Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755301AbdLTQSJ (ORCPT ); Wed, 20 Dec 2017 11:18:09 -0500 Received: from mail-wm0-f66.google.com ([74.125.82.66]:35132 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754353AbdLTQSH (ORCPT ); Wed, 20 Dec 2017 11:18:07 -0500 X-Google-Smtp-Source: ACJfBotgmuvimqyh0gFWQT5XaZXNmkmAn/SRSs27ylNbgNaudhNkdgFAl0GnNLcZ8vwLMW9S+A7DyRF1pY2sv16Dxjk= MIME-Version: 1.0 Reply-To: mtk.manpages@gmail.com In-Reply-To: <20171220092025.GD4831@dhcp22.suse.cz> References: <20171219094848.GE2787@dhcp22.suse.cz> <20171220092025.GD4831@dhcp22.suse.cz> From: "Michael Kerrisk (man-pages)" Date: Wed, 20 Dec 2017 17:17:46 +0100 Message-ID: Subject: Re: shmctl(SHM_STAT) vs. /proc/sysvipc/shm permissions discrepancies To: Michal Hocko Cc: Linux API , Manfred Spraul , Andrew Morton , Al Viro , Kees Cook , Linus Torvalds , Mike Waychison , LKML , "linux-mm@kvack.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1230 Lines: 34 Hello Michal, On 20 December 2017 at 10:20, Michal Hocko 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/