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                 /*
 118                  * Fall through to the SIL_FAULT case.  Both SIL_FAULT_BNDERR
 119                  * and SIL_FAULT_PKUERR are only generated by faults that
 120                  * deliver them synchronously to userspace.  In case someone
 121                  * injects one of these signals and signalfd catches it treat
 122                  * it as SIL_FAULT.
 123                  */
 124         case SIL_FAULT:
 125                 new.ssi_addr = (long) kinfo->si_addr;
 126 #ifdef __ARCH_SI_TRAPNO
 127                 new.ssi_trapno = kinfo->si_trapno;
 128 #endif
 129                 break;
 130         case SIL_FAULT_MCEERR:
 131                 new.ssi_addr = (long) kinfo->si_addr;
 132 #ifdef __ARCH_SI_TRAPNO
 133                 new.ssi_trapno = kinfo->si_trapno;
 134 #endif
 135                 new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
 136                 break;
 137         case SIL_CHLD:
 138                 new.ssi_pid    = kinfo->si_pid;
 139                 new.ssi_uid    = kinfo->si_uid;
 140                 new.ssi_status = kinfo->si_status;
 141                 new.ssi_utime  = kinfo->si_utime;
 142                 new.ssi_stime  = kinfo->si_stime;
 143                 break;
 144         case SIL_RT:
 145                 /*
 146                  * This case catches also the signals queued by sigqueue().
 147                  */
 148                 new.ssi_pid = kinfo->si_pid;
 149                 new.ssi_uid = kinfo->si_uid;
 150                 new.ssi_ptr = (long) kinfo->si_ptr;
 151                 new.ssi_int = kinfo->si_int;
 152                 break;
 153         case SIL_SYS:
 154                 new.ssi_call_addr = (long) kinfo->si_call_addr;
 155                 new.ssi_syscall   = kinfo->si_syscall;
 156                 new.ssi_arch      = kinfo->si_arch;
 157                 break;
 158         }
 159
 160         if (copy_to_user(uinfo, &new, sizeof(struct signalfd_siginfo)))
 161                 return -EFAULT;
 162
 163         return sizeof(*uinfo);
 164 }
 165
 166 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info,
 167                                 int nonblock)
 168 {
 169         ssize_t ret;
 170         DECLARE_WAITQUEUE(wait, current);
 171
 172         spin_lock_irq(&current->sighand->siglock);
 173         ret = dequeue_signal(current, &ctx->sigmask, info);
 174         switch (ret) {
 175         case 0:
 176                 if (!nonblock)
 177                         break;
 178                 ret = -EAGAIN;
 179                 fallthrough;
 180         default:
 181                 spin_unlock_irq(&current->sighand->siglock);
 182                 return ret;
 183         }
 184
 185         add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 186         for (;;) {
 187                 set_current_state(TASK_INTERRUPTIBLE);
 188                 ret = dequeue_signal(current, &ctx->sigmask, info);
 189                 if (ret != 0)
 190                         break;
 191                 if (signal_pending(current)) {
 192                         ret = -ERESTARTSYS;
 193                         break;
 194                 }
 195                 spin_unlock_irq(&current->sighand->siglock);
 196                 schedule();
 197                 spin_lock_irq(&current->sighand->siglock);
 198         }
 199         spin_unlock_irq(&current->sighand->siglock);
 200
 201         remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 202         __set_current_state(TASK_RUNNING);
 203
 204         return ret;
 205 }
 206
 207 /*
 208  * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 209  * error code. The "count" parameter must be at least the size of a
 210  * "struct signalfd_siginfo".
 211  */
 212 static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 213                              loff_t *ppos)
 214 {
 215         struct signalfd_ctx *ctx = file->private_data;
 216         struct signalfd_siginfo __user *siginfo;
 217         int nonblock = file->f_flags & O_NONBLOCK;
 218         ssize_t ret, total = 0;
 219         kernel_siginfo_t info;
 220
 221         count /= sizeof(struct signalfd_siginfo);
 222         if (!count)
 223                 return -EINVAL;
 224
 225         siginfo = (struct signalfd_siginfo __user *) buf;
 226         do {
 227                 ret = signalfd_dequeue(ctx, &info, nonblock);
 228                 if (unlikely(ret <= 0))
 229                         break;
 230                 ret = signalfd_copyinfo(siginfo, &info);
 231                 if (ret < 0)
 232                         break;
 233                 siginfo++;
 234                 total += ret;
 235                 nonblock = 1;
 236         } while (--count);
 237
 238         return total ? total: ret;
 239 }
 240
 241 #ifdef CONFIG_PROC_FS
 242 static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
 243 {
 244         struct signalfd_ctx *ctx = f->private_data;
 245         sigset_t sigmask;
 246
 247         sigmask = ctx->sigmask;
 248         signotset(&sigmask);
 249         render_sigset_t(m, "sigmask:\t", &sigmask);
 250 }
 251 #endif
 252
 253 static const struct file_operations signalfd_fops = {
 254 #ifdef CONFIG_PROC_FS
 255         .show_fdinfo    = signalfd_show_fdinfo,
 256 #endif
 257         .release        = signalfd_release,
 258         .poll           = signalfd_poll,
 259         .read           = signalfd_read,
 260         .llseek         = noop_llseek,
 261 };
 262
 263 static int do_signalfd4(int ufd, sigset_t *mask, int flags)
 264 {
 265         struct signalfd_ctx *ctx;
 266
 267         /* Check the SFD_* constants for consistency.  */
 268         BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 269         BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 270
 271         if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 272                 return -EINVAL;
 273
 274         sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 275         signotset(mask);
 276
 277         if (ufd == -1) {
 278                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 279                 if (!ctx)
 280                         return -ENOMEM;
 281
 282                 ctx->sigmask = *mask;
 283
 284                 /*
 285                  * When we call this, the initialization must be complete, since
 286                  * anon_inode_getfd() will install the fd.
 287                  */
 288                 ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 289                                        O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 290                 if (ufd < 0)
 291                         kfree(ctx);
 292         } else {
 293                 struct fd f = fdget(ufd);
 294                 if (!f.file)
 295                         return -EBADF;
 296                 ctx = f.file->private_data;
 297                 if (f.file->f_op != &signalfd_fops) {
 298                         fdput(f);
 299                         return -EINVAL;
 300                 }
 301                 spin_lock_irq(&current->sighand->siglock);
 302                 ctx->sigmask = *mask;
 303                 spin_unlock_irq(&current->sighand->siglock);
 304
 305                 wake_up(&current->sighand->signalfd_wqh);
 306                 fdput(f);
 307         }
 308
 309         return ufd;
 310 }
 311
 312 SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 313                 size_t, sizemask, int, flags)
 314 {
 315         sigset_t mask;
 316
 317         if (sizemask != sizeof(sigset_t))
 318                 return -EINVAL;
 319         if (copy_from_user(&mask, user_mask, sizeof(mask)))
 320                 return -EFAULT;
 321         return do_signalfd4(ufd, &mask, flags);
 322 }
 323
 324 SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 325                 size_t, sizemask)
 326 {
 327         sigset_t mask;
 328
 329         if (sizemask != sizeof(sigset_t))
 330                 return -EINVAL;
 331         if (copy_from_user(&mask, user_mask, sizeof(mask)))
 332                 return -EFAULT;
 333         return do_signalfd4(ufd, &mask, 0);
 334 }
 335
 336 #ifdef CONFIG_COMPAT
 337 static long do_compat_signalfd4(int ufd,
 338                         const compat_sigset_t __user *user_mask,
 339                         compat_size_t sigsetsize, int flags)
 340 {
 341         sigset_t mask;
 342
 343         if (sigsetsize != sizeof(compat_sigset_t))
 344                 return -EINVAL;
 345         if (get_compat_sigset(&mask, user_mask))
 346                 return -EFAULT;
 347         return do_signalfd4(ufd, &mask, flags);
 348 }
 349
 350 COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
 351                      const compat_sigset_t __user *, user_mask,
 352                      compat_size_t, sigsetsize,
 353                      int, flags)
 354 {
 355         return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
 356 }
 357
 358 COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
 359                      const compat_sigset_t __user *, user_mask,
 360                      compat_size_t, sigsetsize)
 361 {
 362         return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
 363 }
 364 #endif