Re: Understanding Linux addr space, malloc, and heap

[Kyle Moffett]

On Oct 23, 2005, at 06:44:47, Arjan van de Ven wrote:
> > But even if Vincend makes the next malloc/free/whatever to be  
> > fubar, or if he made the world explode, mprotect is still required  
> > to report an error if the requested action failed.
>
> but.. there's no proof yet that it failed...

Precisely.  The only code sample he's sent that exhibits this  
"problem" is buggy because it checks the wrong addresses for  
protected status.  In any case, if you _were_ going to try to change  
protection bits on malloc()ed memory, you would need to make  
_damn_sure_ that you didn't change the protection bits on internal  
data structures that malloc uses to keep track of allocations.  If  
you remove read or write privs on malloc-internal linked-list  
pointers, an attempt to malloc() or free() memory might (and probably  
will) crash.

Cheers,
Kyle Moffett

--
I have yet to see any problem, however complicated, which, when you  
looked at it in the right way, did not become still more complicated.
  -- Poul Anderson



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