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Date:   Fri, 07 Dec 2018 08:03:45 +1300
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Subject: Re: [PATCH v2] signal: add procfd_signal() syscall
To:     Florian Weimer <fweimer@redhat.com>,
        Andy Lutomirski <luto@kernel.org>
CC:     "Eric W. Biederman" <ebiederm@xmission.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "Serge E. Hallyn" <serge@hallyn.com>, Jann Horn <jannh@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Daniel Colascione <dancol@google.com>,
        Tim Murray <timmurray@google.com>,
        linux-man <linux-man@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>
From:   Christian Brauner <christian@brauner.io>
Message-ID: <C5E71146-DE79-4145-B54B-E161E7372D95@brauner.io>
Sender: linux-kernel-owner@vger.kernel.org
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On December 7, 2018 7:56:44 AM GMT+13:00, Florian Weimer <fweimer@redhat=2E=
com> wrote:
>* Andy Lutomirski:
>
>>> I suppose that's fine=2E  Or alternatively, when thread group support
>is
>>> added, introduce a flag that applications have to use to enable it,
>so
>>> that they can probe for support by checking support for the flag=2E
>>>
>>> I wouldn't be opposed to a new system call like this either:
>>>
>>>  int procfd_open (pid_t thread_group, pid_t thread_id, unsigned
>flags);
>>>
>>> But I think this is frowned upon on the kernel side=2E
>>
>> I have no problem with it, except that I think it shouldn=E2=80=99t ret=
urn an
>> fd that can be used for proc filesystem access=2E
>
>Oh no, my intention was that it would just be used with  *_send_signal
>and related functions=2E

Let's postpone that discussion a little=2E
I think we don't need a syscall to base this off of pids=2E
As I said I rather send my revived version of CLONE_NEWFD that would serve=
 the same task=2E
The same way we could also just add a new open() flag that blocks fs acces=
s completely=2E
I just pitched that idea to Serge a few days back: O_NOCHDIR or similar=2E
That could even be part of Aleksa's path resolution patchset=2E

>
>Thanks,
>Florian