From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Brauner <christian@brauner.io>
Subject: Re: [PATCH 3/4] signal: support pidctl() with pidfd_send_signal()
Date: Mon, 25 Mar 2019 20:41:59 +0100
Message-ID: <20190325194158.rapwoa3oeqluwcfn@brauner.io>
References: <20190325162052.28987-1-christian@brauner.io>
 <20190325162052.28987-4-christian@brauner.io>
 <CAG48ez1QSJTOb-DAQuVpa5feUe9K-pr8aYuyd=yXg0n9eSg-LQ@mail.gmail.com>
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To: Jann Horn <jannh@google.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>, Andy Lutomirski <luto@kernel.org>, David Howells <dhowells@redhat.com>, "Serge E. Hallyn" <serge@hallyn.com>, "Eric W. Biederman" <ebiederm@xmission.com>, Linux API <linux-api@vger.kernel.org>, kernel list <linux-kernel@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>, Kees Cook <keescook@chromium.org>, Alexey Dobriyan <adobriyan@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Michael Kerrisk-manpages <mtk.manpages@gmail.com>, bl0pbl33p@gmail.com, "Dmitry V. Levin" <ldv@altlinux.org>, Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>, cyphar@cyphar.com, Al Viro <viro@zeniv.linux.org.uk>, "Joel Fernandes (Google)" <joe>
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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@brauner.io> 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.