linux/fs/signalfd.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 *  fs/signalfd.c
   4 *
   5 *  Copyright (C) 2003  Linus Torvalds
   6 *
   7 *  Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
   8 *      Changed ->read() to return a siginfo strcture instead of signal number.
   9 *      Fixed locking in ->poll().
  10 *      Added sighand-detach notification.
  11 *      Added fd re-use in sys_signalfd() syscall.
  12 *      Now using anonymous inode source.
  13 *      Thanks to Oleg Nesterov for useful code review and suggestions.
  14 *      More comments and suggestions from Arnd Bergmann.
  15 *  Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
  16 *      Retrieve multiple signals with one read() call
  17 *  Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
  18 *      Attach to the sighand only during read() and poll().
  19 */
  20
  21#include <linux/file.h>
  22#include <linux/poll.h>
  23#include <linux/init.h>
  24#include <linux/fs.h>
  25#include <linux/sched.h>
  26#include <linux/slab.h>
  27#include <linux/kernel.h>
  28#include <linux/signal.h>
  29#include <linux/list.h>
  30#include <linux/anon_inodes.h>
  31#include <linux/signalfd.h>
  32#include <linux/syscalls.h>
  33#include <linux/proc_fs.h>
  34#include <linux/compat.h>
  35
  36void signalfd_cleanup(struct sighand_struct *sighand)
  37{
  38        wait_queue_head_t *wqh = &sighand->signalfd_wqh;
  39        /*
  40         * The lockless check can race with remove_wait_queue() in progress,
  41         * but in this case its caller should run under rcu_read_lock() and
  42         * sighand_cachep is SLAB_TYPESAFE_BY_RCU, we can safely return.
  43         */
  44        if (likely(!waitqueue_active(wqh)))
  45                return;
  46
  47        /* wait_queue_entry_t->func(POLLFREE) should do remove_wait_queue() */
  48        wake_up_poll(wqh, EPOLLHUP | POLLFREE);
  49}
  50
  51struct signalfd_ctx {
  52        sigset_t sigmask;
  53};
  54
  55static int signalfd_release(struct inode *inode, struct file *file)
  56{
  57        kfree(file->private_data);
  58        return 0;
  59}
  60
  61static __poll_t signalfd_poll(struct file *file, poll_table *wait)
  62{
  63        struct signalfd_ctx *ctx = file->private_data;
  64        __poll_t events = 0;
  65
  66        poll_wait(file, &current->sighand->signalfd_wqh, wait);
  67
  68        spin_lock_irq(&current->sighand->siglock);
  69        if (next_signal(&current->pending, &ctx->sigmask) ||
  70            next_signal(&current->signal->shared_pending,
  71                        &ctx->sigmask))
  72                events |= EPOLLIN;
  73        spin_unlock_irq(&current->sighand->siglock);
  74
  75        return events;
  76}
  77
  78/*
  79 * Copied from copy_siginfo_to_user() in kernel/signal.c
  80 */
  81static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
  82                             kernel_siginfo_t const *kinfo)
  83{
  84        struct signalfd_siginfo new;
  85
  86        BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  87
  88        /*
  89         * Unused members should be zero ...
  90         */
  91        memset(&new, 0, sizeof(new));
  92
  93        /*
  94         * If you change siginfo_t structure, please be sure
  95         * this code is fixed accordingly.
  96         */
  97        new.ssi_signo = kinfo->si_signo;
  98        new.ssi_errno = kinfo->si_errno;
  99        new.ssi_code  = kinfo->si_code;
 100        switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
 101        case SIL_KILL:
 102                new.ssi_pid = kinfo->si_pid;
 103                new.ssi_uid = kinfo->si_uid;
 104                break;
 105        case SIL_TIMER:
 106                new.ssi_tid = kinfo->si_tid;
 107                new.ssi_overrun = kinfo->si_overrun;
 108                new.ssi_ptr = (long) kinfo->si_ptr;
 109                new.ssi_int = kinfo->si_int;
 110                break;
 111        case SIL_POLL:
 112                new.ssi_band = kinfo->si_band;
 113                new.ssi_fd   = kinfo->si_fd;
 114                break;
 115        case SIL_FAULT_BNDERR:
 116        case SIL_FAULT_PKUERR:
 117                /*
 118                 * Fall through to the SIL_FAULT case.  Both SIL_FAULT_BNDERR
 119                 * and SIL_FAULT_PKUERR are only generated by faults that
 120                 * deliver them synchronously to userspace.  In case someone
 121                 * injects one of these signals and signalfd catches it treat
 122                 * it as SIL_FAULT.
 123                 */
 124        case SIL_FAULT:
 125                new.ssi_addr = (long) kinfo->si_addr;
 126#ifdef __ARCH_SI_TRAPNO
 127                new.ssi_trapno = kinfo->si_trapno;
 128#endif
 129                break;
 130        case SIL_FAULT_MCEERR:
 131                new.ssi_addr = (long) kinfo->si_addr;
 132#ifdef __ARCH_SI_TRAPNO
 133                new.ssi_trapno = kinfo->si_trapno;
 134#endif
 135                new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
 136                break;
 137        case SIL_CHLD:
 138                new.ssi_pid    = kinfo->si_pid;
 139                new.ssi_uid    = kinfo->si_uid;
 140                new.ssi_status = kinfo->si_status;
 141                new.ssi_utime  = kinfo->si_utime;
 142                new.ssi_stime  = kinfo->si_stime;
 143                break;
 144        case SIL_RT:
 145                /*
 146                 * This case catches also the signals queued by sigqueue().
 147                 */
 148                new.ssi_pid = kinfo->si_pid;
 149                new.ssi_uid = kinfo->si_uid;
 150                new.ssi_ptr = (long) kinfo->si_ptr;
 151                new.ssi_int = kinfo->si_int;
 152                break;
 153        case SIL_SYS:
 154                new.ssi_call_addr = (long) kinfo->si_call_addr;
 155                new.ssi_syscall   = kinfo->si_syscall;
 156                new.ssi_arch      = kinfo->si_arch;
 157                break;
 158        }
 159
 160        if (copy_to_user(uinfo, &new, sizeof(struct signalfd_siginfo)))
 161                return -EFAULT;
 162
 163        return sizeof(*uinfo);
 164}
 165
 166static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info,
 167                                int nonblock)
 168{
 169        ssize_t ret;
 170        DECLARE_WAITQUEUE(wait, current);
 171
 172        spin_lock_irq(&current->sighand->siglock);
 173        ret = dequeue_signal(current, &ctx->sigmask, info);
 174        switch (ret) {
 175        case 0:
 176                if (!nonblock)
 177                        break;
 178                ret = -EAGAIN;
 179        default:
 180                spin_unlock_irq(&current->sighand->siglock);
 181                return ret;
 182        }
 183
 184        add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 185        for (;;) {
 186                set_current_state(TASK_INTERRUPTIBLE);
 187                ret = dequeue_signal(current, &ctx->sigmask, info);
 188                if (ret != 0)
 189                        break;
 190                if (signal_pending(current)) {
 191                        ret = -ERESTARTSYS;
 192                        break;
 193                }
 194                spin_unlock_irq(&current->sighand->siglock);
 195                schedule();
 196                spin_lock_irq(&current->sighand->siglock);
 197        }
 198        spin_unlock_irq(&current->sighand->siglock);
 199
 200        remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 201        __set_current_state(TASK_RUNNING);
 202
 203        return ret;
 204}
 205
 206/*
 207 * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 208 * error code. The "count" parameter must be at least the size of a
 209 * "struct signalfd_siginfo".
 210 */
 211static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 212                             loff_t *ppos)
 213{
 214        struct signalfd_ctx *ctx = file->private_data;
 215        struct signalfd_siginfo __user *siginfo;
 216        int nonblock = file->f_flags & O_NONBLOCK;
 217        ssize_t ret, total = 0;
 218        kernel_siginfo_t info;
 219
 220        count /= sizeof(struct signalfd_siginfo);
 221        if (!count)
 222                return -EINVAL;
 223
 224        siginfo = (struct signalfd_siginfo __user *) buf;
 225        do {
 226                ret = signalfd_dequeue(ctx, &info, nonblock);
 227                if (unlikely(ret <= 0))
 228                        break;
 229                ret = signalfd_copyinfo(siginfo, &info);
 230                if (ret < 0)
 231                        break;
 232                siginfo++;
 233                total += ret;
 234                nonblock = 1;
 235        } while (--count);
 236
 237        return total ? total: ret;
 238}
 239
 240#ifdef CONFIG_PROC_FS
 241static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
 242{
 243        struct signalfd_ctx *ctx = f->private_data;
 244        sigset_t sigmask;
 245
 246        sigmask = ctx->sigmask;
 247        signotset(&sigmask);
 248        render_sigset_t(m, "sigmask:\t", &sigmask);
 249}
 250#endif
 251
 252static const struct file_operations signalfd_fops = {
 253#ifdef CONFIG_PROC_FS
 254        .show_fdinfo    = signalfd_show_fdinfo,
 255#endif
 256        .release        = signalfd_release,
 257        .poll           = signalfd_poll,
 258        .read           = signalfd_read,
 259        .llseek         = noop_llseek,
 260};
 261
 262static int do_signalfd4(int ufd, sigset_t *mask, int flags)
 263{
 264        struct signalfd_ctx *ctx;
 265
 266        /* Check the SFD_* constants for consistency.  */
 267        BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 268        BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 269
 270        if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 271                return -EINVAL;
 272
 273        sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 274        signotset(mask);
 275
 276        if (ufd == -1) {
 277                ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 278                if (!ctx)
 279                        return -ENOMEM;
 280
 281                ctx->sigmask = *mask;
 282
 283                /*
 284                 * When we call this, the initialization must be complete, since
 285                 * anon_inode_getfd() will install the fd.
 286                 */
 287                ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 288                                       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 289                if (ufd < 0)
 290                        kfree(ctx);
 291        } else {
 292                struct fd f = fdget(ufd);
 293                if (!f.file)
 294                        return -EBADF;
 295                ctx = f.file->private_data;
 296                if (f.file->f_op != &signalfd_fops) {
 297                        fdput(f);
 298                        return -EINVAL;
 299                }
 300                spin_lock_irq(&current->sighand->siglock);
 301                ctx->sigmask = *mask;
 302                spin_unlock_irq(&current->sighand->siglock);
 303
 304                wake_up(&current->sighand->signalfd_wqh);
 305                fdput(f);
 306        }
 307
 308        return ufd;
 309}
 310
 311SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 312                size_t, sizemask, int, flags)
 313{
 314        sigset_t mask;
 315
 316        if (sizemask != sizeof(sigset_t) ||
 317            copy_from_user(&mask, user_mask, sizeof(mask)))
 318                return -EINVAL;
 319        return do_signalfd4(ufd, &mask, flags);
 320}
 321
 322SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 323                size_t, sizemask)
 324{
 325        sigset_t mask;
 326
 327        if (sizemask != sizeof(sigset_t) ||
 328            copy_from_user(&mask, user_mask, sizeof(mask)))
 329                return -EINVAL;
 330        return do_signalfd4(ufd, &mask, 0);
 331}
 332
 333#ifdef CONFIG_COMPAT
 334static long do_compat_signalfd4(int ufd,
 335                        const compat_sigset_t __user *user_mask,
 336                        compat_size_t sigsetsize, int flags)
 337{
 338        sigset_t mask;
 339
 340        if (sigsetsize != sizeof(compat_sigset_t))
 341                return -EINVAL;
 342        if (get_compat_sigset(&mask, user_mask))
 343                return -EFAULT;
 344        return do_signalfd4(ufd, &mask, flags);
 345}
 346
 347COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
 348                     const compat_sigset_t __user *, user_mask,
 349                     compat_size_t, sigsetsize,
 350                     int, flags)
 351{
 352        return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
 353}
 354
 355COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
 356                     const compat_sigset_t __user *, user_mask,
 357                     compat_size_t, sigsetsize)
 358{
 359        return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
 360}
 361#endif
 362