From 1d09995353dbf92fca45bc15339778e52e564cf2 Mon Sep 17 00:00:00 2001
From: Jacob Moody <moody@posixcafe.org>
Date: Sat, 28 May 2022 17:23:41 +0000
Subject: [PATCH] kernel: be more careful about argc for /dev/drivers writes

Not crashing on 'chdev &' is important.
---
 sys/src/9/port/devcons.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/sys/src/9/port/devcons.c b/sys/src/9/port/devcons.c
index 756a47936..62387dbbb 100644
--- a/sys/src/9/port/devcons.c
+++ b/sys/src/9/port/devcons.c
@@ -705,18 +705,22 @@ conswrite(Chan *c, void *va, long n, vlong off)
 			error(Ebadarg);
 		if(ct->index != CMchdev)
 			error(Ebadarg);
-		if(cb->nf < 2 || cb->nf > 3)
+		if(cb->nf == 1)
 			error(Ebadarg);
 
 		invert = 1;
-		a = cb->f[2];
+		a = "";
 		switch(cb->f[1][0]){
 		case '&':
+			if(cb->nf != 3)
+				error(Ebadarg);
+			a = cb->f[2];
 			if(cb->f[1][1] == '~')
 				invert--;
 			break;
 		case '~':
-			a = "";
+			if(cb->nf != 2)
+				error(Ebadarg);
 			break;
 		default:
 			error(Ebadarg);