Being safe on the internet (was Re: Here we go again - ISP DPI, but is it interception?)

[Roland Perry]

In article <20100810115549.GG29810 at snowy.squish.net>, Jon Ribbens 
<jon+ukcrypto at unequivocal.co.uk> writes
>>> The problem is not something below the stack rising to bite it.  It's
>>> from something "newer" on the stack (i.e. low in memory) overflowing its
>>> reserved space on the stack to rise up and bite something "older" on the
>>> stack (i.e. higher in memory).
>>
>> But if stacks grow downwards, how can a newer item rise upwards?
>
>The code thinks it's going to write, say, a string of 20 bytes, so the
>stack pointer is reduced by 20 bytes to provide this space. The code
>is then persuaded to write a string, started at the lowest address of
>that space and continuing upwards, of more than 20 bytes, thus
>overwriting the older/higher part of the stack.

Ah, so you are using standard write operations to put stuff into the 
stack area. Not a PUSH or a CALL (both of which would automatically grow 
the stack downwards only). That explains it.
-- 
Roland Perry