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 iov_iter *to, kernel_siginfo_t const *kinfo)
  72 {
  73         struct signalfd_siginfo new;
  74
  75         BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  76
  77         /*
  78          * Unused members should be zero ...
  79          */
  80         memset(&new, 0, sizeof(new));
  81
  82         /*
  83          * If you change siginfo_t structure, please be sure
  84          * this code is fixed accordingly.
  85          */
  86         new.ssi_signo = kinfo->si_signo;
  87         new.ssi_errno = kinfo->si_errno;
  88         new.ssi_code  = kinfo->si_code;
  89         switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
  90         case SIL_KILL:
  91                 new.ssi_pid = kinfo->si_pid;
  92                 new.ssi_uid = kinfo->si_uid;
  93                 break;
  94         case SIL_TIMER:
  95                 new.ssi_tid = kinfo->si_tid;
  96                 new.ssi_overrun = kinfo->si_overrun;
  97                 new.ssi_ptr = (long) kinfo->si_ptr;
  98                 new.ssi_int = kinfo->si_int;
  99                 break;
 100         case SIL_POLL:
 101                 new.ssi_band = kinfo->si_band;
 102                 new.ssi_fd   = kinfo->si_fd;
 103                 break;
 104         case SIL_FAULT_BNDERR:
 105         case SIL_FAULT_PKUERR:
 106         case SIL_FAULT_PERF_EVENT:
 107                 /*
 108                  * Fall through to the SIL_FAULT case.  SIL_FAULT_BNDERR,
 109                  * SIL_FAULT_PKUERR, and SIL_FAULT_PERF_EVENT are only
 110                  * generated by faults that deliver them synchronously to
 111                  * userspace.  In case someone injects one of these signals
 112                  * and signalfd catches it treat it as SIL_FAULT.
 113                  */
 114         case SIL_FAULT:
 115                 new.ssi_addr = (long) kinfo->si_addr;
 116                 break;
 117         case SIL_FAULT_TRAPNO:
 118                 new.ssi_addr = (long) kinfo->si_addr;
 119                 new.ssi_trapno = kinfo->si_trapno;
 120                 break;
 121         case SIL_FAULT_MCEERR:
 122                 new.ssi_addr = (long) kinfo->si_addr;
 123                 new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
 124                 break;
 125         case SIL_CHLD:
 126                 new.ssi_pid    = kinfo->si_pid;
 127                 new.ssi_uid    = kinfo->si_uid;
 128                 new.ssi_status = kinfo->si_status;
 129                 new.ssi_utime  = kinfo->si_utime;
 130                 new.ssi_stime  = kinfo->si_stime;
 131                 break;
 132         case SIL_RT:
 133                 /*
 134                  * This case catches also the signals queued by sigqueue().
 135                  */
 136                 new.ssi_pid = kinfo->si_pid;
 137                 new.ssi_uid = kinfo->si_uid;
 138                 new.ssi_ptr = (long) kinfo->si_ptr;
 139                 new.ssi_int = kinfo->si_int;
 140                 break;
 141         case SIL_SYS:
 142                 new.ssi_call_addr = (long) kinfo->si_call_addr;
 143                 new.ssi_syscall   = kinfo->si_syscall;
 144                 new.ssi_arch      = kinfo->si_arch;
 145                 break;
 146         }
 147
 148         if (!copy_to_iter_full(&new, sizeof(struct signalfd_siginfo), to))
 149                 return -EFAULT;
 150
 151         return sizeof(struct signalfd_siginfo);
 152 }
 153
 154 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info,
 155                                 int nonblock)
 156 {
 157         enum pid_type type;
 158         ssize_t ret;
 159         DECLARE_WAITQUEUE(wait, current);
 160
 161         spin_lock_irq(&current->sighand->siglock);
 162         ret = dequeue_signal(&ctx->sigmask, info, &type);
 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(&ctx->sigmask, info, &type);
 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_iter(struct kiocb *iocb, struct iov_iter *to)
 202 {
 203         struct file *file = iocb->ki_filp;
 204         struct signalfd_ctx *ctx = file->private_data;
 205         size_t count = iov_iter_count(to);
 206         ssize_t ret, total = 0;
 207         kernel_siginfo_t info;
 208         bool nonblock;
 209
 210         count /= sizeof(struct signalfd_siginfo);
 211         if (!count)
 212                 return -EINVAL;
 213
 214         nonblock = file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT;
 215         do {
 216                 ret = signalfd_dequeue(ctx, &info, nonblock);
 217                 if (unlikely(ret <= 0))
 218                         break;
 219                 ret = signalfd_copyinfo(to, &info);
 220                 if (ret < 0)
 221                         break;
 222                 total += ret;
 223                 nonblock = 1;
 224         } while (--count);
 225
 226         return total ? total: ret;
 227 }
 228
 229 #ifdef CONFIG_PROC_FS
 230 static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
 231 {
 232         struct signalfd_ctx *ctx = f->private_data;
 233         sigset_t sigmask;
 234
 235         sigmask = ctx->sigmask;
 236         signotset(&sigmask);
 237         render_sigset_t(m, "sigmask:\t", &sigmask);
 238 }
 239 #endif
 240
 241 static const struct file_operations signalfd_fops = {
 242 #ifdef CONFIG_PROC_FS
 243         .show_fdinfo    = signalfd_show_fdinfo,
 244 #endif
 245         .release        = signalfd_release,
 246         .poll           = signalfd_poll,
 247         .read_iter      = signalfd_read_iter,
 248         .llseek         = noop_llseek,
 249 };
 250
 251 static int do_signalfd4(int ufd, sigset_t *mask, int flags)
 252 {
 253         struct signalfd_ctx *ctx;
 254
 255         /* Check the SFD_* constants for consistency.  */
 256         BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 257         BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 258
 259         if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 260                 return -EINVAL;
 261
 262         sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 263         signotset(mask);
 264
 265         if (ufd == -1) {
 266                 struct file *file;
 267
 268                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 269                 if (!ctx)
 270                         return -ENOMEM;
 271
 272                 ctx->sigmask = *mask;
 273
 274                 ufd = get_unused_fd_flags(flags & O_CLOEXEC);
 275                 if (ufd < 0) {
 276                         kfree(ctx);
 277                         return ufd;
 278                 }
 279
 280                 file = anon_inode_getfile("[signalfd]", &signalfd_fops, ctx,
 281                                        O_RDWR | (flags & O_NONBLOCK));
 282                 if (IS_ERR(file)) {
 283                         put_unused_fd(ufd);
 284                         kfree(ctx);
 285                         return PTR_ERR(file);
 286                 }
 287                 file->f_mode |= FMODE_NOWAIT;
 288
 289                 fd_install(ufd, file);
 290         } else {
 291                 struct fd f = fdget(ufd);
 292                 if (!fd_file(f))
 293                         return -EBADF;
 294                 ctx = fd_file(f)->private_data;
 295                 if (fd_file(f)->f_op != &signalfd_fops) {
 296                         fdput(f);
 297                         return -EINVAL;
 298                 }
 299                 spin_lock_irq(&current->sighand->siglock);
 300                 ctx->sigmask = *mask;
 301                 spin_unlock_irq(&current->sighand->siglock);
 302
 303                 wake_up(&current->sighand->signalfd_wqh);
 304                 fdput(f);
 305         }
 306
 307         return ufd;
 308 }
 309
 310 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 311                 size_t, sizemask, int, flags)
 312 {
 313         sigset_t mask;
 314
 315         if (sizemask != sizeof(sigset_t))
 316                 return -EINVAL;
 317         if (copy_from_user(&mask, user_mask, sizeof(mask)))
 318                 return -EFAULT;
 319         return do_signalfd4(ufd, &mask, flags);
 320 }
 321
 322 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 323                 size_t, sizemask)
 324 {
 325         sigset_t mask;
 326
 327         if (sizemask != sizeof(sigset_t))
 328                 return -EINVAL;
 329         if (copy_from_user(&mask, user_mask, sizeof(mask)))
 330                 return -EFAULT;
 331         return do_signalfd4(ufd, &mask, 0);
 332 }
 333
 334 #ifdef CONFIG_COMPAT
 335 static long do_compat_signalfd4(int ufd,
 336                         const compat_sigset_t __user *user_mask,
 337                         compat_size_t sigsetsize, int flags)
 338 {
 339         sigset_t mask;
 340
 341         if (sigsetsize != sizeof(compat_sigset_t))
 342                 return -EINVAL;
 343         if (get_compat_sigset(&mask, user_mask))
 344                 return -EFAULT;
 345         return do_signalfd4(ufd, &mask, flags);
 346 }
 347
 348 COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
 349                      const compat_sigset_t __user *, user_mask,
 350                      compat_size_t, sigsetsize,
 351                      int, flags)
 352 {
 353         return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
 354 }
 355
 356 COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
 357                      const compat_sigset_t __user *, user_mask,
 358                      compat_size_t, sigsetsize)
 359 {
 360         return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
 361 }
 362 #endif