From 87c93f01794232be35da5db855061861fa67bb2f Mon Sep 17 00:00:00 2001
From: visa <visa@openbsd.org>
Date: Mon, 13 Dec 2021 14:56:55 +0000
Subject: [PATCH] Revise EVFILT_EXCEPT filters

Restrict the circumstances where EVFILT_EXCEPT filters trigger:
* when out-of-band data is present and NOTE_OOB is requested.
* when the channel is fully closed and consumer is poll(2).

This should clarify the logic and suppress events that kqueue-based
poll(2) does not except.

OK mpi@
---
 sys/kern/sys_pipe.c            | 13 +++++++------
 sys/kern/tty_pty.c             | 17 +++++++++--------
 sys/kern/uipc_socket.c         | 15 +++++++--------
 sys/miscfs/fifofs/fifo_vnops.c | 12 +++++-------
 4 files changed, 28 insertions(+), 29 deletions(-)

diff --git a/sys/kern/sys_pipe.c b/sys/kern/sys_pipe.c
index fa103c6f4d4..34448410f12 100644
--- a/sys/kern/sys_pipe.c
+++ b/sys/kern/sys_pipe.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sys_pipe.c,v 1.132 2021/12/13 14:54:22 visa Exp $	*/
+/*	$OpenBSD: sys_pipe.c,v 1.133 2021/12/13 14:56:55 visa Exp $	*/
 
 /*
  * Copyright (c) 1996 John S. Dyson
@@ -1079,19 +1079,20 @@ int
 filt_pipeexcept_common(struct knote *kn, struct pipe *rpipe)
 {
 	struct pipe *wpipe;
+	int active = 0;
 
 	rw_assert_wrlock(rpipe->pipe_lock);
 
 	wpipe = pipe_peer(rpipe);
 
-	if ((rpipe->pipe_state & PIPE_EOF) || wpipe == NULL) {
-		kn->kn_flags |= EV_EOF;
-		if (kn->kn_flags & __EV_POLL)
+	if (kn->kn_flags & __EV_POLL) {
+		if ((rpipe->pipe_state & PIPE_EOF) || wpipe == NULL) {
 			kn->kn_flags |= __EV_HUP;
-		return (1);
+			active = 1;
+		}
 	}
 
-	return (0);
+	return (active);
 }
 
 int
diff --git a/sys/kern/tty_pty.c b/sys/kern/tty_pty.c
index bf213d2a118..f719155fa85 100644
--- a/sys/kern/tty_pty.c
+++ b/sys/kern/tty_pty.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tty_pty.c,v 1.110 2021/10/24 00:02:25 jsg Exp $	*/
+/*	$OpenBSD: tty_pty.c,v 1.111 2021/12/13 14:56:55 visa Exp $	*/
 /*	$NetBSD: tty_pty.c,v 1.33.4.1 1996/06/02 09:08:11 mrg Exp $	*/
 
 /*
@@ -727,6 +727,7 @@ filt_ptcexcept(struct knote *kn, long hint)
 {
 	struct pt_softc *pti = (struct pt_softc *)kn->kn_hook;
 	struct tty *tp;
+	int active = 0;
 
 	tp = pti->pt_tty;
 
@@ -736,18 +737,18 @@ filt_ptcexcept(struct knote *kn, long hint)
 		    ((pti->pt_flags & PF_UCNTL) && pti->pt_ucntl)) {
 			kn->kn_fflags |= NOTE_OOB;
 			kn->kn_data = 1;
-			return (1);
+			active = 1;
 		}
-		return (0);
 	}
-	if (!ISSET(tp->t_state, TS_CARR_ON)) {
-		kn->kn_flags |= EV_EOF;
-		if (kn->kn_flags & __EV_POLL)
+
+	if (kn->kn_flags & __EV_POLL) {
+		if (!ISSET(tp->t_state, TS_CARR_ON)) {
 			kn->kn_flags |= __EV_HUP;
-		return (1);
+			active = 1;
+		}
 	}
 
-	return (0);
+	return (active);
 }
 
 const struct filterops ptcread_filtops = {
diff --git a/sys/kern/uipc_socket.c b/sys/kern/uipc_socket.c
index 6c0b47af006..2615019023b 100644
--- a/sys/kern/uipc_socket.c
+++ b/sys/kern/uipc_socket.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uipc_socket.c,v 1.269 2021/11/11 16:35:09 mvs Exp $	*/
+/*	$OpenBSD: uipc_socket.c,v 1.270 2021/12/13 14:56:55 visa Exp $	*/
 /*	$NetBSD: uipc_socket.c,v 1.21 1996/02/04 02:17:52 christos Exp $	*/
 
 /*
@@ -2263,14 +2263,13 @@ filt_soexcept_common(struct knote *kn, struct socket *so)
 			kn->kn_data -= so->so_oobmark;
 			rv = 1;
 		}
-	} else if (so->so_state & SS_CANTRCVMORE) {
-		kn->kn_flags |= EV_EOF;
-		if (kn->kn_flags & __EV_POLL) {
-			if (so->so_state & SS_ISDISCONNECTED)
-				kn->kn_flags |= __EV_HUP;
+	}
+
+	if (kn->kn_flags & __EV_POLL) {
+		if (so->so_state & SS_ISDISCONNECTED) {
+			kn->kn_flags |= __EV_HUP;
+			rv = 1;
 		}
-		kn->kn_fflags = so->so_error;
-		rv = 1;
 	}
 
 	return rv;
diff --git a/sys/miscfs/fifofs/fifo_vnops.c b/sys/miscfs/fifofs/fifo_vnops.c
index 86b4486fc33..d95f34e5a13 100644
--- a/sys/miscfs/fifofs/fifo_vnops.c
+++ b/sys/miscfs/fifofs/fifo_vnops.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fifo_vnops.c,v 1.88 2021/12/13 14:54:22 visa Exp $	*/
+/*	$OpenBSD: fifo_vnops.c,v 1.89 2021/12/13 14:56:55 visa Exp $	*/
 /*	$NetBSD: fifo_vnops.c,v 1.18 1996/03/16 23:52:42 christos Exp $	*/
 
 /*
@@ -708,13 +708,11 @@ filt_fifoexcept_common(struct knote *kn, struct socket *so)
 
 	soassertlocked(so);
 
-	if (so->so_state & SS_CANTRCVMORE) {
-		kn->kn_flags |= EV_EOF;
-		if (kn->kn_flags & __EV_POLL) {
-			if (so->so_state & SS_ISDISCONNECTED)
-				kn->kn_flags |= __EV_HUP;
+	if (kn->kn_flags & __EV_POLL) {
+		if (so->so_state & SS_ISDISCONNECTED) {
+			kn->kn_flags |= __EV_HUP;
+			rv = 1;
 		}
-		rv = 1;
 	}
 
 	return (rv);
-- 
2.20.1