[framework] Is there any way to find the original buffer limit, in the case of buffer overflows

[M.P.Sairam]

Can we know the size only for buf1

At 03:23 PM 5/30/2007, you wrote:
>You can often indirectly estimate it.
>
>Lets say you have in pseudo-code:
>
>function do_stuff(attacker_controlled)
>{
>   buf1[256]
>   buf2[128]
>   strcpy(buf1,attacker_controlled)
>}
>
>Then depending on your architecture, the stack will assign space for 
>buf1, followed by buf2, followed by EBP, followed by saved return 
>address (EIP). If the program has been compile with /GS support 
>you'll see a further 4 byte record for the stack canary if all went 
>as planned.
>
>So if you calculate empirically that you need 392 bytes to align 
>with EIP in this example you know you have ~384 bytes of buffer to 
>fill up, followed by the prologue, before the saved return address. 
>This is the reason why we use slightly more than a power of 2 bytes 
>when overflowing a buffer on the stack, as there are a few bytes 
>after the buffer allocations have finished (and programmers like to 
>use nice powers of 2).
>
>I don't have my TAoSSA reference in front of me, but from memory 
>that's how the stack will be laid out from the MS compiler.
>
>Rhys

Thanks,
    --
Sairam 

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