginfo);
152}
153
154static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info,
155				int nonblock)
156{
157	enum pid_type type;
158	ssize_t ret;
159	DECLARE_WAITQUEUE(wait, current);
160
161	spin_lock_irq(&current->sighand->siglock);
162	ret = dequeue_signal(&ctx->sigmask, info, &type);
163	switch (ret) {
164	case 0:
165		if (!nonblock)
166			break;
167		ret = -EAGAIN;
168		fallthrough;
169	default:
170		spin_unlock_irq(&current->sighand->siglock);
171		return ret;
172	}
173
174	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
175	for (;;) {
176		set_current_state(TASK_INTERRUPTIBLE);
177		ret = dequeue_signal(&ctx->sigmask, info, &type);
178		if (ret != 0)
179			break;
180		if (signal_pending(current)) {
181			ret = -ERESTARTSYS;
182			break;
183		}
184		spin_unlock_irq(&current->sighand->siglock);
185		schedule();
186		spin_lock_irq(&current->sighand->siglock);
187	}
188	spin_unlock_irq(&current->sighand->siglock);
189
190	remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
191	__set_current_state(TASK_RUNNING);
192
193	return ret;
194}
195
196/*
197 * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
198 * error code. The "count" parameter must be at least the size of a
199 * "struct signalfd_siginfo".
200 */
201static ssize_t signalfd_read_iter(struct kiocb *iocb, struct iov_iter *to)
202{
203	struct file *file = iocb->ki_filp;
204	struct signalfd_ctx *ctx = file->private_data;
205	size_t count = iov_iter_count(to);
206	ssize_t ret, total = 0;
207	kernel_siginfo_t info;
208	bool nonblock;
209
210	count /= sizeof(struct signalfd_siginfo);
211	if (!count)
212		return -EINVAL;
213
214	nonblock = file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT;
215	do {
216		ret = signalfd_dequeue(ctx, &info, nonblock);
217		if (unlikely(ret <= 0))
218			break;
219		ret = signalfd_copyinfo(to, &info);
220		if (ret < 0)
221			break;
222		total += ret;
223		nonblock = 1;
224	} while (--count);
225
226	return total ? total: ret;
227}
228
229#ifdef CONFIG_PROC_FS
230static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
231{
232	struct signalfd_ctx *ctx = f->private_data;
233	sigset_t sigmask;
234
235	sigmask = ctx->sigmask;
236	signotset(&sigmask);
237	render_sigset_t(m, "sigmask:\t", &sigmask);
238}
239#endif
240
241static const struct file_operations signalfd_fops = {
242#ifdef CONFIG_PROC_FS
243	.show_fdinfo	= signalfd_show_fdinfo,
244#endif
245	.release	= signalfd_release,
246	.poll		= signalfd_poll,
247	.read_iter	= signalfd_read_iter,
248	.llseek		= noop_llseek,
249};
250
251static int do_signalfd4(int ufd, sigset_t *mask, int flags)
252{
253	/* Check the SFD_* constants for consistency.  */
254	BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
255	BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
256
257	if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
258		return -EINVAL;
259
260	sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
261	signotset(mask);
262
263	if (ufd == -1) {
264		int fd;
265		struct signalfd_ctx *ctx __free(kfree) = NULL;
266
267		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
268		if (!ctx)
269			return -ENOMEM;
270
271		ctx->sigmask = *mask;
272
273		fd = FD_ADD(flags & O_CLOEXEC,
274			    anon_inode_getfile_fmode(
275				    "[signalfd]", &signalfd_fops, ctx,
276				    O_RDWR | (flags & O_NONBLOCK), FMODE_NOWAIT));
277		if (fd >= 0)
278			retain_and_null_ptr(ctx);
279		return fd;
280	} else {
281		struct signalfd_ctx *ctx;
282
283		CLASS(fd, f)(ufd);
284		if (fd_empty(f))
285			return -EBADF;
286		ctx = fd_file(f)->private_data;
287		if (fd_file(f)->f_op != &signalfd_fops)
288			return -EINVAL;
289		spin_lock_irq(&current->sighand->siglock);
290		ctx->sigmask = *mask;
291		spin_unlock_irq(&current->sighand->siglock);
292
293		wake_up(&current->sighand->signalfd_wqh);
294	}
295
296	return ufd;
297}
298
299SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
300		size_t, sizemask, int, flags)
301{
302	sigset_t mask;
303
304	if (sizemask != sizeof(sigset_t))
305		return -EINVAL;
306	if (copy_from_user(&mask, user_mask, sizeof(mask)))
307		return -EFAULT;
308	return do_signalfd4(ufd, &mask, flags);
309}
310
311SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
312		size_t, sizemask)
313{
314	sigset_t mask;
315
316	if (sizemask != sizeof(sigset_t))
317		return -EINVAL;
318	if (copy_from_user(&mask, user_mask, sizeof(mask)))
319		return -EFAULT;
320	return do_signalfd4(ufd, &mask, 0);
321}
322
323#ifdef CONFIG_COMPAT
324static long do_compat_signalfd4(int ufd,
325			const compat_sigset_t __user *user_mask,
326			compat_size_t sigsetsize, int flags)
327{
328	sigset_t mask;
329
330	if (sigsetsize != sizeof(compat_sigset_t))
331		return -EINVAL;
332	if (get_compat_sigset(&mask, user_mask))
333		return -EFAULT;
334	return do_signalfd4(ufd, &mask, flags);
335}
336
337COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
338		     const compat_sigset_t __user *, user_mask,
339		     compat_size_t, sigsetsize,
340		     int, flags)
341{
342	return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
343}
344
345COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
346		     const compat_sigset_t __user *, user_mask,
347		     compat_size_t, sigsetsize)
348{
349	return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
350}
351#endif