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