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From: Jann Horn <jannh@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>,
	John Wood <john.wood@gmx.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 6/6] security/fbfam: Mitigate a fork brute force attack
Date: Fri, 11 Sep 2020 02:20:27 +0200	[thread overview]
Message-ID: <CAG48ez2=8y7jC9vWSPyYNhwASxGrQaewSBczbr02Ri2YnBJwVA@mail.gmail.com> (raw)
In-Reply-To: <202009101649.2A0BF95@keescook>

On Fri, Sep 11, 2020 at 1:56 AM Kees Cook <keescook@chromium.org> wrote:
> On Thu, Sep 10, 2020 at 01:21:07PM -0700, Kees Cook wrote:
> > From: John Wood <john.wood@gmx.com>
> >
> > In order to mitigate a fork brute force attack it is necessary to kill
> > all the offending tasks. This tasks are all the ones that share the
> > statistical data with the current task (the task that has crashed).
> >
> > Since the attack detection is done in the function fbfam_handle_attack()
> > that is called every time a core dump is triggered, only is needed to
> > kill the others tasks that share the same statistical data, not the
> > current one as this is in the path to be killed.
[...]
> > +     for_each_process(p) {
> > +             if (p == current || p->fbfam_stats != stats)
> > +                     continue;
> > +
> > +             do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_PID);
> > +             pr_warn("fbfam: Offending process with PID %d killed\n",
> > +                     p->pid);
[...]
> > +
> > +             killed += 1;
> > +             if (killed >= to_kill)
> > +                     break;
> > +     }
> > +
> > +     rcu_read_unlock();
>
> Can't newly created processes escape this RCU read lock? I think this
> need alternate locking, or something in the task_alloc hook that will
> block any new process from being created within the stats group.

Good point; the proper way to deal with this would probably be to take
the tasklist_lock in read mode around this loop (with
read_lock(&tasklist_lock) / read_unlock(&tasklist_lock)), which pairs
with the write_lock_irq(&tasklist_lock) in copy_process(). Thanks to
the fatal_signal_pending() check while holding the lock in
copy_process(), that would be race-free - any fork() that has not yet
inserted the new task into the global task list would wait for us to
drop the tasklist_lock, then bail out at the fatal_signal_pending()
check.

  reply	other threads:[~2020-09-11  0:21 UTC|newest]

Thread overview: 58+ 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
2020-09-10 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 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
2020-09-10 21:10     ` Jann Horn
2020-09-13 17:54     ` John Wood
2020-09-14 19:42       ` Jann Horn
2020-09-14 19:42         ` Jann Horn
2020-09-15 18:44         ` John Wood
2020-09-10 23:49   ` Kees Cook
2020-09-11  0:01     ` Jann Horn
2020-09-11  0:01       ` Jann Horn
2020-09-13 16:56       ` John Wood
2020-09-14 19:39         ` Jann Horn
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 20:55     ` Jann Horn
2020-09-10 23:56   ` Kees Cook
2020-09-11  0:20     ` Jann Horn [this message]
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 20:39   ` 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
2020-09-12 20:48           ` Ondrej Mosnacek
2020-09-13  7:24           ` John Wood
2020-09-13  7:24             ` John Wood

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