alloca avoidance patches

[Szabolcs Nagy]

On 19/06/17 18:58, Joseph Myers wrote:
> On Mon, 19 Jun 2017, Szabolcs Nagy wrote:
> 
>> in any case i think it's more productive to
>> fix the stack usage bugs, instead of hardening
>> for this class of exploitable stack usage bugs,
>> even if the guard page catches the issue it
>> is an unwanted crash.
> 
> Which gets back to wanting to use appropriate warning options, even if 
> they don't catch all cases - and to needing an ABI-defined size it's safe 
> to allocate, possibly more than a page if you rely on kernel fixes.
> 
> (I expect strtold has one of the larger static stack allocations in glibc.  
> I can see such amounts, possibly more, being needed for fixing cpow{,f,l} 
> inaccuracy as well, on the assumption we should avoid libm functions 
> calling malloc.)
> 

i know at least crypt call in glibc can allocate 128K on the
stack, so glibc has bigger problems than strtold