From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Subject: Re: shmctl(SHM_STAT) vs. /proc/sysvipc/shm permissions discrepancies
Date: Wed, 20 Dec 2017 17:17:46 +0100
Message-ID: <CAKgNAkisD7zDRoqJd6Gk1JMCZ8+Huj5QPV04nh2JXHMA+_R0-A@mail.gmail.com>
References: <20171219094848.GE2787@dhcp22.suse.cz> <CAKgNAkjJrmCFY-h2oqKS3zM_D+Csx-17A27mh08WKahyOVzrgQ@mail.gmail.com>
 <20171220092025.GD4831@dhcp22.suse.cz>
Reply-To: mtk.manpages@gmail.com
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Return-path: <owner-linux-mm@kvack.org>
In-Reply-To: <20171220092025.GD4831@dhcp22.suse.cz>
Sender: owner-linux-mm@kvack.org
To: Michal Hocko <mhocko@kernel.org>
Cc: Linux API <linux-api@vger.kernel.org>, Manfred Spraul <manfred@colorfullife.com>, Andrew Morton <akpm@linux-foundation.org>, Al Viro <viro@zeniv.linux.org.uk>, Kees Cook <keescook@chromium.org>, Linus Torvalds <torvalds@linux-foundation.org>, Mike Waychison <mikew@google.com>, LKML <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>
List-Id: linux-api@vger.kernel.org

Hello Michal,

On 20 December 2017 at 10:20, Michal Hocko <mhocko@kernel.org> wrote:
> On Tue 19-12-17 17:45:40, Michael Kerrisk wrote:
>> But, is
>> there a pressing reason to make the change? (Okay, I guess iterating
>> using *_STAT is nicer than parsing /proc/sysvipc/*.)
>
> The reporter of this issue claims that "Reading /proc/sysvipc/shm is way
> slower than executing the system call." I haven't checked that but I can
> imagine that /proc/sysvipc/shm can take quite some time when there are
> _many_ segments registered.

Yes, that makes sense.

> So they would like to use the syscall but
> the interacting parties do not have compatible permissions.

So, I don't think there is any security issue, since the same info is
available in /proc/sysvipc/*. The only question would be whether
change in the *_STAT behavior might surprise some applications into
behaving differently. I presume the chances of that are low, but if it
was a concert, one could add new shmctl/msgctl/semctl *_STAT_ALL (or
some such) operations that have the desired behavior.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>