linux-kernel - Re: [PATCH v3 0/6] ipc: Clamp *mni to the real IPCMNI limit

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Date:   Thu, 8 Mar 2018 14:02:54 -0500
From:   Waiman Long <longman@...hat.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v3 0/6] ipc: Clamp *mni to the real IPCMNI limit

On 03/08/2018 01:23 PM, Luis R. Rodriguez wrote:
> On Thu, Mar 01, 2018 at 12:43:34PM -0500, Waiman Long wrote:
>> v2->v3:
>>  - Fix kdoc comment errors.
>>  - Incorporate comments and suggestions from Luis R. Rodriguez.
>>  - Add a patch to fix a typo error in fs/proc/proc_sysctl.c.
>>
>> v1->v2:
>>  - Add kdoc comments to the do_proc_do{u}intvec_minmax_conv_param
>>    structures.
>>  - Add a new flags field to the ctl_table structure for specifying
>>    whether range clamping should be activated instead of adding new
>>    sysctl parameter handlers.
>>  - Clamp the semmni value embedded in the multi-values sem parameter.
>>
>> v1 patch: https://lkml.org/lkml/2018/2/19/453
>> v2 patch: https://lkml.org/lkml/2018/2/27/627
>>
>> The sysctl parameters msgmni, shmmni and semmni have an inherent limit
>> of IPC_MNI (32k). However, users may not be aware of that because they
>> can write a value much higher than that without getting any error or
>> notification. Reading the parameters back will show the newly written
>> values which are not real.
>>
>> Enforcing the limit by failing sysctl parameter write, however, can
>> break existing user applications. To address this delemma, a new flags
>> field is introduced into the ctl_table. The value CTL_FLAGS_CLAMP_RANGE
>> can be added to any ctl_table entries to enable a looser range clamping
>> without returning any error. For example,
>>
>>   .flags = CTL_FLAGS_CLAMP_RANGE,
>>
>> This flags value are now used for the range checking of shmmni,
>> msgmni and semmni without breaking existing applications. If any out
>> of range value is written to those sysctl parameters, the following
>> warning will be printed instead.
>>
>>   Kernel parameter "shmmni" was set out of range [0, 32768], clamped to 32768.
>>
>> Reading the values back will show 32768 instead of some fake values.
> I don't see any addition of respective tests cases, I thought I asked
> for this. Please add respective tests cases for all the API you are
> adding on lib/test_sysctl.c and respective tests on
> tools/testing/selftests/sysctl/sysctl.sh
>
>   Luis

I probably missed that. I will add a test case in the next version.

-Longman