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                  err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
  92                 break;
  93         case __SI_POLL:
  94                 err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
  95                 err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
  96                 break;
  97         case __SI_FAULT:
  98                 err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
  99 #ifdef __ARCH_SI_TRAPNO
 100                 err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
 101 #endif
 102                 break;
 103         case __SI_CHLD:
 104                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 105                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 106                 err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
 107                 err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
 108                 err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
 109                 break;
 110         case __SI_RT: /* This is not generated by the kernel as of now. */
 111         case __SI_MESGQ: /* But this is */
 112                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 113                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 114                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 115                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 116                 break;
 117         default:
 118                 /*
 119                  * This case catches also the signals queued by sigqueue().
 120                  */
 121                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 122                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 123                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 124                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 125                 break;
 126         }
 127
 128         return err ? -EFAULT: sizeof(*uinfo);
 129 }
 130
 131 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 132                                 int nonblock)
 133 {
 134         ssize_t ret;
 135         DECLARE_WAITQUEUE(wait, current);
 136
 137         spin_lock_irq(&current->sighand->siglock);
 138         ret = dequeue_signal(current, &ctx->sigmask, info);
 139         switch (ret) {
 140         case 0:
 141                 if (!nonblock)
 142                         break;
 143                 ret = -EAGAIN;
 144         default:
 145                 spin_unlock_irq(&current->sighand->siglock);
 146                 return ret;
 147         }
 148
 149         add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 150         for (;;) {
 151                 set_current_state(TASK_INTERRUPTIBLE);
 152                 ret = dequeue_signal(current, &ctx->sigmask, info);
 153                 if (ret != 0)
 154                         break;
 155                 if (signal_pending(current)) {
 156                         ret = -ERESTARTSYS;
 157                         break;
 158                 }
 159                 spin_unlock_irq(&current->sighand->siglock);
 160                 schedule();
 161                 spin_lock_irq(&current->sighand->siglock);
 162         }
 163         spin_unlock_irq(&current->sighand->siglock);
 164
 165         remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 166         __set_current_state(TASK_RUNNING);
 167
 168         return ret;
 169 }
 170
 171 /*
 172  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 173  * error code. The "count" parameter must be at least the size of a
 174  * "struct signalfd_siginfo".
 175  */
 176 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 177                              loff_t *ppos)
 178 {
 179         struct signalfd_ctx *ctx = file->private_data;
 180         struct signalfd_siginfo __user *siginfo;
 181         int nonblock = file->f_flags & O_NONBLOCK;
 182         ssize_t ret, total = 0;
 183         siginfo_t info;
 184
 185         count /= sizeof(struct signalfd_siginfo);
 186         if (!count)
 187                 return -EINVAL;
 188
 189         siginfo = (struct signalfd_siginfo __user *) buf;
 190         do {
 191                 ret = signalfd_dequeue(ctx, &info, nonblock);
 192                 if (unlikely(ret <= 0))
 193                         break;
 194                 ret = signalfd_copyinfo(siginfo, &info);
 195                 if (ret < 0)
 196                         break;
 197                 siginfo++;
 198                 total += ret;
 199                 nonblock = 1;
 200         } while (--count);
 201
 202         return total ? total: ret;
 203 }
 204
 205 static const struct file_operations signalfd_fops = {
 206         .release        = signalfd_release,
 207         .poll           = signalfd_poll,
 208         .read           = signalfd_read,
 209 };
 210
 211 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 212                 size_t, sizemask, int, flags)
 213 {
 214         sigset_t sigmask;
 215         struct signalfd_ctx *ctx;
 216
 217         /* Check the SFD_* constants for consistency.  */
 218         BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 219         BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 220
 221         if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 222                 return -EINVAL;
 223
 224         if (sizemask != sizeof(sigset_t) ||
 225             copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 226                 return -EINVAL;
 227         sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 228         signotset(&sigmask);
 229
 230         if (ufd == -1) {
 231                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 232                 if (!ctx)
 233                         return -ENOMEM;
 234
 235                 ctx->sigmask = sigmask;
 236
 237                 /*
 238                  * When we call this, the initialization must be complete, since
 239                  * anon_inode_getfd() will install the fd.
 240                  */
 241                 ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 242                                        O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 243                 if (ufd < 0)
 244                         kfree(ctx);
 245         } else {
 246                 struct file *file = fget(ufd);
 247                 if (!file)
 248                         return -EBADF;
 249                 ctx = file->private_data;
 250                 if (file->f_op != &signalfd_fops) {
 251                         fput(file);
 252                         return -EINVAL;
 253                 }
 254                 spin_lock_irq(&current->sighand->siglock);
 255                 ctx->sigmask = sigmask;
 256                 spin_unlock_irq(&current->sighand->siglock);
 257
 258                 wake_up(&current->sighand->signalfd_wqh);
 259                 fput(file);
 260         }
 261
 262         return ufd;
 263 }
 264
 265 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 266                 size_t, sizemask)
 267 {
 268         return sys_signalfd4(ufd, user_mask, sizemask, 0);
 269 }