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/kernel.h>
  26 #include <linux/signal.h>
  27 #include <linux/list.h>
  28 #include <linux/anon_inodes.h>
  29 #include <linux/signalfd.h>
  30
  31 struct signalfd_ctx {
  32         sigset_t sigmask;
  33 };
  34
  35 static int signalfd_release(struct inode *inode, struct file *file)
  36 {
  37         kfree(file->private_data);
  38         return 0;
  39 }
  40
  41 static unsigned int signalfd_poll(struct file *file, poll_table *wait)
  42 {
  43         struct signalfd_ctx *ctx = file->private_data;
  44         unsigned int events = 0;
  45
  46         poll_wait(file, &current->sighand->signalfd_wqh, wait);
  47
  48         spin_lock_irq(&current->sighand->siglock);
  49         if (next_signal(&current->pending, &ctx->sigmask) ||
  50             next_signal(&current->signal->shared_pending,
  51                         &ctx->sigmask))
  52                 events |= POLLIN;
  53         spin_unlock_irq(&current->sighand->siglock);
  54
  55         return events;
  56 }
  57
  58 /*
  59  * Copied from copy_siginfo_to_user() in kernel/signal.c
  60  */
  61 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
  62                              siginfo_t const *kinfo)
  63 {
  64         long err;
  65
  66         BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  67
  68         /*
  69          * Unused memebers should be zero ...
  70          */
  71         err = __clear_user(uinfo, sizeof(*uinfo));
  72
  73         /*
  74          * If you change siginfo_t structure, please be sure
  75          * this code is fixed accordingly.
  76          */
  77         err |= __put_user(kinfo->si_signo, &uinfo->signo);
  78         err |= __put_user(kinfo->si_errno, &uinfo->err);
  79         err |= __put_user((short)kinfo->si_code, &uinfo->code);
  80         switch (kinfo->si_code & __SI_MASK) {
  81         case __SI_KILL:
  82                 err |= __put_user(kinfo->si_pid, &uinfo->pid);
  83                 err |= __put_user(kinfo->si_uid, &uinfo->uid);
  84                 break;
  85         case __SI_TIMER:
  86                  err |= __put_user(kinfo->si_tid, &uinfo->tid);
  87                  err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
  88                  err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
  89                 break;
  90         case __SI_POLL:
  91                 err |= __put_user(kinfo->si_band, &uinfo->band);
  92                 err |= __put_user(kinfo->si_fd, &uinfo->fd);
  93                 break;
  94         case __SI_FAULT:
  95                 err |= __put_user((long)kinfo->si_addr, &uinfo->addr);
  96 #ifdef __ARCH_SI_TRAPNO
  97                 err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
  98 #endif
  99                 break;
 100         case __SI_CHLD:
 101                 err |= __put_user(kinfo->si_pid, &uinfo->pid);
 102                 err |= __put_user(kinfo->si_uid, &uinfo->uid);
 103                 err |= __put_user(kinfo->si_status, &uinfo->status);
 104                 err |= __put_user(kinfo->si_utime, &uinfo->utime);
 105                 err |= __put_user(kinfo->si_stime, &uinfo->stime);
 106                 break;
 107         case __SI_RT: /* This is not generated by the kernel as of now. */
 108         case __SI_MESGQ: /* But this is */
 109                 err |= __put_user(kinfo->si_pid, &uinfo->pid);
 110                 err |= __put_user(kinfo->si_uid, &uinfo->uid);
 111                 err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
 112                 break;
 113         default: /* this is just in case for now ... */
 114                 err |= __put_user(kinfo->si_pid, &uinfo->pid);
 115                 err |= __put_user(kinfo->si_uid, &uinfo->uid);
 116                 break;
 117         }
 118
 119         return err ? -EFAULT: sizeof(*uinfo);
 120 }
 121
 122 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 123                                 int nonblock)
 124 {
 125         ssize_t ret;
 126         DECLARE_WAITQUEUE(wait, current);
 127
 128         spin_lock_irq(&current->sighand->siglock);
 129         ret = dequeue_signal(current, &ctx->sigmask, info);
 130         switch (ret) {
 131         case 0:
 132                 if (!nonblock)
 133                         break;
 134                 ret = -EAGAIN;
 135         default:
 136                 spin_unlock_irq(&current->sighand->siglock);
 137                 return ret;
 138         }
 139
 140         add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 141         for (;;) {
 142                 set_current_state(TASK_INTERRUPTIBLE);
 143                 ret = dequeue_signal(current, &ctx->sigmask, info);
 144                 if (ret != 0)
 145                         break;
 146                 if (signal_pending(current)) {
 147                         ret = -ERESTARTSYS;
 148                         break;
 149                 }
 150                 spin_unlock_irq(&current->sighand->siglock);
 151                 schedule();
 152                 spin_lock_irq(&current->sighand->siglock);
 153         }
 154         spin_unlock_irq(&current->sighand->siglock);
 155
 156         remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 157         __set_current_state(TASK_RUNNING);
 158
 159         return ret;
 160 }
 161
 162 /*
 163  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 164  * error code. The "count" parameter must be at least the size of a
 165  * "struct signalfd_siginfo".
 166  */
 167 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 168                              loff_t *ppos)
 169 {
 170         struct signalfd_ctx *ctx = file->private_data;
 171         struct signalfd_siginfo __user *siginfo;
 172         int nonblock = file->f_flags & O_NONBLOCK;
 173         ssize_t ret, total = 0;
 174         siginfo_t info;
 175
 176         count /= sizeof(struct signalfd_siginfo);
 177         if (!count)
 178                 return -EINVAL;
 179
 180         siginfo = (struct signalfd_siginfo __user *) buf;
 181         do {
 182                 ret = signalfd_dequeue(ctx, &info, nonblock);
 183                 if (unlikely(ret <= 0))
 184                         break;
 185                 ret = signalfd_copyinfo(siginfo, &info);
 186                 if (ret < 0)
 187                         break;
 188                 siginfo++;
 189                 total += ret;
 190                 nonblock = 1;
 191         } while (--count);
 192
 193         return total ? total: ret;
 194 }
 195
 196 static const struct file_operations signalfd_fops = {
 197         .release        = signalfd_release,
 198         .poll           = signalfd_poll,
 199         .read           = signalfd_read,
 200 };
 201
 202 asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
 203 {
 204         int error;
 205         sigset_t sigmask;
 206         struct signalfd_ctx *ctx;
 207         struct file *file;
 208         struct inode *inode;
 209
 210         if (sizemask != sizeof(sigset_t) ||
 211             copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 212                 return -EINVAL;
 213         sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 214         signotset(&sigmask);
 215
 216         if (ufd == -1) {
 217                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 218                 if (!ctx)
 219                         return -ENOMEM;
 220
 221                 ctx->sigmask = sigmask;
 222
 223                 /*
 224                  * When we call this, the initialization must be complete, since
 225                  * anon_inode_getfd() will install the fd.
 226                  */
 227                 error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
 228                                          &signalfd_fops, ctx);
 229                 if (error)
 230                         goto err_fdalloc;
 231         } else {
 232                 file = fget(ufd);
 233                 if (!file)
 234                         return -EBADF;
 235                 ctx = file->private_data;
 236                 if (file->f_op != &signalfd_fops) {
 237                         fput(file);
 238                         return -EINVAL;
 239                 }
 240                 spin_lock_irq(&current->sighand->siglock);
 241                 ctx->sigmask = sigmask;
 242                 spin_unlock_irq(&current->sighand->siglock);
 243
 244                 wake_up(&current->sighand->signalfd_wqh);
 245                 fput(file);
 246         }
 247
 248         return ufd;
 249
 250 err_fdalloc:
 251         kfree(ctx);
 252         return error;
 253 }
 254