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 signalfd_siginfo __user * uinfo,kernel_siginfo_t const * kinfo)71 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
72 			     kernel_siginfo_t const *kinfo)
73 {
74 	struct signalfd_siginfo new;
75 
76 	BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
77 
78 	/*
79 	 * Unused members should be zero ...
80 	 */
81 	memset(&new, 0, sizeof(new));
82 
83 	/*
84 	 * If you change siginfo_t structure, please be sure
85 	 * this code is fixed accordingly.
86 	 */
87 	new.ssi_signo = kinfo->si_signo;
88 	new.ssi_errno = kinfo->si_errno;
89 	new.ssi_code  = kinfo->si_code;
90 	switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
91 	case SIL_KILL:
92 		new.ssi_pid = kinfo->si_pid;
93 		new.ssi_uid = kinfo->si_uid;
94 		break;
95 	case SIL_TIMER:
96 		new.ssi_tid = kinfo->si_tid;
97 		new.ssi_overrun = kinfo->si_overrun;
98 		new.ssi_ptr = (long) kinfo->si_ptr;
99 		new.ssi_int = kinfo->si_int;
100 		break;
101 	case SIL_POLL:
102 		new.ssi_band = kinfo->si_band;
103 		new.ssi_fd   = kinfo->si_fd;
104 		break;
105 	case SIL_FAULT_BNDERR:
106 	case SIL_FAULT_PKUERR:
107 	case SIL_FAULT_PERF_EVENT:
108 		/*
109 		 * Fall through to the SIL_FAULT case.  SIL_FAULT_BNDERR,
110 		 * SIL_FAULT_PKUERR, and SIL_FAULT_PERF_EVENT are only
111 		 * generated by faults that deliver them synchronously to
112 		 * userspace.  In case someone injects one of these signals
113 		 * and signalfd catches it treat it as SIL_FAULT.
114 		 */
115 	case SIL_FAULT:
116 		new.ssi_addr = (long) kinfo->si_addr;
117 		break;
118 	case SIL_FAULT_TRAPNO:
119 		new.ssi_addr = (long) kinfo->si_addr;
120 		new.ssi_trapno = kinfo->si_trapno;
121 		break;
122 	case SIL_FAULT_MCEERR:
123 		new.ssi_addr = (long) kinfo->si_addr;
124 		new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
125 		break;
126 	case SIL_CHLD:
127 		new.ssi_pid    = kinfo->si_pid;
128 		new.ssi_uid    = kinfo->si_uid;
129 		new.ssi_status = kinfo->si_status;
130 		new.ssi_utime  = kinfo->si_utime;
131 		new.ssi_stime  = kinfo->si_stime;
132 		break;
133 	case SIL_RT:
134 		/*
135 		 * This case catches also the signals queued by sigqueue().
136 		 */
137 		new.ssi_pid = kinfo->si_pid;
138 		new.ssi_uid = kinfo->si_uid;
139 		new.ssi_ptr = (long) kinfo->si_ptr;
140 		new.ssi_int = kinfo->si_int;
141 		break;
142 	case SIL_SYS:
143 		new.ssi_call_addr = (long) kinfo->si_call_addr;
144 		new.ssi_syscall   = kinfo->si_syscall;
145 		new.ssi_arch      = kinfo->si_arch;
146 		break;
147 	}
148 
149 	if (copy_to_user(uinfo, &new, sizeof(struct signalfd_siginfo)))
150 		return -EFAULT;
151 
152 	return sizeof(*uinfo);
153 }
154 
signalfd_dequeue(struct signalfd_ctx * ctx,kernel_siginfo_t * info,int nonblock)155 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info,
156 				int nonblock)
157 {
158 	enum pid_type type;
159 	ssize_t ret;
160 	DECLARE_WAITQUEUE(wait, current);
161 
162 	spin_lock_irq(&current->sighand->siglock);
163 	ret = dequeue_signal(current, &ctx->sigmask, info, &type);
164 	switch (ret) {
165 	case 0:
166 		if (!nonblock)
167 			break;
168 		ret = -EAGAIN;
169 		fallthrough;
170 	default:
171 		spin_unlock_irq(&current->sighand->siglock);
172 		return ret;
173 	}
174 
175 	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
176 	for (;;) {
177 		set_current_state(TASK_INTERRUPTIBLE);
178 		ret = dequeue_signal(current, &ctx->sigmask, info, &type);
179 		if (ret != 0)
180 			break;
181 		if (signal_pending(current)) {
182 			ret = -ERESTARTSYS;
183 			break;
184 		}
185 		spin_unlock_irq(&current->sighand->siglock);
186 		schedule();
187 		spin_lock_irq(&current->sighand->siglock);
188 	}
189 	spin_unlock_irq(&current->sighand->siglock);
190 
191 	remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
192 	__set_current_state(TASK_RUNNING);
193 
194 	return ret;
195 }
196 
197 /*
198  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
199  * error code. The "count" parameter must be at least the size of a
200  * "struct signalfd_siginfo".
201  */
signalfd_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)202 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
203 			     loff_t *ppos)
204 {
205 	struct signalfd_ctx *ctx = file->private_data;
206 	struct signalfd_siginfo __user *siginfo;
207 	int nonblock = file->f_flags & O_NONBLOCK;
208 	ssize_t ret, total = 0;
209 	kernel_siginfo_t info;
210 
211 	count /= sizeof(struct signalfd_siginfo);
212 	if (!count)
213 		return -EINVAL;
214 
215 	siginfo = (struct signalfd_siginfo __user *) buf;
216 	do {
217 		ret = signalfd_dequeue(ctx, &info, nonblock);
218 		if (unlikely(ret <= 0))
219 			break;
220 		ret = signalfd_copyinfo(siginfo, &info);
221 		if (ret < 0)
222 			break;
223 		siginfo++;
224 		total += ret;
225 		nonblock = 1;
226 	} while (--count);
227 
228 	return total ? total: ret;
229 }
230 
231 #ifdef CONFIG_PROC_FS
signalfd_show_fdinfo(struct seq_file * m,struct file * f)232 static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
233 {
234 	struct signalfd_ctx *ctx = f->private_data;
235 	sigset_t sigmask;
236 
237 	sigmask = ctx->sigmask;
238 	signotset(&sigmask);
239 	render_sigset_t(m, "sigmask:\t", &sigmask);
240 }
241 #endif
242 
243 static const struct file_operations signalfd_fops = {
244 #ifdef CONFIG_PROC_FS
245 	.show_fdinfo	= signalfd_show_fdinfo,
246 #endif
247 	.release	= signalfd_release,
248 	.poll		= signalfd_poll,
249 	.read		= signalfd_read,
250 	.llseek		= noop_llseek,
251 };
252 
do_signalfd4(int ufd,sigset_t * mask,int flags)253 static int do_signalfd4(int ufd, sigset_t *mask, int flags)
254 {
255 	struct signalfd_ctx *ctx;
256 
257 	/* Check the SFD_* constants for consistency.  */
258 	BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
259 	BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
260 
261 	if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
262 		return -EINVAL;
263 
264 	sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
265 	signotset(mask);
266 
267 	if (ufd == -1) {
268 		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
269 		if (!ctx)
270 			return -ENOMEM;
271 
272 		ctx->sigmask = *mask;
273 
274 		/*
275 		 * When we call this, the initialization must be complete, since
276 		 * anon_inode_getfd() will install the fd.
277 		 */
278 		ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
279 				       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
280 		if (ufd < 0)
281 			kfree(ctx);
282 	} else {
283 		struct fd f = fdget(ufd);
284 		if (!f.file)
285 			return -EBADF;
286 		ctx = f.file->private_data;
287 		if (f.file->f_op != &signalfd_fops) {
288 			fdput(f);
289 			return -EINVAL;
290 		}
291 		spin_lock_irq(&current->sighand->siglock);
292 		ctx->sigmask = *mask;
293 		spin_unlock_irq(&current->sighand->siglock);
294 
295 		wake_up(&current->sighand->signalfd_wqh);
296 		fdput(f);
297 	}
298 
299 	return ufd;
300 }
301 
SYSCALL_DEFINE4(signalfd4,int,ufd,sigset_t __user *,user_mask,size_t,sizemask,int,flags)302 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
303 		size_t, sizemask, int, flags)
304 {
305 	sigset_t mask;
306 
307 	if (sizemask != sizeof(sigset_t))
308 		return -EINVAL;
309 	if (copy_from_user(&mask, user_mask, sizeof(mask)))
310 		return -EFAULT;
311 	return do_signalfd4(ufd, &mask, flags);
312 }
313 
SYSCALL_DEFINE3(signalfd,int,ufd,sigset_t __user *,user_mask,size_t,sizemask)314 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
315 		size_t, sizemask)
316 {
317 	sigset_t mask;
318 
319 	if (sizemask != sizeof(sigset_t))
320 		return -EINVAL;
321 	if (copy_from_user(&mask, user_mask, sizeof(mask)))
322 		return -EFAULT;
323 	return do_signalfd4(ufd, &mask, 0);
324 }
325 
326 #ifdef CONFIG_COMPAT
do_compat_signalfd4(int ufd,const compat_sigset_t __user * user_mask,compat_size_t sigsetsize,int flags)327 static long do_compat_signalfd4(int ufd,
328 			const compat_sigset_t __user *user_mask,
329 			compat_size_t sigsetsize, int flags)
330 {
331 	sigset_t mask;
332 
333 	if (sigsetsize != sizeof(compat_sigset_t))
334 		return -EINVAL;
335 	if (get_compat_sigset(&mask, user_mask))
336 		return -EFAULT;
337 	return do_signalfd4(ufd, &mask, flags);
338 }
339 
COMPAT_SYSCALL_DEFINE4(signalfd4,int,ufd,const compat_sigset_t __user *,user_mask,compat_size_t,sigsetsize,int,flags)340 COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
341 		     const compat_sigset_t __user *, user_mask,
342 		     compat_size_t, sigsetsize,
343 		     int, flags)
344 {
345 	return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
346 }
347 
COMPAT_SYSCALL_DEFINE3(signalfd,int,ufd,const compat_sigset_t __user *,user_mask,compat_size_t,sigsetsize)348 COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
349 		     const compat_sigset_t __user *, user_mask,
350 		     compat_size_t, sigsetsize)
351 {
352 	return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
353 }
354 #endif
355