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

From: Randy Dunlap <rdunlap@infradead.org>
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
Subject: Re: [PATCH v3 3/8] securtiy/brute: Detect a brute force attack
Date: Sun, 21 Feb 2021 18:30:10 -0800	[thread overview]
Message-ID: <4fde79a5-34fe-fd27-b390-e9fd341996fb@infradead.org> (raw)
In-Reply-To: <20210221154919.68050-4-john.wood@gmx.com>

Hi,

one spello in 2 locations:

On 2/21/21 7:49 AM, John Wood wrote:
> To detect a brute force attack it is necessary that the statistics
> shared by all the fork hierarchy processes be updated in every fatal
> crash and the most important data to update is the application crash
> period. To do so, use the new "task_fatal_signal" LSM hook added in a
> previous step.
> 
> The application crash period must be a value that is not prone to change
> due to spurious data and follows the real crash period. So, to compute
> it, the exponential moving average (EMA) is used.
> 
> There are two types of brute force attacks that need to be detected. The
> first one is an attack that happens through the fork system call and the
> second one is an attack that happens through the execve system call. The
> first type uses the statistics shared by all the fork hierarchy
> processes, but the second type cannot use this statistical data due to
> these statistics dissapear when the involved tasks finished. In this

                   disappear

> last scenario the attack info should be tracked by the statistics of a
> higher fork hierarchy (the hierarchy that contains the process that
> forks before the execve system call).
> 
> Moreover, these two attack types have two variants. A slow brute force
> attack that is detected if the maximum number of faults per fork
> hierarchy is reached and a fast brute force attack that is detected if
> the application crash period falls below a certain threshold.
> 
> Also, this patch adds locking to protect the statistics pointer hold by
> every process.
> 
> Signed-off-by: John Wood <john.wood@gmx.com>
> ---
>  security/brute/brute.c | 488 +++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 474 insertions(+), 14 deletions(-)
> 
> diff --git a/security/brute/brute.c b/security/brute/brute.c
> index 70f812bb7763..645bd6e02638 100644
> --- a/security/brute/brute.c
> +++ b/security/brute/brute.c


> +/**
> + * brute_get_exec_stats() - Get the exec statistics.
> + * @stats: When this function is called, this parameter must point to the
> + *         current process' statistical data. When this function returns, this
> + *         parameter points to the parent process' statistics of the fork
> + *         hierarchy that hold the current process' statistics.
> + *
> + * To manage a brute force attack that happens through the execve system call it
> + * is not possible to use the statistical data hold by this process due to these
> + * statistics dissapear when this task is finished. In this scenario this data

                 disappear

> + * should be tracked by the statistics of a higher fork hierarchy (the hierarchy
> + * that contains the process that forks before the execve system call).
> + *
> + * To find these statistics the current fork hierarchy must be traversed up
> + * until new statistics are found.
> + *
> + * Context: Must be called with tasklist_lock and brute_stats_ptr_lock held.
> + */
> +static void brute_get_exec_stats(struct brute_stats **stats)
> +{


-- 
~Randy