From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Manfred Spraul <manfred@colorfullife.com>,
Davidlohr Bueso <davidlohr.bueso@hp.com>,
Kees Cook <keescook@chromium.org>, Tejun Heo <tj@kernel.org>,
Andrew Vagin <avagin@openvz.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Serge Hallyn <serge.hallyn@canonical.com>,
Pavel Emelyanov <xemul@parallels.com>,
Vasiliy Kulikov <segoon@openwall.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Julien Tinnes <jln@google.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] ipc/shm: fix the historical/wrong mm->start_stack check
Date: Sat, 23 Aug 2014 19:22:40 +0400 [thread overview]
Message-ID: <20140823152240.GH25918@moon> (raw)
In-Reply-To: <20140823144327.GA6299@redhat.com>
On Sat, Aug 23, 2014 at 04:43:27PM +0200, Oleg Nesterov wrote:
> The ->start_stack check in do_shmat() looks ugly and simply wrong.
>
> 1. ->start_stack is only valid right after exec(), the application
> can switch to another stack and even unmap this area.
>
> 2. The reason for this check is not clear at all. The application
> should know what it does. And why 4 pages? And why in fact it
> requires 5 pages?
>
> 3. This wrongly assumes that the stack can only grown down.
>
> Personally I think we should simply kill this check, but I did not
> dare to do this. So the patch only fixes the 1st problem (mostly to
> avoid the usage of mm->start_stack) and ignores VM_GROWSUP.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
I don't understand this check either, the comment above it says nothing
but only commits what code is doing not explaining why.
next prev parent reply other threads:[~2014-08-23 15:22 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-23 14:42 [PATCH 0/1] ipc/shm: fix the historical/wrong mm->start_stack check Oleg Nesterov
2014-08-23 14:43 ` [PATCH 1/1] " Oleg Nesterov
2014-08-23 15:22 ` Cyrill Gorcunov [this message]
2014-08-23 15:58 ` Oleg Nesterov
2014-08-25 1:38 ` Hugh Dickins
2014-08-25 15:03 ` Oleg Nesterov
2014-08-25 16:18 ` Hugh Dickins
2014-08-25 17:18 ` Oleg Nesterov
2014-08-25 18:51 ` Hugh Dickins
2014-08-25 19:09 ` Oleg Nesterov
2014-08-24 17:41 ` Manfred Spraul
2014-08-25 14:53 ` Oleg Nesterov
2014-08-25 19:12 ` [PATCH v2] " Oleg Nesterov
2014-08-25 21:22 ` Cyrill Gorcunov
2014-08-26 19:37 ` Oleg Nesterov
2014-08-25 21:49 ` Hugh Dickins
2014-08-26 14:32 ` Oleg Nesterov
2014-08-26 19:31 ` [PATCH v3] ipc/shm: kill " Oleg Nesterov
2014-08-26 20:28 ` Hugh Dickins
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