[PATCH 05/10] ovl: make sure fsync is never called on the lower filesystem.

[NeilBrown <neilb@suse.de>]

If we open a directory O_RDONLY, ->realfile could be on the lower
filesystem.
While fsync is not likely to be called on such a file, we should make
sure never to pass the fsync down as we are treating the lower
filesystem as read-only.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/overlayfs/overlayfs.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/fs/overlayfs/overlayfs.c b/fs/overlayfs/overlayfs.c
index de854e1..f9eea96 100644
--- a/fs/overlayfs/overlayfs.c
+++ b/fs/overlayfs/overlayfs.c
@@ -329,8 +329,15 @@ static loff_t ovl_dir_llseek(struct file *file, loff_t offset, int origin)
 static int ovl_dir_fsync(struct file *file, int datasync)
 {
 	struct ovl_dir_file *od = file->private_data;
+	struct ovl_entry *ue = file->f_path.dentry->d_fsdata;
 
-	return vfs_fsync(od->realfile, datasync);
+	/* realfile could be on lowerdir, but only if this was a read-only open,
+	 * in which case we can ignore the fsync.
+	 */
+	if (file->f_path.dentry == ue->upperpath.dentry)
+		return vfs_fsync(od->realfile, datasync);
+	else
+		return 0;
 }
 
 static int ovl_dir_release(struct inode *inode, struct file *file)