From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by aws-us-west-2-korg-lkml-1.web.codeaurora.org (Postfix) with ESMTP id B11FEC004E4 for ; Mon, 11 Jun 2018 23:18:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68EAC20839 for ; Mon, 11 Jun 2018 23:18:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 68EAC20839 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933219AbeFKXSs (ORCPT ); Mon, 11 Jun 2018 19:18:48 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:49120 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932775AbeFKXSr (ORCPT ); Mon, 11 Jun 2018 19:18:47 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.9.103]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 7FEF912C3; Mon, 11 Jun 2018 23:18:46 +0000 (UTC) Date: Mon, 11 Jun 2018 16:18:45 -0700 From: Andrew Morton To: Takashi Iwai Cc: Davidlohr Bueso , linux-kernel@vger.kernel.org, Waiman Long Subject: Re: [PATCH] ipc: Limit sysctl value to IPCMNI Message-Id: <20180611161845.6164d3a6c2df353fe11895bf@linux-foundation.org> In-Reply-To: References: <20180608134949.12672-1-tiwai@suse.de> <20180608141659.8a517b128c756b4d0b813c9e@linux-foundation.org> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 09 Jun 2018 08:48:48 +0200 Takashi Iwai wrote: > On Fri, 08 Jun 2018 23:16:59 +0200, > Andrew Morton wrote: > > > > On Fri, 8 Jun 2018 15:49:49 +0200 Takashi Iwai 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-longman@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.