linux-kernel - Re: [PATCH v3 3/8] securtiy/brute: Detect a brute force attack

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Message-ID: <a0134e04-213f-2440-6d0b-adb018e49083@infradead.org>
Date:   Tue, 23 Feb 2021 12:44:14 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     John Wood <john.wood@....com>, Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        James Morris <jmorris@...ei.org>, Shuah Khan <shuah@...nel.org>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 3/8] securtiy/brute: Detect a brute force attack

On 2/23/21 10:20 AM, John Wood wrote:
> Hi,
> 
> On Sun, Feb 21, 2021 at 06:47:16PM -0800, Randy Dunlap wrote:
>> Hi--
>>
>> scripts/kernel-doc does not like these items to be marked
>> as being in kernel-doc notation. scripts/kernel-doc does not
>> recognize them as one of: struct, union, enum, typedef, so it
>> defaults to trying to interpret these as functions, and then
>> says:
>>
>> (I copied these blocks to my test megatest.c source file.)
>>
>>
>> ../src/megatest.c:1214: warning: cannot understand function prototype: 'const u64 BRUTE_EMA_WEIGHT_NUMERATOR = 7; '
>> ../src/megatest.c:1219: warning: cannot understand function prototype: 'const u64 BRUTE_EMA_WEIGHT_DENOMINATOR = 10; '
>> ../src/megatest.c:1228: warning: cannot understand function prototype: 'const unsigned char BRUTE_MAX_FAULTS = 200; '
>> ../src/megatest.c:1239: warning: cannot understand function prototype: 'const unsigned char BRUTE_MIN_FAULTS = 5; '
>> ../src/megatest.c:1249: warning: cannot understand function prototype: 'const u64 BRUTE_CRASH_PERIOD_THRESHOLD = 30000; '
>>
>>
>> On 2/21/21 7:49 AM, John Wood wrote:
>>>
>>> +/**
>>> + * brute_stats_ptr_lock - Lock to protect the brute_stats structure pointer.
>>> + */
>>> +static DEFINE_RWLOCK(brute_stats_ptr_lock);
>>
>>> +/**
>>> + * BRUTE_EMA_WEIGHT_NUMERATOR - Weight's numerator of EMA.
>>> + */
>>> +static const u64 BRUTE_EMA_WEIGHT_NUMERATOR = 7;
>>
>>> +/**
>>> + * BRUTE_EMA_WEIGHT_DENOMINATOR - Weight's denominator of EMA.
>>> + */
>>> +static const u64 BRUTE_EMA_WEIGHT_DENOMINATOR = 10;
>>
>>> +/**
>>> + * BRUTE_MAX_FAULTS - Maximum number of faults.
>>> + *
>>> + * If a brute force attack is running slowly for a long time, the application
>>> + * crash period's EMA is not suitable for the detection. This type of attack
>>> + * must be detected using a maximum number of faults.
>>> + */
>>> +static const unsigned char BRUTE_MAX_FAULTS = 200;
>>
>>> +/**
>>> + * BRUTE_MIN_FAULTS - Minimum number of faults.
>>> + *
>>> + * The application crash period's EMA cannot be used until a minimum number of
>>> + * data has been applied to it. This constraint allows getting a trend when this
>>> + * moving average is used. Moreover, it avoids the scenario where an application
>>> + * fails quickly from execve system call due to reasons unrelated to a real
>>> + * attack.
>>> + */
>>> +static const unsigned char BRUTE_MIN_FAULTS = 5;
>>
>>> +/**
>>> + * BRUTE_CRASH_PERIOD_THRESHOLD - Application crash period threshold.
>>> + *
>>> + * The units are expressed in milliseconds.
>>> + *
>>> + * A fast brute force attack is detected when the application crash period falls
>>> + * below this threshold.
>>> + */
>>> +static const u64 BRUTE_CRASH_PERIOD_THRESHOLD = 30000;
>>
>> Basically we don't support scalars in kernel-doc notation...
> 
> So, to keep it commented it would be better to use a normal comment block?
> 
> /*
>  * Documentation here
>  */
> 
> What do you think?

Yes, please, just a normal /* comment block.

thanks.
-- 
~Randy