From a34a8c9c6a452cfd716b8f8bd96df8edb08fa1fe Mon Sep 17 00:00:00 2001
From: sf <sf@openbsd.org>
Date: Mon, 29 May 2017 14:07:16 +0000
Subject: [PATCH] msdosfs & ffs: flush cache if updating mount from r/w to r/o

ok deraadt@
---
 sys/msdosfs/msdosfs_vfsops.c | 11 +++++++++--
 sys/ufs/ffs/ffs_vfsops.c     | 12 +++++++++++-
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/sys/msdosfs/msdosfs_vfsops.c b/sys/msdosfs/msdosfs_vfsops.c
index e13b0b1ea0b..5c426a2c37e 100644
--- a/sys/msdosfs/msdosfs_vfsops.c
+++ b/sys/msdosfs/msdosfs_vfsops.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: msdosfs_vfsops.c,v 1.83 2016/10/10 00:34:50 bluhm Exp $	*/
+/*	$OpenBSD: msdosfs_vfsops.c,v 1.84 2017/05/29 14:07:16 sf Exp $	*/
 /*	$NetBSD: msdosfs_vfsops.c,v 1.48 1997/10/18 02:54:57 briggs Exp $	*/
 
 /*-
@@ -64,6 +64,7 @@
 #include <sys/malloc.h>
 #include <sys/dirent.h>
 #include <sys/disk.h>
+#include <sys/dkio.h>
 #include <sys/stdint.h>
 
 #include <msdosfs/bpb.h>
@@ -128,8 +129,14 @@ msdosfs_mount(struct mount *mp, const char *path, void *data,
 			if (mp->mnt_flag & MNT_FORCE)
 				flags |= FORCECLOSE;
 			error = vflush(mp, NULLVP, flags);
-			if (!error)
+			if (!error) {
+				int force = 0;
+
 				pmp->pm_flags |= MSDOSFSMNT_RONLY;
+				/* may be not supported, ignore error */
+				VOP_IOCTL(pmp->pm_devvp, DIOCCACHESYNC,
+				    &force, FWRITE, FSCRED, p);
+			}
 		}
 		if (!error && (mp->mnt_flag & MNT_RELOAD))
 			/* not yet implemented */
diff --git a/sys/ufs/ffs/ffs_vfsops.c b/sys/ufs/ffs/ffs_vfsops.c
index 0770e9aa45d..d0894ffb408 100644
--- a/sys/ufs/ffs/ffs_vfsops.c
+++ b/sys/ufs/ffs/ffs_vfsops.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ffs_vfsops.c,v 1.165 2017/04/20 14:13:00 visa Exp $	*/
+/*	$OpenBSD: ffs_vfsops.c,v 1.166 2017/05/29 14:07:16 sf Exp $	*/
 /*	$NetBSD: ffs_vfsops.c,v 1.19 1996/02/09 22:22:26 christos Exp $	*/
 
 /*
@@ -456,6 +456,16 @@ success:
 				fs->fs_flags &= ~FS_DOSOFTDEP;
 		}
 		ffs_sbupdate(ump, MNT_WAIT);
+		if (ronly) {
+			int force = 0;
+
+			/*
+			 * Updating mount to readonly. Try a cache flush.
+			 * Ignore error because the ioctl may not be supported.
+			 */
+			VOP_IOCTL(ump->um_devvp, DIOCCACHESYNC, &force,
+			    FWRITE, FSCRED, p);
+               }
 	}
 	return (0);
 
-- 
2.20.1