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,kernel_siginfo_t const * kinfo)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 
signalfd_dequeue(struct signalfd_ctx * ctx,kernel_siginfo_t * info,int nonblock)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  */
signalfd_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)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
signalfd_show_fdinfo(struct seq_file * m,struct file * f)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 
do_signalfd4(int ufd,sigset_t * mask,int flags)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 
SYSCALL_DEFINE4(signalfd4,int,ufd,sigset_t __user *,user_mask,size_t,sizemask,int,flags)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 
SYSCALL_DEFINE3(signalfd,int,ufd,sigset_t __user *,user_mask,size_t,sizemask)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
do_compat_signalfd4(int ufd,const compat_sigset_t __user * user_mask,compat_size_t sigsetsize,int flags)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 
COMPAT_SYSCALL_DEFINE4(signalfd4,int,ufd,const compat_sigset_t __user *,user_mask,compat_size_t,sigsetsize,int,flags)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 
COMPAT_SYSCALL_DEFINE3(signalfd,int,ufd,const compat_sigset_t __user *,user_mask,compat_size_t,sigsetsize)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