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 	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 
signalfd_release(struct inode * inode,struct file * file)55 static int signalfd_release(struct inode *inode, struct file *file)
56 {
57 	kfree(file->private_data);
58 	return 0;
59 }
60 
signalfd_poll(struct file * file,poll_table * wait)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  */
signalfd_copyinfo(struct signalfd_siginfo __user * uinfo,siginfo_t const * kinfo)81 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
82 			     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 
signalfd_dequeue(struct signalfd_ctx * ctx,siginfo_t * info,int nonblock)166 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, 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 	default:
180 		spin_unlock_irq(&current->sighand->siglock);
181 		return ret;
182 	}
183 
184 	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
185 	for (;;) {
186 		set_current_state(TASK_INTERRUPTIBLE);
187 		ret = dequeue_signal(current, &ctx->sigmask, info);
188 		if (ret != 0)
189 			break;
190 		if (signal_pending(current)) {
191 			ret = -ERESTARTSYS;
192 			break;
193 		}
194 		spin_unlock_irq(&current->sighand->siglock);
195 		schedule();
196 		spin_lock_irq(&current->sighand->siglock);
197 	}
198 	spin_unlock_irq(&current->sighand->siglock);
199 
200 	remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
201 	__set_current_state(TASK_RUNNING);
202 
203 	return ret;
204 }
205 
206 /*
207  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
208  * error code. The "count" parameter must be at least the size of a
209  * "struct signalfd_siginfo".
210  */
signalfd_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)211 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
212 			     loff_t *ppos)
213 {
214 	struct signalfd_ctx *ctx = file->private_data;
215 	struct signalfd_siginfo __user *siginfo;
216 	int nonblock = file->f_flags & O_NONBLOCK;
217 	ssize_t ret, total = 0;
218 	siginfo_t info;
219 
220 	count /= sizeof(struct signalfd_siginfo);
221 	if (!count)
222 		return -EINVAL;
223 
224 	siginfo = (struct signalfd_siginfo __user *) buf;
225 	do {
226 		ret = signalfd_dequeue(ctx, &info, nonblock);
227 		if (unlikely(ret <= 0))
228 			break;
229 		ret = signalfd_copyinfo(siginfo, &info);
230 		if (ret < 0)
231 			break;
232 		siginfo++;
233 		total += ret;
234 		nonblock = 1;
235 	} while (--count);
236 
237 	return total ? total: ret;
238 }
239 
240 #ifdef CONFIG_PROC_FS
signalfd_show_fdinfo(struct seq_file * m,struct file * f)241 static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
242 {
243 	struct signalfd_ctx *ctx = f->private_data;
244 	sigset_t sigmask;
245 
246 	sigmask = ctx->sigmask;
247 	signotset(&sigmask);
248 	render_sigset_t(m, "sigmask:\t", &sigmask);
249 }
250 #endif
251 
252 static const struct file_operations signalfd_fops = {
253 #ifdef CONFIG_PROC_FS
254 	.show_fdinfo	= signalfd_show_fdinfo,
255 #endif
256 	.release	= signalfd_release,
257 	.poll		= signalfd_poll,
258 	.read		= signalfd_read,
259 	.llseek		= noop_llseek,
260 };
261 
do_signalfd4(int ufd,sigset_t * mask,int flags)262 static int do_signalfd4(int ufd, sigset_t *mask, int flags)
263 {
264 	struct signalfd_ctx *ctx;
265 
266 	/* Check the SFD_* constants for consistency.  */
267 	BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
268 	BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
269 
270 	if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
271 		return -EINVAL;
272 
273 	sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
274 	signotset(mask);
275 
276 	if (ufd == -1) {
277 		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
278 		if (!ctx)
279 			return -ENOMEM;
280 
281 		ctx->sigmask = *mask;
282 
283 		/*
284 		 * When we call this, the initialization must be complete, since
285 		 * anon_inode_getfd() will install the fd.
286 		 */
287 		ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
288 				       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
289 		if (ufd < 0)
290 			kfree(ctx);
291 	} else {
292 		struct fd f = fdget(ufd);
293 		if (!f.file)
294 			return -EBADF;
295 		ctx = f.file->private_data;
296 		if (f.file->f_op != &signalfd_fops) {
297 			fdput(f);
298 			return -EINVAL;
299 		}
300 		spin_lock_irq(&current->sighand->siglock);
301 		ctx->sigmask = *mask;
302 		spin_unlock_irq(&current->sighand->siglock);
303 
304 		wake_up(&current->sighand->signalfd_wqh);
305 		fdput(f);
306 	}
307 
308 	return ufd;
309 }
310 
SYSCALL_DEFINE4(signalfd4,int,ufd,sigset_t __user *,user_mask,size_t,sizemask,int,flags)311 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
312 		size_t, sizemask, int, flags)
313 {
314 	sigset_t mask;
315 
316 	if (sizemask != sizeof(sigset_t) ||
317 	    copy_from_user(&mask, user_mask, sizeof(mask)))
318 		return -EINVAL;
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 	    copy_from_user(&mask, user_mask, sizeof(mask)))
329 		return -EINVAL;
330 	return do_signalfd4(ufd, &mask, 0);
331 }
332 
333 #ifdef CONFIG_COMPAT
do_compat_signalfd4(int ufd,const compat_sigset_t __user * user_mask,compat_size_t sigsetsize,int flags)334 static long do_compat_signalfd4(int ufd,
335 			const compat_sigset_t __user *user_mask,
336 			compat_size_t sigsetsize, int flags)
337 {
338 	sigset_t mask;
339 
340 	if (sigsetsize != sizeof(compat_sigset_t))
341 		return -EINVAL;
342 	if (get_compat_sigset(&mask, user_mask))
343 		return -EFAULT;
344 	return do_signalfd4(ufd, &mask, flags);
345 }
346 
COMPAT_SYSCALL_DEFINE4(signalfd4,int,ufd,const compat_sigset_t __user *,user_mask,compat_size_t,sigsetsize,int,flags)347 COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
348 		     const compat_sigset_t __user *, user_mask,
349 		     compat_size_t, sigsetsize,
350 		     int, flags)
351 {
352 	return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
353 }
354 
COMPAT_SYSCALL_DEFINE3(signalfd,int,ufd,const compat_sigset_t __user *,user_mask,compat_size_t,sigsetsize)355 COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
356 		     const compat_sigset_t __user *, user_mask,
357 		     compat_size_t, sigsetsize)
358 {
359 	return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
360 }
361 #endif
362