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
