On Sat, 09 Jun 2018 08:48:48 +0200 Takashi Iwai <ti...@suse.de> wrote:
> On Fri, 08 Jun 2018 23:16:59 +0200, > Andrew Morton wrote: > > > > On Fri, 8 Jun 2018 15:49:49 +0200 Takashi Iwai <ti...@suse.de> wrote: > > > > > Currently shmmni proc entry accepts all entered integer values, but > > > the practical limit is IPCMNI (32768). This confuses user as if a > > > bigger value were accepted but not applied correctly. > > > > > > This patch changes the proc entry to use *_minmax variant to limit the > > > accepted values accordingly. > > > > Waiman Long was working on a (vastly more complicated) patchset to > > address this. > > That's great. Any patch available for testing? I think http://lkml.kernel.org/r/1520885744-1546-1-git-send-email-long...@redhat.com is the most recent version. > > > > --- a/ipc/ipc_sysctl.c > > > +++ b/ipc/ipc_sysctl.c > > > @@ -99,6 +99,7 @@ static int proc_ipc_auto_msgmni(struct ctl_table > > > *table, int write, > > > static int zero; > > > static int one = 1; > > > static int int_max = INT_MAX; > > > +static int ipcmni = IPCMNI; > > > > > > static struct ctl_table ipc_kern_table[] = { > > > { > > > @@ -120,7 +121,9 @@ static struct ctl_table ipc_kern_table[] = { > > > .data = &init_ipc_ns.shm_ctlmni, > > > .maxlen = sizeof(init_ipc_ns.shm_ctlmni), > > > .mode = 0644, > > > - .proc_handler = proc_ipc_dointvec, > > > + .proc_handler = proc_ipc_dointvec_minmax, > > > + .extra1 = &zero, > > > + .extra2 = &ipcmni, > > > }, > > > { > > > .procname = "shm_rmid_forced", > > > > What is the back-compatibility situation here? > > It's obviously an error to set such a high value and suppose that it > were accepted. So relying on that behavior must be broken in > anyway... Well the present behaviour is to convert higher values downwards, yes? int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit) { kuid_t euid; kgid_t egid; int id, err; if (limit > IPCMNI) limit = IPCMNI; So if someone out there is presently setting this to 999999 then their kernel will work just fine. After your proposed change, it will no longer do so - the tuning attempt will fail with -EINVAL. It really does us no good to say "you shouldn't have been doing that". The fact that they *are* doing it and that it works OK is the kernel developers' fault for not applying suitable checking on day one. I think we're stuck with continuing to accept such input.
