ovl: add warning on user_ns mismatch

Currently there's no way to create an overlay filesystem outside of the
current user namespace.  Make sure that if this assumption changes it
doesn't go unnoticed.

Reported-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 2bd570c..82cd6d5 100644 (file)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1923,6 +1923,10 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
        unsigned int numlower;
        int err;
 
+       err = -EIO;
+       if (WARN_ON(sb->s_user_ns != current_user_ns()))
+               goto out;
+
        sb->s_d_op = &ovl_dentry_operations;
 
        err = -ENOMEM;