summaryrefslogtreecommitdiffstats
path: root/fs/signalfd.c
blob: 7b941abbcde09401404a73c5298b73611eea23da (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
/*
 *  fs/signalfd.c
 *
 *  Copyright (C) 2003  Linus Torvalds
 *
 *  Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
 *      Changed ->read() to return a siginfo strcture instead of signal number.
 *      Fixed locking in ->poll().
 *      Added sighand-detach notification.
 *      Added fd re-use in sys_signalfd() syscall.
 *      Now using anonymous inode source.
 *      Thanks to Oleg Nesterov for useful code review and suggestions.
 *      More comments and suggestions from Arnd Bergmann.
 * Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
 *      Retrieve multiple signals with one read() call
 */

#include <linux/file.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/list.h>
#include <linux/anon_inodes.h>
#include <linux/signalfd.h>

struct signalfd_ctx {
	struct list_head lnk;
	wait_queue_head_t wqh;
	sigset_t sigmask;
	struct task_struct *tsk;
};

struct signalfd_lockctx {
	struct task_struct *tsk;
	unsigned long flags;
};

/*
 * Tries to acquire the sighand lock. We do not increment the sighand
 * use count, and we do not even pin the task struct, so we need to
 * do it inside an RCU read lock, and we must be prepared for the
 * ctx->tsk going to NULL (in signalfd_deliver()), and for the sighand
 * being detached. We return 0 if the sighand has been detached, or
 * 1 if we were able to pin the sighand lock.
 */
static int signalfd_lock(struct signalfd_ctx *ctx, struct signalfd_lockctx *lk)
{
	struct sighand_struct *sighand = NULL;

	rcu_read_lock();
	lk->tsk = rcu_dereference(ctx->tsk);
	if (likely(lk->tsk != NULL))
		sighand = lock_task_sighand(lk->tsk, &lk->flags);
	rcu_read_unlock();

	if (sighand && !ctx->tsk) {
		unlock_task_sighand(lk->tsk, &lk->flags);
		sighand = NULL;
	}

	return sighand != NULL;
}

static void signalfd_unlock(struct signalfd_lockctx *lk)
{
	unlock_task_sighand(lk->tsk, &lk->flags);
}

/*
 * This must be called with the sighand lock held.
 */
void signalfd_deliver(struct task_struct *tsk, int sig)
{
	struct sighand_struct *sighand = tsk->sighand;
	struct signalfd_ctx *ctx, *tmp;

	BUG_ON(!sig);
	list_for_each_entry_safe(ctx, tmp, &sighand->signalfd_list, lnk) {
		/*
		 * We use a negative signal value as a way to broadcast that the
		 * sighand has been orphaned, so that we can notify all the
		 * listeners about this. Remember the ctx->sigmask is inverted,
		 * so if the user is interested in a signal, that corresponding
		 * bit will be zero.
		 */
		if (sig < 0) {
			if (ctx->tsk == tsk) {
				ctx->tsk = NULL;
				list_del_init(&ctx->lnk);
				wake_up(&ctx->wqh);
			}
		} else {
			if (!sigismember(&ctx->sigmask, sig))
				wake_up(&ctx->wqh);
		}
	}
}

static void signalfd_cleanup(struct signalfd_ctx *ctx)
{
	struct signalfd_lockctx lk;

	/*
	 * This is tricky. If the sighand is gone, we do not need to remove
	 * context from the list, the list itself won't be there anymore.
	 */
	if (signalfd_lock(ctx, &lk)) {
		list_del(&ctx->lnk);
		signalfd_unlock(&lk);
	}
	kfree(ctx);
}

static int signalfd_release(struct inode *inode, struct file *file)
{
	signalfd_cleanup(file->private_data);
	return 0;
}

static unsigned int signalfd_poll(struct file *file, poll_table *wait)
{
	struct signalfd_ctx *ctx = file->private_data;
	unsigned int events = 0;
	struct signalfd_lockctx lk;

	poll_wait(file, &ctx->wqh, wait);

	/*
	 * Let the caller get a POLLIN in this case, ala socket recv() when
	 * the peer disconnects.
	 */
	if (signalfd_lock(ctx, &lk)) {
		if ((lk.tsk == current &&
		     next_signal(&lk.tsk->pending, &ctx->sigmask) > 0) ||
		    next_signal(&lk.tsk->signal->shared_pending,
				&ctx->sigmask) > 0)
			events |= POLLIN;
		signalfd_unlock(&lk);
	} else
		events |= POLLIN;

	return events;
}

/*
 * Copied from copy_siginfo_to_user() in kernel/signal.c
 */
static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
			     siginfo_t const *kinfo)
{
	long err;

	BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);

	/*
	 * Unused memebers should be zero ...
	 */
	err = __clear_user(uinfo, sizeof(*uinfo));

	/*
	 * If you change siginfo_t structure, please be sure
	 * this code is fixed accordingly.
	 */
	err |= __put_user(kinfo->si_signo, &uinfo->signo);
	err |= __put_user(kinfo->si_errno, &uinfo->err);
	err |= __put_user((short)kinfo->si_code, &uinfo->code);
	switch (kinfo->si_code & __SI_MASK) {
	case __SI_KILL:
		err |= __put_user(kinfo->si_pid, &uinfo->pid);
		err |= __put_user(kinfo->si_uid, &uinfo->uid);
		break;
	case __SI_TIMER:
		 err |= __put_user(kinfo->si_tid, &uinfo->tid);
		 err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
		 err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
		break;
	case __SI_POLL:
		err |= __put_user(kinfo->si_band, &uinfo->band);
		err |= __put_user(kinfo->si_fd, &uinfo->fd);
		break;
	case __SI_FAULT:
		err |= __put_user((long)kinfo->si_addr, &uinfo->addr);
#ifdef __ARCH_SI_TRAPNO
		err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
#endif
		break;
	case __SI_CHLD:
		err |= __put_user(kinfo->si_pid, &uinfo->pid);
		err |= __put_user(kinfo->si_uid, &uinfo->uid);
		err |= __put_user(kinfo->si_status, &uinfo->status);
		err |= __put_user(kinfo->si_utime, &uinfo->utime);
		err |= __put_user(kinfo->si_stime, &uinfo->stime);
		break;
	case __SI_RT: /* This is not generated by the kernel as of now. */
	case __SI_MESGQ: /* But this is */
		err |= __put_user(kinfo->si_pid, &uinfo->pid);
		err |= __put_user(kinfo->si_uid, &uinfo->uid);
		err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
		break;
	default: /* this is just in case for now ... */
		err |= __put_user(kinfo->si_pid, &uinfo->pid);
		err |= __put_user(kinfo->si_uid, &uinfo->uid);
		break;
	}

	return err ? -EFAULT: sizeof(*uinfo);
}

static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
				int nonblock)
{
	ssize_t ret;
	struct signalfd_lockctx lk;
	DECLARE_WAITQUEUE(wait, current);

	if (!signalfd_lock(ctx, &lk))
		return 0;

	ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
	switch (ret) {
	case 0:
		if (!nonblock)
			break;
		ret = -EAGAIN;
	default:
		signalfd_unlock(&lk);
		return ret;
	}

	add_wait_queue(&ctx->wqh, &wait);
	for (;;) {
		set_current_state(TASK_INTERRUPTIBLE);
		ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
		signalfd_unlock(&lk);
		if (ret != 0)
			break;
		if (signal_pending(current)) {
			ret = -ERESTARTSYS;
			break;
		}
		schedule();
		ret = signalfd_lock(ctx, &lk);
		if (unlikely(!ret)) {
			/*
			 * Let the caller read zero byte, ala socket
			 * recv() when the peer disconnect. This test
			 * must be done before doing a dequeue_signal(),
			 * because if the sighand has been orphaned,
			 * the dequeue_signal() call is going to crash
			 * because ->sighand will be long gone.
			 */
			 break;
		}
	}

	remove_wait_queue(&ctx->wqh, &wait);
	__set_current_state(TASK_RUNNING);

	return ret;
}

/*
 * Returns either the size of a "struct signalfd_siginfo", or zero if the
 * sighand we are attached to, has been orphaned. The "count" parameter
 * must be at least the size of a "struct signalfd_siginfo".
 */
static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
			     loff_t *ppos)
{
	struct signalfd_ctx *ctx = file->private_data;
	struct signalfd_siginfo __user *siginfo;
	int nonblock = file->f_flags & O_NONBLOCK;
	ssize_t ret, total = 0;
	siginfo_t info;

	count /= sizeof(struct signalfd_siginfo);
	if (!count)
		return -EINVAL;

	siginfo = (struct signalfd_siginfo __user *) buf;

	do {
		ret = signalfd_dequeue(ctx, &info, nonblock);
		if (unlikely(ret <= 0))
			break;
		ret = signalfd_copyinfo(siginfo, &info);
		if (ret < 0)
			break;
		siginfo++;
		total += ret;
		nonblock = 1;
	} while (--count);

	return total ? total : ret;
}

static const struct file_operations signalfd_fops = {
	.release	= signalfd_release,
	.poll		= signalfd_poll,
	.read		= signalfd_read,
};

/*
 * Create a file descriptor that is associated with our signal
 * state. We can pass it around to others if we want to, but
 * it will always be _our_ signal state.
 */
asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
{
	int error;
	sigset_t sigmask;
	struct signalfd_ctx *ctx;
	struct sighand_struct *sighand;
	struct file *file;
	struct inode *inode;
	struct signalfd_lockctx lk;

	if (sizemask != sizeof(sigset_t) ||
	    copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
		return -EINVAL;
	sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
	signotset(&sigmask);

	if (ufd == -1) {
		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
		if (!ctx)
			return -ENOMEM;

		init_waitqueue_head(&ctx->wqh);
		ctx->sigmask = sigmask;
		ctx->tsk = current;

		sighand = current->sighand;
		/*
		 * Add this fd to the list of signal listeners.
		 */
		spin_lock_irq(&sighand->siglock);
		list_add_tail(&ctx->lnk, &sighand->signalfd_list);
		spin_unlock_irq(&sighand->siglock);

		/*
		 * When we call this, the initialization must be complete, since
		 * anon_inode_getfd() will install the fd.
		 */
		error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
					 &signalfd_fops, ctx);
		if (error)
			goto err_fdalloc;
	} else {
		file = fget(ufd);
		if (!file)
			return -EBADF;
		ctx = file->private_data;
		if (file->f_op != &signalfd_fops) {
			fput(file);
			return -EINVAL;
		}
		/*
		 * We need to be prepared of the fact that the sighand this fd
		 * is attached to, has been detched. In that case signalfd_lock()
		 * will return 0, and we'll just skip setting the new mask.
		 */
		if (signalfd_lock(ctx, &lk)) {
			ctx->sigmask = sigmask;
			signalfd_unlock(&lk);
		}
		wake_up(&ctx->wqh);
		fput(file);
	}

	return ufd;

err_fdalloc:
	signalfd_cleanup(ctx);
	return error;
}

OpenPOWER on IntegriCloud