LXR linux/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
  33void signalfd_cleanup(struct sighand_struct *sighand)
  34{
  35        wait_queue_head_t *wqh = &sighand->signalfd_wqh;
  36        /*
  37         * The lockless check can race with remove_wait_queue() in progress,
  38         * but in this case its caller should run under rcu_read_lock() and
  39         * sighand_cachep is SLAB_DESTROY_BY_RCU, we can safely return.
  40         */
  41        if (likely(!waitqueue_active(wqh)))
  42                return;
  43
  44        /* wait_queue_t->func(POLLFREE) should do remove_wait_queue() */
  45        wake_up_poll(wqh, POLLHUP | POLLFREE);
  46}
  47
  48struct signalfd_ctx {
  49        sigset_t sigmask;
  50};
  51
  52static int signalfd_release(struct inode *inode, struct file *file)
  53{
  54        kfree(file->private_data);
  55        return 0;
  56}
  57
  58static unsigned int signalfd_poll(struct file *file, poll_table *wait)
  59{
  60        struct signalfd_ctx *ctx = file->private_data;
  61        unsigned int events = 0;
  62
  63        poll_wait(file, &current->sighand->signalfd_wqh, wait);
  64
  65        spin_lock_irq(&current->sighand->siglock);
  66        if (next_signal(&current->pending, &ctx->sigmask) ||
  67            next_signal(&current->signal->shared_pending,
  68                        &ctx->sigmask))
  69                events |= POLLIN;
  70        spin_unlock_irq(&current->sighand->siglock);
  71
  72        return events;
  73}
  74
  75/*
  76 * Copied from copy_siginfo_to_user() in kernel/signal.c
  77 */
  78static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
  79                             siginfo_t const *kinfo)
  80{
  81        long err;
  82
  83        BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  84
  85        /*
  86         * Unused members should be zero ...
  87         */
  88        err = __clear_user(uinfo, sizeof(*uinfo));
  89
  90        /*
  91         * If you change siginfo_t structure, please be sure
  92         * this code is fixed accordingly.
  93         */
  94        err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
  95        err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
  96        err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
  97        switch (kinfo->si_code & __SI_MASK) {
  98        case __SI_KILL:
  99                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 100                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 101                break;
 102        case __SI_TIMER:
 103                 err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
 104                 err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
 105                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 106                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 107                break;
 108        case __SI_POLL:
 109                err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
 110                err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
 111                break;
 112        case __SI_FAULT:
 113                err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
 114#ifdef __ARCH_SI_TRAPNO
 115                err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
 116#endif
 117#ifdef BUS_MCEERR_AO
 118                /* 
 119                 * Other callers might not initialize the si_lsb field,
 120                 * so check explicitly for the right codes here.
 121                 */
 122                if (kinfo->si_code == BUS_MCEERR_AR ||
 123                    kinfo->si_code == BUS_MCEERR_AO)
 124                        err |= __put_user((short) kinfo->si_addr_lsb,
 125                                          &uinfo->ssi_addr_lsb);
 126#endif
 127                break;
 128        case __SI_CHLD:
 129                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 130                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 131                err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
 132                err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
 133                err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
 134                break;
 135        case __SI_RT: /* This is not generated by the kernel as of now. */
 136        case __SI_MESGQ: /* But this is */
 137                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 138                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 139                err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 140                err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 141                break;
 142        default:
 143                /*
 144                 * This case catches also the signals queued by sigqueue().
 145                 */
 146                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 147                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 148                err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 149                err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 150                break;
 151        }
 152
 153        return err ? -EFAULT: sizeof(*uinfo);
 154}
 155
 156static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 157                                int nonblock)
 158{
 159        ssize_t ret;
 160        DECLARE_WAITQUEUE(wait, current);
 161
 162        spin_lock_irq(&current->sighand->siglock);
 163        ret = dequeue_signal(current, &ctx->sigmask, info);
 164        switch (ret) {
 165        case 0:
 166                if (!nonblock)
 167                        break;
 168                ret = -EAGAIN;
 169        default:
 170                spin_unlock_irq(&current->sighand->siglock);
 171                return ret;
 172        }
 173
 174        add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 175        for (;;) {
 176                set_current_state(TASK_INTERRUPTIBLE);
 177                ret = dequeue_signal(current, &ctx->sigmask, info);
 178                if (ret != 0)
 179                        break;
 180                if (signal_pending(current)) {
 181                        ret = -ERESTARTSYS;
 182                        break;
 183                }
 184                spin_unlock_irq(&current->sighand->siglock);
 185                schedule();
 186                spin_lock_irq(&current->sighand->siglock);
 187        }
 188        spin_unlock_irq(&current->sighand->siglock);
 189
 190        remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 191        __set_current_state(TASK_RUNNING);
 192
 193        return ret;
 194}
 195
 196/*
 197 * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 198 * error code. The "count" parameter must be at least the size of a
 199 * "struct signalfd_siginfo".
 200 */
 201static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 202                             loff_t *ppos)
 203{
 204        struct signalfd_ctx *ctx = file->private_data;
 205        struct signalfd_siginfo __user *siginfo;
 206        int nonblock = file->f_flags & O_NONBLOCK;
 207        ssize_t ret, total = 0;
 208        siginfo_t info;
 209
 210        count /= sizeof(struct signalfd_siginfo);
 211        if (!count)
 212                return -EINVAL;
 213
 214        siginfo = (struct signalfd_siginfo __user *) buf;
 215        do {
 216                ret = signalfd_dequeue(ctx, &info, nonblock);
 217                if (unlikely(ret <= 0))
 218                        break;
 219                ret = signalfd_copyinfo(siginfo, &info);
 220                if (ret < 0)
 221                        break;
 222                siginfo++;
 223                total += ret;
 224                nonblock = 1;
 225        } while (--count);
 226
 227        return total ? total: ret;
 228}
 229
 230static const struct file_operations signalfd_fops = {
 231        .release        = signalfd_release,
 232        .poll           = signalfd_poll,
 233        .read           = signalfd_read,
 234        .llseek         = noop_llseek,
 235};
 236
 237SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 238                size_t, sizemask, int, flags)
 239{
 240        sigset_t sigmask;
 241        struct signalfd_ctx *ctx;
 242
 243        /* Check the SFD_* constants for consistency.  */
 244        BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 245        BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 246
 247        if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 248                return -EINVAL;
 249
 250        if (sizemask != sizeof(sigset_t) ||
 251            copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 252                return -EINVAL;
 253        sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 254        signotset(&sigmask);
 255
 256        if (ufd == -1) {
 257                ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 258                if (!ctx)
 259                        return -ENOMEM;
 260
 261                ctx->sigmask = sigmask;
 262
 263                /*
 264                 * When we call this, the initialization must be complete, since
 265                 * anon_inode_getfd() will install the fd.
 266                 */
 267                ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 268                                       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 269                if (ufd < 0)
 270                        kfree(ctx);
 271        } else {
 272                struct fd f = fdget(ufd);
 273                if (!f.file)
 274                        return -EBADF;
 275                ctx = f.file->private_data;
 276                if (f.file->f_op != &signalfd_fops) {
 277                        fdput(f);
 278                        return -EINVAL;
 279                }
 280                spin_lock_irq(&current->sighand->siglock);
 281                ctx->sigmask = sigmask;
 282                spin_unlock_irq(&current->sighand->siglock);
 283
 284                wake_up(&current->sighand->signalfd_wqh);
 285                fdput(f);
 286        }
 287
 288        return ufd;
 289}
 290
 291SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 292                size_t, sizemask)
 293{
 294        return sys_signalfd4(ufd, user_mask, sizemask, 0);
 295}
 296