linux-kernel - Re: [PATCH v5 2/9] proc/sysctl: Provide additional ctl

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Date:   Mon, 19 Mar 2018 11:35:19 -0400
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, linux-doc@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v5 2/9] proc/sysctl: Provide additional ctl_table.flags
 checks

On 03/16/2018 08:54 PM, Luis R. Rodriguez wrote:
> On Fri, Mar 16, 2018 at 02:13:43PM -0400, Waiman Long wrote:
>> Checking code is added to provide the following additional
>> ctl_table.flags checks:
>>
>>  1) No unknown flag is allowed.
>>  2) Minimum of a range cannot be larger than the maximum value.
>>  3) The signed and unsigned flags are mutually exclusive.
>>  4) The proc_handler should be consistent with the signed or unsigned
>>     flags.
>>
>> Two new flags are added to indicate if the min/max values are signed
>> or unsigned - CTL_FLAGS_SIGNED_RANGE & CTL_FLAGS_UNSIGNED_RANGE.
>> These 2 flags can be optionally enabled for range checking purpose.
>> But either one of them must be set with CTL_FLAGS_CLAMP_RANGE.
>>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>> ---
>> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
>> index e446e1f..088f032 100644
>> --- a/include/linux/sysctl.h
>> +++ b/include/linux/sysctl.h
>> @@ -134,14 +134,26 @@ struct ctl_table
>>   *	the input value. No lower bound or upper bound checking will be
>>   *	done if the corresponding minimum or maximum value isn't provided.
>>   *
>> + * @CTL_FLAGS_SIGNED_RANGE: Set to indicate that the extra1 and extra2
>> + *	fields are pointers to minimum and maximum signed values of
>> + *	an allowable range.
>> + *
>> + * @CTL_FLAGS_UNSIGNED_RANGE: Set to indicate that the extra1 and extra2
>> + *	fields are pointers to minimum and maximum unsigned values of
>> + *	an allowable range.
>> + *
>>   * At most 16 different flags are allowed.
>>   */
>>  enum ctl_table_flags {
>>  	CTL_FLAGS_CLAMP_RANGE		= BIT(0),
>> -	__CTL_FLAGS_MAX			= BIT(1),
>> +	CTL_FLAGS_SIGNED_RANGE		= BIT(1),
>> +	CTL_FLAGS_UNSIGNED_RANGE	= BIT(2),
>> +	__CTL_FLAGS_MAX			= BIT(3),
>>  };
> You are adding new flags which the user can set, and yet these are used
> internally.
>
> It would be best if internal flags are just that, not flags that a user can set.
>
> This patch should be folded with the first one.
>
> I'm starting to loose hope on these patch sets.
>
>   Luis

In order to do the correct min > max check, I need to know if the
quantity is signed or not. Just looking at the proc_handler alone is not
a reliable indicator if it is signed or unsigned.

Yes, I can put the signed bit into the previous patch.

-Longman