From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out03.mta.xmission.com ([166.70.13.233]:54219 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751806AbeCMSSL (ORCPT ); Tue, 13 Mar 2018 14:18:11 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Waiman Long Cc: "Luis R. Rodriguez" , Kees Cook , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Al Viro , Matthew Wilcox References: <1520885744-1546-1-git-send-email-longman@redhat.com> <1520885744-1546-5-git-send-email-longman@redhat.com> Date: Tue, 13 Mar 2018 13:17:24 -0500 In-Reply-To: <1520885744-1546-5-git-send-email-longman@redhat.com> (Waiman Long's message of "Mon, 12 Mar 2018 16:15:42 -0400") Message-ID: <87woyfyh57.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [PATCH v4 4/6] ipc: Clamp msgmni and shmmni to the real IPCMNI limit Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Waiman Long writes: > A user can write arbitrary integer values to msgmni and shmmni sysctl > parameters without getting error, but the actual limit is really > IPCMNI (32k). This can mislead users as they think they can get a > value that is not real. > > Enforcing the limit by failing the sysctl parameter write, however, > can break existing user applications. Which applications examples please. I am seeing this patchset late but it looks like a whole lot of changes to avoid a theoretical possibility. Changes that have an impact on more than just the ipc code you are patching. That makes me feel very uncomfortable with these changes. Eric > Instead, the range clamping flag > is set to enforce the limit without failing existing user code. Users > can easily figure out if the sysctl parameter value is out of range > by either reading back the parameter value or checking the kernel > ring buffer for warning. > > Signed-off-by: Waiman Long > --- > ipc/ipc_sysctl.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c > index 8ad93c2..1955dd4 100644 > --- 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 ipc_mni = IPCMNI; > > static struct ctl_table ipc_kern_table[] = { > { > @@ -120,7 +121,10 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write, > .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 = &ipc_mni, > + .flags = CTL_FLAGS_CLAMP_RANGE, > }, > { > .procname = "shm_rmid_forced", > @@ -147,7 +151,8 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write, > .mode = 0644, > .proc_handler = proc_ipc_dointvec_minmax, > .extra1 = &zero, > - .extra2 = &int_max, > + .extra2 = &ipc_mni, > + .flags = CTL_FLAGS_CLAMP_RANGE, > }, > { > .procname = "auto_msgmni",