[PATCH v5 15/42] fs: add file_user_ns() helper

[Jann Horn]

On Wed, Jan 13, 2021 at 1:52 AM Christian Brauner
<christian.brauner at ubuntu.com> wrote:
> Add a simple helper to retrieve the user namespace associated with the
> vfsmount of a file. Christoph correctly points out that this makes
> codepaths (e.g. ioctls) way easier to follow that would otherwise
> dereference via mnt_user_ns(file->f_path.mnt).
>
> In order to make file_user_ns() static inline we'd need to include
> mount.h in either file.h or fs.h which seems undesirable so let's simply
> not force file_user_ns() to be inline.
[...]
> +struct user_namespace *file_user_ns(struct file *file)
> +{
> +       return mnt_user_ns(file->f_path.mnt);
> +}

That name is confusing to me, because when I think of "the userns of a
file", it's file->f_cred->user_ns. There are a bunch of places that
look at that, as you can see from grepping for "f_cred->user_ns".

If you really want this to be a separate helper, can you maybe give it
a clearer name? file_mnt_user_ns(), or something like that, idk.