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 
signalfd_cleanup(struct sighand_struct * sighand)36 void signalfd_cleanup(struct sighand_struct *sighand)
37 {
38 	wake_up_pollfree(&sighand->signalfd_wqh);
39 }
40 
41 struct signalfd_ctx {
42 	sigset_t sigmask;
43 };
44 
signalfd_release(struct inode * inode,struct file * file)45 static int signalfd_release(struct inode *inode, struct file *file)
46 {
47 	kfree(file->private_data);
48 	return 0;
49 }
50 
signalfd_poll(struct file * file,poll_table * wait)51 static __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  */
signalfd_copyinfo(struct iov_iter * to,kernel_siginfo_t const * kinfo)71 static 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 
signalfd_dequeue(struct signalfd_ctx * ctx,kernel_siginfo_t * info,int nonblock)154 static 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  */
signalfd_read_iter(struct kiocb * iocb,struct iov_iter * to)201 static 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
signalfd_show_fdinfo(struct seq_file * m,struct file * f)230 static 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 
241 static 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 
do_signalfd4(int ufd,sigset_t * mask,int flags)251 static int do_signalfd4(int ufd, sigset_t *mask, int flags)
252 {
253 	struct signalfd_ctx *ctx;
254 
255 	/* Check the SFD_* constants for consistency.  */
256 	BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
257 	BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
258 
259 	if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
260 		return -EINVAL;
261 
262 	sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
263 	signotset(mask);
264 
265 	if (ufd == -1) {
266 		struct file *file;
267 
268 		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
269 		if (!ctx)
270 			return -ENOMEM;
271 
272 		ctx->sigmask = *mask;
273 
274 		ufd = get_unused_fd_flags(flags & O_CLOEXEC);
275 		if (ufd < 0) {
276 			kfree(ctx);
277 			return ufd;
278 		}
279 
280 		file = anon_inode_getfile("[signalfd]", &signalfd_fops, ctx,
281 				       O_RDWR | (flags & O_NONBLOCK));
282 		if (IS_ERR(file)) {
283 			put_unused_fd(ufd);
284 			kfree(ctx);
285 			return PTR_ERR(file);
286 		}
287 		file->f_mode |= FMODE_NOWAIT;
288 
289 		fd_install(ufd, file);
290 	} else {
291 		struct fd f = fdget(ufd);
292 		if (!fd_file(f))
293 			return -EBADF;
294 		ctx = fd_file(f)->private_data;
295 		if (fd_file(f)->f_op != &signalfd_fops) {
296 			fdput(f);
297 			return -EINVAL;
298 		}
299 		spin_lock_irq(&current->sighand->siglock);
300 		ctx->sigmask = *mask;
301 		spin_unlock_irq(&current->sighand->siglock);
302 
303 		wake_up(&current->sighand->signalfd_wqh);
304 		fdput(f);
305 	}
306 
307 	return ufd;
308 }
309 
SYSCALL_DEFINE4(signalfd4,int,ufd,sigset_t __user *,user_mask,size_t,sizemask,int,flags)310 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
311 		size_t, sizemask, int, flags)
312 {
313 	sigset_t mask;
314 
315 	if (sizemask != sizeof(sigset_t))
316 		return -EINVAL;
317 	if (copy_from_user(&mask, user_mask, sizeof(mask)))
318 		return -EFAULT;
319 	return do_signalfd4(ufd, &mask, flags);
320 }
321 
SYSCALL_DEFINE3(signalfd,int,ufd,sigset_t __user *,user_mask,size_t,sizemask)322 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
323 		size_t, sizemask)
324 {
325 	sigset_t mask;
326 
327 	if (sizemask != sizeof(sigset_t))
328 		return -EINVAL;
329 	if (copy_from_user(&mask, user_mask, sizeof(mask)))
330 		return -EFAULT;
331 	return do_signalfd4(ufd, &mask, 0);
332 }
333 
334 #ifdef CONFIG_COMPAT
do_compat_signalfd4(int ufd,const compat_sigset_t __user * user_mask,compat_size_t sigsetsize,int flags)335 static long do_compat_signalfd4(int ufd,
336 			const compat_sigset_t __user *user_mask,
337 			compat_size_t sigsetsize, int flags)
338 {
339 	sigset_t mask;
340 
341 	if (sigsetsize != sizeof(compat_sigset_t))
342 		return -EINVAL;
343 	if (get_compat_sigset(&mask, user_mask))
344 		return -EFAULT;
345 	return do_signalfd4(ufd, &mask, flags);
346 }
347 
COMPAT_SYSCALL_DEFINE4(signalfd4,int,ufd,const compat_sigset_t __user *,user_mask,compat_size_t,sigsetsize,int,flags)348 COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
349 		     const compat_sigset_t __user *, user_mask,
350 		     compat_size_t, sigsetsize,
351 		     int, flags)
352 {
353 	return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
354 }
355 
COMPAT_SYSCALL_DEFINE3(signalfd,int,ufd,const compat_sigset_t __user *,user_mask,compat_size_t,sigsetsize)356 COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
357 		     const compat_sigset_t __user *, user_mask,
358 		     compat_size_t, sigsetsize)
359 {
360 	return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
361 }
362 #endif
363