From 5a74f403f040e0ca4bab4551aa5dde1b4bcba109 Mon Sep 17 00:00:00 2001
From: visa <visa@openbsd.org>
Date: Wed, 15 Dec 2021 15:30:47 +0000
Subject: [PATCH] Adjust pty and tty event filters

* Implement EVFILT_EXCEPT for ttys for HUP condition detection.
  This filter is used when pollfd.events has no read/write events.

* Add HUP condition detection to filt_ptcwrite() and filt_ttywrite()
  to reflect ptcpoll() and ttpoll(). Only poll(2) and select(2) can
  utilize the code; kevent(2) should behave as before with EVFILT_WRITE.

* Clear EV_EOF and __EV_HUP if the EOF/HUP condition ends.

OK mpi@
---
 sys/kern/tty.c     | 62 +++++++++++++++++++++++++++++++++++++++++++---
 sys/kern/tty_pty.c | 26 ++++++++++++++++---
 2 files changed, 80 insertions(+), 8 deletions(-)

diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index 37e9ab5efbd..ae6cffb56ed 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tty.c,v 1.172 2021/12/14 15:32:20 visa Exp $	*/
+/*	$OpenBSD: tty.c,v 1.173 2021/12/15 15:30:47 visa Exp $	*/
 /*	$NetBSD: tty.c,v 1.68.4.2 1996/06/06 16:04:52 thorpej Exp $	*/
 
 /*-
@@ -78,6 +78,7 @@ int	filt_ttyread(struct knote *kn, long hint);
 void 	filt_ttyrdetach(struct knote *kn);
 int	filt_ttywrite(struct knote *kn, long hint);
 void 	filt_ttywdetach(struct knote *kn);
+int	filt_ttyexcept(struct knote *kn, long hint);
 void	ttystats_init(struct itty **, int *, size_t *);
 int	ttywait_nsec(struct tty *, uint64_t);
 int	ttysleep_nsec(struct tty *, void *, int, char *, uint64_t);
@@ -1110,6 +1111,13 @@ const struct filterops ttywrite_filtops = {
 	.f_event	= filt_ttywrite,
 };
 
+const struct filterops ttyexcept_filtops = {
+	.f_flags	= FILTEROP_ISFD,
+	.f_attach	= NULL,
+	.f_detach	= filt_ttyrdetach,
+	.f_event	= filt_ttyexcept,
+};
+
 int
 ttkqfilter(dev_t dev, struct knote *kn)
 {
@@ -1126,6 +1134,18 @@ ttkqfilter(dev_t dev, struct knote *kn)
 		klist = &tp->t_wsel.si_note;
 		kn->kn_fop = &ttywrite_filtops;
 		break;
+	case EVFILT_EXCEPT:
+		if (kn->kn_flags & __EV_SELECT) {
+			/* Prevent triggering exceptfds. */
+			return (EPERM);
+		}
+		if ((kn->kn_flags & __EV_POLL) == 0) {
+			/* Disallow usage through kevent(2). */
+			return (EINVAL);
+		}
+		klist = &tp->t_rsel.si_note;
+		kn->kn_fop = &ttyexcept_filtops;
+		break;
 	default:
 		return (EINVAL);
 	}
@@ -1164,6 +1184,8 @@ filt_ttyread(struct knote *kn, long hint)
 		if (kn->kn_flags & __EV_POLL)
 			kn->kn_flags |= __EV_HUP;
 		active = 1;
+	} else {
+		kn->kn_flags &= ~(EV_EOF | __EV_HUP);
 	}
 	splx(s);
 	return (active);
@@ -1184,13 +1206,45 @@ int
 filt_ttywrite(struct knote *kn, long hint)
 {
 	struct tty *tp = kn->kn_hook;
-	int canwrite, s;
+	int active, s;
 
 	s = spltty();
 	kn->kn_data = tp->t_outq.c_cn - tp->t_outq.c_cc;
-	canwrite = (tp->t_outq.c_cc <= tp->t_lowat);
+	active = (tp->t_outq.c_cc <= tp->t_lowat);
+
+	/* Write-side HUP condition is only for poll(2) and select(2). */
+	if (kn->kn_flags & (__EV_POLL | __EV_SELECT)) {
+		if (!ISSET(tp->t_cflag, CLOCAL) &&
+		    !ISSET(tp->t_state, TS_CARR_ON)) {
+			kn->kn_flags |= __EV_HUP;
+			active = 1;
+		} else {
+			kn->kn_flags &= ~__EV_HUP;
+		}
+	}
+	splx(s);
+	return (active);
+}
+
+int
+filt_ttyexcept(struct knote *kn, long hint)
+{
+	struct tty *tp = kn->kn_hook;
+	int active = 0;
+	int s;
+
+	s = spltty();
+	if (kn->kn_flags & __EV_POLL) {
+		if (!ISSET(tp->t_cflag, CLOCAL) &&
+		    !ISSET(tp->t_state, TS_CARR_ON)) {
+			kn->kn_flags |= __EV_HUP;
+			active = 1;
+		} else {
+			kn->kn_flags &= ~__EV_HUP;
+		}
+	}
 	splx(s);
-	return (canwrite);
+	return (active);
 }
 
 static int
diff --git a/sys/kern/tty_pty.c b/sys/kern/tty_pty.c
index f719155fa85..684b5402a3c 100644
--- a/sys/kern/tty_pty.c
+++ b/sys/kern/tty_pty.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tty_pty.c,v 1.111 2021/12/13 14:56:55 visa Exp $	*/
+/*	$OpenBSD: tty_pty.c,v 1.112 2021/12/15 15:30:47 visa Exp $	*/
 /*	$NetBSD: tty_pty.c,v 1.33.4.1 1996/06/02 09:08:11 mrg Exp $	*/
 
 /*
@@ -667,6 +667,7 @@ filt_ptcread(struct knote *kn, long hint)
 {
 	struct pt_softc *pti = (struct pt_softc *)kn->kn_hook;
 	struct tty *tp;
+	int active;
 
 	tp = pti->pt_tty;
 	kn->kn_data = 0;
@@ -678,15 +679,18 @@ filt_ptcread(struct knote *kn, long hint)
 		    ((pti->pt_flags & PF_UCNTL) && pti->pt_ucntl))
 			kn->kn_data++;
 	}
+	active = (kn->kn_data > 0);
 
 	if (!ISSET(tp->t_state, TS_CARR_ON)) {
 		kn->kn_flags |= EV_EOF;
 		if (kn->kn_flags & __EV_POLL)
 			kn->kn_flags |= __EV_HUP;
-		return (1);
+		active = 1;
+	} else {
+		kn->kn_flags &= ~(EV_EOF | __EV_HUP);
 	}
 
-	return (kn->kn_data > 0);
+	return (active);
 }
 
 void
@@ -705,6 +709,7 @@ filt_ptcwrite(struct knote *kn, long hint)
 {
 	struct pt_softc *pti = (struct pt_softc *)kn->kn_hook;
 	struct tty *tp;
+	int active;
 
 	tp = pti->pt_tty;
 	kn->kn_data = 0;
@@ -718,8 +723,19 @@ filt_ptcwrite(struct knote *kn, long hint)
 			kn->kn_data = tp->t_canq.c_cn -
 			    (tp->t_rawq.c_cc + tp->t_canq.c_cc);
 	}
+	active = (kn->kn_data > 0);
 
-	return (kn->kn_data > 0);
+	/* Write-side HUP condition is only for poll(2) and select(2). */
+	if (kn->kn_flags & (__EV_POLL | __EV_SELECT)) {
+		if (!ISSET(tp->t_state, TS_CARR_ON)) {
+			kn->kn_flags |= __EV_HUP;
+			active = 1;
+		} else {
+			kn->kn_flags &= ~__EV_HUP;
+		}
+	}
+
+	return (active);
 }
 
 int
@@ -745,6 +761,8 @@ filt_ptcexcept(struct knote *kn, long hint)
 		if (!ISSET(tp->t_state, TS_CARR_ON)) {
 			kn->kn_flags |= __EV_HUP;
 			active = 1;
+		} else {
+			kn->kn_flags &= ~__EV_HUP;
 		}
 	}
 
-- 
2.20.1