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

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Message-ID: <54A870C2.9080102@nod.at>
Date:	Sat, 03 Jan 2015 23:44:18 +0100
From:	Richard Weinberger <richard@....at>
To:	Pavel Machek <pavel@....cz>
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

Am 03.01.2015 um 23:36 schrieb Pavel Machek:
> 
>>>> 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.
>>
>> The patch does not add random delays nor is hope involved.
>>
>> It has a very clear purpose, it makes brute force attacks to forking
>> services unattractive.
>> Exploits often use the fact that after fork() the child has the same memory
>> as the parent and therefore an attacker can start fruitful brute force attacks
>> to brute stack canaries, offsets, etc. as the new child will always have mostly
>> the same memory layout as before.
>>
>> But I'll happily add your NAK to this series.
> 
> Please do.
> 
>>> If really neccessary, "kill_me_slowly()" syscall would be acceptable,
>>> but it seems just sleep(); abort(); combination is enough.
>>
>> The goal of the patch is not to protect only against brute forcing the stack canary.
>> It should protect against all kind of brute forcing using forking services.
>>
>>> glibc should cover 99% cases where this matters, please just fix glibc,
>>> others will follow.
>>
>> There are a lot of systems out there without glibc.
> 
> Only "interesting" systems that are without glibc are androids, and
> they usually run very old kernels.
> 
> If you implement sleep() in glibc, distros will enable it and you'll
> protect all the desktop users.
> 
> If you implement it in kernel, it will not be compatible-enough to be
> enabled by default, and you'll be protecting special "high security"
> distros at most.
> 
>> And many applications make system calls without going though any libc wrapper.
>> Hey, we want also protect esoteric distros like http://sta.li. :-)
> 
> No, we don't. We want to maximize number of protected users. And
> patching glibc does that. (And then you can patch bionic. And then the
> small players will follow).

And what about static linked programs or programs which do not use a libc wrapper
for system calls?
Say, any program written in go?

Thanks,
//richard
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