fs/signalfd.c

   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
  33 struct signalfd_ctx {
  34         sigset_t sigmask;
  35 };
  36
  37 static int signalfd_release(struct inode *inode, struct file *file)
  38 {
  39         kfree(file->private_data);
  40         return 0;
  41 }
  42
  43 static unsigned int signalfd_poll(struct file *file, poll_table *wait)
  44 {
  45         struct signalfd_ctx *ctx = file->private_data;
  46         unsigned int events = 0;
  47
  48         poll_wait(file, &current->sighand->signalfd_wqh, wait);
  49
  50         spin_lock_irq(&current->sighand->siglock);
  51         if (next_signal(&current->pending, &ctx->sigmask) ||
  52             next_signal(&current->signal->shared_pending,
  53                         &ctx->sigmask))
  54                 events |= POLLIN;
  55         spin_unlock_irq(&current->sighand->siglock);
  56
  57         return events;
  58 }
  59
  60 /*
  61  * Copied from copy_siginfo_to_user() in kernel/signal.c
  62  */
  63 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
  64                              siginfo_t const *kinfo)
  65 {
  66         long err;
  67
  68         BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  69
  70         /*
  71          * Unused members should be zero ...
  72          */
  73         err = __clear_user(uinfo, sizeof(*uinfo));
  74
  75         /*
  76          * If you change siginfo_t structure, please be sure
  77          * this code is fixed accordingly.
  78          */
  79         err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
  80         err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
  81         err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
  82         switch (kinfo->si_code & __SI_MASK) {
  83         case __SI_KILL:
  84                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
  85                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
  86                 break;
  87         case __SI_TIMER:
  88                  err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
  89                  err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
  90                  err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
  91                 break;
  92         case __SI_POLL:
  93                 err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
  94                 err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
  95                 break;
  96         case __SI_FAULT:
  97                 err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
  98 #ifdef __ARCH_SI_TRAPNO
  99                 err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
 100 #endif
 101                 break;
 102         case __SI_CHLD:
 103                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 104                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 105                 err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
 106                 err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
 107                 err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
 108                 break;
 109         case __SI_RT: /* This is not generated by the kernel as of now. */
 110         case __SI_MESGQ: /* But this is */
 111                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 112                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 113                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 114                 break;
 115         default:
 116                 /*
 117                  * This case catches also the signals queued by sigqueue().
 118                  */
 119                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 120                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 121                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 122                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 123                 break;
 124         }
 125
 126         return err ? -EFAULT: sizeof(*uinfo);
 127 }
 128
 129 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 130                                 int nonblock)
 131 {
 132         ssize_t ret;
 133         DECLARE_WAITQUEUE(wait, current);
 134
 135         spin_lock_irq(&current->sighand->siglock);
 136         ret = dequeue_signal(current, &ctx->sigmask, info);
 137         switch (ret) {
 138         case 0:
 139                 if (!nonblock)
 140                         break;
 141                 ret = -EAGAIN;
 142         default:
 143                 spin_unlock_irq(&current->sighand->siglock);
 144                 return ret;
 145         }
 146
 147         add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 148         for (;;) {
 149                 set_current_state(TASK_INTERRUPTIBLE);
 150                 ret = dequeue_signal(current, &ctx->sigmask, info);
 151                 if (ret != 0)
 152                         break;
 153                 if (signal_pending(current)) {
 154                         ret = -ERESTARTSYS;
 155                         break;
 156                 }
 157                 spin_unlock_irq(&current->sighand->siglock);
 158                 schedule();
 159                 spin_lock_irq(&current->sighand->siglock);
 160         }
 161         spin_unlock_irq(&current->sighand->siglock);
 162
 163         remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 164         __set_current_state(TASK_RUNNING);
 165
 166         return ret;
 167 }
 168
 169 /*
 170  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 171  * error code. The "count" parameter must be at least the size of a
 172  * "struct signalfd_siginfo".
 173  */
 174 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 175                              loff_t *ppos)
 176 {
 177         struct signalfd_ctx *ctx = file->private_data;
 178         struct signalfd_siginfo __user *siginfo;
 179         int nonblock = file->f_flags & O_NONBLOCK;
 180         ssize_t ret, total = 0;
 181         siginfo_t info;
 182
 183         count /= sizeof(struct signalfd_siginfo);
 184         if (!count)
 185                 return -EINVAL;
 186
 187         siginfo = (struct signalfd_siginfo __user *) buf;
 188         do {
 189                 ret = signalfd_dequeue(ctx, &info, nonblock);
 190                 if (unlikely(ret <= 0))
 191                         break;
 192                 ret = signalfd_copyinfo(siginfo, &info);
 193                 if (ret < 0)
 194                         break;
 195                 siginfo++;
 196                 total += ret;
 197                 nonblock = 1;
 198         } while (--count);
 199
 200         return total ? total: ret;
 201 }
 202
 203 static const struct file_operations signalfd_fops = {
 204         .release        = signalfd_release,
 205         .poll           = signalfd_poll,
 206         .read           = signalfd_read,
 207 };
 208
 209 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 210                 size_t, sizemask, int, flags)
 211 {
 212         sigset_t sigmask;
 213         struct signalfd_ctx *ctx;
 214
 215         /* Check the SFD_* constants for consistency.  */
 216         BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 217         BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 218
 219         if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 220                 return -EINVAL;
 221
 222         if (sizemask != sizeof(sigset_t) ||
 223             copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 224                 return -EINVAL;
 225         sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 226         signotset(&sigmask);
 227
 228         if (ufd == -1) {
 229                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 230                 if (!ctx)
 231                         return -ENOMEM;
 232
 233                 ctx->sigmask = sigmask;
 234
 235                 /*
 236                  * When we call this, the initialization must be complete, since
 237                  * anon_inode_getfd() will install the fd.
 238                  */
 239                 ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 240                                        O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 241                 if (ufd < 0)
 242                         kfree(ctx);
 243         } else {
 244                 struct file *file = fget(ufd);
 245                 if (!file)
 246                         return -EBADF;
 247                 ctx = file->private_data;
 248                 if (file->f_op != &signalfd_fops) {
 249                         fput(file);
 250                         return -EINVAL;
 251                 }
 252                 spin_lock_irq(&current->sighand->siglock);
 253                 ctx->sigmask = sigmask;
 254                 spin_unlock_irq(&current->sighand->siglock);
 255
 256                 wake_up(&current->sighand->signalfd_wqh);
 257                 fput(file);
 258         }
 259
 260         return ufd;
 261 }
 262
 263 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 264                 size_t, sizemask)
 265 {
 266         return sys_signalfd4(ufd, user_mask, sizemask, 0);
 267 }