linux-kernel - Re: [PATCH] [RFC] Deter exploit bruteforcing

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Message-ID: <20150102230837.GA4482@amd>
Date:	Sat, 3 Jan 2015 00:08:37 +0100
From:	Pavel Machek <pavel@....cz>
To:	Richard Weinberger <richard@....at>
Cc:	Jiri Kosina <jkosina@...e.cz>, Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Aaron Tomlin <atomlin@...hat.com>,
	DaeSeok Youn <daeseok.youn@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>, vdavydov@...allels.com,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andy Lutomirski <luto@...capital.net>,
	Brad Spengler <spender@...ecurity.net>
Subject: Re: [PATCH] [RFC] Deter exploit bruteforcing

On Sat 2015-01-03 00:00:22, Richard Weinberger wrote:
> Am 02.01.2015 um 23:54 schrieb Pavel Machek:
> > On Fri 2015-01-02 23:49:52, Jiri Kosina wrote:
> >> On Fri, 2 Jan 2015, Pavel Machek wrote:
> >>
> >>>> You also want to protect against binaries that are evil on purpose,
> >>>> right?
> >>>
> >>> Umm. No. Not by default. We don't want to break crashme or trinity by
> >>> default.
> >>
> >> I thought trinity is issuing syscalls directly (would make more sense than 
> >> going through glibc, wouldn't it?) ... haven't checked the source though.
> > 
> > Patch in this thread wanted to insert delays into kernel on SIGSEGV
> > processing. That's bad idea by default.
> 
> No. This is not what this patch does.
> 
> > But changing glibc to do sleep(30); abort(); instead of abort(); to
> > slow down bruteforcing of canaries makes some kind of sense... and
> > should be ok by default.
> 
> As I saidn only focusing one the specific stack canary case is not enough.

Ok, so I am now saying "adding random delays to the kernel, hoping
they slow attacker down" is bad idea. Feel free to add my NAK to the
patch.

If really neccessary, "kill_me_slowly()" syscall would be acceptable,
but it seems just sleep(); abort(); combination is enough.

glibc should cover 99% cases where this matters, please just fix glibc,
others will follow.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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