From a2afae524a5e42f54cc75d1aca34c2650a8ad44a Mon Sep 17 00:00:00 2001
From: Mark Johnston <markj@FreeBSD.org>
Date: Sat, 24 Nov 2018 16:58:34 +0000
Subject: [PATCH] Ensure that knotes do not get registered when KQ_CLOSING is
 set.

KQ_CLOSING is set before draining the knotes associated with a kqueue,
so we must ensure that new knotes are not added after that point.  In
particular, some kernel facilities may register for events on behalf
of a userspace process and race with a close of the kqueue.

PR:		228858
Reviewed by:	kib
Tested by:	pho
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D18316
---
 sys/kern/kern_event.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index 387a9a6fc6bc..94c415286f34 100644
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -1460,8 +1460,11 @@ kqueue_register(struct kqueue *kq, struct kevent *kev, struct thread *td, int wa
 					break;
 		}
 	} else {
-		if ((kev->flags & EV_ADD) == EV_ADD)
-			kqueue_expand(kq, fops, kev->ident, waitok);
+		if ((kev->flags & EV_ADD) == EV_ADD) {
+			error = kqueue_expand(kq, fops, kev->ident, waitok);
+			if (error != 0)
+				goto done;
+		}
 
 		KQ_LOCK(kq);
 
@@ -1693,12 +1696,12 @@ kqueue_expand(struct kqueue *kq, struct filterops *fops, uintptr_t ident,
 {
 	struct klist *list, *tmp_knhash, *to_free;
 	u_long tmp_knhashmask;
-	int size;
-	int fd;
+	int error, fd, size;
 	int mflag = waitok ? M_WAITOK : M_NOWAIT;
 
 	KQ_NOTOWNED(kq);
 
+	error = 0;
 	to_free = NULL;
 	if (fops->f_isfd) {
 		fd = ident;
@@ -1710,9 +1713,11 @@ kqueue_expand(struct kqueue *kq, struct filterops *fops, uintptr_t ident,
 			if (list == NULL)
 				return ENOMEM;
 			KQ_LOCK(kq);
-			if (kq->kq_knlistsize > fd) {
+			if ((kq->kq_state & KQ_CLOSING) != 0) {
+				to_free = list;
+				error = EBADF;
+			} else if (kq->kq_knlistsize > fd) {
 				to_free = list;
-				list = NULL;
 			} else {
 				if (kq->kq_knlist != NULL) {
 					bcopy(kq->kq_knlist, list,
@@ -1734,9 +1739,12 @@ kqueue_expand(struct kqueue *kq, struct filterops *fops, uintptr_t ident,
 			    &tmp_knhashmask,
 			    waitok ? HASH_WAITOK : HASH_NOWAIT);
 			if (tmp_knhash == NULL)
-				return ENOMEM;
+				return (ENOMEM);
 			KQ_LOCK(kq);
-			if (kq->kq_knhashmask == 0) {
+			if ((kq->kq_state & KQ_CLOSING) != 0) {
+				to_free = tmp_knhash;
+				error = EBADF;
+			} else if (kq->kq_knhashmask == 0) {
 				kq->kq_knhash = tmp_knhash;
 				kq->kq_knhashmask = tmp_knhashmask;
 			} else {
@@ -1748,7 +1756,7 @@ kqueue_expand(struct kqueue *kq, struct filterops *fops, uintptr_t ident,
 	free(to_free, M_KQUEUE);
 
 	KQ_NOTOWNED(kq);
-	return 0;
+	return (error);
 }
 
 static void
@@ -2597,6 +2605,8 @@ knote_attach(struct knote *kn, struct kqueue *kq)
 	KASSERT(kn_in_flux(kn), ("knote %p not marked influx", kn));
 	KQ_OWNED(kq);
 
+	if ((kq->kq_state & KQ_CLOSING) != 0)
+		return (EBADF);
 	if (kn->kn_fop->f_isfd) {
 		if (kn->kn_id >= kq->kq_knlistsize)
 			return (ENOMEM);