From 31d4eb94b0ffbfdd02141dc2a7527f2d61926589 Mon Sep 17 00:00:00 2001
From: beck <beck@openbsd.org>
Date: Mon, 30 Jul 2018 00:16:59 +0000
Subject: [PATCH] Allow for us to do a CREATE style lookup on a read only
 filesystem if and only if we are unveil doing it. Fixes an issue noticed by
 kn@ where unveil would fail with EROFS on a read only filesystem

---
 sys/kern/vfs_lookup.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
index 484889c7cd2..efda601ea0d 100644
--- a/sys/kern/vfs_lookup.c
+++ b/sys/kern/vfs_lookup.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vfs_lookup.c,v 1.71 2018/07/13 09:25:23 beck Exp $	*/
+/*	$OpenBSD: vfs_lookup.c,v 1.72 2018/07/30 00:16:59 beck Exp $	*/
 /*	$NetBSD: vfs_lookup.c,v 1.17 1996/02/09 19:00:59 christos Exp $	*/
 
 /*
@@ -558,11 +558,13 @@ dirloop:
 		}
 		/*
 		 * If creating and at end of pathname, then can consider
-		 * allowing file to be created.
+		 * allowing file to be created. Check for a read only
+		 * filesystem and disallow this unless we are unveil'ing
 		 */
-		if (rdonly || (ndp->ni_dvp->v_mount->mnt_flag & MNT_RDONLY)) {
-			error = EROFS;
-			goto bad;
+		if (ndp->ni_pledge != PLEDGE_UNVEIL && (rdonly ||
+		    (ndp->ni_dvp->v_mount->mnt_flag & MNT_RDONLY))) {
+			    error = EROFS;
+			    goto bad;
 		}
 		/*
 		 * We return with ni_vp NULL to indicate that the entry
-- 
2.20.1