]>
Commit | Line | Data |
---|---|---|
fba2afaa DL |
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 | ||
27 | struct signalfd_ctx { | |
28 | struct list_head lnk; | |
29 | wait_queue_head_t wqh; | |
30 | sigset_t sigmask; | |
31 | struct task_struct *tsk; | |
32 | }; | |
33 | ||
34 | struct 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 | */ | |
47 | static 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 | ||
65 | static 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 | */ | |
73 | void 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 | ||
100 | static 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 | ||
115 | static int signalfd_release(struct inode *inode, struct file *file) | |
116 | { | |
117 | signalfd_cleanup(file->private_data); | |
118 | return 0; | |
119 | } | |
120 | ||
121 | static 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 | */ | |
148 | static 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 | */ | |
214 | static 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 | ||
269 | static 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 | */ | |
280 | asmlinkage 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 | ||
345 | err_fdalloc: | |
346 | signalfd_cleanup(ctx); | |
347 | return error; | |
348 | } | |
349 |