xref: /openbmc/linux/fs/signalfd.c (revision 4cff79e9) 
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 
36 void signalfd_cleanup(struct sighand_struct *sighand)
37 {
38 	wait_queue_head_t *wqh = &sighand->signalfd_wqh;
39 	/*
40 	 * The lockless check can race with remove_wait_queue() in progress,
41 	 * but in this case its caller should run under rcu_read_lock() and
42 	 * sighand_cachep is SLAB_TYPESAFE_BY_RCU, we can safely return.
43 	 */
44 	if (likely(!waitqueue_active(wqh)))
45 		return;
46 
47 	/* wait_queue_entry_t->func(POLLFREE) should do remove_wait_queue() */
48 	wake_up_poll(wqh, EPOLLHUP | POLLFREE);
49 }
50 
51 struct signalfd_ctx {
52 	sigset_t sigmask;
53 };
54 
55 static int signalfd_release(struct inode *inode, struct file *file)
56 {
57 	kfree(file->private_data);
58 	return 0;
59 }
60 
61 static __poll_t signalfd_poll(struct file *file, poll_table *wait)
62 {
63 	struct signalfd_ctx *ctx = file->private_data;
64 	__poll_t events = 0;
65 
66 	poll_wait(file, &current->sighand->signalfd_wqh, wait);
67 
68 	spin_lock_irq(&current->sighand->siglock);
69 	if (next_signal(&current->pending, &ctx->sigmask) ||
70 	    next_signal(&current->signal->shared_pending,
71 			&ctx->sigmask))
72 		events |= EPOLLIN;
73 	spin_unlock_irq(&current->sighand->siglock);
74 
75 	return events;
76 }
77 
78 /*
79  * Copied from copy_siginfo_to_user() in kernel/signal.c
80  */
81 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
82 			     siginfo_t const *kinfo)
83 {
84 	long err;
85 
86 	BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
87 
88 	/*
89 	 * Unused members should be zero ...
90 	 */
91 	err = __clear_user(uinfo, sizeof(*uinfo));
92 
93 	/*
94 	 * If you change siginfo_t structure, please be sure
95 	 * this code is fixed accordingly.
96 	 */
97 	err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
98 	err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
99 	err |= __put_user(kinfo->si_code, &uinfo->ssi_code);
100 	switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
101 	case SIL_KILL:
102 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
103 		err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
104 		break;
105 	case SIL_TIMER:
106 		 err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
107 		 err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
108 		 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
109 		 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
110 		break;
111 	case SIL_POLL:
112 		err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
113 		err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
114 		break;
115 	case SIL_FAULT:
116 		err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
117 #ifdef __ARCH_SI_TRAPNO
118 		err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
119 #endif
120 #ifdef BUS_MCEERR_AO
121 		/*
122 		 * Other callers might not initialize the si_lsb field,
123 		 * so check explicitly for the right codes here.
124 		 */
125 		if (kinfo->si_signo == SIGBUS &&
126 		     kinfo->si_code == BUS_MCEERR_AO)
127 			err |= __put_user((short) kinfo->si_addr_lsb,
128 					  &uinfo->ssi_addr_lsb);
129 #endif
130 #ifdef BUS_MCEERR_AR
131 		/*
132 		 * Other callers might not initialize the si_lsb field,
133 		 * so check explicitly for the right codes here.
134 		 */
135 		if (kinfo->si_signo == SIGBUS &&
136 		    kinfo->si_code == BUS_MCEERR_AR)
137 			err |= __put_user((short) kinfo->si_addr_lsb,
138 					  &uinfo->ssi_addr_lsb);
139 #endif
140 		break;
141 	case SIL_CHLD:
142 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
143 		err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
144 		err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
145 		err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
146 		err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
147 		break;
148 	case SIL_RT:
149 	default:
150 		/*
151 		 * This case catches also the signals queued by sigqueue().
152 		 */
153 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
154 		err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
155 		err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
156 		err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
157 		break;
158 	}
159 
160 	return err ? -EFAULT: sizeof(*uinfo);
161 }
162 
163 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
164 				int nonblock)
165 {
166 	ssize_t ret;
167 	DECLARE_WAITQUEUE(wait, current);
168 
169 	spin_lock_irq(&current->sighand->siglock);
170 	ret = dequeue_signal(current, &ctx->sigmask, info);
171 	switch (ret) {
172 	case 0:
173 		if (!nonblock)
174 			break;
175 		ret = -EAGAIN;
176 	default:
177 		spin_unlock_irq(&current->sighand->siglock);
178 		return ret;
179 	}
180 
181 	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
182 	for (;;) {
183 		set_current_state(TASK_INTERRUPTIBLE);
184 		ret = dequeue_signal(current, &ctx->sigmask, info);
185 		if (ret != 0)
186 			break;
187 		if (signal_pending(current)) {
188 			ret = -ERESTARTSYS;
189 			break;
190 		}
191 		spin_unlock_irq(&current->sighand->siglock);
192 		schedule();
193 		spin_lock_irq(&current->sighand->siglock);
194 	}
195 	spin_unlock_irq(&current->sighand->siglock);
196 
197 	remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
198 	__set_current_state(TASK_RUNNING);
199 
200 	return ret;
201 }
202 
203 /*
204  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
205  * error code. The "count" parameter must be at least the size of a
206  * "struct signalfd_siginfo".
207  */
208 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
209 			     loff_t *ppos)
210 {
211 	struct signalfd_ctx *ctx = file->private_data;
212 	struct signalfd_siginfo __user *siginfo;
213 	int nonblock = file->f_flags & O_NONBLOCK;
214 	ssize_t ret, total = 0;
215 	siginfo_t info;
216 
217 	count /= sizeof(struct signalfd_siginfo);
218 	if (!count)
219 		return -EINVAL;
220 
221 	siginfo = (struct signalfd_siginfo __user *) buf;
222 	do {
223 		ret = signalfd_dequeue(ctx, &info, nonblock);
224 		if (unlikely(ret <= 0))
225 			break;
226 		ret = signalfd_copyinfo(siginfo, &info);
227 		if (ret < 0)
228 			break;
229 		siginfo++;
230 		total += ret;
231 		nonblock = 1;
232 	} while (--count);
233 
234 	return total ? total: ret;
235 }
236 
237 #ifdef CONFIG_PROC_FS
238 static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
239 {
240 	struct signalfd_ctx *ctx = f->private_data;
241 	sigset_t sigmask;
242 
243 	sigmask = ctx->sigmask;
244 	signotset(&sigmask);
245 	render_sigset_t(m, "sigmask:\t", &sigmask);
246 }
247 #endif
248 
249 static const struct file_operations signalfd_fops = {
250 #ifdef CONFIG_PROC_FS
251 	.show_fdinfo	= signalfd_show_fdinfo,
252 #endif
253 	.release	= signalfd_release,
254 	.poll		= signalfd_poll,
255 	.read		= signalfd_read,
256 	.llseek		= noop_llseek,
257 };
258 
259 static int do_signalfd4(int ufd, sigset_t __user *user_mask, size_t sizemask,
260 			int flags)
261 {
262 	sigset_t sigmask;
263 	struct signalfd_ctx *ctx;
264 
265 	/* Check the SFD_* constants for consistency.  */
266 	BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
267 	BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
268 
269 	if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
270 		return -EINVAL;
271 
272 	if (sizemask != sizeof(sigset_t) ||
273 	    copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
274 		return -EINVAL;
275 	sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
276 	signotset(&sigmask);
277 
278 	if (ufd == -1) {
279 		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
280 		if (!ctx)
281 			return -ENOMEM;
282 
283 		ctx->sigmask = sigmask;
284 
285 		/*
286 		 * When we call this, the initialization must be complete, since
287 		 * anon_inode_getfd() will install the fd.
288 		 */
289 		ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
290 				       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
291 		if (ufd < 0)
292 			kfree(ctx);
293 	} else {
294 		struct fd f = fdget(ufd);
295 		if (!f.file)
296 			return -EBADF;
297 		ctx = f.file->private_data;
298 		if (f.file->f_op != &signalfd_fops) {
299 			fdput(f);
300 			return -EINVAL;
301 		}
302 		spin_lock_irq(&current->sighand->siglock);
303 		ctx->sigmask = sigmask;
304 		spin_unlock_irq(&current->sighand->siglock);
305 
306 		wake_up(&current->sighand->signalfd_wqh);
307 		fdput(f);
308 	}
309 
310 	return ufd;
311 }
312 
313 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
314 		size_t, sizemask, int, flags)
315 {
316 	return do_signalfd4(ufd, user_mask, sizemask, flags);
317 }
318 
319 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
320 		size_t, sizemask)
321 {
322 	return do_signalfd4(ufd, user_mask, sizemask, 0);
323 }
324 
325 #ifdef CONFIG_COMPAT
326 static long do_compat_signalfd4(int ufd,
327 			const compat_sigset_t __user *sigmask,
328 			compat_size_t sigsetsize, int flags)
329 {
330 	sigset_t tmp;
331 	sigset_t __user *ksigmask;
332 
333 	if (sigsetsize != sizeof(compat_sigset_t))
334 		return -EINVAL;
335 	if (get_compat_sigset(&tmp, sigmask))
336 		return -EFAULT;
337 	ksigmask = compat_alloc_user_space(sizeof(sigset_t));
338 	if (copy_to_user(ksigmask, &tmp, sizeof(sigset_t)))
339 		return -EFAULT;
340 
341 	return do_signalfd4(ufd, ksigmask, sizeof(sigset_t), flags);
342 }
343 
344 COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
345 		     const compat_sigset_t __user *, sigmask,
346 		     compat_size_t, sigsetsize,
347 		     int, flags)
348 {
349 	return do_compat_signalfd4(ufd, sigmask, sigsetsize, flags);
350 }
351 
352 COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
353 		     const compat_sigset_t __user *,sigmask,
354 		     compat_size_t, sigsetsize)
355 {
356 	return do_compat_signalfd4(ufd, sigmask, sigsetsize, 0);
357 }
358 #endif
359