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                              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         case SIL_PERF_EVENT:
 118                 /*
 119                  * Fall through to the SIL_FAULT case.  SIL_FAULT_BNDERR,
 120                  * SIL_FAULT_PKUERR, and SIL_PERF_EVENT are only
 121                  * generated by faults that deliver them synchronously to
 122                  * userspace.  In case someone injects one of these signals
 123                  * and signalfd catches it treat it as SIL_FAULT.
 124                  */
 125         case SIL_FAULT:
 126                 new.ssi_addr = (long) kinfo->si_addr;
 127                 break;
 128         case SIL_FAULT_TRAPNO:
 129                 new.ssi_addr = (long) kinfo->si_addr;
 130                 new.ssi_trapno = kinfo->si_trapno;
 131                 break;
 132         case SIL_FAULT_MCEERR:
 133                 new.ssi_addr = (long) kinfo->si_addr;
 134                 new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
 135                 break;
 136         case SIL_CHLD:
 137                 new.ssi_pid    = kinfo->si_pid;
 138                 new.ssi_uid    = kinfo->si_uid;
 139                 new.ssi_status = kinfo->si_status;
 140                 new.ssi_utime  = kinfo->si_utime;
 141                 new.ssi_stime  = kinfo->si_stime;
 142                 break;
 143         case SIL_RT:
 144                 /*
 145                  * This case catches also the signals queued by sigqueue().
 146                  */
 147                 new.ssi_pid = kinfo->si_pid;
 148                 new.ssi_uid = kinfo->si_uid;
 149                 new.ssi_ptr = (long) kinfo->si_ptr;
 150                 new.ssi_int = kinfo->si_int;
 151                 break;
 152         case SIL_SYS:
 153                 new.ssi_call_addr = (long) kinfo->si_call_addr;
 154                 new.ssi_syscall   = kinfo->si_syscall;
 155                 new.ssi_arch      = kinfo->si_arch;
 156                 break;
 157         }
 158
 159         if (copy_to_user(uinfo, &new, sizeof(struct signalfd_siginfo)))
 160                 return -EFAULT;
 161
 162         return sizeof(*uinfo);
 163 }
 164
 165 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info,
 166                                 int nonblock)
 167 {
 168         ssize_t ret;
 169         DECLARE_WAITQUEUE(wait, current);
 170
 171         spin_lock_irq(&current->sighand->siglock);
 172         ret = dequeue_signal(current, &ctx->sigmask, info);
 173         switch (ret) {
 174         case 0:
 175                 if (!nonblock)
 176                         break;
 177                 ret = -EAGAIN;
 178                 fallthrough;
 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  */
 211 static 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
 241 static 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
 252 static 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
 262 static 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
 311 SYSCALL_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                 return -EINVAL;
 318         if (copy_from_user(&mask, user_mask, sizeof(mask)))
 319                 return -EFAULT;
 320         return do_signalfd4(ufd, &mask, flags);
 321 }
 322
 323 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 324                 size_t, sizemask)
 325 {
 326         sigset_t mask;
 327
 328         if (sizemask != sizeof(sigset_t))
 329                 return -EINVAL;
 330         if (copy_from_user(&mask, user_mask, sizeof(mask)))
 331                 return -EFAULT;
 332         return do_signalfd4(ufd, &mask, 0);
 333 }
 334
 335 #ifdef CONFIG_COMPAT
 336 static long do_compat_signalfd4(int ufd,
 337                         const compat_sigset_t __user *user_mask,
 338                         compat_size_t sigsetsize, int flags)
 339 {
 340         sigset_t mask;
 341
 342         if (sigsetsize != sizeof(compat_sigset_t))
 343                 return -EINVAL;
 344         if (get_compat_sigset(&mask, user_mask))
 345                 return -EFAULT;
 346         return do_signalfd4(ufd, &mask, flags);
 347 }
 348
 349 COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
 350                      const compat_sigset_t __user *, user_mask,
 351                      compat_size_t, sigsetsize,
 352                      int, flags)
 353 {
 354         return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
 355 }
 356
 357 COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
 358                      const compat_sigset_t __user *, user_mask,
 359                      compat_size_t, sigsetsize)
 360 {
 361         return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
 362 }
 363 #endif