Re: [PATCH 3/4] signal: support pidctl() with pidfd_send_signal()

[Jann Horn]

On Mon, Mar 25, 2019 at 5:21 PM Christian Brauner <christian@xxxxxxxxxx> wrote:
> Let pidfd_send_signal() use pidfds retrieved via pidctl(). With this patch
> pidfd_send_signal() becomes independent of procfs. This fullfils the
> request made when we merged the pidfd_send_signal() patchset. The
> pidfd_send_signal() syscall is now always available allowing for it to be
> used by users without procfs mounted or even users without procfs support
> compiled into the kernel.
[...]
>  static bool access_pidfd_pidns(struct pid *pid)
>  {
> +       int ret;
>         struct pid_namespace *active = task_active_pid_ns(current);
>         struct pid_namespace *p = ns_of_pid(pid);
>
> -       for (;;) {
> -               if (!p)
> -                       return false;
> -               if (p == active)
> -                       break;
> -               p = p->parent;
> -       }
> +       ret = pidnscmp(active, p);
> +       if (ret < 0)
> +               return false;
>
>         return true;
>  }

Nit, if we keep this function: "if (...) return false; return true;"
seems like an antipattern to me. How about "return ret >= 0", or even
"return pidnscmp(active, p) >= 0"?