fs/signalfd.c

   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
  36 void 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
  51 struct signalfd_ctx {
  52         sigset_t sigmask;
  53 };
  54
  55 static int signalfd_release(struct inode *inode, struct file *file)
  56 {
  57         kfree(file->private_data);
  58         return 0;
  59 }
  60
  61 static __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  */
  81 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
  82                              siginfo_t const *kinfo)
  83 {
  84         long err;
  85
  86         BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  87
  88         /*
  89          * Unused members should be zero ...
  90          */
  91         err = __clear_user(uinfo, sizeof(*uinfo));
  92
  93         /*
  94          * If you change siginfo_t structure, please be sure
  95          * this code is fixed accordingly.
  96          */
  97         err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
  98         err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
  99         err |= __put_user(kinfo->si_code, &uinfo->ssi_code);
 100         switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
 101         case SIL_KILL:
 102                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 103                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 104                 break;
 105         case SIL_TIMER:
 106                  err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
 107                  err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
 108                  err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 109                  err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 110                 break;
 111         case SIL_POLL:
 112                 err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
 113                 err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
 114                 break;
 115         case SIL_FAULT:
 116                 err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
 117 #ifdef __ARCH_SI_TRAPNO
 118                 err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
 119 #endif
 120 #ifdef BUS_MCEERR_AO
 121                 /*
 122                  * Other callers might not initialize the si_lsb field,
 123                  * so check explicitly for the right codes here.
 124                  */
 125                 if (kinfo->si_signo == SIGBUS &&
 126                      kinfo->si_code == BUS_MCEERR_AO)
 127                         err |= __put_user((short) kinfo->si_addr_lsb,
 128                                           &uinfo->ssi_addr_lsb);
 129 #endif
 130 #ifdef BUS_MCEERR_AR
 131                 /*
 132                  * Other callers might not initialize the si_lsb field,
 133                  * so check explicitly for the right codes here.
 134                  */
 135                 if (kinfo->si_signo == SIGBUS &&
 136                     kinfo->si_code == BUS_MCEERR_AR)
 137                         err |= __put_user((short) kinfo->si_addr_lsb,
 138                                           &uinfo->ssi_addr_lsb);
 139 #endif
 140                 break;
 141         case SIL_CHLD:
 142                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 143                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 144                 err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
 145                 err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
 146                 err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
 147                 break;
 148         case SIL_RT:
 149         default:
 150                 /*
 151                  * This case catches also the signals queued by sigqueue().
 152                  */
 153                 err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 154                 err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 155                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 156                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 157                 break;
 158         }
 159
 160         return err ? -EFAULT: sizeof(*uinfo);
 161 }
 162
 163 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 164                                 int nonblock)
 165 {
 166         ssize_t ret;
 167         DECLARE_WAITQUEUE(wait, current);
 168
 169         spin_lock_irq(&current->sighand->siglock);
 170         ret = dequeue_signal(current, &ctx->sigmask, info);
 171         switch (ret) {
 172         case 0:
 173                 if (!nonblock)
 174                         break;
 175                 ret = -EAGAIN;
 176         default:
 177                 spin_unlock_irq(&current->sighand->siglock);
 178                 return ret;
 179         }
 180
 181         add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 182         for (;;) {
 183                 set_current_state(TASK_INTERRUPTIBLE);
 184                 ret = dequeue_signal(current, &ctx->sigmask, info);
 185                 if (ret != 0)
 186                         break;
 187                 if (signal_pending(current)) {
 188                         ret = -ERESTARTSYS;
 189                         break;
 190                 }
 191                 spin_unlock_irq(&current->sighand->siglock);
 192                 schedule();
 193                 spin_lock_irq(&current->sighand->siglock);
 194         }
 195         spin_unlock_irq(&current->sighand->siglock);
 196
 197         remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 198         __set_current_state(TASK_RUNNING);
 199
 200         return ret;
 201 }
 202
 203 /*
 204  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 205  * error code. The "count" parameter must be at least the size of a
 206  * "struct signalfd_siginfo".
 207  */
 208 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 209                              loff_t *ppos)
 210 {
 211         struct signalfd_ctx *ctx = file->private_data;
 212         struct signalfd_siginfo __user *siginfo;
 213         int nonblock = file->f_flags & O_NONBLOCK;
 214         ssize_t ret, total = 0;
 215         siginfo_t info;
 216
 217         count /= sizeof(struct signalfd_siginfo);
 218         if (!count)
 219                 return -EINVAL;
 220
 221         siginfo = (struct signalfd_siginfo __user *) buf;
 222         do {
 223                 ret = signalfd_dequeue(ctx, &info, nonblock);
 224                 if (unlikely(ret <= 0))
 225                         break;
 226                 ret = signalfd_copyinfo(siginfo, &info);
 227                 if (ret < 0)
 228                         break;
 229                 siginfo++;
 230                 total += ret;
 231                 nonblock = 1;
 232         } while (--count);
 233
 234         return total ? total: ret;
 235 }
 236
 237 #ifdef CONFIG_PROC_FS
 238 static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
 239 {
 240         struct signalfd_ctx *ctx = f->private_data;
 241         sigset_t sigmask;
 242
 243         sigmask = ctx->sigmask;
 244         signotset(&sigmask);
 245         render_sigset_t(m, "sigmask:\t", &sigmask);
 246 }
 247 #endif
 248
 249 static const struct file_operations signalfd_fops = {
 250 #ifdef CONFIG_PROC_FS
 251         .show_fdinfo    = signalfd_show_fdinfo,
 252 #endif
 253         .release        = signalfd_release,
 254         .poll           = signalfd_poll,
 255         .read           = signalfd_read,
 256         .llseek         = noop_llseek,
 257 };
 258
 259 static int do_signalfd4(int ufd, sigset_t __user *user_mask, size_t sizemask,
 260                         int flags)
 261 {
 262         sigset_t sigmask;
 263         struct signalfd_ctx *ctx;
 264
 265         /* Check the SFD_* constants for consistency.  */
 266         BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 267         BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 268
 269         if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 270                 return -EINVAL;
 271
 272         if (sizemask != sizeof(sigset_t) ||
 273             copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 274                 return -EINVAL;
 275         sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 276         signotset(&sigmask);
 277
 278         if (ufd == -1) {
 279                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 280                 if (!ctx)
 281                         return -ENOMEM;
 282
 283                 ctx->sigmask = sigmask;
 284
 285                 /*
 286                  * When we call this, the initialization must be complete, since
 287                  * anon_inode_getfd() will install the fd.
 288                  */
 289                 ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 290                                        O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 291                 if (ufd < 0)
 292                         kfree(ctx);
 293         } else {
 294                 struct fd f = fdget(ufd);
 295                 if (!f.file)
 296                         return -EBADF;
 297                 ctx = f.file->private_data;
 298                 if (f.file->f_op != &signalfd_fops) {
 299                         fdput(f);
 300                         return -EINVAL;
 301                 }
 302                 spin_lock_irq(&current->sighand->siglock);
 303                 ctx->sigmask = sigmask;
 304                 spin_unlock_irq(&current->sighand->siglock);
 305
 306                 wake_up(&current->sighand->signalfd_wqh);
 307                 fdput(f);
 308         }
 309
 310         return ufd;
 311 }
 312
 313 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 314                 size_t, sizemask, int, flags)
 315 {
 316         return do_signalfd4(ufd, user_mask, sizemask, flags);
 317 }
 318
 319 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 320                 size_t, sizemask)
 321 {
 322         return do_signalfd4(ufd, user_mask, sizemask, 0);
 323 }
 324
 325 #ifdef CONFIG_COMPAT
 326 static long do_compat_signalfd4(int ufd,
 327                         const compat_sigset_t __user *sigmask,
 328                         compat_size_t sigsetsize, int flags)
 329 {
 330         sigset_t tmp;
 331         sigset_t __user *ksigmask;
 332
 333         if (sigsetsize != sizeof(compat_sigset_t))
 334                 return -EINVAL;
 335         if (get_compat_sigset(&tmp, sigmask))
 336                 return -EFAULT;
 337         ksigmask = compat_alloc_user_space(sizeof(sigset_t));
 338         if (copy_to_user(ksigmask, &tmp, sizeof(sigset_t)))
 339                 return -EFAULT;
 340
 341         return do_signalfd4(ufd, ksigmask, sizeof(sigset_t), flags);
 342 }
 343
 344 COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
 345                      const compat_sigset_t __user *, sigmask,
 346                      compat_size_t, sigsetsize,
 347                      int, flags)
 348 {
 349         return do_compat_signalfd4(ufd, sigmask, sigsetsize, flags);
 350 }
 351
 352 COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
 353                      const compat_sigset_t __user *,sigmask,
 354                      compat_size_t, sigsetsize)
 355 {
 356         return do_compat_signalfd4(ufd, sigmask, sigsetsize, 0);
 357 }
 358 #endif