Re: do_change_type(): refuse to operate on unmounted/not ours mounts

[Tycho Andersen]

On Wed, Aug 13, 2025 at 07:56:01PM +0100, Al Viro wrote:
> @@ -3347,18 +3360,11 @@ static int do_set_group(struct path *from_path, struct path *to_path)
>  
>  	namespace_lock();
>  
> -	err = -EINVAL;
> -	/* To and From must be mounted */
> -	if (!is_mounted(&from->mnt))
> -		goto out;
> -	if (!is_mounted(&to->mnt))
> -		goto out;
> -
> -	err = -EPERM;
> -	/* We should be allowed to modify mount namespaces of both mounts */
> -	if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN))
> +	err = may_change_propagation(from);
> +	if (err)
>  		goto out;
> -	if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN))
> +	err = may_change_propagation(from);

Just driving by, but I guess you mean "to" here.

Tycho