Re: [PATCH v6 3/5] seccomp: add a way to get a listener fd from ptrace

Jann Horn
2018-09-06T15:45:25Z

On Thu, Sep 6, 2018 at 5:29 PM Tycho Andersen <tycho@tycho.ws> wrote:
>
> As an alternative to SECCOMP_FILTER_FLAG_GET_LISTENER, perhaps a ptrace()
> version which can acquire filters is useful. There are at least two reasons
> this is preferable, even though it uses ptrace:
>
> 1. You can control tasks that aren't cooperating with you
> 2. You can control tasks whose filters block sendmsg() and socket(); if the
> task installs a filter which blocks these calls, there's no way with
> SECCOMP_FILTER_FLAG_GET_LISTENER to get the fd out to the privileged task.
[...]
> +long seccomp_new_listener(struct task_struct *task,
> + unsigned long filter_off)
> +{
> + struct seccomp_filter *filter;
> + struct file *listener;
> + int fd;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EACCES;
> +
> + filter = get_nth_filter(task, filter_off);
> + if (IS_ERR(filter))
> + return PTR_ERR(filter);
> +
> + fd = get_unused_fd_flags(0);
> + if (fd < 0) {
> + __put_seccomp_filter(filter);
> + return fd;
> + }
> +
> + listener = init_listener(task, task->seccomp.filter);

Did you mean to write something like `init_listener(task, filter)` here?