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Message-ID: <20110702173136.GF26232@openwall.com>
Date: Sat, 2 Jul 2011 21:31:36 +0400
From: Solar Designer <solar@...nwall.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Vasiliy Kulikov <segoon@...nwall.com>,
kernel-hardening@...ts.openwall.com,
Randy Dunlap <rdunlap@...otime.net>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
"Serge E. Hallyn" <serge.hallyn@...onical.com>,
Daniel Lezcano <daniel.lezcano@...e.fr>,
Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
Ingo Molnar <mingo@...e.hu>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [RFC] ipc: introduce shm_rmid_forced sysctl
On Wed, Jun 29, 2011 at 03:14:36PM -0700, Andrew Morton wrote:
> What a horrid patch. But given the POSIX (mis?)feature I don't see a
> better way, and the feature seems desirable. Sigh.
>
> What sort of users would want to turn this on, and why?
Originally, I introduced it into Linux 2.0.x-ow to allow for resource
limits to be enforced on shared servers, such as with shared web
hosting. A user is supposed to be limited by RLIMIT_AS * RLIMIT_NPROC.
(This is awfully inflexible, lacking a separate per-user memory limit,
but at least it's something.) However, with shared memory segments a
user could bypass that limit, because those segments don't have to be
tied to a process. So the patch changed that, requiring that any shm
segment be tied to a process, or be destroyed.
Alexander
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