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

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Message-ID: <20210223182054.GB3068@ubuntu>
Date:   Tue, 23 Feb 2021 19:20:54 +0100
From:   John Wood <john.wood@....com>
To:     Randy Dunlap <rdunlap@...radead.org>,
        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:     John Wood <john.wood@....com>,
        "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

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?

Thanks,
John Wood

> --
> ~Randy
>