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

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Date:	Fri, 02 Jan 2015 22:40:14 +0100
From:	Richard Weinberger <richard@....at>
To:	Pavel Machek <pavel@....cz>
CC:	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

Am 02.01.2015 um 20:46 schrieb Pavel Machek:
>>> Does this break trinity, crashme, and similar programs?
>>
>> If they fork() without execve() and a child dies very fast the next fork()
>> will be throttled.
>> This is why I'd like to make this feature disabled by default.
>>
>>> Can you detect it died due to the stack canary? Then, the patch might
>>> be actually acceptable.
>>
>> I don't think so as this is glibc specific.
> 
> Can the slowdown be impelmented in glibc, then?

glibc has a lot of asserts where it can detect stack smashing and kills the
current process using abort(). Here it could of course also call sleep().

> If not, can glibc provide enough information to the kernel to allow us
> to do the right thing?

IMHO we should not strictly focus on the stack canary.
If an attacker can kind of control the attacked child and it segfaults the generic
in-kernel bruteforce detection will still work.
Many exploits use the fact that after fork() the child has the same memory as before
and brute force is possible. A user space solution won't help here.

Thanks,
//richard
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