signalfd.c

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/*
 *  fs/signalfd.c
 *
 *  Copyright (C) 2003  Linus Torvalds
 *
 *  Mon Mar 5, 2007: Davide Libenzi <[email protected]>
 *      Changed ->read() to return a siginfo strcture instead of signal number.
 *      Fixed locking in ->poll().
 *      Added sighand-detach notification.
 *      Added fd re-use in sys_signalfd() syscall.
 *      Now using anonymous inode source.
 *      Thanks to Oleg Nesterov for useful code review and suggestions.
 *      More comments and suggestions from Arnd Bergmann.
 *  Sat May 19, 2007: Davi E. M. Arnaut <[email protected]>
 *      Retrieve multiple signals with one read() call
 *  Sun Jul 15, 2007: Davide Libenzi <[email protected]>
 *      Attach to the sighand only during read() and poll().
 */

#include <linux/file.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/list.h>
#include <linux/anon_inodes.h>
#include <linux/signalfd.h>
#include <linux/syscalls.h>

void signalfd_cleanup(struct sighand_struct *sighand)
{
    wait_queue_head_t *wqh = &sighand->signalfd_wqh;
    /*
     * The lockless check can race with remove_wait_queue() in progress,
     * but in this case its caller should run under rcu_read_lock() and
     * sighand_cachep is SLAB_DESTROY_BY_RCU, we can safely return.
     */
    if (likely(!waitqueue_active(wqh)))
        return;

    /* wait_queue_t->func(POLLFREE) should do remove_wait_queue() */
    wake_up_poll(wqh, POLLHUP | POLLFREE);
}

struct signalfd_ctx {
    sigset_t sigmask;
};

static int signalfd_release(struct inode *inode, struct file *file)
{
    kfree(file->private_data);
    return 0;
}

static unsigned int signalfd_poll(struct file *file, poll_table *wait)
{
    struct signalfd_ctx *ctx = file->private_data;
    unsigned int events = 0;

    poll_wait(file, &current->sighand->signalfd_wqh, wait);

    spin_lock_irq(&current->sighand->siglock);
    if (next_signal(&current->pending, &ctx->sigmask) ||
        next_signal(&current->signal->shared_pending,
            &ctx->sigmask))
        events |= POLLIN;
    spin_unlock_irq(&current->sighand->siglock);

    return events;
}

/*
 * Copied from copy_siginfo_to_user() in kernel/signal.c
 */
static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
                 siginfo_t const *kinfo)
{
    long err;

    BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);

    /*
     * Unused members should be zero ...
     */
    err = __clear_user(uinfo, sizeof(*uinfo));

    /*
     * If you change siginfo_t structure, please be sure
     * this code is fixed accordingly.
     */
    err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
    err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
    err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
    switch (kinfo->si_code & __SI_MASK) {
    case __SI_KILL:
        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
        break;
    case __SI_TIMER:
         err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
         err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
         err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
         err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
        break;
    case __SI_POLL:
        err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
        err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
        break;
    case __SI_FAULT:
        err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
#ifdef __ARCH_SI_TRAPNO
        err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
#endif
#ifdef BUS_MCEERR_AO
        /* 
         * Other callers might not initialize the si_lsb field,
         * so check explicitly for the right codes here.
         */
        if (kinfo->si_code == BUS_MCEERR_AR ||
            kinfo->si_code == BUS_MCEERR_AO)
            err |= __put_user((short) kinfo->si_addr_lsb,
                      &uinfo->ssi_addr_lsb);
#endif
        break;
    case __SI_CHLD:
        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
        err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
        err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
        err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
        break;
    case __SI_RT: /* This is not generated by the kernel as of now. */
    case __SI_MESGQ: /* But this is */
        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
        err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
        err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
        break;
    default:
        /*
         * This case catches also the signals queued by sigqueue().
         */
        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
        err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
        err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
        break;
    }

    return err ? -EFAULT: sizeof(*uinfo);
}

static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
                int nonblock)
{
    ssize_t ret;
    DECLARE_WAITQUEUE(wait, current);

    spin_lock_irq(&current->sighand->siglock);
    ret = dequeue_signal(current, &ctx->sigmask, info);
    switch (ret) {
    case 0:
        if (!nonblock)
            break;
        ret = -EAGAIN;
    default:
        spin_unlock_irq(&current->sighand->siglock);
        return ret;
    }

    add_wait_queue(&current->sighand->signalfd_wqh, &wait);
    for (;;) {
        set_current_state(TASK_INTERRUPTIBLE);
        ret = dequeue_signal(current, &ctx->sigmask, info);
        if (ret != 0)
            break;
        if (signal_pending(current)) {
            ret = -ERESTARTSYS;
            break;
        }
        spin_unlock_irq(&current->sighand->siglock);
        schedule();
        spin_lock_irq(&current->sighand->siglock);
    }
    spin_unlock_irq(&current->sighand->siglock);

    remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
    __set_current_state(TASK_RUNNING);

    return ret;
}

/*
 * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 * error code. The "count" parameter must be at least the size of a
 * "struct signalfd_siginfo".
 */
static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
                 loff_t *ppos)
{
    struct signalfd_ctx *ctx = file->private_data;
    struct signalfd_siginfo __user *siginfo;
    int nonblock = file->f_flags & O_NONBLOCK;
    ssize_t ret, total = 0;
    siginfo_t info;

    count /= sizeof(struct signalfd_siginfo);
    if (!count)
        return -EINVAL;

    siginfo = (struct signalfd_siginfo __user *) buf;
    do {
        ret = signalfd_dequeue(ctx, &info, nonblock);
        if (unlikely(ret <= 0))
            break;
        ret = signalfd_copyinfo(siginfo, &info);
        if (ret < 0)
            break;
        siginfo++;
        total += ret;
        nonblock = 1;
    } while (--count);

    return total ? total: ret;
}

static const struct file_operations signalfd_fops = {
    .release    = signalfd_release,
    .poll       = signalfd_poll,
    .read       = signalfd_read,
    .llseek     = noop_llseek,
};

SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
        size_t, sizemask, int, flags)
{
    sigset_t sigmask;
    struct signalfd_ctx *ctx;

    /* Check the SFD_* constants for consistency.  */
    BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
    BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);

    if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
        return -EINVAL;

    if (sizemask != sizeof(sigset_t) ||
        copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
        return -EINVAL;
    sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
    signotset(&sigmask);

    if (ufd == -1) {
        ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
        if (!ctx)
            return -ENOMEM;

        ctx->sigmask = sigmask;

        /*
         * When we call this, the initialization must be complete, since
         * anon_inode_getfd() will install the fd.
         */
        ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
                       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
        if (ufd < 0)
            kfree(ctx);
    } else {
        struct fd f = fdget(ufd);
        if (!f.file)
            return -EBADF;
        ctx = f.file->private_data;
        if (f.file->f_op != &signalfd_fops) {
            fdput(f);
            return -EINVAL;
        }
        spin_lock_irq(&current->sighand->siglock);
        ctx->sigmask = sigmask;
        spin_unlock_irq(&current->sighand->siglock);

        wake_up(&current->sighand->signalfd_wqh);
        fdput(f);
    }

    return ufd;
}

SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
        size_t, sizemask)
{
    return sys_signalfd4(ufd, user_mask, sizemask, 0);
}