linux-kernel - Re: [PATCH 1/9] Known exploit detection

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Date:	Fri, 13 Dec 2013 14:06:48 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Ryan Mallon <rmallon@...il.com>
Cc:	Kees Cook <keescook@...omium.org>, Theodore Ts'o <tytso@....edu>,
	vegard.nossum@...cle.com, LKML <linux-kernel@...r.kernel.org>,
	Tommi Rantala <tt.rantala@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andy Lutomirski <luto@...capital.net>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jason Wang <jasowang@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	James Morris <james.l.morris@...cle.com>
Subject: Re: [PATCH 1/9] Known exploit detection

* Ryan Mallon <rmallon@...il.com> wrote:

> On 13/12/13 08:13, Kees Cook wrote:
> > On Thu, Dec 12, 2013 at 11:06 AM, Theodore Ts'o <tytso@....edu> wrote:
> >> On Thu, Dec 12, 2013 at 05:52:24PM +0100, vegard.nossum@...cle.com wrote:
> >>> From: Vegard Nossum <vegard.nossum@...cle.com>
> >>>
> >>> The idea is simple -- since different kernel versions are vulnerable to
> >>> different root exploits, hackers most likely try multiple exploits before
> >>> they actually succeed.
> > 
> > I like this idea. It serves a few purposes, not the least of which is
> > very clearly marking in code where we've had problems, regardless of
> > the fact that it reports badness to the system owner. And I think
> > getting any additional notifications about bad behavior is a nice idea
> > too.
> 
> Though, if an attacker is running through a series of exploits, and 
> one eventually succeeds then the first thing to do would be to clean 
> traces of the _exploit() notifications from the syslog. [...]

There are several solutions to that:

1)

Critical sites use remote logging over a fast LAN, so a successful 
exploit would have to zap the remote logging daemon pretty quickly 
before the log message goes out over the network.

2)

Some sites also log to append-only media [such as a printer] or other 
append-only storage interfaces - which cannot be manipulated from the 
attacked system alone after a successful break-in.

3)

In future the exploit() code could trigger actual active defensive 
measures, such as immediately freezing all tasks of that UID and 
blocking further fork()s/exec()s of that UID.

Depending on how critical the security of the system is, such active 
measures might still be a preferable outcome even if there's a chance 
of false positives. (Such active measures that freeze the UID will 
also help with forensics, if the attack is indeed real.)

> [...] Since running through a series of exploits is pretty quick, 
> this can probably all be done before the sysadmin ever notices.

It's not necessarily the sysadmin the attacker is racing against, but 
against append-only logging and other defensive measures - which too 
are programs.

> The _exploit() notifications could also be used to spam the syslogs. 
> Although they are individually ratelimited, if there are enough 
> _exploit() markers in the kernel then an annoying person can cycle 
> through them all to generate large amounts of useless syslog.

AFAICS they are globally rate-limited, just like many other 
attacker-triggerable printk()s the kernel may generate.

Thanks,

	Ingo
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