When tring to find out if this is a request for a write in

kernel_sysctl and userland_sysctl, check for whether new is NULL, not
whether newlen is 0.  This allows one to set a string sysctl to "".

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/kern/kern_sysctl.c b/sys/kern/kern_sysctl.c
index 99f2d69..b3bf555 100644
--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -862,7 +862,7 @@ kernel_sysctl(struct proc *p, int *name, u_int namelen, void *old,
 		req.oldptr= old;
 	}
 
-	if (newlen) {
+	if (new != NULL) {
 		req.newlen = newlen;
 		req.newptr = new;
 	}
@@ -1126,7 +1126,7 @@ userland_sysctl(struct proc *p, int *name, u_int namelen, void *old, size_t *old
 		req.oldptr= old;
 	}
 
-	if (newlen) {
+	if (new != NULL) {
 		if (!useracc(new, req.newlen, VM_PROT_READ))
 			return (EFAULT);
 		req.newlen = newlen;