xref: /openbmc/linux/fs/signalfd.c (revision 643d1f7f)
1 /*
2  *  fs/signalfd.c
3  *
4  *  Copyright (C) 2003  Linus Torvalds
5  *
6  *  Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
7  *      Changed ->read() to return a siginfo strcture instead of signal number.
8  *      Fixed locking in ->poll().
9  *      Added sighand-detach notification.
10  *      Added fd re-use in sys_signalfd() syscall.
11  *      Now using anonymous inode source.
12  *      Thanks to Oleg Nesterov for useful code review and suggestions.
13  *      More comments and suggestions from Arnd Bergmann.
14  *  Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
15  *      Retrieve multiple signals with one read() call
16  *  Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
17  *      Attach to the sighand only during read() and poll().
18  */
19 
20 #include <linux/file.h>
21 #include <linux/poll.h>
22 #include <linux/init.h>
23 #include <linux/fs.h>
24 #include <linux/sched.h>
25 #include <linux/kernel.h>
26 #include <linux/signal.h>
27 #include <linux/list.h>
28 #include <linux/anon_inodes.h>
29 #include <linux/signalfd.h>
30 
31 struct signalfd_ctx {
32 	sigset_t sigmask;
33 };
34 
35 static int signalfd_release(struct inode *inode, struct file *file)
36 {
37 	kfree(file->private_data);
38 	return 0;
39 }
40 
41 static unsigned int signalfd_poll(struct file *file, poll_table *wait)
42 {
43 	struct signalfd_ctx *ctx = file->private_data;
44 	unsigned int events = 0;
45 
46 	poll_wait(file, &current->sighand->signalfd_wqh, wait);
47 
48 	spin_lock_irq(&current->sighand->siglock);
49 	if (next_signal(&current->pending, &ctx->sigmask) ||
50 	    next_signal(&current->signal->shared_pending,
51 			&ctx->sigmask))
52 		events |= POLLIN;
53 	spin_unlock_irq(&current->sighand->siglock);
54 
55 	return events;
56 }
57 
58 /*
59  * Copied from copy_siginfo_to_user() in kernel/signal.c
60  */
61 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
62 			     siginfo_t const *kinfo)
63 {
64 	long err;
65 
66 	BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
67 
68 	/*
69 	 * Unused members should be zero ...
70 	 */
71 	err = __clear_user(uinfo, sizeof(*uinfo));
72 
73 	/*
74 	 * If you change siginfo_t structure, please be sure
75 	 * this code is fixed accordingly.
76 	 */
77 	err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
78 	err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
79 	err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
80 	switch (kinfo->si_code & __SI_MASK) {
81 	case __SI_KILL:
82 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
83 		err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
84 		break;
85 	case __SI_TIMER:
86 		 err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
87 		 err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
88 		 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
89 		break;
90 	case __SI_POLL:
91 		err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
92 		err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
93 		break;
94 	case __SI_FAULT:
95 		err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
96 #ifdef __ARCH_SI_TRAPNO
97 		err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
98 #endif
99 		break;
100 	case __SI_CHLD:
101 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
102 		err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
103 		err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
104 		err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
105 		err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
106 		break;
107 	case __SI_RT: /* This is not generated by the kernel as of now. */
108 	case __SI_MESGQ: /* But this is */
109 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
110 		err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
111 		err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
112 		break;
113 	default: /* this is just in case for now ... */
114 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
115 		err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
116 		break;
117 	}
118 
119 	return err ? -EFAULT: sizeof(*uinfo);
120 }
121 
122 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
123 				int nonblock)
124 {
125 	ssize_t ret;
126 	DECLARE_WAITQUEUE(wait, current);
127 
128 	spin_lock_irq(&current->sighand->siglock);
129 	ret = dequeue_signal(current, &ctx->sigmask, info);
130 	switch (ret) {
131 	case 0:
132 		if (!nonblock)
133 			break;
134 		ret = -EAGAIN;
135 	default:
136 		spin_unlock_irq(&current->sighand->siglock);
137 		return ret;
138 	}
139 
140 	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
141 	for (;;) {
142 		set_current_state(TASK_INTERRUPTIBLE);
143 		ret = dequeue_signal(current, &ctx->sigmask, info);
144 		if (ret != 0)
145 			break;
146 		if (signal_pending(current)) {
147 			ret = -ERESTARTSYS;
148 			break;
149 		}
150 		spin_unlock_irq(&current->sighand->siglock);
151 		schedule();
152 		spin_lock_irq(&current->sighand->siglock);
153 	}
154 	spin_unlock_irq(&current->sighand->siglock);
155 
156 	remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
157 	__set_current_state(TASK_RUNNING);
158 
159 	return ret;
160 }
161 
162 /*
163  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
164  * error code. The "count" parameter must be at least the size of a
165  * "struct signalfd_siginfo".
166  */
167 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
168 			     loff_t *ppos)
169 {
170 	struct signalfd_ctx *ctx = file->private_data;
171 	struct signalfd_siginfo __user *siginfo;
172 	int nonblock = file->f_flags & O_NONBLOCK;
173 	ssize_t ret, total = 0;
174 	siginfo_t info;
175 
176 	count /= sizeof(struct signalfd_siginfo);
177 	if (!count)
178 		return -EINVAL;
179 
180 	siginfo = (struct signalfd_siginfo __user *) buf;
181 	do {
182 		ret = signalfd_dequeue(ctx, &info, nonblock);
183 		if (unlikely(ret <= 0))
184 			break;
185 		ret = signalfd_copyinfo(siginfo, &info);
186 		if (ret < 0)
187 			break;
188 		siginfo++;
189 		total += ret;
190 		nonblock = 1;
191 	} while (--count);
192 
193 	return total ? total: ret;
194 }
195 
196 static const struct file_operations signalfd_fops = {
197 	.release	= signalfd_release,
198 	.poll		= signalfd_poll,
199 	.read		= signalfd_read,
200 };
201 
202 asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
203 {
204 	int error;
205 	sigset_t sigmask;
206 	struct signalfd_ctx *ctx;
207 	struct file *file;
208 	struct inode *inode;
209 
210 	if (sizemask != sizeof(sigset_t) ||
211 	    copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
212 		return -EINVAL;
213 	sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
214 	signotset(&sigmask);
215 
216 	if (ufd == -1) {
217 		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
218 		if (!ctx)
219 			return -ENOMEM;
220 
221 		ctx->sigmask = sigmask;
222 
223 		/*
224 		 * When we call this, the initialization must be complete, since
225 		 * anon_inode_getfd() will install the fd.
226 		 */
227 		error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
228 					 &signalfd_fops, ctx);
229 		if (error)
230 			goto err_fdalloc;
231 	} else {
232 		file = fget(ufd);
233 		if (!file)
234 			return -EBADF;
235 		ctx = file->private_data;
236 		if (file->f_op != &signalfd_fops) {
237 			fput(file);
238 			return -EINVAL;
239 		}
240 		spin_lock_irq(&current->sighand->siglock);
241 		ctx->sigmask = sigmask;
242 		spin_unlock_irq(&current->sighand->siglock);
243 
244 		wake_up(&current->sighand->signalfd_wqh);
245 		fput(file);
246 	}
247 
248 	return ufd;
249 
250 err_fdalloc:
251 	kfree(ctx);
252 	return error;
253 }
254 
255