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Subject: Re: [PATCH v3 3/8] securtiy/brute: Detect a brute force attack
To:     John Wood <john.wood@gmx.com>, Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
        James Morris <jmorris@namei.org>, Shuah Khan <shuah@kernel.org>
Cc:     "Serge E. Hallyn" <serge@hallyn.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-kselftest@vger.kernel.org
References: <20210221154919.68050-1-john.wood@gmx.com>
 <20210221154919.68050-4-john.wood@gmx.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <f4fd9e44-539e-279e-a3a6-8af39f863f73@infradead.org>
Date:   Sun, 21 Feb 2021 18:47:16 -0800
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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...

-- 
~Randy