linux-kernel - Re: [PATCH 1/9] exec: add a global execve counter

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Message-ID: <CA+55aFy-ktC3NG5Wc+vhWB+18aqj9a0VLUSKQg+KR=FsVqfoJQ@mail.gmail.com>
Date:	Sat, 10 Mar 2012 16:36:12 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Djalal Harouni <tixxdz@...ndz.org>
Cc:	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Kees Cook <keescook@...omium.org>,
	Solar Designer <solar@...nwall.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	James Morris <james.l.morris@...cle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Greg KH <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...e.hu>, Stephen Wilson <wilsons@...rt.ca>,
	"Jason A. Donenfeld" <Jason@...c4.com>
Subject: Re: [PATCH 1/9] exec: add a global execve counter

On Sat, Mar 10, 2012 at 4:12 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I wonder if we couldn't make something much cheaper, since we don't
> actually care about it being globally incrementing, we just care about
> it being globally unique.

Actually, we don't even need it to be "globally unique" afaik. It
really needs to be "relatively unique", since it's always compared
within the confines of a particular task.

So the problem with using the existing "self_exec_id" is that it's
trivially the same across tasks. But a  *tuple* of <struct
task_struct, thread-specific exec_id> doesn't have that issue, so as
far as I can tell we could easily make *that* the unique ID.

I wonder if the number part of exec_id would even have to be 64-bit. I
think I can do about 10000 execves per second if I make the program a
small static one - and that's on a fast CPU. And it's a per-thread
counter, so you can't scale it with lots of CPU's. So it would take
something like four days to wrap. Hmm..

                  Linus
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