linux-kernel - Re: [PATCH v2 7/8] exec: Generic execfd support

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Message-ID: <871rnccctx.fsf@x220.int.ebiederm.org>
Date:   Fri, 22 May 2020 08:35:06 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Rob Landley <rob@...dley.net>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        linux-fsdevel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        linux-security-module@...r.kernel.org,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v2 7/8] exec: Generic execfd support

Rob Landley <rob@...dley.net> writes:

> On 5/21/20 10:28 PM, Eric W. Biederman wrote:
>> 
>> Rob Landley <rob@...dley.net> writes:
>> 
>>> On 5/20/20 11:05 AM, Eric W. Biederman wrote:
>> 
>>>> The file descriptor is stored in mm->exe_file.
>>>> Probably the most straight forward implementation is to allow
>>>> execveat(AT_EXE_FILE, ...).
>>>
>>> Cool, that works.
>>>
>>>> You can look at binfmt_misc for how to reopen an open file descriptor.
>>>
>>> Added to the todo heap.
>> 
>> Yes I don't think it would be a lot of code.
>> 
>> I think you might be better served with clone(CLONE_VM) as it doesn't
>> block so you don't need to feed yourself your context over a pipe.
>
> Except that doesn't fix it.
>
> Yes I could use threads instead, but the cure is worse than the disease and the
> result is your shell background processes are threads rather than independent
> processes (is $$ reporting PID or TID, I really don't want to go
> there).

I was just suggesting clone(CLONE_VM) because it creates a thread in a
separate process.  Which on nommu sounds like it could be almost exactly
what you want.

If you need the separate copies of all of your global variables etc,
re-exec'ing your self could be the easier way to go.

Eric