Enable unprivileged user namespace mounts of overlayfs.  Overlayfs's
permission model (*) ensures that the mounter itself cannot gain additional
privileges by the act of creating an overlayfs mount.

This feature request is coming from the "rootless" container crowd.

(*) Documentation/filesystems/overlayfs.txt#Permission model

Signed-off-by: Miklos Szeredi <redacted>
---
 fs/overlayfs/super.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 189380b946be..019e6f1834b0 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c

@@ -2073,6 +2073,7 @@ static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
 static struct file_system_type ovl_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "overlay",
+	.fs_flags	= FS_USERNS_MOUNT,
 	.mount		= ovl_mount,
 	.kill_sb	= kill_anon_super,
 };

-- 
2.26.2