Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754634AbdLTJNc (ORCPT ); Wed, 20 Dec 2017 04:13:32 -0500 Received: from mx2.suse.de ([195.135.220.15]:34222 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751936AbdLTJN3 (ORCPT ); Wed, 20 Dec 2017 04:13:29 -0500 Date: Wed, 20 Dec 2017 10:13:26 +0100 From: Michal Hocko To: "Michael Kerrisk (man-pages)" Cc: "Dr. Manfred Spraul" , Linux API , Andrew Morton , Al Viro , Kees Cook , Linus Torvalds , Mike Waychison , LKML , "linux-mm@kvack.org" Subject: Re: shmctl(SHM_STAT) vs. /proc/sysvipc/shm permissions discrepancies Message-ID: <20171220091326.GC4831@dhcp22.suse.cz> References: <20171219094848.GE2787@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1797 Lines: 47 On Wed 20-12-17 09:44:47, Michael Kerrisk wrote: > Hi Manfred, > > On 20 December 2017 at 09:32, Dr. Manfred Spraul > wrote: > > Hi Michal, > > > > On 12/19/2017 10:48 AM, Michal Hocko wrote: > >> > >> Hi, > >> we have been contacted by our partner about the following permission > >> discrepancy > >> 1. Create a shared memory segment with permissions 600 with user A using > >> shmget(key, 1024, 0600 | IPC_CREAT) > >> 2. ipcs -m should return an output as follows: > >> > >> ------ Shared Memory Segments -------- > >> key shmid owner perms bytes nattch status > >> 0x58b74326 759562241 A 600 1024 0 > >> > >> 3. Try to read the metadata with shmctl(0, SHM_STAT,...) as user B. > >> 4. shmctl will return -EACCES > >> > >> The supper set information provided by shmctl can be retrieved by > >> reading /proc/sysvipc/shm which does not require read permissions > >> because it is 444. > >> > >> It seems that the discrepancy is there since ae7817745eef ("[PATCH] ipc: > >> add generic struct ipc_ids seq_file iteration") when the proc interface > >> has been introduced. The changelog is really modest on information or > >> intention but I suspect this just got overlooked during review. SHM_STAT > >> has always been about read permission and it is explicitly documented > >> that way. > > > > Are you sure that this patch changed the behavior? > > The proc interface is much older. > > Yes, I think that's correct. The /proc/sysvipc interface appeared in > 2.3.x, and AFAIK the behavior was already different from *_STAT back > then. I have probably misread the patch. It surely adds sysvipc_proc_fops, maybe there was a different implementation previously. I haven't checked. -- Michal Hocko SUSE Labs