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 #include <linux/proc_fs.h>
  33 #include <linux/compat.h>
  34
  35 void 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
  50 struct signalfd_ctx {
  51         sigset_t sigmask;
  52 };
  53
  54 static int signalfd_release(struct inode *inode, struct file *file)
  55 {
  56         kfree(file->private_data);
  57         return 0;
  58 }
  59
  60 static 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  */
  80 static 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_signo == SIGBUS &&
 125                     (kinfo->si_code == BUS_MCEERR_AR ||
 126                      kinfo->si_code == BUS_MCEERR_AO))
 127                         err |= __put_user((short) kinfo->si_addr_lsb,
 128                                           &uinfo->ssi_addr_lsb);
 129 #endif
 130                 break;
 131         case __SI_CHLD:
 132                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 133                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 134                 err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
 135                 err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
 136                 err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
 137                 break;
 138         case __SI_RT: /* This is not generated by the kernel as of now. */
 139         case __SI_MESGQ: /* But this is */
 140                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 141                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 142                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 143                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 144                 break;
 145         default:
 146                 /*
 147                  * This case catches also the signals queued by sigqueue().
 148                  */
 149                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 150                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 151                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 152                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 153                 break;
 154         }
 155
 156         return err ? -EFAULT: sizeof(*uinfo);
 157 }
 158
 159 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 160                                 int nonblock)
 161 {
 162         ssize_t ret;
 163         DECLARE_WAITQUEUE(wait, current);
 164
 165         spin_lock_irq(&current->sighand->siglock);
 166         ret = dequeue_signal(current, &ctx->sigmask, info);
 167         switch (ret) {
 168         case 0:
 169                 if (!nonblock)
 170                         break;
 171                 ret = -EAGAIN;
 172         default:
 173                 spin_unlock_irq(&current->sighand->siglock);
 174                 return ret;
 175         }
 176
 177         add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 178         for (;;) {
 179                 set_current_state(TASK_INTERRUPTIBLE);
 180                 ret = dequeue_signal(current, &ctx->sigmask, info);
 181                 if (ret != 0)
 182                         break;
 183                 if (signal_pending(current)) {
 184                         ret = -ERESTARTSYS;
 185                         break;
 186                 }
 187                 spin_unlock_irq(&current->sighand->siglock);
 188                 schedule();
 189                 spin_lock_irq(&current->sighand->siglock);
 190         }
 191         spin_unlock_irq(&current->sighand->siglock);
 192
 193         remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 194         __set_current_state(TASK_RUNNING);
 195
 196         return ret;
 197 }
 198
 199 /*
 200  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 201  * error code. The "count" parameter must be at least the size of a
 202  * "struct signalfd_siginfo".
 203  */
 204 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 205                              loff_t *ppos)
 206 {
 207         struct signalfd_ctx *ctx = file->private_data;
 208         struct signalfd_siginfo __user *siginfo;
 209         int nonblock = file->f_flags & O_NONBLOCK;
 210         ssize_t ret, total = 0;
 211         siginfo_t info;
 212
 213         count /= sizeof(struct signalfd_siginfo);
 214         if (!count)
 215                 return -EINVAL;
 216
 217         siginfo = (struct signalfd_siginfo __user *) buf;
 218         do {
 219                 ret = signalfd_dequeue(ctx, &info, nonblock);
 220                 if (unlikely(ret <= 0))
 221                         break;
 222                 ret = signalfd_copyinfo(siginfo, &info);
 223                 if (ret < 0)
 224                         break;
 225                 siginfo++;
 226                 total += ret;
 227                 nonblock = 1;
 228         } while (--count);
 229
 230         return total ? total: ret;
 231 }
 232
 233 #ifdef CONFIG_PROC_FS
 234 static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
 235 {
 236         struct signalfd_ctx *ctx = f->private_data;
 237         sigset_t sigmask;
 238
 239         sigmask = ctx->sigmask;
 240         signotset(&sigmask);
 241         render_sigset_t(m, "sigmask:\t", &sigmask);
 242 }
 243 #endif
 244
 245 static const struct file_operations signalfd_fops = {
 246 #ifdef CONFIG_PROC_FS
 247         .show_fdinfo    = signalfd_show_fdinfo,
 248 #endif
 249         .release        = signalfd_release,
 250         .poll           = signalfd_poll,
 251         .read           = signalfd_read,
 252         .llseek         = noop_llseek,
 253 };
 254
 255 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 256                 size_t, sizemask, int, flags)
 257 {
 258         sigset_t sigmask;
 259         struct signalfd_ctx *ctx;
 260
 261         /* Check the SFD_* constants for consistency.  */
 262         BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 263         BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 264
 265         if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 266                 return -EINVAL;
 267
 268         if (sizemask != sizeof(sigset_t) ||
 269             copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 270                 return -EINVAL;
 271         sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 272         signotset(&sigmask);
 273
 274         if (ufd == -1) {
 275                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 276                 if (!ctx)
 277                         return -ENOMEM;
 278
 279                 ctx->sigmask = sigmask;
 280
 281                 /*
 282                  * When we call this, the initialization must be complete, since
 283                  * anon_inode_getfd() will install the fd.
 284                  */
 285                 ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 286                                        O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 287                 if (ufd < 0)
 288                         kfree(ctx);
 289         } else {
 290                 struct fd f = fdget(ufd);
 291                 if (!f.file)
 292                         return -EBADF;
 293                 ctx = f.file->private_data;
 294                 if (f.file->f_op != &signalfd_fops) {
 295                         fdput(f);
 296                         return -EINVAL;
 297                 }
 298                 spin_lock_irq(&current->sighand->siglock);
 299                 ctx->sigmask = sigmask;
 300                 spin_unlock_irq(&current->sighand->siglock);
 301
 302                 wake_up(&current->sighand->signalfd_wqh);
 303                 fdput(f);
 304         }
 305
 306         return ufd;
 307 }
 308
 309 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 310                 size_t, sizemask)
 311 {
 312         return sys_signalfd4(ufd, user_mask, sizemask, 0);
 313 }
 314
 315 #ifdef CONFIG_COMPAT
 316 COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
 317                      const compat_sigset_t __user *,sigmask,
 318                      compat_size_t, sigsetsize,
 319                      int, flags)
 320 {
 321         compat_sigset_t ss32;
 322         sigset_t tmp;
 323         sigset_t __user *ksigmask;
 324
 325         if (sigsetsize != sizeof(compat_sigset_t))
 326                 return -EINVAL;
 327         if (copy_from_user(&ss32, sigmask, sizeof(ss32)))
 328                 return -EFAULT;
 329         sigset_from_compat(&tmp, &ss32);
 330         ksigmask = compat_alloc_user_space(sizeof(sigset_t));
 331         if (copy_to_user(ksigmask, &tmp, sizeof(sigset_t)))
 332                 return -EFAULT;
 333
 334         return sys_signalfd4(ufd, ksigmask, sizeof(sigset_t), flags);
 335 }
 336
 337 COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
 338                      const compat_sigset_t __user *,sigmask,
 339                      compat_size_t, sigsetsize)
 340 {
 341         return compat_sys_signalfd4(ufd, sigmask, sigsetsize, 0);
 342 }
 343 #endif