text: // SPDX-License-Identifier: GPL-2.0
  /*
   *  fs/signalfd.c
   *
   *  Copyright (C) 2003  Linus Torvalds
   *
   *  Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
   *      Changed ->read() to return a siginfo strcture instead of signal number.
   *      Fixed locking in ->poll().
   *      Added sighand-detach notification.
   *      Added fd re-use in sys_signalfd() syscall.
   *      Now using anonymous inode source.
   *      Thanks to Oleg Nesterov for useful code review and suggestions.
   *      More comments and suggestions from Arnd Bergmann.
   *  Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
   *      Retrieve multiple signals with one read() call
   *  Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
   *      Attach to the sighand only during read() and poll().
   */
  
  #include <linux/file.h>
  #include <linux/poll.h>
  #include <linux/init.h>
  #include <linux/fs.h>
  #include <linux/sched.h>
  #include <linux/slab.h>
  #include <linux/kernel.h>
  #include <linux/signal.h>
  #include <linux/list.h>
  #include <linux/anon_inodes.h>
  #include <linux/signalfd.h>
  #include <linux/syscalls.h>
  #include <linux/proc_fs.h>
  #include <linux/compat.h>
  
  void signalfd_cleanup(struct sighand_struct *sighand)
  {
  	wait_queue_head_t *wqh = &sighand->signalfd_wqh;
  	/*
  	 * The lockless check can race with remove_wait_queue() in progress,
  	 * but in this case its caller should run under rcu_read_lock() and
  	 * sighand_cachep is SLAB_TYPESAFE_BY_RCU, we can safely return.
  	 */
  	if (likely(!waitqueue_active(wqh)))
  		return;
  
  	/* wait_queue_entry_t->func(POLLFREE) should do remove_wait_queue() */
  	wake_up_poll(wqh, EPOLLHUP | POLLFREE);
  }
  
  struct signalfd_ctx {
  	sigset_t sigmask;
  };
  
  static int signalfd_release(struct inode *inode, struct file *file)
  {
  	kfree(file->private_data);
  	return 0;
  }
  
  static __poll_t signalfd_poll(struct file *file, poll_table *wait)
  {
  	struct signalfd_ctx *ctx = file->private_data;
  	__poll_t events = 0;
  
  	poll_wait(file, &current->sighand->signalfd_wqh, wait);
  
  	spin_lock_irq(&current->sighand->siglock);
  	if (next_signal(&current->pending, &ctx->sigmask) ||
  	    next_signal(&current->signal->shared_pending,
  			&ctx->sigmask))
  		events |= EPOLLIN;
  	spin_unlock_irq(&current->sighand->siglock);
  
  	return events;
  }
  
  /*
   * Copied from copy_siginfo_to_user() in kernel/signal.c
   */
  static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
  			     kernel_siginfo_t const *kinfo)
  {
  	struct signalfd_siginfo new;
  
  	BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  
  	/*
  	 * Unused members should be zero ...
  	 */
  	memset(&new, 0, sizeof(new));
  
  	/*
  	 * If you change siginfo_t structure, please be sure
  	 * this code is fixed accordingly.
  	 */
  	new.ssi_signo = kinfo->si_signo;
  	new.ssi_errno = kinfo->si_errno;
  	new.ssi_code  = kinfo->si_code;
  	switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
  	case SIL_KILL:
  		new.ssi_pid = kinfo->si_pid;
  		new.ssi_uid = kinfo->si_uid;
  		break;
  	case SIL_TIMER:
  		new.ssi_tid = kinfo->si_tid;
  		new.ssi_overrun = kinfo->si_overrun;
  		new.ssi_ptr = (long) kinfo->si_ptr;
  		new.ssi_int = kinfo->si_int;
  		break;
  	case SIL_POLL:
  		new.ssi_band = kinfo->si_band;
  		new.ssi_fd   = kinfo->si_fd;
  		break;
  	case SIL_FAULT_BNDERR:
  	case SIL_FAULT_PKUERR:
  		/*
  		 * Fall through to the SIL_FAULT case.  Both SIL_FAULT_BNDERR
  		 * and SIL_FAULT_PKUERR are only generated by faults that
  		 * deliver them synchronously to userspace.  In case someone
  		 * injects one of these signals and signalfd catches it treat
  		 * it as SIL_FAULT.
  		 */
  	case SIL_FAULT:
  		new.ssi_addr = (long) kinfo->si_addr;
  #ifdef __ARCH_SI_TRAPNO
  		new.ssi_trapno = kinfo->si_trapno;
  #endif
  		break;
  	case SIL_FAULT_MCEERR:
  		new.ssi_addr = (long) kinfo->si_addr;
  #ifdef __ARCH_SI_TRAPNO
  		new.ssi_trapno = kinfo->si_trapno;
  #endif
  		new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
  		break;
  	case SIL_CHLD:
  		new.ssi_pid    = kinfo->si_pid;
  		new.ssi_uid    = kinfo->si_uid;
  		new.ssi_status = kinfo->si_status;
  		new.ssi_utime  = kinfo->si_utime;
  		new.ssi_stime  = kinfo->si_stime;
  		break;
  	case SIL_RT:
  		/*
  		 * This case catches also the signals queued by sigqueue().
  		 */
  		new.ssi_pid = kinfo->si_pid;
  		new.ssi_uid = kinfo->si_uid;
  		new.ssi_ptr = (long) kinfo->si_ptr;
  		new.ssi_int = kinfo->si_int;
  		break;
  	case SIL_SYS:
  		new.ssi_call_addr = (long) kinfo->si_call_addr;
  		new.ssi_syscall   = kinfo->si_syscall;
  		new.ssi_arch      = kinfo->si_arch;
  		break;
  	}
  
  	if (copy_to_user(uinfo, &new, sizeof(struct signalfd_siginfo)))
  		return -EFAULT;
  
  	return sizeof(*uinfo);
  }
  
  static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info,
  				int nonblock)
  {
  	ssize_t ret;
  	DECLARE_WAITQUEUE(wait, current);
  
  	spin_lock_irq(&current->sighand->siglock);
  	ret = dequeue_signal(current, &ctx->sigmask, info);
  	switch (ret) {
  	case 0:
  		if (!nonblock)
  			break;
  		ret = -EAGAIN;
  		/* fall through */
  	default:
  		spin_unlock_irq(&current->sighand->siglock);
  		return ret;
  	}
  
  	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
  	for (;;) {
  		set_current_state(TASK_INTERRUPTIBLE);
  		ret = dequeue_signal(current, &ctx->sigmask, info);
  		if (ret != 0)
  			break;
  		if (signal_pending(current)) {
  			ret = -ERESTARTSYS;
  			break;
  		}
  		spin_unlock_irq(&current->sighand->siglock);
  		schedule();
  		spin_lock_irq(&current->sighand->siglock);
  	}
  	spin_unlock_irq(&current->sighand->siglock);
  
  	remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
  	__set_current_state(TASK_RUNNING);
  
  	return ret;
  }
  
  /*
   * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
   * error code. The "count" parameter must be at least the size of a
   * "struct signalfd_siginfo".
   */
  static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
  			     loff_t *ppos)
  {
  	struct signalfd_ctx *ctx = file->private_data;
  	struct signalfd_siginfo __user *siginfo;
  	int nonblock = file->f_flags & O_NONBLOCK;
  	ssize_t ret, total = 0;
  	kernel_siginfo_t info;
  
  	count /= sizeof(struct signalfd_siginfo);
  	if (!count)
  		return -EINVAL;
  
  	siginfo = (struct signalfd_siginfo __user *) buf;
  	do {
  		ret = signalfd_dequeue(ctx, &info, nonblock);
  		if (unlikely(ret <= 0))
  			break;
  		ret = signalfd_copyinfo(siginfo, &info);
  		if (ret < 0)
  			break;
  		siginfo++;
  		total += ret;
  		nonblock = 1;
  	} while (--count);
  
  	return total ? total: ret;
  }
  
  #ifdef CONFIG_PROC_FS
  static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
  {
  	struct signalfd_ctx *ctx = f->private_data;
  	sigset_t sigmask;
  
  	sigmask = ctx->sigmask;
  	signotset(&sigmask);
  	render_sigset_t(m, "sigmask:\t", &sigmask);
  }
  #endif
  
  static const struct file_operations signalfd_fops = {
  #ifdef CONFIG_PROC_FS
  	.show_fdinfo	= signalfd_show_fdinfo,
  #endif
  	.release	= signalfd_release,
  	.poll		= signalfd_poll,
  	.read		= signalfd_read,
  	.llseek		= noop_llseek,
  };
  
  static int do_signalfd4(int ufd, sigset_t *mask, int flags)
  {
  	struct signalfd_ctx *ctx;
  
  	/* Check the SFD_* constants for consistency.  */
  	BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
  	BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
  
  	if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
  		return -EINVAL;
  
  	sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
  	signotset(mask);
  
  	if (ufd == -1) {
  		ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
  		if (!ctx)
  			return -ENOMEM;
  
  		ctx->sigmask = *mask;
  
  		/*
  		 * When we call this, the initialization must be complete, since
  		 * anon_inode_getfd() will install the fd.
  		 */
  		ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
  				       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
  		if (ufd < 0)
  			kfree(ctx);
  	} else {
  		struct fd f = fdget(ufd);
  		if (!f.file)
  			return -EBADF;
  		ctx = f.file->private_data;
  		if (f.file->f_op != &signalfd_fops) {
  			fdput(f);
  			return -EINVAL;
  		}
  		spin_lock_irq(&current->sighand->siglock);
  		ctx->sigmask = *mask;
  		spin_unlock_irq(&current->sighand->siglock);
  
  		wake_up(&current->sighand->signalfd_wqh);
  		fdput(f);
  	}
  
  	return ufd;
  }
  
  SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
  		size_t, sizemask, int, flags)
  {
  	sigset_t mask;
  
  	if (sizemask != sizeof(sigset_t) ||
  	    copy_from_user(&mask, user_mask, sizeof(mask)))
  		return -EINVAL;
  	return do_signalfd4(ufd, &mask, flags);
  }
  
  SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
  		size_t, sizemask)
  {
  	sigset_t mask;
  
  	if (sizemask != sizeof(sigset_t) ||
  	    copy_from_user(&mask, user_mask, sizeof(mask)))
  		return -EINVAL;
  	return do_signalfd4(ufd, &mask, 0);
  }
  
  #ifdef CONFIG_COMPAT
  static long do_compat_signalfd4(int ufd,
  			const compat_sigset_t __user *user_mask,
  			compat_size_t sigsetsize, int flags)
  {
  	sigset_t mask;
  
  	if (sigsetsize != sizeof(compat_sigset_t))
  		return -EINVAL;
  	if (get_compat_sigset(&mask, user_mask))
  		return -EFAULT;
  	return do_signalfd4(ufd, &mask, flags);
  }
  
  COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
  		     const compat_sigset_t __user *, user_mask,
  		     compat_size_t, sigsetsize,
  		     int, flags)
  {
  	return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
  }
  
  COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
  		     const compat_sigset_t __user *, user_mask,
  		     compat_size_t, sigsetsize)
  {
  	return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
  }
  #endif
  