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Linux/fs/signalfd.c

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  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 
 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 
 55 static int signalfd_release(struct inode *inode, struct file *file)
 56 {
 57         kfree(file->private_data);
 58         return 0;
 59 }
 60 
 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  */
 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 
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  */
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
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 
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 
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 
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
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 
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 
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 

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