linux/fs/signalfd.c
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   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#include <linux/proc_fs.h>
  33#include <linux/compat.h>
  34
  35void signalfd_cleanup(struct sighand_struct *sighand)
  36{
  37        wait_queue_head_t *wqh = &sighand->signalfd_wqh;
  38        /*
  39         * The lockless check can race with remove_wait_queue() in progress,
  40         * but in this case its caller should run under rcu_read_lock() and
  41         * sighand_cachep is SLAB_DESTROY_BY_RCU, we can safely return.
  42         */
  43        if (likely(!waitqueue_active(wqh)))
  44                return;
  45
  46        /* wait_queue_t->func(POLLFREE) should do remove_wait_queue() */
  47        wake_up_poll(wqh, POLLHUP | POLLFREE);
  48}
  49
  50struct signalfd_ctx {
  51        sigset_t sigmask;
  52};
  53
  54static int signalfd_release(struct inode *inode, struct file *file)
  55{
  56        kfree(file->private_data);
  57        return 0;
  58}
  59
  60static unsigned int signalfd_poll(struct file *file, poll_table *wait)
  61{
  62        struct signalfd_ctx *ctx = file->private_data;
  63        unsigned int events = 0;
  64
  65        poll_wait(file, &current->sighand->signalfd_wqh, wait);
  66
  67        spin_lock_irq(&current->sighand->siglock);
  68        if (next_signal(&current->pending, &ctx->sigmask) ||
  69            next_signal(&current->signal->shared_pending,
  70                        &ctx->sigmask))
  71                events |= POLLIN;
  72        spin_unlock_irq(&current->sighand->siglock);
  73
  74        return events;
  75}
  76
  77/*
  78 * Copied from copy_siginfo_to_user() in kernel/signal.c
  79 */
  80static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
  81                             siginfo_t const *kinfo)
  82{
  83        long err;
  84
  85        BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  86
  87        /*
  88         * Unused members should be zero ...
  89         */
  90        err = __clear_user(uinfo, sizeof(*uinfo));
  91
  92        /*
  93         * If you change siginfo_t structure, please be sure
  94         * this code is fixed accordingly.
  95         */
  96        err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
  97        err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
  98        err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
  99        switch (kinfo->si_code & __SI_MASK) {
 100        case __SI_KILL:
 101                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 102                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 103                break;
 104        case __SI_TIMER:
 105                 err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
 106                 err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
 107                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 108                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 109                break;
 110        case __SI_POLL:
 111                err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
 112                err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
 113                break;
 114        case __SI_FAULT:
 115                err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
 116#ifdef __ARCH_SI_TRAPNO
 117                err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
 118#endif
 119#ifdef BUS_MCEERR_AO
 120                /* 
 121                 * Other callers might not initialize the si_lsb field,
 122                 * so check explicitly for the right codes here.
 123                 */
 124                if (kinfo->si_code == BUS_MCEERR_AR ||
 125                    kinfo->si_code == BUS_MCEERR_AO)
 126                        err |= __put_user((short) kinfo->si_addr_lsb,
 127                                          &uinfo->ssi_addr_lsb);
 128#endif
 129                break;
 130        case __SI_CHLD:
 131                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 132                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 133                err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
 134                err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
 135                err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
 136                break;
 137        case __SI_RT: /* This is not generated by the kernel as of now. */
 138        case __SI_MESGQ: /* But this is */
 139                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 140                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 141                err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 142                err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 143                break;
 144        default:
 145                /*
 146                 * This case catches also the signals queued by sigqueue().
 147                 */
 148                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 149                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 150                err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 151                err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 152                break;
 153        }
 154
 155        return err ? -EFAULT: sizeof(*uinfo);
 156}
 157
 158static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 159                                int nonblock)
 160{
 161        ssize_t ret;
 162        DECLARE_WAITQUEUE(wait, current);
 163
 164        spin_lock_irq(&current->sighand->siglock);
 165        ret = dequeue_signal(current, &ctx->sigmask, info);
 166        switch (ret) {
 167        case 0:
 168                if (!nonblock)
 169                        break;
 170                ret = -EAGAIN;
 171        default:
 172                spin_unlock_irq(&current->sighand->siglock);
 173                return ret;
 174        }
 175
 176        add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 177        for (;;) {
 178                set_current_state(TASK_INTERRUPTIBLE);
 179                ret = dequeue_signal(current, &ctx->sigmask, info);
 180                if (ret != 0)
 181                        break;
 182                if (signal_pending(current)) {
 183                        ret = -ERESTARTSYS;
 184                        break;
 185                }
 186                spin_unlock_irq(&current->sighand->siglock);
 187                schedule();
 188                spin_lock_irq(&current->sighand->siglock);
 189        }
 190        spin_unlock_irq(&current->sighand->siglock);
 191
 192        remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 193        __set_current_state(TASK_RUNNING);
 194
 195        return ret;
 196}
 197
 198/*
 199 * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 200 * error code. The "count" parameter must be at least the size of a
 201 * "struct signalfd_siginfo".
 202 */
 203static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 204                             loff_t *ppos)
 205{
 206        struct signalfd_ctx *ctx = file->private_data;
 207        struct signalfd_siginfo __user *siginfo;
 208        int nonblock = file->f_flags & O_NONBLOCK;
 209        ssize_t ret, total = 0;
 210        siginfo_t info;
 211
 212        count /= sizeof(struct signalfd_siginfo);
 213        if (!count)
 214                return -EINVAL;
 215
 216        siginfo = (struct signalfd_siginfo __user *) buf;
 217        do {
 218                ret = signalfd_dequeue(ctx, &info, nonblock);
 219                if (unlikely(ret <= 0))
 220                        break;
 221                ret = signalfd_copyinfo(siginfo, &info);
 222                if (ret < 0)
 223                        break;
 224                siginfo++;
 225                total += ret;
 226                nonblock = 1;
 227        } while (--count);
 228
 229        return total ? total: ret;
 230}
 231
 232#ifdef CONFIG_PROC_FS
 233static int signalfd_show_fdinfo(struct seq_file *m, struct file *f)
 234{
 235        struct signalfd_ctx *ctx = f->private_data;
 236        sigset_t sigmask;
 237
 238        sigmask = ctx->sigmask;
 239        signotset(&sigmask);
 240        render_sigset_t(m, "sigmask:\t", &sigmask);
 241
 242        return 0;
 243}
 244#endif
 245
 246static const struct file_operations signalfd_fops = {
 247#ifdef CONFIG_PROC_FS
 248        .show_fdinfo    = signalfd_show_fdinfo,
 249#endif
 250        .release        = signalfd_release,
 251        .poll           = signalfd_poll,
 252        .read           = signalfd_read,
 253        .llseek         = noop_llseek,
 254};
 255
 256SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 257                size_t, sizemask, int, flags)
 258{
 259        sigset_t sigmask;
 260        struct signalfd_ctx *ctx;
 261
 262        /* Check the SFD_* constants for consistency.  */
 263        BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 264        BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 265
 266        if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 267                return -EINVAL;
 268
 269        if (sizemask != sizeof(sigset_t) ||
 270            copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 271                return -EINVAL;
 272        sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 273        signotset(&sigmask);
 274
 275        if (ufd == -1) {
 276                ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 277                if (!ctx)
 278                        return -ENOMEM;
 279
 280                ctx->sigmask = sigmask;
 281
 282                /*
 283                 * When we call this, the initialization must be complete, since
 284                 * anon_inode_getfd() will install the fd.
 285                 */
 286                ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 287                                       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 288                if (ufd < 0)
 289                        kfree(ctx);
 290        } else {
 291                struct fd f = fdget(ufd);
 292                if (!f.file)
 293                        return -EBADF;
 294                ctx = f.file->private_data;
 295                if (f.file->f_op != &signalfd_fops) {
 296                        fdput(f);
 297                        return -EINVAL;
 298                }
 299                spin_lock_irq(&current->sighand->siglock);
 300                ctx->sigmask = sigmask;
 301                spin_unlock_irq(&current->sighand->siglock);
 302
 303                wake_up(&current->sighand->signalfd_wqh);
 304                fdput(f);
 305        }
 306
 307        return ufd;
 308}
 309
 310SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 311                size_t, sizemask)
 312{
 313        return sys_signalfd4(ufd, user_mask, sizemask, 0);
 314}
 315
 316#ifdef CONFIG_COMPAT
 317COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
 318                     const compat_sigset_t __user *,sigmask,
 319                     compat_size_t, sigsetsize,
 320                     int, flags)
 321{
 322        compat_sigset_t ss32;
 323        sigset_t tmp;
 324        sigset_t __user *ksigmask;
 325
 326        if (sigsetsize != sizeof(compat_sigset_t))
 327                return -EINVAL;
 328        if (copy_from_user(&ss32, sigmask, sizeof(ss32)))
 329                return -EFAULT;
 330        sigset_from_compat(&tmp, &ss32);
 331        ksigmask = compat_alloc_user_space(sizeof(sigset_t));
 332        if (copy_to_user(ksigmask, &tmp, sizeof(sigset_t)))
 333                return -EFAULT;
 334
 335        return sys_signalfd4(ufd, ksigmask, sizeof(sigset_t), flags);
 336}
 337
 338COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
 339                     const compat_sigset_t __user *,sigmask,
 340                     compat_size_t, sigsetsize)
 341{
 342        return compat_sys_signalfd4(ufd, sigmask, sigsetsize, 0);
 343}
 344#endif
 345
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