On Fri, Mar 23, 2018 at 04:41:40PM -0500, Eric W. Biederman wrote:

>  struct dentry *mount_ns(struct file_system_type *fs_type,
>       int flags, void *data, void *ns, struct user_namespace *user_ns,
> +     struct vfsmount *(*ns_to_mnt)(void *ns),
>       int (*fill_super)(struct super_block *, void *, int))
>  {
>       struct super_block *sb;
> -
> +     int (*test_super)(struct super_block *, void *) = ns_test_super;
>       /* Don't allow mounting unless the caller has CAP_SYS_ADMIN
>        * over the namespace.
>        */
>       if (!(flags & SB_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN))
>               return ERR_PTR(-EPERM);
>  
> -     sb = sget_userns(fs_type, ns_test_super, ns_set_super, flags,
> -                      user_ns, ns);
> +     if (ns_to_mnt) {
> +             test_super = NULL;
> +             if (!(flags & SB_KERNMOUNT)) {
> +                     struct vfsmount *m = ns_to_mnt(ns);
> +                     if (IS_ERR(m))
> +                             return ERR_CAST(m);
> +                     atomic_inc(&m->mnt_sb->s_active);
> +                     down_write(&m->mnt_sb->s_umount);
> +                     return dget(m->mnt_root);

This is completely wrong.  Look:
        * SB_KERNMOUNT and !SB_KERNMOUNT cases are almost entirely isolated;
completely so once that ns_to_mnt becomes unconditionally non-NULL.  
        * in !SB_KERNMOUNT passing ns_to_mnt() is pointless - you might as
well pass existing vfsmount (or ERR_PTR()) and use _that_.  fill_super()
is not used at all in that case.
        * is SB_KERNMOUNT ns_to_mnt serves only as a flag, eventually
constant true.

So let's split it in two helpers and give them sane arguments.

Reply via email to