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

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Date:   Tue, 23 Feb 2021 19:13:57 +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 06:25:51PM -0800, Randy Dunlap wrote:
> Hi--
>
> On 2/21/21 7:49 AM, John Wood wrote:
> >
> > +/**
> > + * print_fork_attack_running() - Warn about a fork brute force attack.
> > + */
> > +static inline void print_fork_attack_running(void)
> > +{
> > +	pr_warn("Fork brute force attack detected [%s]\n", current->comm);
> > +}
>
> Do these pr_warn() calls need to be rate-limited so that they don't
> flood the kernel log?

I think it is not necessary since when a brute force attack through the fork
system call is detected, a fork warning appears only once. Then, all the
offending tasks involved in the attack are killed. But if the parent try to run
again the same app already killed, a new crash will trigger a brute force attack
through the execve system call, then this parent is killed, and a new warning
message appears. Now, the parent and childs are killed, the attacks are
mitigated and only a few messages (one or two) have been shown in the kernel
log.

Thanks,
John Wood

> > +/**
> > + * print_exec_attack_running() - Warn about an exec brute force attack.
> > + * @stats: Statistical data shared by all the fork hierarchy processes.
> > + *
> > + * The statistical data shared by all the fork hierarchy processes cannot be
> > + * NULL.
> > + *
> > + * Before showing the process name it is mandatory to find a process that holds
> > + * a pointer to the exec statistics.
> > + *
> > + * Context: Must be called with tasklist_lock and brute_stats_ptr_lock held.
> > + */
> > +static void print_exec_attack_running(const struct brute_stats *stats)
> > +{
> > +	struct task_struct *p;
> > +	struct brute_stats **p_stats;
> > +	bool found = false;
> > +
> > +	for_each_process(p) {
> > +		p_stats = brute_stats_ptr(p);
> > +		if (*p_stats == stats) {
> > +			found = true;
> > +			break;
> > +		}
> >  	}
> > +
> > +	if (WARN(!found, "No exec process\n"))
> > +		return;
> > +
> > +	pr_warn("Exec brute force attack detected [%s]\n", p->comm);
> > +}
>
>
> thanks.
> --
> ~Randy
>