From: Jann Horn <jannh@google.com>
To: John Wood <john.wood@gmx.com>
Cc: Kees Cook <keescook@chromium.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Matthew Wilcox <willy@infradead.org>,
Jonathan Corbet <corbet@lwn.net>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Luis Chamberlain <mcgrof@kernel.org>,
Iurii Zaikin <yzaikin@google.com>,
James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
linux-doc@vger.kernel.org,
kernel list <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-security-module <linux-security-module@vger.kernel.org>
Subject: Re: [RFC PATCH 5/6] security/fbfam: Detect a fork brute force attack
Date: Mon, 14 Sep 2020 21:42:37 +0200 [thread overview]
Message-ID: <CAG48ez0BcSY0is2LzdkizcOQYkaOJwfa=5ZSwjKb+faRwG9QCA@mail.gmail.com> (raw)
In-Reply-To: <20200913172415.GA2880@ubuntu>
On Sun, Sep 13, 2020 at 7:55 PM John Wood <john.wood@gmx.com> wrote:
> On Thu, Sep 10, 2020 at 11:10:38PM +0200, Jann Horn wrote:
> > On Thu, Sep 10, 2020 at 10:22 PM Kees Cook <keescook@chromium.org> wrote:
> > > To detect a fork brute force attack it is necessary to compute the
> > > crashing rate of the application. This calculation is performed in each
> > > fatal fail of a task, or in other words, when a core dump is triggered.
> > > If this rate shows that the application is crashing quickly, there is a
> > > clear signal that an attack is happening.
> > >
> > > Since the crashing rate is computed in milliseconds per fault, if this
> > > rate goes under a certain threshold a warning is triggered.
[...]
> > > + delta_jiffies = get_jiffies_64() - stats->jiffies;
> > > + delta_time = jiffies64_to_msecs(delta_jiffies);
> > > + crashing_rate = delta_time / (u64)stats->faults;
> >
> > Do I see this correctly, is this computing the total runtime of this
> > process hierarchy divided by the total number of faults seen in this
> > process hierarchy? If so, you may want to reconsider whether that's
> > really the behavior you want. For example, if I configure the minimum
> > period between crashes to be 30s (as is the default in the sysctl
> > patch), and I try to attack a server that has been running without any
> > crashes for a month, I'd instantly be able to crash around
> > 30*24*60*60/30 = 86400 times before the detection kicks in. That seems
> > suboptimal.
>
> You are right. This is not the behaviour we want. So, for the next
> version it would be better to compute the crashing period as the time
> between two faults, or the time between the execve call and the first
> fault (first fault case).
>
> However, I am afraid of a premature detection if a child process fails
> twice in a short period.
>
> So, I think it would be a good idea add a new sysctl to setup a
> minimum number of faults before the time between faults starts to be
> computed. And so, the attack detection only will be triggered if the
> application crashes quickly but after a number of crashes.
>
> What do you think?
You could keep a list of the timestamps of the last five crashes or
so, and then take action if the last five crashes happened within
(5-1)*crash_period_limit time.
next prev parent reply other threads:[~2020-09-14 19:43 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-10 20:21 [RESEND][RFC PATCH 0/6] Fork brute force attack mitigation (fbfam) Kees Cook
2020-09-10 20:21 ` [RFC PATCH 1/6] security/fbfam: Add a Kconfig to enable the fbfam feature Kees Cook
2020-09-10 21:21 ` Jann Horn
2020-09-17 17:32 ` John Wood
2020-09-10 23:18 ` Kees Cook
2020-09-17 18:40 ` John Wood
2020-09-17 22:05 ` Kees Cook
2020-09-18 14:50 ` John Wood
2020-09-10 20:21 ` [RFC PATCH 2/6] security/fbfam: Add the api to manage statistics Kees Cook
2020-09-10 23:23 ` Kees Cook
2020-09-10 20:21 ` [RFC PATCH 3/6] security/fbfam: Use " Kees Cook
2020-09-10 20:27 ` Jann Horn
2020-09-10 23:33 ` Kees Cook
2020-09-29 23:47 ` Steven Rostedt
2020-09-29 23:49 ` Steven Rostedt
2020-10-03 9:52 ` John Wood
2020-09-10 20:21 ` [RFC PATCH 4/6] security/fbfam: Add a new sysctl to control the crashing rate threshold Kees Cook
2020-09-10 23:14 ` Kees Cook
2020-09-13 14:33 ` John Wood
2020-09-10 20:21 ` [RFC PATCH 5/6] security/fbfam: Detect a fork brute force attack Kees Cook
2020-09-10 21:10 ` Jann Horn
2020-09-13 17:54 ` John Wood
2020-09-14 19:42 ` Jann Horn [this message]
2020-09-15 18:44 ` John Wood
2020-09-10 23:49 ` Kees Cook
2020-09-11 0:01 ` Jann Horn
2020-09-13 16:56 ` John Wood
2020-09-14 19:39 ` Jann Horn
2020-09-15 17:36 ` John Wood
2020-09-10 20:21 ` [RFC PATCH 6/6] security/fbfam: Mitigate " Kees Cook
2020-09-10 20:55 ` Jann Horn
2020-09-10 23:56 ` Kees Cook
2020-09-11 0:20 ` Jann Horn
2020-09-18 16:02 ` John Wood
2020-09-18 21:35 ` Kees Cook
2020-09-19 8:01 ` John Wood
2020-09-10 20:39 ` [RESEND][RFC PATCH 0/6] Fork brute force attack mitigation (fbfam) Jann Horn
2020-09-10 23:58 ` Kees Cook
2020-09-11 14:48 ` John Wood
2020-09-12 7:55 ` Kees Cook
2020-09-12 12:24 ` John Wood
2020-09-12 0:03 ` James Morris
2020-09-12 7:56 ` Kees Cook
2020-09-12 9:36 ` John Wood
2020-09-12 14:47 ` Mel Gorman
2020-09-12 20:48 ` Ondrej Mosnacek
2020-09-13 7:24 ` John Wood
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