linux-kernel - Re: [PATCH v2] signal: add procfd

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Message-ID: <C5E71146-DE79-4145-B54B-E161E7372D95@brauner.io>
Date:   Fri, 07 Dec 2018 08:03:45 +1300
From:   Christian Brauner <christian@...uner.io>
To:     Florian Weimer <fweimer@...hat.com>,
        Andy Lutomirski <luto@...nel.org>
CC:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Daniel Colascione <dancol@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        linux-man <linux-man@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2] signal: add procfd_signal() syscall

On December 7, 2018 7:56:44 AM GMT+13:00, Florian Weimer <fweimer@...hat.com> wrote:
>* Andy Lutomirski:
>
>>> I suppose that's fine.  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.
>>>
>>> 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.
>>
>> I have no problem with it, except that I think it shouldn’t return an
>> fd that can be used for proc filesystem access.
>
>Oh no, my intention was that it would just be used with  *_send_signal
>and related functions.

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

>
>Thanks,
>Florian