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

[Jon Ribbens]

On Tue, Aug 10, 2010 at 11:04:16AM +0100, Roland Perry wrote:
>> 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.