This is especially good:
http://grsecurity.net/~spender/cheddar_bay.tgz
On 7/19/09, Lisa Kachold <
lisakachold@obnosis.com> wrote:
> Well, that's assumed; but thanks for clarifying it Ryan.
>
> "dereference" is the word in C stack jargon - BTW
>
> On 7/19/09, Ryan Rix <phrkonaleash@gmail.com> wrote:
>> On Sun 19 July 2009 10:33:00 am Lisa Kachold wrote:
>>> This code looks perfectly acceptable, right? Well, it is, until the
>>> compiler takes this into its hands. While optimizing the code, the
>>> compiler will see that the variable has already been assigned and will
>>> actually remove the if block (the check if tun is NULL) completely
>>> from the resulting compiled code. In other words, the compiler will
>>> introduce the vulnerability to the binary code, which didn't exist in
>>> the source code. This will cause the kernel to try to read/write data
>>> from 0x00000000, which the attacker can map to userland – and this
>>> finally pwns the box
>>
>> No, it reads from (NULL+offsetof(sk))
>> Doing pointer arithetic on NULL is perfectly legal (but not dereferencing
>> NULL), and basically that's what this relies on.
>> sk = tun->sk;
>> is the same as writing
>> sk = *(&tun+offsetof(sk)); // idk what that offset is, let's say it's 42
>> bytes
>> which, in the case would be dereferencing (0x00000000+0x00000042) which
>> is
>> perfectly legal and accessible memory. Therein lies the problem.
>>
>> Some say it is a problem with the compiler optimisation, some say it's a
>> kernel bug. Both should be fixed, imo.
>>
>> Ryan
>>
>> --
>> ---
>> Ryan Rix
>> (623)-826-0051
>>
>> The problem here (as someon else stated) is that when multiple dists
>> use the same package format it only gives a "false sense of
>> compatibility".
>> -- Stephen Carpenter <sjc@delphi.com>
>>
>> http://hackersramblings.wordpress.com | http://twitter.com/phrkonaleash
>> XMPP: phrkonaleash@gmail.com | MSN: phrkonaleash@yahoo.com
>> AIM: phrkonaleash | Yahoo: phrkonaleash
>> IRC: PhrkOnLsh@irc.freenode.net/#srcedit,#teensonlinux,#plugaz and
>> countless other FOSS channels.
>>
>>
>
>
> --
> http://linuxgazette.net/164/kachold.html
> (623)239-3392
> (503)754-4452 www.obnosis.com
>
--
http://linuxgazette.net/164/kachold.html
(623)239-3392
(503)754-4452
www.obnosis.com
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