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

[Christian Brauner]

On Mon, Mar 25, 2019 at 07:39:25PM +0100, Jann Horn wrote:
> 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"?

Yip, sounds good.