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TOMOYO Linux Cross Reference
Linux/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  *  Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
 15  *      Retrieve multiple signals with one read() call
 16  *  Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
 17  *      Attach to the sighand only during read() and poll().
 18  */
 19 
 20 #include <linux/file.h>
 21 #include <linux/poll.h>
 22 #include <linux/init.h>
 23 #include <linux/fs.h>
 24 #include <linux/sched.h>
 25 #include <linux/slab.h>
 26 #include <linux/kernel.h>
 27 #include <linux/signal.h>
 28 #include <linux/list.h>
 29 #include <linux/anon_inodes.h>
 30 #include <linux/signalfd.h>
 31 #include <linux/syscalls.h>
 32 #include <linux/proc_fs.h>
 33 
 34 void signalfd_cleanup(struct sighand_struct *sighand)
 35 {
 36         wait_queue_head_t *wqh = &sighand->signalfd_wqh;
 37         /*
 38          * The lockless check can race with remove_wait_queue() in progress,
 39          * but in this case its caller should run under rcu_read_lock() and
 40          * sighand_cachep is SLAB_DESTROY_BY_RCU, we can safely return.
 41          */
 42         if (likely(!waitqueue_active(wqh)))
 43                 return;
 44 
 45         /* wait_queue_t->func(POLLFREE) should do remove_wait_queue() */
 46         wake_up_poll(wqh, POLLHUP | POLLFREE);
 47 }
 48 
 49 struct signalfd_ctx {
 50         sigset_t sigmask;
 51 };
 52 
 53 static int signalfd_release(struct inode *inode, struct file *file)
 54 {
 55         kfree(file->private_data);
 56         return 0;
 57 }
 58 
 59 static unsigned int signalfd_poll(struct file *file, poll_table *wait)
 60 {
 61         struct signalfd_ctx *ctx = file->private_data;
 62         unsigned int events = 0;
 63 
 64         poll_wait(file, &current->sighand->signalfd_wqh, wait);
 65 
 66         spin_lock_irq(&current->sighand->siglock);
 67         if (next_signal(&current->pending, &ctx->sigmask) ||
 68             next_signal(&current->signal->shared_pending,
 69                         &ctx->sigmask))
 70                 events |= POLLIN;
 71         spin_unlock_irq(&current->sighand->siglock);
 72 
 73         return events;
 74 }
 75 
 76 /*
 77  * Copied from copy_siginfo_to_user() in kernel/signal.c
 78  */
 79 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
 80                              siginfo_t const *kinfo)
 81 {
 82         long err;
 83 
 84         BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
 85 
 86         /*
 87          * Unused members should be zero ...
 88          */
 89         err = __clear_user(uinfo, sizeof(*uinfo));
 90 
 91         /*
 92          * If you change siginfo_t structure, please be sure
 93          * this code is fixed accordingly.
 94          */
 95         err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
 96         err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
 97         err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
 98         switch (kinfo->si_code & __SI_MASK) {
 99         case __SI_KILL:
100                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
101                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
102                 break;
103         case __SI_TIMER:
104                  err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
105                  err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
106                  err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
107                  err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
108                 break;
109         case __SI_POLL:
110                 err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
111                 err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
112                 break;
113         case __SI_FAULT:
114                 err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
115 #ifdef __ARCH_SI_TRAPNO
116                 err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
117 #endif
118 #ifdef BUS_MCEERR_AO
119                 /* 
120                  * Other callers might not initialize the si_lsb field,
121                  * so check explicitly for the right codes here.
122                  */
123                 if (kinfo->si_code == BUS_MCEERR_AR ||
124                     kinfo->si_code == BUS_MCEERR_AO)
125                         err |= __put_user((short) kinfo->si_addr_lsb,
126                                           &uinfo->ssi_addr_lsb);
127 #endif
128                 break;
129         case __SI_CHLD:
130                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
131                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
132                 err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
133                 err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
134                 err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
135                 break;
136         case __SI_RT: /* This is not generated by the kernel as of now. */
137         case __SI_MESGQ: /* But this is */
138                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
139                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
140                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
141                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
142                 break;
143         default:
144                 /*
145                  * This case catches also the signals queued by sigqueue().
146                  */
147                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
148                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
149                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
150                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
151                 break;
152         }
153 
154         return err ? -EFAULT: sizeof(*uinfo);
155 }
156 
157 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
158                                 int nonblock)
159 {
160         ssize_t ret;
161         DECLARE_WAITQUEUE(wait, current);
162 
163         spin_lock_irq(&current->sighand->siglock);
164         ret = dequeue_signal(current, &ctx->sigmask, info);
165         switch (ret) {
166         case 0:
167                 if (!nonblock)
168                         break;
169                 ret = -EAGAIN;
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);
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  */
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         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
232 static int 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         return 0;
242 }
243 #endif
244 
245 static const struct file_operations signalfd_fops = {
246 #ifdef CONFIG_PROC_FS
247         .show_fdinfo    = signalfd_show_fdinfo,
248 #endif
249         .release        = signalfd_release,
250         .poll           = signalfd_poll,
251         .read           = signalfd_read,
252         .llseek         = noop_llseek,
253 };
254 
255 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
256                 size_t, sizemask, int, flags)
257 {
258         sigset_t sigmask;
259         struct signalfd_ctx *ctx;
260 
261         /* Check the SFD_* constants for consistency.  */
262         BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
263         BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
264 
265         if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
266                 return -EINVAL;
267 
268         if (sizemask != sizeof(sigset_t) ||
269             copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
270                 return -EINVAL;
271         sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
272         signotset(&sigmask);
273 
274         if (ufd == -1) {
275                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
276                 if (!ctx)
277                         return -ENOMEM;
278 
279                 ctx->sigmask = sigmask;
280 
281                 /*
282                  * When we call this, the initialization must be complete, since
283                  * anon_inode_getfd() will install the fd.
284                  */
285                 ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
286                                        O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
287                 if (ufd < 0)
288                         kfree(ctx);
289         } else {
290                 struct fd f = fdget(ufd);
291                 if (!f.file)
292                         return -EBADF;
293                 ctx = f.file->private_data;
294                 if (f.file->f_op != &signalfd_fops) {
295                         fdput(f);
296                         return -EINVAL;
297                 }
298                 spin_lock_irq(&current->sighand->siglock);
299                 ctx->sigmask = sigmask;
300                 spin_unlock_irq(&current->sighand->siglock);
301 
302                 wake_up(&current->sighand->signalfd_wqh);
303                 fdput(f);
304         }
305 
306         return ufd;
307 }
308 
309 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
310                 size_t, sizemask)
311 {
312         return sys_signalfd4(ufd, user_mask, sizemask, 0);
313 }
314 

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