Re: [PATCH] [RFC] Deter exploit bruteforcing

From: Richard Weinberger <richard@nod.at>
To: Pavel Machek <pavel@ucw.cz>
Cc: Jiri Kosina <jkosina@suse.cz>, Kees Cook <keescook@chromium.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	David Rientjes <rientjes@google.com>,
	Aaron Tomlin <atomlin@redhat.com>,
	DaeSeok Youn <daeseok.youn@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	vdavydov@parallels.com, Rik van Riel <riel@redhat.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@amacapital.net>,
	Brad Spengler <spender@grsecurity.net>
Subject: Re: [PATCH] [RFC] Deter exploit bruteforcing
Date: Sat, 03 Jan 2015 23:44:18 +0100	[thread overview]
Message-ID: <54A870C2.9080102@nod.at> (raw)
In-Reply-To: <20150103223644.GB27979@amd>

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