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  */
  17
  18 #include <linux/file.h>
  19 #include <linux/poll.h>
  20 #include <linux/init.h>
  21 #include <linux/fs.h>
  22 #include <linux/sched.h>
  23 #include <linux/kernel.h>
  24 #include <linux/signal.h>
  25 #include <linux/list.h>
  26 #include <linux/anon_inodes.h>
  27 #include <linux/signalfd.h>
  28
  29 struct signalfd_ctx {
  30         struct list_head lnk;
  31         wait_queue_head_t wqh;
  32         sigset_t sigmask;
  33         struct task_struct *tsk;
  34 };
  35
  36 struct signalfd_lockctx {
  37         struct task_struct *tsk;
  38         unsigned long flags;
  39 };
  40
  41 /*
  42  * Tries to acquire the sighand lock. We do not increment the sighand
  43  * use count, and we do not even pin the task struct, so we need to
  44  * do it inside an RCU read lock, and we must be prepared for the
  45  * ctx->tsk going to NULL (in signalfd_deliver()), and for the sighand
  46  * being detached. We return 0 if the sighand has been detached, or
  47  * 1 if we were able to pin the sighand lock.
  48  */
  49 static int signalfd_lock(struct signalfd_ctx *ctx, struct signalfd_lockctx *lk)
  50 {
  51         struct sighand_struct *sighand = NULL;
  52
  53         rcu_read_lock();
  54         lk->tsk = rcu_dereference(ctx->tsk);
  55         if (likely(lk->tsk != NULL))
  56                 sighand = lock_task_sighand(lk->tsk, &lk->flags);
  57         rcu_read_unlock();
  58
  59         if (!sighand)
  60                 return 0;
  61
  62         if (!ctx->tsk) {
  63                 unlock_task_sighand(lk->tsk, &lk->flags);
  64                 return 0;
  65         }
  66
  67         if (lk->tsk->tgid == current->tgid)
  68                 lk->tsk = current;
  69
  70         return 1;
  71 }
  72
  73 static void signalfd_unlock(struct signalfd_lockctx *lk)
  74 {
  75         unlock_task_sighand(lk->tsk, &lk->flags);
  76 }
  77
  78 /*
  79  * This must be called with the sighand lock held.
  80  */
  81 void signalfd_deliver(struct task_struct *tsk, int sig)
  82 {
  83         struct sighand_struct *sighand = tsk->sighand;
  84         struct signalfd_ctx *ctx, *tmp;
  85
  86         BUG_ON(!sig);
  87         list_for_each_entry_safe(ctx, tmp, &sighand->signalfd_list, lnk) {
  88                 /*
  89                  * We use a negative signal value as a way to broadcast that the
  90                  * sighand has been orphaned, so that we can notify all the
  91                  * listeners about this. Remember the ctx->sigmask is inverted,
  92                  * so if the user is interested in a signal, that corresponding
  93                  * bit will be zero.
  94                  */
  95                 if (sig < 0) {
  96                         if (ctx->tsk == tsk) {
  97                                 ctx->tsk = NULL;
  98                                 list_del_init(&ctx->lnk);
  99                                 wake_up(&ctx->wqh);
 100                         }
 101                 } else {
 102                         if (!sigismember(&ctx->sigmask, sig))
 103                                 wake_up(&ctx->wqh);
 104                 }
 105         }
 106 }
 107
 108 static void signalfd_cleanup(struct signalfd_ctx *ctx)
 109 {
 110         struct signalfd_lockctx lk;
 111
 112         /*
 113          * This is tricky. If the sighand is gone, we do not need to remove
 114          * context from the list, the list itself won't be there anymore.
 115          */
 116         if (signalfd_lock(ctx, &lk)) {
 117                 list_del(&ctx->lnk);
 118                 signalfd_unlock(&lk);
 119         }
 120         kfree(ctx);
 121 }
 122
 123 static int signalfd_release(struct inode *inode, struct file *file)
 124 {
 125         signalfd_cleanup(file->private_data);
 126         return 0;
 127 }
 128
 129 static unsigned int signalfd_poll(struct file *file, poll_table *wait)
 130 {
 131         struct signalfd_ctx *ctx = file->private_data;
 132         unsigned int events = 0;
 133         struct signalfd_lockctx lk;
 134
 135         poll_wait(file, &ctx->wqh, wait);
 136
 137         /*
 138          * Let the caller get a POLLIN in this case, ala socket recv() when
 139          * the peer disconnects.
 140          */
 141         if (signalfd_lock(ctx, &lk)) {
 142                 if ((lk.tsk == current &&
 143                      next_signal(&lk.tsk->pending, &ctx->sigmask) > 0) ||
 144                     next_signal(&lk.tsk->signal->shared_pending,
 145                                 &ctx->sigmask) > 0)
 146                         events |= POLLIN;
 147                 signalfd_unlock(&lk);
 148         } else
 149                 events |= POLLIN;
 150
 151         return events;
 152 }
 153
 154 /*
 155  * Copied from copy_siginfo_to_user() in kernel/signal.c
 156  */
 157 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
 158                              siginfo_t const *kinfo)
 159 {
 160         long err;
 161
 162         BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
 163
 164         /*
 165          * Unused memebers should be zero ...
 166          */
 167         err = __clear_user(uinfo, sizeof(*uinfo));
 168
 169         /*
 170          * If you change siginfo_t structure, please be sure
 171          * this code is fixed accordingly.
 172          */
 173         err |= __put_user(kinfo->si_signo, &uinfo->signo);
 174         err |= __put_user(kinfo->si_errno, &uinfo->err);
 175         err |= __put_user((short)kinfo->si_code, &uinfo->code);
 176         switch (kinfo->si_code & __SI_MASK) {
 177         case __SI_KILL:
 178                 err |= __put_user(kinfo->si_pid, &uinfo->pid);
 179                 err |= __put_user(kinfo->si_uid, &uinfo->uid);
 180                 break;
 181         case __SI_TIMER:
 182                  err |= __put_user(kinfo->si_tid, &uinfo->tid);
 183                  err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
 184                  err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
 185                 break;
 186         case __SI_POLL:
 187                 err |= __put_user(kinfo->si_band, &uinfo->band);
 188                 err |= __put_user(kinfo->si_fd, &uinfo->fd);
 189                 break;
 190         case __SI_FAULT:
 191                 err |= __put_user((long)kinfo->si_addr, &uinfo->addr);
 192 #ifdef __ARCH_SI_TRAPNO
 193                 err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
 194 #endif
 195                 break;
 196         case __SI_CHLD:
 197                 err |= __put_user(kinfo->si_pid, &uinfo->pid);
 198                 err |= __put_user(kinfo->si_uid, &uinfo->uid);
 199                 err |= __put_user(kinfo->si_status, &uinfo->status);
 200                 err |= __put_user(kinfo->si_utime, &uinfo->utime);
 201                 err |= __put_user(kinfo->si_stime, &uinfo->stime);
 202                 break;
 203         case __SI_RT: /* This is not generated by the kernel as of now. */
 204         case __SI_MESGQ: /* But this is */
 205                 err |= __put_user(kinfo->si_pid, &uinfo->pid);
 206                 err |= __put_user(kinfo->si_uid, &uinfo->uid);
 207                 err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
 208                 break;
 209         default: /* this is just in case for now ... */
 210                 err |= __put_user(kinfo->si_pid, &uinfo->pid);
 211                 err |= __put_user(kinfo->si_uid, &uinfo->uid);
 212                 break;
 213         }
 214
 215         return err ? -EFAULT: sizeof(*uinfo);
 216 }
 217
 218 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 219                                 int nonblock)
 220 {
 221         ssize_t ret;
 222         struct signalfd_lockctx lk;
 223         DECLARE_WAITQUEUE(wait, current);
 224
 225         if (!signalfd_lock(ctx, &lk))
 226                 return 0;
 227
 228         ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
 229         switch (ret) {
 230         case 0:
 231                 if (!nonblock)
 232                         break;
 233                 ret = -EAGAIN;
 234         default:
 235                 signalfd_unlock(&lk);
 236                 return ret;
 237         }
 238
 239         add_wait_queue(&ctx->wqh, &wait);
 240         for (;;) {
 241                 set_current_state(TASK_INTERRUPTIBLE);
 242                 ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
 243                 signalfd_unlock(&lk);
 244                 if (ret != 0)
 245                         break;
 246                 if (signal_pending(current)) {
 247                         ret = -ERESTARTSYS;
 248                         break;
 249                 }
 250                 schedule();
 251                 ret = signalfd_lock(ctx, &lk);
 252                 if (unlikely(!ret)) {
 253                         /*
 254                          * Let the caller read zero byte, ala socket
 255                          * recv() when the peer disconnect. This test
 256                          * must be done before doing a dequeue_signal(),
 257                          * because if the sighand has been orphaned,
 258                          * the dequeue_signal() call is going to crash
 259                          * because ->sighand will be long gone.
 260                          */
 261                          break;
 262                 }
 263         }
 264
 265         remove_wait_queue(&ctx->wqh, &wait);
 266         __set_current_state(TASK_RUNNING);
 267
 268         return ret;
 269 }
 270
 271 /*
 272  * Returns either the size of a "struct signalfd_siginfo", or zero if the
 273  * sighand we are attached to, has been orphaned. The "count" parameter
 274  * must be at least the size of a "struct signalfd_siginfo".
 275  */
 276 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 277                              loff_t *ppos)
 278 {
 279         struct signalfd_ctx *ctx = file->private_data;
 280         struct signalfd_siginfo __user *siginfo;
 281         int nonblock = file->f_flags & O_NONBLOCK;
 282         ssize_t ret, total = 0;
 283         siginfo_t info;
 284
 285         count /= sizeof(struct signalfd_siginfo);
 286         if (!count)
 287                 return -EINVAL;
 288
 289         siginfo = (struct signalfd_siginfo __user *) buf;
 290
 291         do {
 292                 ret = signalfd_dequeue(ctx, &info, nonblock);
 293                 if (unlikely(ret <= 0))
 294                         break;
 295                 ret = signalfd_copyinfo(siginfo, &info);
 296                 if (ret < 0)
 297                         break;
 298                 siginfo++;
 299                 total += ret;
 300                 nonblock = 1;
 301         } while (--count);
 302
 303         return total ? total : ret;
 304 }
 305
 306 static const struct file_operations signalfd_fops = {
 307         .release        = signalfd_release,
 308         .poll           = signalfd_poll,
 309         .read           = signalfd_read,
 310 };
 311
 312 /*
 313  * Create a file descriptor that is associated with our signal
 314  * state. We can pass it around to others if we want to, but
 315  * it will always be _our_ signal state.
 316  */
 317 asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
 318 {
 319         int error;
 320         sigset_t sigmask;
 321         struct signalfd_ctx *ctx;
 322         struct sighand_struct *sighand;
 323         struct file *file;
 324         struct inode *inode;
 325         struct signalfd_lockctx lk;
 326
 327         if (sizemask != sizeof(sigset_t) ||
 328             copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 329                 return error = -EINVAL;
 330         sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 331         signotset(&sigmask);
 332
 333         if (ufd == -1) {
 334                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 335                 if (!ctx)
 336                         return -ENOMEM;
 337
 338                 init_waitqueue_head(&ctx->wqh);
 339                 ctx->sigmask = sigmask;
 340                 ctx->tsk = current->group_leader;
 341
 342                 sighand = current->sighand;
 343                 /*
 344                  * Add this fd to the list of signal listeners.
 345                  */
 346                 spin_lock_irq(&sighand->siglock);
 347                 list_add_tail(&ctx->lnk, &sighand->signalfd_list);
 348                 spin_unlock_irq(&sighand->siglock);
 349
 350                 /*
 351                  * When we call this, the initialization must be complete, since
 352                  * anon_inode_getfd() will install the fd.
 353                  */
 354                 error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
 355                                          &signalfd_fops, ctx);
 356                 if (error)
 357                         goto err_fdalloc;
 358         } else {
 359                 file = fget(ufd);
 360                 if (!file)
 361                         return -EBADF;
 362                 ctx = file->private_data;
 363                 if (file->f_op != &signalfd_fops) {
 364                         fput(file);
 365                         return -EINVAL;
 366                 }
 367                 /*
 368                  * We need to be prepared of the fact that the sighand this fd
 369                  * is attached to, has been detched. In that case signalfd_lock()
 370                  * will return 0, and we'll just skip setting the new mask.
 371                  */
 372                 if (signalfd_lock(ctx, &lk)) {
 373                         ctx->sigmask = sigmask;
 374                         signalfd_unlock(&lk);
 375                 }
 376                 wake_up(&ctx->wqh);
 377                 fput(file);
 378         }
 379
 380         return ufd;
 381
 382 err_fdalloc:
 383         signalfd_cleanup(ctx);
 384         return error;
 385 }
 386