From d8703cd80247ca203b817305753bda2b7dbfb5ef Mon Sep 17 00:00:00 2001
From: Mark Johnston <markj@FreeBSD.org>
Date: Thu, 20 Mar 2025 01:34:18 +0000
Subject: [PATCH] vfs: Return early from sysctl_vfs_ctl() if no input was given

Otherwise we end up searching for a mountpoint using an uninitialized
key, and likely failing the version test.  This violates KMSAN's
invariants, so simply return immediately instead.

MFC after:	2 weeks
---
 sys/kern/vfs_subr.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index 95ed98d3217..96e8bb76597 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -6519,6 +6519,8 @@ sysctl_vfs_ctl(SYSCTL_HANDLER_ARGS)
 	int error;
 	struct mount *mp;
 
+	if (req->newptr == NULL)
+		return (EINVAL);
 	error = SYSCTL_IN(req, &vc, sizeof(vc));
 	if (error)
 		return (error);