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-rw-r--r--fs/signalfd.c349
1 files changed, 349 insertions, 0 deletions
diff --git a/fs/signalfd.c b/fs/signalfd.c
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1/*
2 * fs/signalfd.c
3 *
4 * Copyright (C) 2003 Linus Torvalds
5 *
6 * Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
7 * Changed ->read() to return a siginfo strcture instead of signal number.
8 * Fixed locking in ->poll().
9 * Added sighand-detach notification.
10 * Added fd re-use in sys_signalfd() syscall.
11 * Now using anonymous inode source.
12 * Thanks to Oleg Nesterov for useful code review and suggestions.
13 * More comments and suggestions from Arnd Bergmann.
14 */
15
16#include <linux/file.h>
17#include <linux/poll.h>
18#include <linux/init.h>
19#include <linux/fs.h>
20#include <linux/sched.h>
21#include <linux/kernel.h>
22#include <linux/signal.h>
23#include <linux/list.h>
24#include <linux/anon_inodes.h>
25#include <linux/signalfd.h>
26
27struct signalfd_ctx {
28 struct list_head lnk;
29 wait_queue_head_t wqh;
30 sigset_t sigmask;
31 struct task_struct *tsk;
32};
33
34struct signalfd_lockctx {
35 struct task_struct *tsk;
36 unsigned long flags;
37};
38
39/*
40 * Tries to acquire the sighand lock. We do not increment the sighand
41 * use count, and we do not even pin the task struct, so we need to
42 * do it inside an RCU read lock, and we must be prepared for the
43 * ctx->tsk going to NULL (in signalfd_deliver()), and for the sighand
44 * being detached. We return 0 if the sighand has been detached, or
45 * 1 if we were able to pin the sighand lock.
46 */
47static int signalfd_lock(struct signalfd_ctx *ctx, struct signalfd_lockctx *lk)
48{
49 struct sighand_struct *sighand = NULL;
50
51 rcu_read_lock();
52 lk->tsk = rcu_dereference(ctx->tsk);
53 if (likely(lk->tsk != NULL))
54 sighand = lock_task_sighand(lk->tsk, &lk->flags);
55 rcu_read_unlock();
56
57 if (sighand && !ctx->tsk) {
58 unlock_task_sighand(lk->tsk, &lk->flags);
59 sighand = NULL;
60 }
61
62 return sighand != NULL;
63}
64
65static void signalfd_unlock(struct signalfd_lockctx *lk)
66{
67 unlock_task_sighand(lk->tsk, &lk->flags);
68}
69
70/*
71 * This must be called with the sighand lock held.
72 */
73void signalfd_deliver(struct task_struct *tsk, int sig)
74{
75 struct sighand_struct *sighand = tsk->sighand;
76 struct signalfd_ctx *ctx, *tmp;
77
78 BUG_ON(!sig);
79 list_for_each_entry_safe(ctx, tmp, &sighand->signalfd_list, lnk) {
80 /*
81 * We use a negative signal value as a way to broadcast that the
82 * sighand has been orphaned, so that we can notify all the
83 * listeners about this. Remember the ctx->sigmask is inverted,
84 * so if the user is interested in a signal, that corresponding
85 * bit will be zero.
86 */
87 if (sig < 0) {
88 if (ctx->tsk == tsk) {
89 ctx->tsk = NULL;
90 list_del_init(&ctx->lnk);
91 wake_up(&ctx->wqh);
92 }
93 } else {
94 if (!sigismember(&ctx->sigmask, sig))
95 wake_up(&ctx->wqh);
96 }
97 }
98}
99
100static void signalfd_cleanup(struct signalfd_ctx *ctx)
101{
102 struct signalfd_lockctx lk;
103
104 /*
105 * This is tricky. If the sighand is gone, we do not need to remove
106 * context from the list, the list itself won't be there anymore.
107 */
108 if (signalfd_lock(ctx, &lk)) {
109 list_del(&ctx->lnk);
110 signalfd_unlock(&lk);
111 }
112 kfree(ctx);
113}
114
115static int signalfd_release(struct inode *inode, struct file *file)
116{
117 signalfd_cleanup(file->private_data);
118 return 0;
119}
120
121static unsigned int signalfd_poll(struct file *file, poll_table *wait)
122{
123 struct signalfd_ctx *ctx = file->private_data;
124 unsigned int events = 0;
125 struct signalfd_lockctx lk;
126
127 poll_wait(file, &ctx->wqh, wait);
128
129 /*
130 * Let the caller get a POLLIN in this case, ala socket recv() when
131 * the peer disconnects.
132 */
133 if (signalfd_lock(ctx, &lk)) {
134 if (next_signal(&lk.tsk->pending, &ctx->sigmask) > 0 ||
135 next_signal(&lk.tsk->signal->shared_pending,
136 &ctx->sigmask) > 0)
137 events |= POLLIN;
138 signalfd_unlock(&lk);
139 } else
140 events |= POLLIN;
141
142 return events;
143}
144
145/*
146 * Copied from copy_siginfo_to_user() in kernel/signal.c
147 */
148static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
149 siginfo_t const *kinfo)
150{
151 long err;
152
153 BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
154
155 /*
156 * Unused memebers should be zero ...
157 */
158 err = __clear_user(uinfo, sizeof(*uinfo));
159
160 /*
161 * If you change siginfo_t structure, please be sure
162 * this code is fixed accordingly.
163 */
164 err |= __put_user(kinfo->si_signo, &uinfo->signo);
165 err |= __put_user(kinfo->si_errno, &uinfo->err);
166 err |= __put_user((short)kinfo->si_code, &uinfo->code);
167 switch (kinfo->si_code & __SI_MASK) {
168 case __SI_KILL:
169 err |= __put_user(kinfo->si_pid, &uinfo->pid);
170 err |= __put_user(kinfo->si_uid, &uinfo->uid);
171 break;
172 case __SI_TIMER:
173 err |= __put_user(kinfo->si_tid, &uinfo->tid);
174 err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
175 err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
176 break;
177 case __SI_POLL:
178 err |= __put_user(kinfo->si_band, &uinfo->band);
179 err |= __put_user(kinfo->si_fd, &uinfo->fd);
180 break;
181 case __SI_FAULT:
182 err |= __put_user((long)kinfo->si_addr, &uinfo->addr);
183#ifdef __ARCH_SI_TRAPNO
184 err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
185#endif
186 break;
187 case __SI_CHLD:
188 err |= __put_user(kinfo->si_pid, &uinfo->pid);
189 err |= __put_user(kinfo->si_uid, &uinfo->uid);
190 err |= __put_user(kinfo->si_status, &uinfo->status);
191 err |= __put_user(kinfo->si_utime, &uinfo->utime);
192 err |= __put_user(kinfo->si_stime, &uinfo->stime);
193 break;
194 case __SI_RT: /* This is not generated by the kernel as of now. */
195 case __SI_MESGQ: /* But this is */
196 err |= __put_user(kinfo->si_pid, &uinfo->pid);
197 err |= __put_user(kinfo->si_uid, &uinfo->uid);
198 err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
199 break;
200 default: /* this is just in case for now ... */
201 err |= __put_user(kinfo->si_pid, &uinfo->pid);
202 err |= __put_user(kinfo->si_uid, &uinfo->uid);
203 break;
204 }
205
206 return err ? -EFAULT: sizeof(*uinfo);
207}
208
209/*
210 * Returns either the size of a "struct signalfd_siginfo", or zero if the
211 * sighand we are attached to, has been orphaned. The "count" parameter
212 * must be at least the size of a "struct signalfd_siginfo".
213 */
214static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
215 loff_t *ppos)
216{
217 struct signalfd_ctx *ctx = file->private_data;
218 ssize_t res = 0;
219 int locked, signo;
220 siginfo_t info;
221 struct signalfd_lockctx lk;
222 DECLARE_WAITQUEUE(wait, current);
223
224 if (count < sizeof(struct signalfd_siginfo))
225 return -EINVAL;
226 locked = signalfd_lock(ctx, &lk);
227 if (!locked)
228 return 0;
229 res = -EAGAIN;
230 signo = dequeue_signal(lk.tsk, &ctx->sigmask, &info);
231 if (signo == 0 && !(file->f_flags & O_NONBLOCK)) {
232 add_wait_queue(&ctx->wqh, &wait);
233 for (;;) {
234 set_current_state(TASK_INTERRUPTIBLE);
235 signo = dequeue_signal(lk.tsk, &ctx->sigmask, &info);
236 if (signo != 0)
237 break;
238 if (signal_pending(current)) {
239 res = -ERESTARTSYS;
240 break;
241 }
242 signalfd_unlock(&lk);
243 schedule();
244 locked = signalfd_lock(ctx, &lk);
245 if (unlikely(!locked)) {
246 /*
247 * Let the caller read zero byte, ala socket
248 * recv() when the peer disconnect. This test
249 * must be done before doing a dequeue_signal(),
250 * because if the sighand has been orphaned,
251 * the dequeue_signal() call is going to crash.
252 */
253 res = 0;
254 break;
255 }
256 }
257 remove_wait_queue(&ctx->wqh, &wait);
258 __set_current_state(TASK_RUNNING);
259 }
260 if (likely(locked))
261 signalfd_unlock(&lk);
262 if (likely(signo))
263 res = signalfd_copyinfo((struct signalfd_siginfo __user *) buf,
264 &info);
265
266 return res;
267}
268
269static const struct file_operations signalfd_fops = {
270 .release = signalfd_release,
271 .poll = signalfd_poll,
272 .read = signalfd_read,
273};
274
275/*
276 * Create a file descriptor that is associated with our signal
277 * state. We can pass it around to others if we want to, but
278 * it will always be _our_ signal state.
279 */
280asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
281{
282 int error;
283 sigset_t sigmask;
284 struct signalfd_ctx *ctx;
285 struct sighand_struct *sighand;
286 struct file *file;
287 struct inode *inode;
288 struct signalfd_lockctx lk;
289
290 if (sizemask != sizeof(sigset_t) ||
291 copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
292 return error = -EINVAL;
293 sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
294 signotset(&sigmask);
295
296 if (ufd == -1) {
297 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
298 if (!ctx)
299 return -ENOMEM;
300
301 init_waitqueue_head(&ctx->wqh);
302 ctx->sigmask = sigmask;
303 ctx->tsk = current;
304
305 sighand = current->sighand;
306 /*
307 * Add this fd to the list of signal listeners.
308 */
309 spin_lock_irq(&sighand->siglock);
310 list_add_tail(&ctx->lnk, &sighand->signalfd_list);
311 spin_unlock_irq(&sighand->siglock);
312
313 /*
314 * When we call this, the initialization must be complete, since
315 * anon_inode_getfd() will install the fd.
316 */
317 error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
318 &signalfd_fops, ctx);
319 if (error)
320 goto err_fdalloc;
321 } else {
322 file = fget(ufd);
323 if (!file)
324 return -EBADF;
325 ctx = file->private_data;
326 if (file->f_op != &signalfd_fops) {
327 fput(file);
328 return -EINVAL;
329 }
330 /*
331 * We need to be prepared of the fact that the sighand this fd
332 * is attached to, has been detched. In that case signalfd_lock()
333 * will return 0, and we'll just skip setting the new mask.
334 */
335 if (signalfd_lock(ctx, &lk)) {
336 ctx->sigmask = sigmask;
337 signalfd_unlock(&lk);
338 }
339 wake_up(&ctx->wqh);
340 fput(file);
341 }
342
343 return ufd;
344
345err_fdalloc:
346 signalfd_cleanup(ctx);
347 return error;
348}
349
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