From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dr. Manfred Spraul" Subject: Re: shmctl(SHM_STAT) vs. /proc/sysvipc/shm permissions discrepancies Date: Wed, 20 Dec 2017 09:32:01 +0100 Message-ID: References: <20171219094848.GE2787@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20171219094848.GE2787-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> Content-Language: en-US Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Michal Hocko , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: Andrew Morton , Al Viro , Kees Cook , Linus Torvalds , Mike Waychison , LKML , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org List-Id: linux-api@vger.kernel.org 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. --     Manfred