xref: /openbmc/linux/fs/signalfd.c (revision 3116a9931fa6fa067986a2cb0cc447c58530b1f0)
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  			     kernel_siginfo_t const *kinfo)
83  {
84  	struct signalfd_siginfo new;
85  
86  	BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
87  
88  	/*
89  	 * Unused members should be zero ...
90  	 */
91  	memset(&new, 0, sizeof(new));
92  
93  	/*
94  	 * If you change siginfo_t structure, please be sure
95  	 * this code is fixed accordingly.
96  	 */
97  	new.ssi_signo = kinfo->si_signo;
98  	new.ssi_errno = kinfo->si_errno;
99  	new.ssi_code  = kinfo->si_code;
100  	switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
101  	case SIL_KILL:
102  		new.ssi_pid = kinfo->si_pid;
103  		new.ssi_uid = kinfo->si_uid;
104  		break;
105  	case SIL_TIMER:
106  		new.ssi_tid = kinfo->si_tid;
107  		new.ssi_overrun = kinfo->si_overrun;
108  		new.ssi_ptr = (long) kinfo->si_ptr;
109  		new.ssi_int = kinfo->si_int;
110  		break;
111  	case SIL_POLL:
112  		new.ssi_band = kinfo->si_band;
113  		new.ssi_fd   = kinfo->si_fd;
114  		break;
115  	case SIL_FAULT_BNDERR:
116  	case SIL_FAULT_PKUERR:
117  		/*
118  		 * Fall through to the SIL_FAULT case.  Both SIL_FAULT_BNDERR
119  		 * and SIL_FAULT_PKUERR are only generated by faults that
120  		 * deliver them synchronously to userspace.  In case someone
121  		 * injects one of these signals and signalfd catches it treat
122  		 * it as SIL_FAULT.
123  		 */
124  	case SIL_FAULT:
125  		new.ssi_addr = (long) kinfo->si_addr;
126  #ifdef __ARCH_SI_TRAPNO
127  		new.ssi_trapno = kinfo->si_trapno;
128  #endif
129  		break;
130  	case SIL_FAULT_MCEERR:
131  		new.ssi_addr = (long) kinfo->si_addr;
132  #ifdef __ARCH_SI_TRAPNO
133  		new.ssi_trapno = kinfo->si_trapno;
134  #endif
135  		new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
136  		break;
137  	case SIL_CHLD:
138  		new.ssi_pid    = kinfo->si_pid;
139  		new.ssi_uid    = kinfo->si_uid;
140  		new.ssi_status = kinfo->si_status;
141  		new.ssi_utime  = kinfo->si_utime;
142  		new.ssi_stime  = kinfo->si_stime;
143  		break;
144  	case SIL_RT:
145  		/*
146  		 * This case catches also the signals queued by sigqueue().
147  		 */
148  		new.ssi_pid = kinfo->si_pid;
149  		new.ssi_uid = kinfo->si_uid;
150  		new.ssi_ptr = (long) kinfo->si_ptr;
151  		new.ssi_int = kinfo->si_int;
152  		break;
153  	case SIL_SYS:
154  		new.ssi_call_addr = (long) kinfo->si_call_addr;
155  		new.ssi_syscall   = kinfo->si_syscall;
156  		new.ssi_arch      = kinfo->si_arch;
157  		break;
158  	}
159  
160  	if (copy_to_user(uinfo, &new, sizeof(struct signalfd_siginfo)))
161  		return -EFAULT;
162  
163  	return sizeof(*uinfo);
164  }
165  
166  static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info,
167  				int nonblock)
168  {
169  	ssize_t ret;
170  	DECLARE_WAITQUEUE(wait, current);
171  
172  	spin_lock_irq(&current->sighand->siglock);
173  	ret = dequeue_signal(current, &ctx->sigmask, info);
174  	switch (ret) {
175  	case 0:
176  		if (!nonblock)
177  			break;
178  		ret = -EAGAIN;
179  		fallthrough;
180  	default:
181  		spin_unlock_irq(&current->sighand->siglock);
182  		return ret;
183  	}
184  
185  	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
186  	for (;;) {
187  		set_current_state(TASK_INTERRUPTIBLE);
188  		ret = dequeue_signal(current, &ctx->sigmask, info);
189  		if (ret != 0)
190  			break;
191  		if (signal_pending(current)) {
192  			ret = -ERESTARTSYS;
193  			break;
194  		}
195  		spin_unlock_irq(&current->sighand->siglock);
196  		schedule();
197  		spin_lock_irq(&current->sighand->siglock);
198  	}
199  	spin_unlock_irq(&current->sighand->siglock);
200  
201  	remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
202  	__set_current_state(TASK_RUNNING);
203  
204  	return ret;
205  }
206  
207  /*
208   * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
209   * error code. The "count" parameter must be at least the size of a
210   * "struct signalfd_siginfo".
211   */
212  static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
213  			     loff_t *ppos)
214  {
215  	struct signalfd_ctx *ctx = file->private_data;
216  	struct signalfd_siginfo __user *siginfo;
217  	int nonblock = file->f_flags & O_NONBLOCK;
218  	ssize_t ret, total = 0;
219  	kernel_siginfo_t info;
220  
221  	count /= sizeof(struct signalfd_siginfo);
222  	if (!count)
223  		return -EINVAL;
224  
225  	siginfo = (struct signalfd_siginfo __user *) buf;
226  	do {
227  		ret = signalfd_dequeue(ctx, &info, nonblock);
228  		if (unlikely(ret <= 0))
229  			break;
230  		ret = signalfd_copyinfo(siginfo, &info);
231  		if (ret < 0)
232  			break;
233  		siginfo++;
234  		total += ret;
235  		nonblock = 1;
236  	} while (--count);
237  
238  	return total ? total: ret;
239  }
240  
241  #ifdef CONFIG_PROC_FS
242  static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
243  {
244  	struct signalfd_ctx *ctx = f->private_data;
245  	sigset_t sigmask;
246  
247  	sigmask = ctx->sigmask;
248  	signotset(&sigmask);
249  	render_sigset_t(m, "sigmask:\t", &sigmask);
250  }
251  #endif
252  
253  static const struct file_operations signalfd_fops = {
254  #ifdef CONFIG_PROC_FS
255  	.show_fdinfo	= signalfd_show_fdinfo,
256  #endif
257  	.release	= signalfd_release,
258  	.poll		= signalfd_poll,
259  	.read		= signalfd_read,
260  	.llseek		= noop_llseek,
261  };
262  
263  static int do_signalfd4(int ufd, sigset_t *mask, int flags)
264  {
265  	struct signalfd_ctx *ctx;
266  
267  	/* Check the SFD_* constants for consistency.  */
268  	BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
269  	BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
270  
271  	if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
272  		return -EINVAL;
273  
274  	sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
275  	signotset(mask);
276  
277  	if (ufd == -1) {
278  		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
279  		if (!ctx)
280  			return -ENOMEM;
281  
282  		ctx->sigmask = *mask;
283  
284  		/*
285  		 * When we call this, the initialization must be complete, since
286  		 * anon_inode_getfd() will install the fd.
287  		 */
288  		ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
289  				       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
290  		if (ufd < 0)
291  			kfree(ctx);
292  	} else {
293  		struct fd f = fdget(ufd);
294  		if (!f.file)
295  			return -EBADF;
296  		ctx = f.file->private_data;
297  		if (f.file->f_op != &signalfd_fops) {
298  			fdput(f);
299  			return -EINVAL;
300  		}
301  		spin_lock_irq(&current->sighand->siglock);
302  		ctx->sigmask = *mask;
303  		spin_unlock_irq(&current->sighand->siglock);
304  
305  		wake_up(&current->sighand->signalfd_wqh);
306  		fdput(f);
307  	}
308  
309  	return ufd;
310  }
311  
312  SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
313  		size_t, sizemask, int, flags)
314  {
315  	sigset_t mask;
316  
317  	if (sizemask != sizeof(sigset_t))
318  		return -EINVAL;
319  	if (copy_from_user(&mask, user_mask, sizeof(mask)))
320  		return -EFAULT;
321  	return do_signalfd4(ufd, &mask, flags);
322  }
323  
324  SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
325  		size_t, sizemask)
326  {
327  	sigset_t mask;
328  
329  	if (sizemask != sizeof(sigset_t))
330  		return -EINVAL;
331  	if (copy_from_user(&mask, user_mask, sizeof(mask)))
332  		return -EFAULT;
333  	return do_signalfd4(ufd, &mask, 0);
334  }
335  
336  #ifdef CONFIG_COMPAT
337  static long do_compat_signalfd4(int ufd,
338  			const compat_sigset_t __user *user_mask,
339  			compat_size_t sigsetsize, int flags)
340  {
341  	sigset_t mask;
342  
343  	if (sigsetsize != sizeof(compat_sigset_t))
344  		return -EINVAL;
345  	if (get_compat_sigset(&mask, user_mask))
346  		return -EFAULT;
347  	return do_signalfd4(ufd, &mask, flags);
348  }
349  
350  COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
351  		     const compat_sigset_t __user *, user_mask,
352  		     compat_size_t, sigsetsize,
353  		     int, flags)
354  {
355  	return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
356  }
357  
358  COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
359  		     const compat_sigset_t __user *, user_mask,
360  		     compat_size_t, sigsetsize)
361  {
362  	return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
363  }
364  #endif
365