From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:44114 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752135AbeCHRvN (ORCPT ); Thu, 8 Mar 2018 12:51:13 -0500 Date: Thu, 8 Mar 2018 17:51:09 +0000 From: "Luis R. Rodriguez" To: Andrew Morton Cc: Waiman Long , "Luis R. Rodriguez" , Kees Cook , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Al Viro , Matthew Wilcox Subject: Re: [PATCH v3 3/6] sysctl: Add flags to support min/max range clamping Message-ID: <20180308175109.GA4449@wotan.suse.de> References: <1519926220-7453-1-git-send-email-longman@redhat.com> <1519926220-7453-4-git-send-email-longman@redhat.com> <20180301133117.1d4b27e327f8e51275c82489@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180301133117.1d4b27e327f8e51275c82489@linux-foundation.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Thu, Mar 01, 2018 at 01:31:17PM -0800, Andrew Morton wrote: > On Thu, 1 Mar 2018 12:43:37 -0500 Waiman Long wrote: > > > When minimum/maximum values are specified for a sysctl parameter in > > the ctl_table structure with proc_dointvec_minmax() handler, update > > to that parameter will fail with error if the given value is outside > > of the required range. > > > > There are use cases where it may be better to clamp the value of > > the sysctl parameter to the given range without failing the update, > > especially if the users are not aware of the actual range limits. > > Reading the value back after the update will now be a good practice > > to see if the provided value exceeds the range limits. > > > > To provide this less restrictive form of range checking, a new flags > > field is added to the ctl_table structure. The new field is a 16-bit > > value that just fits into the hole left by the 16-bit umode_t field > > without increasing the size of the structure. > > > > When the CTL_FLAGS_CLAMP_RANGE flag is set in the ctl_table entry, > > any update from the userspace will be clamped to the given range > > without error. > > > > ... > > > > --- a/include/linux/sysctl.h > > +++ b/include/linux/sysctl.h > > @@ -116,6 +116,7 @@ struct ctl_table > > void *data; > > int maxlen; > > umode_t mode; > > + uint16_t flags; > > It would be nice to make this have type `enum ctl_table_flags', but I > guess there's then no reliable way of forcing it to be 16-bit. > > I guess this is the best we can do... > We can add this to the enum: enum ctl_table_flags { CTL_FLAGS_CLAMP_RANGE = BIT(0), + __CTL_FLAGS_CLAMP_MAX = BIT(16), }; Then also: #define CTL_TABLE_FLAGS_ALL ((BIT(__CTL_FLAGS_CLAMP_MAX + 1))-1) at the end of the definition, then a helper which can be used during parsing: static int check_ctl_table_flags(u16 flags) { if (flags & ~(CTL_TABLE_FLAGS_ALL)) return -ERANGE; return 0; } Waiman please evaluate and add. Luis